Peripheral regulation of the growth hormone-insulin-like growth factor system in fish and other vertebrates

Characterizing Growth-Retarded Japanese Eels (Anguilla japonica): Insights into Metabolic and Appetite Regulation

During field surveys and culture procedures, large growth disparities in Anguilla japonica have been observed. However, the potential causes are unknown. This study explored differences in digestive ability, metabolic levels, and transcriptomic profiles of appetite-related genes between growth-retarded eel (GRE) and normal-growing eel (NGE) under the same rearing conditions. The results showed that growth hormone (gh) mRNA expression in GREs was considerably lower than NGEs. The levels of total protein (TP), total cholesterol (T-CHO), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), blood ammonia (BA), blood urea nitrogen (BUN), and alkaline phosphatase (ALP) in GREs were significantly lower than in NGEs. Conversely, levels of glucose (GLU), alanine aminotransferase (ALT), and aspartate transaminase (AST) were higher in GREs. The activities of SOD, CAT, and T-AOC levels were also significantly lower in GREs, as were the activities of glucose-related enzymes including hexokinase (HK), pyruvate kinase (PK), phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase (G6PASE). Additionally, orexigenic genes (npy and ghrelin) were dramatically downregulated, whereas anorexigenic genes (crh and pyy) were significantly upregulated in GREs. These findings suggested that variances in growth hormone, metabolic activities, and appetite level could be associated with the different growth rates of A. japonica. The present research not only revealed the characteristics of the growth, metabolism, and appetite of GREs but also offered new perspectives into the substantial growth discrepancies in A. japonica, providing novel ideas for enhancing fish growth.

Insulin-like growth factor binding protein-3 (igfbp-3) and igfbp-5 in yellowtail kingfish (Seriola lalandi): molecular characterization and expression levels under different nutritional status and stocking density

Insulin-like growth factor-binding proteins (IGFBPs) play important roles in regulating growth and development by binding to IGF, where IGFBP-3 and IGFBP-5 are the main binding carriers of IGF in the circulation system. In the present study, the gene sequences of igfbp-3, igfbp-5a, and igfbp-5b were cloned from the liver of yellowtail kingfish (Seriola lalandi). The ORF sequences of igfbp-3, igfbp-5a, and igfbp-5b were 888, 801, and 804 bp in length, which encoded 295, 266, and 267 amino acids, respectively. The above three genes were widely expressed in yellowtail kingfish tissues, with igfbp-3 being the most highly expressed in the heart, brain, and gonads, while igfbp-5a and igfbp-5b were both most highly expressed in the liver and kidney. The expression levels of igfbp-3, igfbp-5a, and igfbp-5b were detected throughout the embryonic and larval stages, suggesting their roles in early development and growth regulation of yellowtail kingfish. Besides, igfbp-3 and igfbp-5a were significantly up-regulated in the liver under food deprivation and high-density rearing conditions, which was exactly opposite to the growth performance of yellowtail kingfish, implying that they may serve as biomarkers of adverse culture conditions. Overall, the above results initially identified the molecular characteristics of igfbp-3/-5a/-5b in yellowtail kingfish and implied that they might play important roles in the growth and development, providing a basis for further research on underlying regulatory mechanisms.

IGF-1 induces sex-specific oxidative damage and mortality in a songbird

The insulin-like growth factor 1 (IGF-1) is a pleiotropic hormone that regulates essential life-history traits and is known for its major contribution to determining individual ageing processes. High levels of IGF-1 have been linked to increased mortality and are hypothesised to cause oxidative stress. This effect has been observed in laboratory animals, but whether it pertains to wild vertebrates has not been tested. This is surprising because studying the mechanisms that shape individual differences in lifespan is important to understanding mortality patterns in populations of free-living animals. We tested this hypothesis under semi-natural conditions by simulating elevated IGF-1 levels in captive bearded reedlings, a songbird species with an exceptionally fast pace of life. We subcutaneously injected slow-release biodegradable microspheres loaded with IGF-1 and achieved a systemic 3.7-fold increase of the hormone within the natural range for at least 24 h. Oxidative damage to lipids showed marked sexual differences: it significantly increased the day after the manipulation in treated males and returned to baseline levels four days post-treatment, while no treatment effect was apparent in females. Although there was no overall difference in survival between the treatment groups, high initial (pre-treatment) IGF-1 and low post-treatment plasma malondialdehyde levels were associated with enhanced survival prospects in males. These results suggest that males may be more susceptible to IGF-1-induced oxidative stress than females and quickly restoring oxidative balance may be related to fitness. IGF-1 levels evolve under opposing selection forces, and natural variation in this hormone's level may reflect the outcome of individual optimization.

Genomic structures of insulin-like growth factor from golden pompano (Trachinotus ovatus) and their expression responses to the feed types

Golden pompano is an important aquaculture product in the coastal regions of southern China, which is highly dependent on insulin-like growth factor (IGF) for various biological processes. The cDNAs of ToIGF1, ToIGF2, and ToIGF3 are 1718 bp, 1658 bp, and 2272 bp in length, respectively, with corresponding amino acid sequences of 185 aa, 215 aa, and 194 aa. These sequences consist of 5 parts, including the signal peptide, the B domain, the C domain, the A domain, the D domain, and the E domain, which are also found in other species. While ToIGF1 has no SSR polymorphism, ToIGF2 and ToIGF3 have 3 and 1 SSR polymorphism sites, respectively. In terms of tissue expression, ToIGF1 is predominantly expressed in the liver, ToIGF2 shows its highest expression in the gills, and ToIGF3 also shows its highest expression in the gills, but no expression in the liver and spleen. These tissue distribution results suggest that ToIGFs are not only present in growth-related tissues such as the brain, muscle, and liver, but also in reproductive tissues, tissues that regulate osmotic pressure, and tissues related to food intake. This observation is consistent with other bony fish species and highlights the extensive biological functions of ToIGFs that need to be further explored and exploited. In addition, the expression levels of ToIGFs were found to be different in the different dietary groups, including the pelleted food group, the frozen squid group, and the frozen fish group. In the pelleted diet group, ToIGF1 and ToIGF2 were highly expressed in the liver and intestinal tissues, followed by the frozen fish group. These results suggest that the type of diet can affect the body's energy metabolism by influencing tissue expression of growth-related genes, which in turn affects individual growth.

Endocrine control of gill ionocyte function in euryhaline fishes

The endocrine system is an essential regulator of the osmoregulatory organs that enable euryhaline fishes to maintain hydromineral balance in a broad range of environmental salinities. Because branchial ionocytes are the primary site for the active exchange of Na+, Cl-, and Ca2+ with the external environment, their functional regulation is inextricably linked with adaptive responses to changes in salinity. Here, we review the molecular-level processes that connect osmoregulatory hormones with branchial ion transport. We focus on how factors such as prolactin, growth hormone, cortisol, and insulin-like growth-factors operate through their cognate receptors to direct the expression of specific ion transporters/channels, Na+/K+-ATPases, tight-junction proteins, and aquaporins in ion-absorptive (freshwater-type) and ion-secretory (seawater-type) ionocytes. While these connections have historically been deduced in teleost models, more recently, increased attention has been given to understanding the nature of these connections in basal lineages. We conclude our review by proposing areas for future investigation that aim to fill gaps in the collective understanding of how hormonal signaling underlies ionocyte-based processes.

Gene expression analyses of GH/IGF axis in triploid crucian carp with growth heterosis

Hybridization and polyploid breeding are the main approaches used to obtain new aquaculture varieties. Allotriploid crucian carp (3n) with rapid growth performance was generated by mating red crucian carp (RCC) with allotetraploids (4n). Fish growth is controlled by the growth hormone (GH)/insulin-like growth factor (IGF) axis. In the present study, we examined the expression characteristics of GH/IGF axis genes in hybrids F1, 4n, 3n, RCC and common carp (CC). The results showed that GHRa, GHRb, IGF1, IGF2, and IGF-1Ra were highly expressed in 3n compared with RCC and CC, whereas IGF3 was undetectable in the liver in RCC, CC and 3n. GHRa and GHRb had low expression in the 4n group. In hybrid F1, GHRa expression was low, whereas GHRb was highly expressed compared to the levels in RCC and CC. Moreover, in hybrid F1, the expression of IGF3 was higher, and the expression of IGF1 and IGF2 was lower than that in the RCC and CC, whereas the expression of IGF-1Ra was similar to that in RCC and CC. For the IGFBP genes, IGFBP1 had higher expression in 3n compared than that in RCC and CC, while other IGFBP genes were not high expressed in 3n. Among the genes detected in this study, 11 genes were nonadditively expressed in 3n, with 5 genes in the transgressive upregulation model. We proposed that the 11 nonadditive expression of GH/IGF axis genes is related to growth heterosis in 3n. This evidence provides new insights into hybridization and polyploid breeding from the perspective of hormone regulation.

Excess feeding increases adipogenesis but lowers leptin transcript abundance in zebrafish larvae

Although fish exposed to municipal wastewater effluents (MWWE) show higher lipid accumulation, whether this is due to adipogenesis is unclear. The objective here was to identify molecular markers of adipogenesis in zebrafish (Danio rerio) larvae for use as high throughput screening tools for environmental contaminants, including obesogens in MWWE. Zebrafish larvae were fed a commercial diet at a maintenance level (5 % body mass) or in excess (25 or 50 % body mass) from day 6 to 30 days post-fertilization (dpf) to stimulate adipogenesis. We monitored fat accumulation and markers of lipid metabolism, including peroxisome proliferator-activated receptor γ (ppar γ), fatty acid synthase (fas), ELOVL fatty acid elongase 2 (elovl2), diacylglycerol O-acyltransferase 2 (dgat2), leptin (lepa and lepb), leptin receptor (lepr), and lipoprotein lipase (lpl). Excess feeding led to a higher growth rate, protein content and an increase in igf1 transcript abundance. Also, these larvae had higher triglyceride levels and accumulated lipids droplets in the abdominal cavity and viscera. The molecular markers of adipogenesis, including fas, elovl2, and dgat2, were upregulated, while the transcript abundance of lpl, a lipolytic gene, was transiently lower due to excess feeding. The increased adiposity seen at 30 dpf due to excess feeding coincided with a lower lep but not lepr transcript abundance in zebrafish. Our results demonstrate that excess feeding alters the developmental programming of key genes involved in lipid homeostasis, leading to excess lipid accumulation in zebrafish larvae. Overall, fas, elovl2, lpl, and dgat2, but not lep or ppar γ, have the potential to be biomarkers of adipogenesis in zebrafish larvae.

Food deprivation reduces sensitivity of liver Igf1 synthesis pathways to growth hormone in juvenile gopher rockfish (Sebastes carnatus)

Growth hormone (Gh) regulates growth in part by stimulating the liver to synthesize and release insulin-like growth factor-1 (Igf1), which then promotes somatic growth. However, for fish experiencing food limitation, elevated blood Gh can occur even with low circulating Igf1 and slow growth, suggesting that nutritional stress can alter the sensitivity of liver Igf1 synthesis pathways to Gh. Here, we examined how recent feeding experience affected Gh regulation of liver Igf1 synthesis pathways in juvenile gopher rockfish (Sebastes carnatus) to illuminate mechanisms underlying the nutritional modulation of Igf1 production. Juvenile gopher rockfish were maintained under conditions of feeding or complete food deprivation (fasting) for 14 d and then treated with recombinant sea bream (Sparus aurata) Gh or saline control. Gh upregulated hepatic igf1 mRNA levels in fed fish but not in fasted fish. The liver of fasted rockfish also showed a lower relative abundance of gene transcripts encoding teleost Gh receptors 1 (ghr1) and 2 (ghr2), as well as reduced protein levels of phosphorylated janus tyrosine kinase 2 (pJak2) and signal transducer and activator of transcription 5 (pStat5), which function to induce igf1 gene transcription following Gh binding to Gh receptors. Relative hepatic mRNA levels for suppressors of cytokine signaling (Socs) genes socs2, socs3a, and socs3b were also lower in fasted rockfish. Socs2 can suppress Gh activation of Jak2/Stat5, and fasting-related variation in socs expression may reflect modulated inhibitory control of igf1 gene transcription. Fasted rockfish also had elevated liver mRNA abundances for lipolytic hormone-sensitive lipase 1 (hsl1) and Igf binding proteins igfbp1a, -1b and -3a, reduced liver mRNAs encoding igfbp2b and an Igfbp acid labile subunit-like (igfals) gene, and higher transcript abundances for Igf1 receptors igf1ra and igf1rb in skeletal muscle. Together, these findings suggest that food deprivation impacts liver Igf1 responsiveness to Gh via multiple mechanisms that include a downregulation of hepatic Gh receptors, modulation of the intracellular Jak2/Stat5 transduction pathway, and possible shifts in Socs-inhibitory control of igf1 gene transcription, while also demonstrating that these changes occur in concert with shifts in liver Igfbp expression and muscle Gh/Igf1 signaling pathway components.

Transcriptional regulation of esophageal, intestinal, and branchial solute transporters by salinity, growth hormone, and cortisol in Atlantic salmon

In marine habitats, Atlantic salmon (Salmo salar) imbibe seawater (SW) to replace body water that is passively lost to the ambient environment. By desalinating consumed SW, the esophagus enables solute-linked water absorption across the intestinal epithelium. The processes underlying esophageal desalination in salmon and their hormonal regulation during smoltification and following SW exposure are unresolved. To address this, we considered whether two Na+ /H+ exchangers (Nhe2 and -3) expressed in the esophagus contribute to the uptake of Na+ from lumenal SW. There were no seasonal changes in esophageal nhe2 or -3 expression during smoltification; however, nhe3 increased following 48 h of SW exposure in May. Esophageal nhe2, -3, and growth hormone receptor b1 were elevated in smolts acclimated to SW for 2.5 weeks. Treatment with cortisol stimulated branchial Na+ /K+ -ATPase (Nka) activity, and Na+ /K+ /2Cl- cotransporter 1 (nkcc1), cystic fibrosis transmembrane regulator 1 (cftr1), and nka-α1b expression. Esophageal nhe2, but not nhe3 expression, was stimulated by cortisol. In anterior intestine, cortisol stimulated nkcc2, cftr2, and nka-α1b. Our findings indicate that salinity stimulates esophageal nhe2 and -3, and that cortisol coordinates the expression of esophageal, intestinal, and branchial solute transporters to support the SW adaptability of Atlantic salmon.

Molecular cloning and expression profiling of insulin-like growth factor 2 and IGF-binding protein 6 in Clarias magur (Hamilton 1822)

Growth is an important trait in aquaculture and the major genes that regulate it are Insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs). In this study, the full-length coding sequences of IGF2 and IGFBP6 genes in the Indian catfish Clarias magur were cloned and characterized. The full-length cDNA sequences of IGF2 and IGFBP6 were 885 bp (ORF 642 bp) and 928 bp (ORF 600 bp), encoding 213 and 199 amino acids, respectively. Bioinformatics analyses revealed that the magur IGF2 and IGFBP6 proteins are hydrophilic and secretory in nature. Sequence alignment with other teleosts and mammalian orthologues shows conservation of the functional domains. Gene expression analysis in 6 individuals each of high (298 ± 5.0 g) and low (210 ± 6.0 g) growth performing families showed significantly (p < 0.05) higher expression (2.5-3 fold) of IGF2, and lower expression (∼2.5 fold) of IGFBP6 in liver and muscle of fast-growing fish. This study suggests that IGF2 could be playing a major role in the growth regulation of magur. These genes and their expression patterns could be developed into growth-associated markers for magur and other catfishes.

Growth Axis Somatostatin, Growth Hormone Receptor, and Insulin-like Growth Factor-1 Genes Express and Are Affected by the Injection of Exogenous Growth Hormone in Chinemys reevesii

In this study, to explore the effect of growth hormone changes on the related genes and regulatory roles of the turtle, PCR amplification, real-time fluorescence quantitative analysis, and enzyme cutting technology were used to clone and sequence the somatostatin (SS) gene, growth hormone receptor (GHR), and insulin-like growth factor-1 (IGF-I) sequence of Chinemys reevesii. The effects of human growth hormone on the mRNA expression of growth-axis-related genes SS, GHR, and IGF-1 in different sexes were observed. The study of the SS gene in turtles using real-time fluorescence quantitative PCR showed that the SS gene was mainly expressed in the nervous system and the digestive system, with the highest expression found in the brain, while the GHR gene and the IGF-I gene were expressed in all tissues of Chinemys reevesii. The SS gene was expressed in the brain, pituitary, liver, stomach, and intestine, with the highest expression in the brain and the lowest expression in the liver. Within 4 weeks of the injection of exogenous growth hormone, the expression level of the SS gene in the brain of both sexes first increased and then decreased, showing a parabolic trend, and the expression level of the experimental group was lower than that of the control group. After the injection of growth hormone (GH), the expression of the GHR gene in the liver of both sexes showed a significant increase in the first week, decreasing to the control group level in the second week, and then gradually increasing. Finally, a significant level of difference in the expression of the GHR gene was reached at 3 and 4 weeks. In terms of the IGF-I gene, the changing trend of the expression level in the liver was the same as that of the GHR gene. After the injection of exogenous growth hormone, although the expression of the SS gene increased the inhibition of the secretion of the GHR gene by the Reeves' turtle, exogenous growth hormone could replace the synthesis of GH and GHR, accelerating the growth of the turtle. The experiments showed that the injection of recombinant human growth hormone affects the expression of SS, GHR, and IGF-1 genes, and promotes the growth of the Reeves' turtle.

Expressions of Insulin-like Growth Factor System among Different Breeds Impact Piglets' Growth during Weaning

The present study investigated the insulin-like growth factors (IGFs) and their receptors and binding proteins among three pig breeds during weaning. Sixty Duroc (DR), Taoyuan black (TYB), and Xiangcun black (XCB) piglets (20 piglets per breed) were selected at 21 and 24 (3 days of post-weaning) days of age to analyze organ indices, plasma concentrations of IGF and IGF-binding proteins (IGFBPs) using ELISA kits, and gene expression of IGF-system-related components in different tissues. The plasma IGFBP-3 concentration in TYB piglets was higher (p > 0.05) than in the XCB and DR piglets at 21 days of age. At 21 days of age, compared with the DR piglets, the IGF-1 expression was lower (p < 0.05) in the kidney, but it was higher (p < 0.05) in the spleen of XCB and TYB piglets. At 24 days of age, the IGF-1 expression was higher (p < 0.05) in the kidney of TYB piglets than in the XCB and DR piglets, while IGFBP-3 in the stomach and IGFBP-4 in the liver of XCB and TYB piglets were lower (p < 0.05) compared with the DR piglets. Weaning down-regulated (p < 0.05) IGF-1 expression in the jejunum, spleen, and liver of piglets, while it up-regulated (p < 0.05) IGFBP-3 expression in the stomach, IGFBP-4 in the liver, IGFBP-5 in the ileum, and IGFBP-6 in the jejunum of DR piglets. Spearman's correlation analysis showed a negative correlation (p < 0.05) between plasma IGFBP-2 and IGFBP-5 concentration and the organ indices of piglets. Collectively, there were significant differences in the IGF system components among the three pig breeds. The IGF system components were altered during weaning, which might be involved in weaning stress to decrease the growth of piglets.

Assessment of Dietary Supplementation of Lactobacillus rhamnosus Probiotic on Growth Performance and Disease Resistance in Oreochromis niloticus

Probiotics play a significant role in aquaculture by improving the growth, health, and survival rate of fish against pathogenic organisms. In the present study, we have evaluated the effects of a Lactobacillus rhamnosus (L. rhamnosus) probiotic on growth performance and disease resistance in Oreochromis niloticus (O. niloticus) fingerlings. Four different concentrations of L. rhamnosus (T1: 0.5 × 10¹⁰, T2: 1 × 10¹⁰, T3: 1.5 × 10¹⁰, and T4: 2 × 10¹⁰ CFU/kg feed) were administered to fish over a period of three months. L. rhamnosus treated fish revealed a high growth increment as compared to the control, and the values of macromolecules (amino acids, fatty acids, and carbohydrates) varied significantly among the treated and control groups. Levels of thyroid hormones were noted to be high in the probiotic-treated groups. A challenge assay was performed with Aeromonas hydrophila (A. hydrophila). The optimum calculated concentration of probiotics from the growth assay (1.5 × 10¹⁰ CFU/kg feed) was used for the challenge assay. Fish were divided into four groups as follows: control (Con), probiotic-treated (PL), infected (I), and infected + probiotic-treated (I + PL) groups. Significant variations in hematological parameters were observed among control and treated groups. Histopathological changes were recorded in infected fish, while the infected + probiotic-treated group showed less deformations indicating the positive effect of the probiotic supplementation. The survival rate of fish was also better in the probiotic-treated group. Based on these findings, we conclude that probiotic supplementation enhances the growth and improves immunity of O. niloticus. Therefore, we propose that probiotics can be used as promising feed supplements for promoting fish production and disease resistance in aquaculture.

Insulin-like growth factor-1 (Igf1) signaling responses to food consumption after fasting in the Pacific rockfish Sebastes carnatus

Fish adjust rates of somatic growth in the face of changing food consumption. As in other vertebrates, growth in fish is regulated by the growth hormone (Gh)/insulin-like growth factor-1 (Igf1) endocrine axis, and changes in food intake impact growth via alterations to Gh/Igf1 signaling. Understanding the time course by which the Gh/Igf1 axis responds to food consumption is crucial to predict how rapidly changes in food abundance might lead to altered growth dynamics. Here, we looked at the response times of plasma Igf1 and liver Igf1 signaling-associated gene expression to refeeding after food deprivation in juvenile gopher rockfish (Sebastes carnatus), one of several species of northern Pacific Ocean Sebastes rockfishes targeted by fisheries or utilized for aquaculture. Gopher rockfish were fasted for 30 d, after which a subset was fed to satiation for 2 h, while other rockfish continued to be fasted. Refed fish exhibited higher hepatosomatic index (HSI) values and increased Igf1 after food consumption. Gene transcripts for Gh receptor 1 (ghr1), but not ghr2, increased in the liver after eating. Transcripts encoding igf1 also increased in the liver of refed fish 2-4 d after feeding, only to return to levels similar as continually fasted rockfish by 9 d after feeding. Liver mRNA abundances for Igf binding protein (Igfbp) genes igfbp1a, igfbp1b, and igfbp3a declined within 2 d of feeding. These findings provide evidence that circulating Igf1 in rockfish reflects a fish's feeding experience within the previous few days, and suggest that feeding-induced increases in Igf1 are being mediated in part by altered liver sensitivity to Gh due to upregulated Gh receptor 1 expression.

Nutritional status affects Igf1 regulation of skeletal muscle myogenesis, myostatin, and myofibrillar protein degradation pathways in gopher rockfish (Sebastes carnatus)

Insulin-like growth factor-1 (Igf1) regulates skeletal muscle growth in fishes by increasing protein synthesis and promoting muscle hypertrophy. When fish experience periods of insufficient food intake, they undergo slower muscle growth or even muscle wasting, and those changes emerge in part from nutritional modulation of Igf1 signaling. Here, we examined how food deprivation (fasting) modulates Igf1 regulation of liver and skeletal muscle gene expression in gopher rockfish (Sebastes carnatus), a nearshore rockfish of importance for commercial and recreational fisheries in the northeastern Pacific Ocean, to understand how food limitation impacts Igf regulation of muscle growth pathways. Rockfish were either fed or fasted for 14 d, after which a subset of fish from each group was treated with recombinant Igf1 from sea bream (Sparus aurata). Fish that were fasted lost body mass and had lower body condition, reduced hepatosomatic index, and lower plasma Igf1 concentrations, as well as a decreased abundance of igf1 gene transcripts in the liver, increased hepatic mRNAs for Igf binding proteins igfbp1a, igfbp1b, and igfbp3a, and decreased mRNA abundances for igfbp2b and a putative Igf acid labile subunit (igfals) gene. In skeletal muscle, fasted fish showed a reduced abundance of intramuscular igf1 mRNAs but elevated gene transcripts encoding Igf1 receptors A (igf1ra) and B (igf1rb), which also showed downregulation by Igf1. Fasting increased skeletal muscle mRNAs for myogenin and myostatin1, as well as ubiquitin ligase F-box only protein 32 (fbxo32) and muscle RING-finger protein-1 (murf1) genes involved in muscle atrophy, while concurrently downregulating mRNAs for myoblast determination protein 2 (myod2), myostatin2, and myogenic factors 5 (myf5) and 6 (myf6 encoding Mrf4). Treatment with Igf1 downregulated muscle myostatin1 and fbxo32 under both feeding conditions, but showed feeding-dependent effects on murf1, myf5, and myf6/Mrf4 gene expression indicating that Igf1 effects on muscle growth and atrophy pathways is contingent on recent food consumption experience.

The GH/IGF axis in the sea lamprey during metamorphosis and seawater acclimation

How the growth hormone (GH)/insulin-like growth factor (IGF) system affects osmoregulation in basal vertebrates remains unknown. We examined changes in the expression of components of the GH/IGF axis and gill ion transporters during metamorphosis and following seawater (SW) exposure of sea lamprey. During metamorphosis, increases in gill nka and nkcc1 and salinity tolerance were accompanied by increases in pituitary gh, liver igf1, gill ghr and igf1, but not liver ghr. SW exposure of fully metamorphosed sea lamprey resulted in slight increases in plasma chloride concentrations after SW exposure, indicating a high level of SW tolerance, but no major changes in mRNA levels of gill ion transporters or components of the GH/IGF axis. Our results indicate that metamorphosis is a critical point in the lifecycle of sea lamprey for stimulation of the GH/IGF axis and is temporally associated with and likely promotes metamorphosis and SW tolerance.

Feeding after spawning and energy balance at spawning are associated with repeat spawning interval in steelhead trout

Consecutive and skip repeat spawning (1- or ≥2-year spawning interval) life histories commonly occur in seasonally breeding iteroparous fishes. Spawning interval variation is driven by energetic status and impacts fisheries management. In salmonids, energetic status (either absolute level of energy reserves or the rate of change of energy reserves, i.e., energy balance) is thought to determine reproductive trajectory during a critical period ∼1 year prior to initial spawning. However, information on repeat spawners is lacking. To examine the timing and the aspects of energetic status that regulate repeat spawning interval, female steelhead trout (Oncorhynchus mykiss) were fasted for 10 weeks after spawning and then fed ad libitum and compared to ad libitum fed controls. Plasma growth hormone (GH) and insulin-like growth factor-I (IGF-I) levels were measured to assess long-term energy balance. Plasma estradiol levels showed that some fish in both groups initiated a consecutive spawning cycle. In fasted fish, GH was lower at spawning in consecutive versus skip spawners. In consecutive spawners, GH was higher at spawning in fed versus fasted fish. These results suggest that fish with a less negative energy balance at spawning initiated reproductive development in the absence of feeding, but that feeding during the post-spawning period enabled initiation of reproduction in some fish with a more negative energy balance at spawning. Thus, both energy balance at spawning and feeding after spawning regulated reproductive schedules. These results show that the critical period model of salmonid maturation applies to regulation of repeat spawning, and that the reproductive decision window extends into the first 10 weeks after spawning.

Myostatin-mediated regulation of skeletal muscle damage post-acute Aeromonas hydrophila infection in Nile tilapia (Oreochromis niloticus L.)

This study focuses on the relationship between myostatin (MyoS), myogenin (MyoG), and the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis for muscle growth and histopathological changes in muscle after an Aeromonas hydrophila infection. A total number of 90 Nile tilapia (55.85 g) were randomly allocated into two equal groups of three replicates each. The first group was an uninfected control group that was injected intraperitoneally (ip) with 0.2 ml phosphate buffer saline (PBS), while the second group was injected ip with 0.2 ml (1.3 × 10⁸ CFU/ml) Aeromonas hydrophila culture suspension. Sections of white muscle and liver tissues were taken from each group 24 h, 48 h, 72 h, and 1 week after infection for molecular analysis and histopathological examination. The results revealed that with time progression, the severity of muscle lesions increased from edema between bundles and mononuclear inflammatory cell infiltration 24 h post-challenge to severe atrophy of muscle bundles with irregular and curved fibers with hyalinosis of the fibers 1 week postinfection. The molecular analysis showed that bacterial infection was able to induce the muscle expression levels of GH with reduced ILGF-1, MyoS, and MyoG at 24 h postinfection. However, time progression postinfection reversed these findings through elevated muscle expression levels of MyoS with regressed expression levels of muscle GH, ILGF-1, and MyoG. There have been no previous reports on the molecular expression analysis of the aforementioned genes and muscle histopathological changes in Nile tilapia following acute Aeromonas hydrophila infection. Our findings, collectively, revealed that the up-and down-regulation of the myostatin signaling is likely to be involved in the postinfection-induced muscle wasting through the negative regulation of genes involved in muscle growth, such as GH, ILGF-1, and myogenin, in response to acute Aeromonas hydrophila infection in Nile tilapia, Oreochromis niloticus.

Environmental estrogens inhibit insulin-like growth factor (IGF) receptor mRNA expression, IGF binding, and IGF signaling ex vivo in rainbow trout (Oncorhynchus mykiss)

In this study, we used juvenile rainbow trout to examine the direct effects of selected environmental estrogens (EE), specifically, 17 β-estradiol (E2), β-sitosterol (βS), and 4-n-nonylphenol (NP), on target tissue sensitivity to insulin-like growth factor (IGF) as assessed by expression of IGF receptor type 1 (IGFR1) mRNAs and IGF-1 binding capacity, as well as on the cell signaling pathways through which EE exert their effects. E2 and NP inhibited IGFR1A and IGFR1B mRNA expression in a time- and concentration-related manner in gill and muscle; however, βS had no effect on expression of IGFR1 mRNAs in either tissue. NP reduced ¹²⁵I-IGF binding in gill and E2 and NP reduced ¹²⁵I-IGF in white muscle; βS had no effect on ¹²⁵I-IGF binding in either gill or white muscle. Treatment of gill filaments with either E2 or NP rapidly deactivated (via reduced proportion of phosphorylation) JAK2, STAT5, Akt, and ERK; βS had no effect on the activation state of any cell signaling elements tested. The effects of EE on IGFR mRNA expression in gill were estrogen receptor (ER) dependent as the inhibitory effects were rescued by the ER antagonist, ICI 182,780. All EE tested blocked growth hormone (GH)-stimulated IGFR mRNA expression in gill filaments. GH-stimulated activation of JAK2, STAT5, Akt, and ERK were blocked by E2, βS, and NP. Lastly, E2 and NP stimulated suppressor of cytokine signaling 2 (SOCS-2) mRNA expression, an effect that also was ER dependent. These results indicate that EE directly reduce the sensitivity of peripheral tissues to IGF by reducing mRNA and functional expression of IGFRs. Such inhibitory actions of EE are mediated, at least in part, by ER-dependent mechanisms that deactivate JAK, STAT, Akt, and ERK and enhance expression of SOCS-2. These findings together with our previous results show that EE retard growth of post-embryonic rainbow trout through widespread direct effects on the GH-IGF system, specifically, by reducing tissue sensitivity to GH, inhibiting IGF production, reducing tissue sensitivity to IGF, and by deactivating post-receptor IGF cell signaling pathways.

The effect of environmental stressors on growth in fish and its endocrine control

Fish body growth is a trait of major importance for individual survival and reproduction. It has implications in population, ecology, and evolution. Somatic growth is controlled by the GH/IGF endocrine axis and is influenced by nutrition, feeding, and reproductive-regulating hormones as well as abiotic factors such as temperature, oxygen levels, and salinity. Global climate change and anthropogenic pollutants will modify environmental conditions affecting directly or indirectly fish growth performance. In the present review, we offer an overview of somatic growth and its interplay with the feeding regulatory axis and summarize the effects of global warming and the main anthropogenic pollutants on these endocrine axes.

Sex-specific responses to growth hormone and luteinizing hormone in a model teleost, the Mozambique tilapia

Across the vertebrate lineage, sexual dimorphism in body size is a common phenomenon that results from trade-offs between growth and reproduction. To address how key hormones that regulate growth and reproduction interact in teleost fishes, we studied Mozambique tilapia (Oreochromis mossambicus) to determine whether the activities of luteinizing hormone (Lh) are modulated by growth hormone (Gh), and conversely, whether targets of Gh are affected by the presence of Lh. In particular, we examined how gonadal morphology and specific gene transcripts responded to ovine GH (oGH) and/or LH (oLH) in hypophysectomized male and female tilapia. Hypophysectomized females exhibited a diminished gonadosomatic index (GSI) concomitant with ovarian follicular atresia. The combination of oGH and oLH restored GSI and ovarian morphology to conditions observed in sham-operated controls. A similar pattern was observed for GSI in males. In control fish, gonadal gh receptor (ghr2) and estrogen receptor β (erβ) expression was higher in females versus males. A combination of oGH and oLH restored erβ and arβ in females. In males, testicular insulin-like growth factor 3 (igf3) expression was reduced following hypophysectomy and subsequently restored to control levels by either oGH or oLH. By contrast, the combination of both hormones was required to recover ovarian igf3 expression in females. In muscle, ghr2 expression was more responsive to oGH in males versus females. In the liver of hypophysectomized males, igf2 expression was diminished by both oGH and oLH; there was no effect of hypophysectomy, oGH, or oLH on igf2 expression in females. Collectively, our results indicate that gene transcripts associated with growth and reproduction exhibit sex-specific responses to oGH and oLH. These responses reflect, at least in part, how hormones mediate trade-offs between growth and reproduction, and thus sexual dimorphism, in teleost fishes.

Hydroxytyrosol-rich extract from olive juice as an additive in gilthead sea bream juveniles fed a high-fat diet: Regulation of somatic growth

The dietary inclusion of plant-based products in fish feeds formulation is required for the sustainable development of aquaculture. Moreover, considering functional diets, hydroxytyrosol, one of the major phenolic compounds found in olives (Olea europaea), has been identified as a potential candidate to be used in the aquafeeds industry due to its health promoting abilities. The aim of this study was to evaluate the effects of the inclusion of an olive juice extract rich in hydroxytyrosol as an additive (0.52 g HT/kg feed) in a high-fat (24% lipids) diet in gilthead sea bream (Sparus aurata) juveniles. Moreover, the experimental diets, with or without the extract, were administered daily at a standard (3% of total biomass in the tank) or restricted ration (40% reduction) for 8–9 weeks. Growth and biometric parameters, insulin-like growth factor 1 (IGF-1) plasma levels and growth hormone/IGF axis-, myogenic- and osteogenic-related genes expression in liver, white muscle and/or bone were analyzed. Moreover, in vitro cultures of vertebra bone-derived cells from fish fed the diets at a standard ration were performed at weeks 3 and 9 to explore the effects of hydroxytyrosol on osteoblasts development. Although neither body weight or any other biometric parameter were affected by diet composition after 4 or 8 weeks, the addition of the hydroxytyrosol-rich extract to the diet increased IGF-1 plasma levels, regardless of the ration regime, suggesting an anabolic condition. In muscle, the higher mRNA levels of the binding protein igfbp-5b and the myoblast fusion marker dock5 in fish fed with the hydroxytyrosol-rich diet suggested that this compound may have a role in muscle, inducing development and a better muscular condition. Furthermore in bone, increased osteogenic potential while delayed matrix mineralization after addition to the diet of the olive juice extract was supported by the upregulated expression of igf-1 and bmp4 and reduced transcript levels of osteopontin. Overall, this study provides new insights into the beneficial use of hydroxytyrosol as a dietary additive in gilthead sea bream functional diets to improve muscle-skeletal condition and, the aquaculture industry.

Effects of long-term sex steroid hormones (estradiol and testosterone)-supplemented feeds on the growth performance of Chinese tongue sole (Cynoglossus semilaevis)

The phenomenon of sexual size dimorphism (SSD), existing in mammals, birds, reptiles, spiders, amphibians, insects, and fishes, is generally related to feeding efficiency, energy allocation, sex steroids, and somatotropic and reproductive endocrine axes. Recently, positive and negative regulations of sex steroids have been reported on SSD in various species. Chinese tongue soles (Cynoglossus semilaevis) at 4 months were fed with 17β-estradiol (E2) and testosterone (T) supplemented feeds for 8 months to assess the effect of sex steroids on growth traits in different sexes. The potential genetic regulation was examined using several growth-related genes. The results showed that two sex steroid hormones had inhibitory effects on the growth performance of different sexes of C. semilaevis. At the age of 8 months, the expression of insulin-like growth factor 2 gene (igf2), 24-dehydrocholesterol reductase (dhcr24), leptin, and estrogen receptor 2 (esr2) in the liver showed an overall downward trend. The expression of insulin-like growth factor 1 (igf1) was reduced, while thyroid hormone receptor-associated protein 3 (thrap3) expression tended to increase in the gonad after T and E2 treatments. In the brain, somatostatin 1, tandem duplicate 2 (sst1.2) expression increased with the treatment of T and E2 (P < 0.05), while growth hormone-releasing hormone (ghrh) expression decreased. E2 and T had different effects on growth differentiation factor 8 (gdf8) and insulin-like growth factor-binding protein 7 (igfbp7) expression in the muscle. Expression of gdf8 increased in the treated fishes in contrast to the reduction expression of igfbp7. This study provided important clues for understanding the role of sex steroids in flatfish SSD.

Social status-dependent regulation and function of the somatotropic axis in juvenile rainbow trout

Juvenile rainbow trout (Oncorhynchus mykiss) develop social hierarchies when competing for resources in a constrained environment. Among the physiological consequences of social status are changes in organismal energy metabolism, which generally favour anabolic pathways in dominant fish and catabolic pathways in subordinate fish. The somatotropic axis is an important regulator of metabolism and growth that could be involved in mediating metabolic changes in response to social status in juvenile rainbow trout. Here we used juvenile trout housed either in dyads or individually (sham controls) to determine whether social status changes indices of somatotropic axis function. Although pituitary growth hormone expression (gh1 and gh2) did not differ among groups, circulating growth hormone (GH) increased ∼12-fold in subordinate fish compared to sham and dominant fish. Social status caused consistent differential expression of GH receptor paralogues in liver and muscle, two principal target tissues of GH. Compared to dominant and/or sham fish, ghra paralogue expression (ghra1 and ghra2) was lower, while ghrb1 expression was higher in subordinate fish. Across tissues, ghra paralogue expression was generally positively correlated with expression of insulin growth factors (igf1, igf2), while ghrb1 expression was positively correlated with transcript abundance of hormone sensitive lipase (hsl1). Because igf and hsl expression are subject to context-dependent GH control in rainbow trout, these results suggest that increased circulating GH in conjunction with differential expression of ghr paralogues may translate into prioritization of downstream catabolic lipolytic pathways in subordinate rainbow trout. These findings support a social context-dependent role for GH signalling in mediating metabolic changes in juvenile rainbow trout.

Insights into the mechanisms of tris(2-chloroethyl) phosphate-induced growth inhibition in juvenile yellow catfish Pelteobagrus fulvidraco

With the gradual elimination of brominated flame retardants (BFRs), the production and application of tris (2-chloroethyl) phosphate (TCEP), as a substitute of BFRs, has increased greatly. The objective of the present study was to comprehensively explore the potential adverse effects of TCEP on fish growth and the possible underlying mechanisms. To this end, juvenile yellow catfish (Pelteobagrus fulvidraco) were exposed to environmentally relevant concentrations of TCEP (0, 1, 10 and 100 µg/L) for 30 days. The results showed that exposure to high concentrations of TCEP (10 and 100 µg/L) significantly decreased body weight, body length and specific growth rate (SGR). Plasma IGF-I levels and hepatic mRNA levels of igf1 and igf1r were all reduced, while the transcriptional levels of IGFBPs (igfbp2, igfbp3, igfbp5) were significantly up-regulated in the liver of yellow catfish under exposure to 10 and 100 µg/L TCEP. TCEP-induced growth inhibition might be related to somatostatin (SS) signaling system, as evidenced by elevated mRNA transcriptions of ss in brain and its receptors (sstr2, sstr3, sstr5) in liver. In addition, fish exposed to high concentrations of TCEP displayed multiple histological alterations in liver. Taken together, these findings suggested that TCEP (>10 µg/L) might exert its inhibitory effect on fish growth through interfering with the GH/IGF axis and SS signaling system, and by impairing hepatic structures.

Repeated intraperitoneal injection of ovine growth hormone accelerates growth in sub-yearling Siberian sturgeon Acipenser baerii

The role of growth hormone (GH) in chondrosteans is poorly understood, particularly with regard to its effects on growth. In this study, we examined the influence of exogenous GH on growth performance and body composition in juvenile Siberian sturgeon (Acipenser baerii). Fish with initial weight of 80.2 ± 0.1 g (mean ± S.E) were injected once every 10 days with either purified ovine GH (oGH) at 1, 2, 4, and 8 μg oGH/g body weight (BW) or with saline over a 50-day period. Treatment with the highest dose of oGH significantly enhanced growth performance (final body weight and length, body weight increase and specific growth rate, SGR). Notably, 8 μg oGH/g BW increased body weight by 33% and SGR_w by 141% compared to control fish. GH-stimulated (8 μg oGH/g BW) growth was accompanied by increased crude protein content; however, oGH treatment did not affect levels of total protein, total lipid, cholesterol, triglyceride, or glucose in plasma. oGH decreased plasma levels of thyroxine (at 4 μg oGH/g BW), but had no significant effect on plasma levels of triiodothyronine or cortisol compared to controls. These findings indicate that 8 μg oGH/g BW enhances somatic growth and synthesis of body protein in juvenile Siberian sturgeon and demonstrate the feasibility of exogenous oGH treatment in conservation and aquaculture programs for this ancient species.

Metabolic and molecular signatures of improved growth in Atlantic salmon (Salmo salar) fed surplus levels of methionine, folic acid, vitamin B6 and B12 throughout smoltification

A moderate surplus of the one carbon (1C) nutrients methionine, folic acid, vitamin B₆ and B₁₂ above dietary recommendations for Atlantic salmon has shown to improve growth and reduce hepatosomatic index in the on-growing saltwater period when fed throughout smoltification. Metabolic properties and molecular mechanisms determining the improved growth are unexplored. Here, we investigate metabolic and transcriptional signatures in skeletal muscle taken before and after smoltification to acquire deeper insight into pathways and possible nutrient–gene interactions. A control feed (Ctrl) or 1C nutrient surplus feed (1C+) were fed to Atlantic salmon 6 weeks prior to smoltification until 3 months after saltwater transfer. Both metabolic and gene expression signatures revealed significant 1C nutrient-dependent changes already at pre-smolt, but differences intensified when analysing post-smolt muscle. Transcriptional differences revealed lower expression of genes related to translation, growth and amino acid metabolisation in post-smolt muscle when fed additional 1C nutrients. The 1C+ group showed less free amino acid and putrescine levels, and higher methionine and glutathione amounts in muscle. For Ctrl muscle, the overall metabolic profile suggests a lower amino acid utilisation for protein synthesis, and increased methionine metabolisation in polyamine and redox homoeostasis, whereas transcription changes are indicative of compensatory growth regulation at local tissue level. These findings point to fine-tuned nutrient–gene interactions fundamental for improved growth capacity through better amino acid utilisation for protein accretion when salmon was fed additional 1C nutrients throughout smoltification. It also highlights potential nutritional programming strategies on improved post-smolt growth through 1C+ supplementation before and throughout smoltification.

Transcriptomes of testis and pituitary from male Nile tilapia (O. niloticus L.) in the context of social status

African cichlids are well established models for studying social hierarchies in teleosts and elucidating the effects social dominance has on gene expression. Ascension in the social hierarchy has been found to increase plasma levels of steroid hormones, follicle stimulating hormone (Fsh) and luteinizing hormone (Lh) as well as gonadosomatic index (GSI). Furthermore, the expression of genes related to gonadotropins and steroidogenesis and signaling along the brain-pituitary-gonad axis (BPG-axis) is affected by changes of an animal’s social status. In this study, we use RNA-sequencing to obtain an in-depth look at the transcriptomes of testes and pituitaries from dominant and subordinate male Nile tilapia living in long-term stable social hierarchies. This allows us to draw conclusions about factors along the brain-pituitary-gonad axis that are involved in maintaining dominance over weeks or even months. We identify a number of genes that are differentially regulated between dominant and subordinate males and show that in high-ranking fish this subset of genes is generally upregulated. Genes differentially expressed between the two social groups comprise growth factors, related binding proteins and receptors, components of Wnt-, Tgfβ- and retinoic acid-signaling pathway, gonadotropin signaling and steroidogenesis pathways. The latter is backed up by elevated levels of 11-ketotestosterone, testosterone and estradiol in dominant males. Luteinizing hormone (Lh) is found in higher concentration in the plasma of long-term dominant males than in subordinate animals. Our results both strengthen the existing models and propose new candidates for functional studies to expand our understanding of social phenomena in teleost fish.

Roles of leptin in initiation of acquired growth hormone resistance and control of metabolism in rainbow trout

Catabolic conditions often induce concomitant changes in plasma leptin (Lep), growth hormone (GH) and insulin growth factor I (IGF-I) levels in teleost fish, but it is unclear whether these parts of the endocrine system are responding independently or functionally linked. In this study, fasted rainbow trout was used to study the effects of Lep on the GH-IGF-I system and metabolism. Fish were implanted intraperitoneally with recombinant rainbow trout Lep pellets and remained unfed. After 4 days, plasma GH levels were elevated in the Lep-treated fish in a dose-dependent manner; the expression of hepatic igf1 and plasma IGF-I levels were suppressed accordingly. In vitro Lep treatment reversed ovine GH (oGH)-stimulated expression of igf1 and igf2 in hepatocytes isolated from fasted fish, similar to the inhibitory effects of the MEK1/2 inhibitor U0126 treatment. However, Lep treatment alone had no effect on the expression of igfs or oGH-stimulated ghr2a expression in the hepatocytes. These results demonstrate an additive effect of Lep on suppression of IGF-I under catabolic conditions, indicating that Lep is likely involved in initiation of acquired GH resistance. Although the Lep-implant treatment had no effect on standard metabolic rate, it significantly suppressed gene expression of hepatic hydroxyacyl-CoA dehydrogenase, phosphoenolpyruvate carboxykinase and glucose 6-phosphatase, which are key enzymes in lipid utilization and gluconeogenesis, in different patterns. Overall, this study indicates that the Lep increase in fasting salmonids is an important regulatory component for physiological adaptation during periods of food deprivation, involved in suppressing growth and hepatic metabolism to spare energy expenditure.

Effects of seawater and freshwater challenges on the Gh/Igf system in the saline-tolerant blackchin tilapia (Sarotherodon melanotheron)

Prolactin (Prl) and growth hormone (Gh) as well as insulin-like growth factor 1 (Igf1) are involved in the physiological adaptation of fish to varying salinities. The Igfs have been also ascribed other physiological roles during development, growth, reproduction and immune regulation. However, the main emphasis in the investigation of osmoregulatory responses has been the endocrine, liver-derived Igf1 route and local regulation within the liver and osmoregulatory organs. Few studies have focused on the impact of salinity alterations on the Gh/Igf-system within the neuroendocrine and immune systems and particularly in a salinity-tolerant species, such as the blackchin tilapia Sarotherodon melanotheron. This species is tolerant to hypersalinity and saline variations, but it is confronted by severe climate changes in the Saloum inverse estuary. Here we investigated bidirectional effects of increased salinity followed by its decrease on the gene regulation of prl, gh, igf1, igf2, Gh receptor and the tumor-necrosis factor a. A mixed population of sexually mature 14-month old blackchin tilapia adapted to freshwater were first exposed to seawater for one week and then to fresh water for another week. Brain, pituitary, head kidney and spleen were excised at 4 h, 1, 2, 3 and 7 days after both exposures and revealed differential expression patterns. This investigation should give us a better understanding of the role of the Gh/Igf system within the neuroendocrine and immune organs and the impact of bidirectional saline challenges on fish osmoregulation in non-osmoregulatory organs, notably the complex orchestration of growth factors and cytokines.

Low Temperature Effect on the Endocrine and Circadian Systems of Adult Danio rerio

The control of the biological rhythms begins with the activation of photo- and thermosensitive cells located in various organs of the fish such as brain, eye, and skin, but a central clock is still to be identified in teleosts. Thermal changes are stressors which increase cortisol and affect the rhythm of other hormones such as melatonin and growth hormone (GH), in both endo- and ectothermic organisms. Our aim was to investigate how temperature (23°C for 6 days) lower than the optimal (28°C) modulates expression of several gene pathways including growth hormone (gh1) and its receptors (ghra, ghrb), insulin-like growth factor1 (igf1a, igf1b) and its receptors (igf1ra, igf1rb), cortisol and its receptor (gr), the limiting enzyme of melatonin synthesis (arylalkylamine N-acetyltransferase, aanat) and melatonin receptors (mtnr1aa, mtnr1bb), as well as their relationship with clock genes in Danio rerio in early light and early dark phases of the day. Lower temperature reduced the expression of the hormone gene gh1, and of the related receptors ghra, ghrb, igf1ra, and igf1rb. Cortisol levels were higher at the lower temperature, with a decrease of its receptor (gr) transcripts in the liver. Interestingly, we found higher levels of aanat transcripts in the brain at 23°C. Overall, lower temperature downregulated the transcription of hormone related genes and clock genes. The results suggest a strong correlation of temperature challenge with the clock molecular mechanism and the endocrine systems analyzed, especially the growth hormone and melatonin axes, in D. rerio tissues.

Recombinant Bovine Growth Hormone-Induced Metabolic Remodelling Enhances Growth of Gilthead Sea-Bream (Sparus aurata): Insights from Stable Isotopes Composition and Proteomics

Growth hormone and insulin-like growth factors (GH/IGF axis) regulate somatic growth in mammals and fish, although their action on metabolism is not fully understood in the latter. An intraperitoneal injection of extended-release recombinant bovine growth hormone (rbGH, Posilac^®) was used in gilthead sea bream fingerlings and juveniles to analyse the metabolic response of liver and red and white muscles by enzymatic, isotopic and proteomic analyses. GH-induced lipolysis and glycogenolysis were reflected in liver composition, and metabolic and redox enzymes reported higher lipid use and lower protein oxidation. In white and red muscle reserves, rBGH increased glycogen while reducing lipid. The isotopic analysis of muscles showed a decrease in the recycling of proteins and a greater recycling of lipids and glycogen in the rBGH groups, which favoured a protein sparing effect. The protein synthesis capacity (RNA/protein) of white muscle increased, while cytochrome-c-oxidase (COX) protein expression decreased in rBGH group. Proteomic analysis of white muscle revealed only downregulation of 8 proteins, related to carbohydrate metabolic processes. The global results corroborated that GH acted by saving dietary proteins for muscle growth mainly by promoting the use of lipids as energy in the muscles of the gilthead sea bream. There was a fuel switch from carbohydrates to lipids with compensatory changes in antioxidant pathways that overall resulted in enhanced somatic growth.

Venlafaxine deposition in the zygote disrupts the endocrine control of growth in juvenile zebrafish

The antidepressant venlafaxine can be found at levels nearing μg/L in waterways receiving municipal wastewater effluent, exposing non-target organisms, such as fish, to this chemical. We showed previously that zygotic exposure to venlafaxine alters neurodevelopment and behaviour in zebrafish (Danio rerio) larvae. Here, we tested the hypothesis that the zygotic deposition of venlafaxine disrupts endocrine pathways related to growth in zebrafish. This was carried out by microinjecting embryos (1-4 cell stage) with either 0, 1, or 10 ng venlafaxine. Zygotic venlafaxine deposition reduced the growth of fish after 30 days post-fertilization. Specific growth rate was particularly impacted by 1 ng venlafaxine. This growth retardation corresponded with the disruption of endocrine pathways involved in growth and metabolism. Venlafaxine exposed embryos displayed reduced transcript abundance of key genes involved in anabolic hormone action. Early-life venlafaxine exposure also reduced whole-body insulin and glucose content in juveniles. Target-tissue glucose uptake measurements indicated that high venlafaxine deposition preferentially increased glucose uptake to the brain. Zygotic venlafaxine did not affect feed intake nor altered the transcript abundance of key feeding-related peptides. Taken together, zygotic venlafaxine deposition compromises zebrafish growth by disrupting multiple endocrine pathways, and this study has identified key markers for potential use in risk assessment.

Perfluorinated compounds disrupted osmoregulation in Oryzias melastigma during acclimation to hypoosmotic environment

Perfluorinated compounds (PFCs) are a type of ubiquitous contaminants spreading in the estuarine and coastal areas. Anadromous fish should deal with hypoosmotic challenge with PFCs stress during their migration from seawater to estuaries. However, few studies have been carried out to investigate the adverse impact of PFCs on fish osmoregulation and the underlying mechanism. In this study, Oryzias melastigma, an euryhaline fish model, were exposed to four representative PFC congeners including perfluorobutane sulfonate (PFBS), perfluorooctane sulfonates (PFOS), perfluorooctanoic acid (PFOA), and perfluorododecanoic acid (PFDoA) separately under both seawater and freshwater conditions. Histopathological changes in gills, ion homeostasis, Na⁺/K⁺-ATPase (NKA) activity, as well as the expression of related genes was detected upon exposure. Results showed that PFCs induced morphological changes in gills, disturbed the levels of major ions (Na⁺, Ca²⁺, Mg²⁺), and inhibited the NKA activity. Transcriptome analysis in fish gills during the acclimation to freshwater revealed that PFCs influenced the osmoregulation mainly by interfering with the endocrine system, signal transduction, as well as cellular community and motility. Validation with qRT-PCR confirmed that the mRNA expressions of osmoregulatory genes encoding hormones and receptors, as well as ion transmembrane transporters were disturbed by PFCs. Longer chain homolog (PFOS) showed a greater impact on osmoregulation than the shorter chain homolog (PFBS). Within the same carbon chain, sulfonic congener (PFOS) induced more serious injury to gills than carboxylic congener (PFOA). The interaction between PFCs and salinity varied in different adverse outcome. These results help to further understand the mechanism of how PFCs influence osmoregulation and elicit the need to assess the ecological risk of PFCs and other pollutants on anadromous migration.

Coordinate regulation of feeding, metabolism, and growth: Perspectives from studies in fish

This paper develops a model for coordinate regulation of feeding, metabolism, and growth based on studies in fish. Many factors involved with the control of feeding [e.g., cholecystokinin (CCK) and ghrelin (GRLN)], energy metabolism [e.g., insulin (INS), glucagon (GLU), glucagon-like peptide (GLP), and somatostatins (SS), produced in the endocrine pancreas; and leptin (LEP) produced broadly], and growth [e.g., GRLN, growth hormone (GH), insulin-like growth factors (IGFs), GH receptors (GHR), IGF receptors (IGFR)] interact at various levels. Many such interactions serve to coordinate these systems to favor anabolic processes (i.e., lipid and protein synthesis, glycogenesis) and growth, including GH promotion of feeding and stimulation of INS production/secretion and the upregulation of GHR and IGFR by GRLN. As nutrient and stored energy status change, various feedbacks serve to curtail feeding and transition the animal from an anabolic/growth state to a catabolic state. Many factors, including LEP and IGF, promote satiety, whereas SS downregulates INS signaling as well as IGF production and GHR and IGFR abundance. As INS and IGF levels fall, GH becomes disconnected from growth as a result of altered linkage of GHR to cell signaling pathways. As a result, the catabolic actions of GH, GLU, GLP, LEP, and SS prevail, mobilizing stored energy reserves. Coordinate regulation involves relative abundances of blood-borne hormones as well as the ability to adjust responsiveness to hormones (via receptor and post-receptor events) in a cell-/tissue-specific manner that results from genetic and epigenetic programming and modulation by the local milieu of hormones, nutrients, and autocrine/paracrine interactions. The proposed model of coordinate regulation demonstrates how feeding, metabolism, and growth are integrated with each other and with other processes, such as reproduction, and how adaptive adjustments can be made to energy allocation during an animal's life history and/or in response to changes in environmental conditions.

Growth Hormone Overexpression Induces Hyperphagia and Intestinal Morphophysiological Adaptations to Improve Nutrient Uptake in Zebrafish

The excess of circulating growth hormone (GH) in most transgenic animals implies mandatory growth resulting in higher metabolic demand. Considering that the intestine is the main organ responsible for the digestion, absorption, and direction of dietary nutrients to other tissues, this study aimed to investigate the mechanisms by which gh overexpression modulates the intestine to support higher growth. For this purpose, we designed an 8-weeks feeding trial to evaluate growth parameters, feed intake, and intestinal morphometric indices in the adult gh-transgenic zebrafish (Danio rerio) model. To access the sensitivity of the intestine to the excess of circulating GH, the messenger RNA (mRNA) expression of intestine GH receptors (GHRs) (ghra and ghrb) was analyzed. In addition, the expression of insulin-like growth factor 1a (igf1a) and genes encoding for di and tripeptide transporters (pept1a and pept1b) were assessed. Gh-transgenic zebrafish had better growth performance and higher feed intake compared to non-transgenic sibling controls. Chronic excess of GH upregulates the expression of its cognate receptor (ghrb) and the main growth factor related to trophic effects in the intestine (igf1a). Moreover, transgenic zebrafish showed an increased intestinal absorptive area and higher expression of crucial genes related to the absorption of products from meal protein degradation. These results reinforce the ability of GH to modulate intestinal morphology and the mechanisms of assimilation of nutrients to sustain the energy demand for the continuous growth induced by the excess of circulating GH.

Higher acclimation temperature affects growth of rohu (Labeorohita) through suppression of GH and IGFs genes expression actuating stress response

Water temperature alone can affect the growth, metabolic rates and physiological responses of aquatic organisms. Our earlier study reported that higher temperature affects cellular and hemato-biochemical responses in rohu, Labeo rohita. In this backdrop, the present study assessed the effect of higher acclimation temperature on the regulatory mechanisms of growth and stress responses of juvenile L. rohita acclimatized in three temperature conditions (30 °C, 33 °C, and 36 °C) for a period of 30 days. The relative expression of genes for growth hormone (GH), insulin-like growth factors (IGF-1 and IGF-2) and heat shock proteins (hsp70 and hsp90) were measured by real-time quantitative PCR. The results revealed that the highest acclimation temperature (36 °C) significantly decreased the weight gain (WG) and specific growth rate (SGR), and increased the feed conversion ratio (FCR) compared to 30 °C (control), while increased WG, SGR and lowered FCR were observed in fish reared at the intermediate temperature (33 °C) compared to 30 °C. Similarly, the GH gene expression in the pituitary was significantly decreased and increased at 36 °C and 33 °C, respectively as compared to 30 °C. A significantly lower expression of IGF-1 and IGF-2, and higher expression of hsp70 and hsp90 were observed in the liver of fish at 36 °C. The results of the present study indicate that although slightly elevated temperature promotes the growth of juvenile L. rohita, the higher acclimation temperature may induce stress response and impair growth performance by suppressing GH/IGF system.

Expression of insulin-like growth factors depends on both mass and resource availability in female green anoles (Anolis carolinensis)

The insulin and insulin-like signaling (IIS) network is an important mediator of cellular growth and metabolism in animals, and is sensitive to environmental conditions such as temperature and resource availability. The two main hormones of the IIS network, insulin-like growth factor 1 (IGF1) and insulin-like growth factor 2 (IGF2), are present in all vertebrates, yet little is known regarding the responsiveness of IGF2 in particular to external stimuli in non-mammalian animals. We manipulated diet (low or high quantity of food: low and high diet group, respectively) in adult green anole (Anolis carolinensis) females to test the effect of energetic state on hepatic gene expression of IGF1 and IGF2. The absolute expression of IGF2 in female green anoles was 100 times higher than that of IGF1 regardless of diet treatment, and IGF1 and IGF2 expression interacted with post-treatment body mass and treatment, as did the expression of the purported housekeeping genes glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and eukaryotic elongation factor 2 (EEF2). The low diet group showed a negative relationship between body mass and gene expression for all genes, whereas the relationships between body mass and gene expression in the high diet group were either absent (in the case of IGF1) or positive (for all other genes). After accounting for total change in mass, the low diet group expressed IGF2, GAPDH and EEF2 at higher levels compared with individuals in the high diet group of a similar change in mass. These results illustrate that expression of IGF1 and IGF2, and of the housekeeping genes is affected by energe-tic status in reptiles.

Environmental estrogens inhibit the expression of insulin-like growth factor mRNAs in rainbow trout in vitro by altering activation of the JAK-STAT, AKT-PI3K, and ERK signaling pathways

Environmental estrogens (EE) have been found to disrupt a host of developmental, reproductive, metabolic, and osmoregulatory process in a wide-range of animals, particularly those in aquatic ecosystems where such compounds concentrate. Previously, we showed that EE inhibited post-embryonic organismal growth of rainbow trout in vivo, but the precise mechanism(s) through which EE exert their growth inhibiting effects remain unknown. In this study, we used rainbow trout (Oncorhynchus mykiss) as a model to investigate the direct effects of 17β-estradiol (E2), β-sitosterol (βS), and 4-n-nonylphenol (NP) on the synthesis of insulin-like growth factors (IGFs) and to elucidate the mechanism(s) by which EEs exert such effects. E2, βS, and NP significantly inhibited the expression of both IGF-1 and IGF-2 mRNAs in liver and gill in a time- and concentration-related manner. Although the response evoked by each EEs on the expression of IGF mRNAs was similar, the potency and efficacy varied with EE; the rank order potency/efficacy was as follows: E2 > NP > βS. The effects of EEs on the expression of IGF mRNAs was blocked by the estrogen receptor (ER) antagonist, ICI 182780. The mechanism(s) through which EEs inhibit IGF mRNA expression were investigated in isolated liver cells in vitro. EE treatment deactivated JAK, STAT, ERK, and AKT. Moreover, blockade of growth hormone (GH)-stimulated IGF expression by EE was accompanied by deactivation of JAK, STAT, ERK, and AKT. EEs also increased the expression of suppressor of cytokine signaling 2 (SOCS-2), a known inhibitor of JAK-2--an action that also was blocked by ICI 182780. These results indicate that EEs directly inhibit the expression of IGF mRNAs by disrupting GH post-receptor signaling pathways (e.g., JAK, STAT, ERK, and AKT) in an ER-dependent manner.

Insulin-like growth factor signalling and its significance as a biomarker in fish and shellfish research

The insulin-like growth factor signalling system comprises insulin-like growth factors, insulin-like growth factor receptors and insulin-like growth factor-binding proteins. Along with the growth hormones, insulin-like growth factor signalling is very pivotal in the growth and development of all vertebrates. In fishes, insulin-like growth factors play an important role in osmoregulation, besides the neuroendocrine regulation of growth. Insulin-like growth factor concentration in plasma can assess the growth in fishes and shellfishes and therefore widely applied in nutritional research as an indicator to evaluate the performance of selected nutrients. The present review summarizes the role of insulin-like growth factor signalling in fishes and shellfishes, its significance in aquaculture and in evaluating growth, reproduction and development, and discusses the utility of this system as biomarkers for early indication of growth in aquaculture.

Diet and Exercise Modulate GH-IGFs Axis, Proteolytic Markers and Myogenic Regulatory Factors in Juveniles of Gilthead Sea Bream (Sparus aurata)

Simple Summary

The effects of exercise and diet on growth markers were analyzed in gilthead sea bream juveniles. Under voluntary swimming, fish fed with a high-lipid diet showed lower growth, growth hormone (GH) plasma levels, flesh texture, and higher expression of main muscle proteolytic markers than those fed with a high-protein diet. However, under sustained exercise, most of the differences disappeared and fish growth was similar regardless of the diet, suggesting that exercise improves nutrients use allowing a reduction of the dietary protein, which results in an enhanced aquaculture production.

Abstract

The physiological and endocrine benefits of sustained exercise in fish were largely demonstrated, and this work examines how the swimming activity can modify the effects of two diets (high-protein, HP: 54% proteins, 15% lipids; high-energy, HE: 50% proteins, 20% lipids) on different growth performance markers in gilthead sea bream juveniles. After 6 weeks of experimentation, fish under voluntary swimming and fed with HP showed significantly higher circulating growth hormone (GH) levels and plasma GH/insulin-like growth-1 (IGF-1) ratio than fish fed with HE, but under exercise, differences disappeared. The transcriptional profile of the GH-IGFs axis molecules and myogenic regulatory factors in liver and muscle was barely affected by diet and swimming conditions. Under voluntary swimming, fish fed with HE showed significantly increased mRNA levels of capn1, capn2, capn3, capns1a, n3, and ub, decreased gene and protein expression of Ctsl and Mafbx and lower muscle texture than fish fed with HP. When fish were exposed to sustained exercise, diet-induced differences in proteases’ expression and muscle texture almost disappeared. Overall, these results suggest that exercise might be a useful tool to minimize nutrient imbalances and that proteolytic genes could be good markers of the culture conditions and dietary treatments in fish.

Insulin-like growth factors 1 and 2 are associated with testicular germ cell proliferation and apoptosis during fish reproduction

To support sperm production, fish testes undergo intense tissue remodelling, with endocrine, paracrine and autocrine signals regulating gonad physiology. The aim of this study was to investigate the testicular expression of insulin-like growth factor (Igf) 1 and Igf2 during spermatogenesis, and their relationship with cell proliferation and apoptosis throughout the reproductive cycle. The study was performed in male Hypostomus garmani, a catfish living in headwater rivers of the São Francisco River basin, Brazil. Spermatogenesis was analysed using histology, morphometry, immunohistochemistry and terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling (TUNEL) analysis at different maturity stages. The results showed the proliferation of spermatogonia throughout the reproductive cycle, with a higher rate during the ripe stage. Germ and Sertoli cells expressed Igf1 at all stages of testicular maturity, Igf2 was predominant at the ripe stage and both Igf1 and Igf2 occurred at the spent stage. Caspase-3 and TUNEL analysis revealed a higher rate of apoptosis at the spent stage associated with reduced expression of Igf1 and Igf2. Sertoli cell proliferation was associated with spermatogonia and spermatocyte cysts at different stages of the reproductive cycle. Together, the data support a proliferative role for Igf1 and Igf2 in regulating testicular apoptosis in H. garmani, with cyclical variation in their expression during gonad maturation.

Sub-chronic exposure to ammonia inhibits the growth of juvenile Wuchang bream (Megalobrama amblycephala) mainly by downregulation of growth hormone/insulin-like growth factor axis

In this study, healthy Wuchang bream (Megalobrama amblycephala) juveniles were exposed to 0, 5, 10, 20 and 30 mg/L total ammonia nitrogen for 30 days to elucidate toxic effects and mechanisms of ammonia on growth performance involved with the regulation of growth hormone/insulin-like growth factor (GH/IGF) and hypothalamic-pituitary-thyroid (HPT) axes. Our results showed that the increasing total ammonia nitrogen concentrations caused dose-depend decreases in the weight gain and specific growth rate but increases in the food conversion ratio and mortality in juvenile bream, indicating growth inhibitory effects induced by ammonia. Concurrently, GH, IGF-1 at protein and mRNA levels were significantly decreased in ammonia exposure groups (p < .05), while serum thyroid stimulating hormone, free thyroxine, free triiodothyronine levels were significantly reduced only in fish exposed to higher concentrations of 20 and 30 mg/L ammonia (p < .05), suggesting that ammonia exposure could perturb both GH/IGF-axis and HPT-axis functions. Furthermore, transcriptional levels of extracellular regulated protein kinases 2 (erk2), phosphatidylinositol 3-kinase (pi3k), protein kinase B (akt), target of rapamycin (tom) and ribosomal protein S6 kinase-polypeptide 1(s6k1) in the dorsal muscle were significantly down-regulated in the fish exposed to ammonia (p < .05). This fact indicated that MAPK/ERK pathway and PI3K/AKT pathway should be responsible for the growth inhibition. Combining the results of spearman correlation coefficient, it should be noted that the GH/IGF axis played a more important role in regulating the growth than the HPT axis in Wuchang bream under persistent ammonia stress.

Testosterone Reduces Growth and Hepatic IGF-1 mRNA in a Female-Larger Lizard, Sceloporus undulatus: Evidence of an Evolutionary Reversal in Growth Regulation

Previous research has demonstrated that testosterone (T) can inhibit growth in female-larger species and stimulate growth in male-larger species, but the underlying mechanisms of this regulatory bipotentiality have not been investigated. In this study, we investigated the effects of T on the expression of hepatic insulin-like growth factor-1 (IGF-1) mRNA and circulating IGF-1 hormone in Sceloporus undulatus, a species of lizard in which females grow faster to become larger than males and in which T inhibits growth. Experiments were performed in captivity on mature female and male adults in the asymptotic phase of their growth curve and on actively growing, pre-reproductive juveniles. In adult males, the expression of hepatic IGF-1 mRNA increased following surgical castration and returned to control levels with T replacement; in intact adult females, exogenous T had no effect on IGF-1 mRNA expression. In juveniles, T significantly reduced both growth and the expression of hepatic IGF-1 mRNA to similar extents in intact females and in castrated males. The relative inhibitory effects of T on mRNA expression were greater in juveniles than in adults. Plasma IGF-1 hormone was about four times higher in juveniles than in adults, but T had no significant effect on IGF-1 hormone in either sex or in either age group. Our finding of inhibition of the expression of hepatic IGF-1 mRNA stands in contrast to the stimulatory effects of T in the published body of literature. We attribute our novel finding to our use of a species in which T inhibits rather than stimulates growth. Our findings begin to explain how T has the regulatory bipotentiality to be stimulatory in some species and inhibitory in others, requiring only an evolutionary reversal in the molecular regulation of growth-regulatory genes including IGF-1. Further comparative transcriptomic studies will be required to fully resolve the molecular mechanism of growth inhibition.

Musculoskeletal Growth Modulation in Gilthead Sea Bream Juveniles Reared at High Water Temperature and Fed with Palm and Rapeseed Oils-Based Diets

The upward trend of seawater temperature has encouraged improving the knowledge of its consequences on fish, considering also the development of diets including vegetable ingredients as an approach to achieve a more sustainable aquaculture. This study aims to determine the effects on musculoskeletal growth of: (1) a high-water temperature of 28 °C (versus 21 °C) in gilthead sea bream juveniles (Sparus aurata) fed with a diet rich in palm oil and, (2) feeding the fish reared at 28 °C with two other diets containing rapeseed oil or an equilibrated combination of both vegetable oils. Somatic parameters and mRNA levels of growth hormone-insulin-like growth factors (GH-IGFs) axis-, osteogenic-, myogenic-, lipid metabolism- and oxidative stress-related genes in vertebra bone and/or white muscle are analyzed. Overall, the data indicate that high-water rearing temperature in this species leads to different adjustments through modulating the gene expression of members of the GH-IGFs axis (down-regulating igf-1, its receptors, and binding proteins) and also, to bone turnover (reducing the resorption-activity genes cathepsin K (ctsk) and matrix metalloproteinase-9 (mmp9)) to achieve harmonic musculoskeletal growth. Moreover, the combination of palm and rapeseed oils seems to be the most beneficial at high-water rearing temperature for both balanced somatic growth and muscular fatty acid uptake and oxidation.

Efficacy of nano zinc oxide dietary supplements on growth performance, immunomodulation and disease resistance of African catfish Clarias gariepinus

Zinc (Zn) is an important trace element in fish diets that is required for growth, immunity and antioxidant defense mechanisms. The current study assessed the effects of both organic and nanoparticle zinc oxide (ZnO and ZnO-NPs, respectively) on growth performance, immune response and the antimicrobial effect against Pseudomonas aeruginosa in African catfish Clarias gariepinus. Fish were fed either a control diet or diets supplemented with organic ZnO at concentrations of 20 and 30 mg kg-1 or ZnO-NPs at concentrations of 20 and 30 mg kg-1. After 60 d, a subset of the fish was injected intraperitoneally with 3 × 107 CFU ml-1 of P. aeruginosa. Results showed that body weight gain, feed conversion ratio and specific growth rates were significantly increased in ZnO-NPs20 compared to all other groups. The dietary supplementation with 20 mg kg-1 of ZnO-NPs improved the antioxidant status of fish. Moreover, IgM, lysozyme and nitric oxide showed a significant increase in the fish which received the ZnO-NPs20-supplemented diet. A significant upregulation of growth and stress-related genes was seen in the ZnO-NPs20-supplemented group compared to other groups. However, there was no significant difference in the expression of immune-related genes among ZnO-NPs20, ZnO-NPs30 and ZnO30 groups. These findings highlight the potential use of nano-ZnO for improving growth performance, antioxidant status, immunological status and antibacterial activity against P. aeruginosa in African catfish.

Compensatory Response of the Somatotropic Axis from IGFBP-2b Gene Editing in Rainbow Trout (Oncorhynchus mykiss)

Rainbow trout with gene editing-induced reductions in serum insulin-like growth factor binding protein (IGFBP)-2b exhibit similar growth performance compared to fish without IGFBP-2b gene disruption. The objective of this study is to determine how the components of the insulin-like growth factor (IGF)/IGFBP system respond to a reduction in serum IGFBP-2b abundance. Editing the IGFBP-2b genes in rainbow trout resulted in an 83% decrease in serum IGFBP-2b in mutants. This resulted in a 35% reduction in serum IGF-I, which was offset by reduced expression of hepatic igfbp-1a2 and increased muscle igfr-1a; these responses suggest that an increased IGF-I signaling capacity offset reductions in serum IGF-I. During feed deprivation, the differential expression of igfbp genes supports the attenuation of the growth inhibitory response, likely due to the further reduction in serum IGF-I that alleviated the need for an IGF-inhibitory response. Unique igfbp expression patterns occurred during refeeding, suggesting an enhanced IGF-I signaling capacity in controls. Collectively, these findings support that the role of IGFBP-2b is to regulate serum IGF-I concentrations. The compensatory regulation of IGF/IGFBP system genes indicates that adjustments in other IGFBP, both circulating and at the local level, maintain IGF-I signaling at a level appropriate for the nutritional state of the fish.

Nutrient regulation of somatic growth in teleost fish. The interaction between somatic growth, feeding and metabolism

This review covers the current knowledge on the regulation of the somatic growth axis and its interaction with metabolism and feeding regulation. The main endocrine and neuroendocrine factors regulating both the growth axis and feeding behavior will be briefly summarized. Recently discovered neuropeptides and peptide hormones will be mentioned in relation to feeding control as well as growth hormone regulation. In addition, the influence of nutrient and nutrient sensing mechanisms on growth axis will be highlighted. We expect that in this process gaps of knowledge will be exposed, stimulating future research in those areas.

Cortisol regulates insulin-like growth-factor binding protein (igfbp) gene expression in Atlantic salmon parr

The growth hormone (Gh)/insulin-like growth-factor (Igf)/Igf binding protein (Igfbp) system regulates growth and osmoregulation in salmonid fishes, but how this system interacts with other endocrine systems is largely unknown. Given the well-documented consequences of mounting a glucocorticoid stress response on growth, we hypothesized that cortisol inhibits anabolic processes by modulating the expression of hepatic igfbp mRNAs. Atlantic salmon (Salmo salar) parr were implanted intraperitoneally with cortisol implants (0, 10, and 40 μg g^-1 body weight) and sampled after 3 or 14 days. Cortisol elicited a dose-dependent reduction in specific growth rate (SGR) after 14 days. While plasma Gh and Igf1 levels were unchanged, hepatic igf1 mRNA was diminished and hepatic igfbp1b1 and -1b2 were stimulated by the high cortisol dose. Plasma Igf1 was positively correlated with SGR at 14 days. Hepatic gh receptor (ghr), igfbp1a, -2a, -2b1, and -2b2 levels were not impacted by cortisol. Muscle igf2, but not igf1 or ghr, levels were stimulated at 3 days by the high cortisol dose. As both cortisol and the Gh/Igf axis promote seawater (SW) tolerance, and particular igfbps respond to SW exposure, we also assessed whether cortisol coordinates the expression of branchial igfbps and genes associated with ion transport. Cortisol stimulated branchial igfbp5b2 levels in parallel with Na⁺/K⁺-ATPase (NKA) activity and nka-α1b, Na⁺/K⁺/2Cl^--cotransporter 1 (nkcc1), and cystic fibrosis transmembrane regulator 1 (cftr1) mRNA levels. The collective results indicate that cortisol modulates the growth of juvenile salmon via the regulation of hepatic igfbp1s whereas no clear links between cortisol and branchial igfbps previously shown to be salinity-responsive could be established.