Effects of aquaculture related stressors and nutritional restriction on circulating growth factors (GH, IGF-I and IGF-II) in Atlantic salmon and rainbow trout

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.

Stocking density affects immune and stress-related gene expression of Butter catfish (Ompok bimaculatus) fry in biofloc landscapes

Scientific research into fish wellness is critical, and the concerns about crowding-related stress due to increased stocking density are inevitable. Taking this into consideration, the study defines the physiological signature of Ompok bimaculatus (Butter catfish) in a biofloc system when subjected to varying levels of stocking density. Fish (mean weight = 1.21 g ± 0.08, n = 600) were randomly stocked in 40-L glass aquaria at stocking densities of 0.5 g/L (T1), 1 g/L (T2), 1.5 g/L (T3), and 2 g/L (T4) and fed a 35% protein diet. After the 90-day trial, the physio-biochemical, molecular, and tissue-level changes were assessed. An integrated biomarker response (IBR) analysis for the key stress indicators aided us in better understanding them. There was a significant difference in blood count between T1 and T4 (total erythrocyte count, hemoglobin, and packed cell volume). T1 had higher levels of globulin and total plasma protein, but T2 had higher levels of albumin. Only in T1 did the respiratory burst and lysozyme activity appear to be higher (p < 0.05). Increased stocking densities had a significant impact on the liver function enzymes, GOT and GPT (p < 0.05). In comparison to lower densities (T1 & T2), higher stocking density (T3 & T4) was found to raise glucose and cortisol levels (p < 0.05). Antioxidant enzymes such as catalase, glutathione-S-transferase, and malondialdehyde were found to be more pronounced in lower density tissues (T1). Furthermore, the IBR plots show that lower densities have better health than higher densities. At higher stocking densities, mRNA expression of HSP70, IL-1, and IL-20 increased (p < 0.05) in kidney and liver tissues. The Nrf-2 and Tlr-9 genes were also upregulated. Also, when stocking density was increased, tissue-level histo-architectural changes were more pronounced than when stocking density was kept low. The findings of this study show that the welfare of Butter catfish cultured at high density in biofloc systems suffers from severe stress, and therefore draw more attention to the development of a species-specific standard rearing methodology in the pursuit of a profitable aqua-farming enterprise.

Understanding how high stocking densities and concurrent limited oxygen availability drive social cohesion and adaptive features in regulatory growth, antioxidant defense and lipid metabolism in farmed gilthead sea bream (Sparus aurata)

The study combined the use of biometric, behavioral, physiological and external tissue damage scoring systems to better understand how high stocking densities drive schooling behavior and other adaptive features during the finishing growing phase of farmed gilthead sea bream in the Western Mediterranean. Fish were grown at three different final stocking densities (LD, 8.5 kg/m3; MD, 17 kg/m3; HD, 25 kg/m3). Water oxygen concentration varied between 5 and 6 ppm in LD fish to 3-4 ppm in HD fish with the summer rise of water temperature from 19°C to 26°C (May-July). HD fish showed a reduction of feed intake and growth rates, but they also showed a reinforced social cohesion with a well-defined endogenous swimming activity rhythm with feeding time as a main synchronization factor. The monitored decrease of the breathing/swimming activity ratio by means of the AEFishBIT data-logger also indicated a decreased energy partitioning for growth in the HD environment with a limited oxygen availability. Plasma glucose and cortisol levels increased with the rise of stocking density, and the close association of glycaemia with the expression level of antioxidant enzymes (mn-sod, gpx4, prdx5) in liver and molecular chaperones (grp170, grp75) in skeletal muscle highlighted the involvement of glucose in redox processes via rerouting in the pentose-phosphate-pathway. Other adaptive features included the depletion of oxidative metabolism that favored lipid storage rather than fatty acid oxidation to decrease the oxygen demand as last electron acceptor in the mitochondrial respiratory chain. This was coincident with the metabolic readjustment of the Gh/Igf endocrine-growth cascade that promoted the regulation of muscle growth at the local level rather than a systemic action via the liver Gh/Igf axis. Moreover, correlation analyses within HD fish displayed negative correlations of hepatic transcripts of igf1 and igf2 with the data-logger measurements of activity and respiration, whereas the opposite was found for muscle igf2, ghr1 and ghr2. This was indicative of a growth-regulatory transition that supported a proactive instead of a reactive behavior in HD fish, which was considered adaptive to preserve an active and synchronized feeding behavior with a minimized risk of oxidative stress and epidermal skin damage.

Short- and long-term effects of nutritional state on IGF-1 levels in nestlings of a wild passerine

Growth trajectories of young animals are intimately connected to their fitness prospects, but we have little knowledge of growth regulation mechanisms, particularly in the wild. Insulin-like growth factor 1 (IGF-1) is a central hormone in regulating resource allocation, with higher IGF-1 levels resulting in more growth. IGF-1 levels generally increase in conjunction with nutritional state, but whether IGF-1 levels are adjusted in response to current nutrient availability or to the nutrient availability integrated over a longer term is not well known. We tested for such effects by supplementary feeding the jackdaw (Corvus monedula) nestlings in experimentally reduced or enlarged broods with either water (control) or a food solution; these manipulations have long- and short-term effects on the nutritional state, respectively. Baseline plasma IGF-1 levels were higher in reduced broods. Food supplementation induced an increase in plasma IGF-1 levels measured one hour later, and this effect was significantly more substantial in nestlings in reduced broods. Changes in plasma IGF-1 levels increased with increased retention of the supplementary food, which was higher in reduced broods, explaining the stronger IGF-1 response. Thus, IGF-1 levels respond to short-term variations in the nutritional state, but this effect is amplified by longer-term variations in the nutritional state. We discuss our findings using a graphical model that integrates the results of the two treatments.

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.

Rationed and satiated growth hormone transgenic Coho Salmon (Oncorhynchus kisutch) show tissue specific differences in energy stores

Growth hormone transgenic coho salmon experience increased growth rates, driven primarily through elevated feed intake and feed conversion. However, neuropeptides that signal appetite stimulation have been shown to exhibit variable responses across fed states, suggesting a more complex system mediating growth in these fish. Studies have proposed that growth hormone may have a modulatory role on the energy reserves of fish, possibly through AMP-activated protein kinase (AMPK) activation. AMPK, an energy sensor in cells, has previously been shown to be upregulated in growth hormone transgenic salmon when compared to wild type, however, whether this effect is seen across fed states is unknown. Here, we tested the hypothesis that growth hormone induces an energetic deficit in metabolic tissues, leading to constitutive AMPK activation in growth hormone transgenic salmon. This study compared AMPK activity, ATP, and glycogen, of the liver, heart, and muscle of wild-type, and growth hormone transgenic salmon either fed to satiation or a wild-type ration. The results suggest that white muscle ATP levels in growth hormone salmon are elevated in satiation and rationed conditions. In the liver, growth hormone transgenic salmon fed a rationed wild-type diet experience reductions in ATP level and glycogen. In none of the tissues examined, did AMPK activity change. Taken together, these results indicate that growth hormone transgenic salmon experience metabolic duress when not fed to satiation.

Validation and utility of hair cortisol analysis as a measure of long-term physiological stress in the Pallas's squirrel Callosciurus erythraeus

In various mammalian species, there has been an increase in the use of hair cortisol analysis to evaluate long-term stress. This trend is because of some advantages relative to the standard tools, such as hormone analysis using blood, urine, or feces. Here, I carried out assay validation and adrenocorticotrophic hormone (ACTH) challenge to measure long-term stress in Pallas's squirrel Callosciurus erythraeus. In addition, I investigated the effects of sex, body condition, season, and reproductive conditions on hair cortisol concentrations (HCC) in free-living individuals. The assay validation was reported in this study. Hair cortisol concentrations in squirrels given repeated ACTH injections were significantly higher than those that received a single-ACTH injection and a saline injection. I found a negative effect of body condition on adult HCC. In contrast, body condition had a positive effect on HCC in juveniles. I found no effects of other factors in either adult or juvenile squirrels. Furthermore, although I investigated whether reproductive conditions, such as pregnancy, lactation, and non-breeding in females or testis size in males, affected HCC, I found that there were no effects of reproductive conditions. This study validated the assay and utility of hair cortisol analysis to assess long-term stress, and continuous investigation of the relationship between HCC and fitness is important for determining whether hair cortisol analysis is a reliable method for estimating population health in Pallas's squirrels.

Endoplasmic reticulum stress as a key mechanism in stunted growth of seawater rainbow trout (Oncorhynchus mykiss)

BACKGROUND

Rainbow trout (Oncorhynchus mykiss) is a salmonid species with a complex life-history. Wild populations are naturally divided into freshwater residents and sea-run migrants. Migrants undergo an energy-demanding adaptation for life in seawater, known as smoltification, while freshwater residents display these changes in an attenuated magnitude and rate. Despite this, in seawater rainbow trout farming all fish are transferred to seawater. Under these circumstances, weeks after seawater transfer, a significant portion of the fish die (around 10%) or experience growth stunting (GS; around 10%), which represents an important profitability and welfare issue. The underlying causes leading to GS in seawater-transferred rainbow trout remain unknown. In this study, we aimed at characterising the GS phenotype in seawater-transferred rainbow trout using untargeted and targeted approaches. To this end, the liver proteome (LC-MS/MS) and lipidome (LC-MS) of GS and fast-growing phenotypes were profiled to identify molecules and processes that are characteristic of the GS phenotype. Moreover, the transcription, abundance or activity of key proteins and hormones related to osmoregulation (Gill Na+, K + -ATPase activity), growth (plasma IGF-I, and liver igf1, igfbp1b, ghr1 and ctsl) and stress (plasma cortisol) were measured using targeted approaches.

RESULTS

No differences in Gill Na+, K + -ATPase activity and plasma cortisol were detected between the two groups. However, a significant downregulation in plasma IGF-I and liver igf1 transcription pointed at this growth factor as an important pathomechanism for GS. Changes in the liver proteome revealed reactive-oxygen-species-mediated endoplasmic reticulum stress as a key mechanism underlying the GS phenotype. From the lipidomic analysis, key observations include a reduction in triacylglycerols and elevated amounts of cardiolipins, a characteristic lipid class associated with oxidative stress, in GS phenotype.

CONCLUSION

While the triggers to the activation of endoplasmic reticulum stress are still unknown, data from this study point towards a nutritional deficiency as an underlying driver of this phenotype.

Effects of starvation and refeeding on growth performance, appetite, growth hormone-insulin-like growth factor axis levels and digestive function of Acipenser dabryanus

The aim of this study was to explore the effects and mechanisms of different starvation treatments on the compensatory growth of Acipenser dabryanus. A total of 120 fish (60·532 (sem 0·284) g) were randomly assigned to four groups (fasting 0, 3, 7 or 14 d and then refed for 14 d). During fasting, middle body weight decreased significantly with prolonged starvation. The whole-body and muscle composition, serum biochemical indexes, visceral indexes and digestive enzyme activities had been effected with varying degrees of changes. The growth hormone (GH) level in serum was significantly increased in 14D; however, insulin-like growth factor-1 (IGF-1) showed the opposite trend. The neuropeptide Y (npy) mRNA level in brain was significantly improved in 7D; peptide YY (pyy) mRNA level in intestine was significantly decreased during fasting. After refeeding, the final body weight, percentage weight gain, specific growth rate, feed intake, feed efficiency and protein efficiency ratio showed no difference between 0D and 3D. The changes of whole-body and muscle composition, serum biochemical indexes, visceral indexes and digestive enzyme activities had taken place in varying degrees. GH levels in 3D and 7D were significantly higher than those in the 0D; the IGF-1 content decreased significantly during refeeding. There was no significant difference in npy and pyy mRNA levels. These results indicated that short-term fasting followed by refeeding resulted in full compensation and the physiological and biochemical effects on A. dabryanus were the lowest after 3 d of starvation and 14 d of refeeding. Additionally, compensation in A. dabryanus may be mediated by appetite genes and GH, and the degree of compensation is also affected by the duration of starvation.

Extreme winter cold-induced osmoregulatory, metabolic, and physiological responses in European seabass (Dicentrarchus labrax) acclimatized at different salinities

Despite climate-change challenges, for most aquaculture species, physiological responses to different salinities during ambient extreme cold events remain unknown. Here, European seabass acclimatized at 3, 6, 12, and 30 PSU were subjected to 20 days of an ambient extreme winter cold event (8 °C), and monitored for growth and physiological performance. Growth performance decreased significantly (p < 0.05) in fish exposed at 3 and 30 PSU compared to 6 and 12 PSU. During cold stress exposure, serum Na+, Cl-, and K+ concentrations were significantly (p < 0.05) increased in fish exposed at 30 PSU. Serum cortisol, glucose, and blood urea nitrogen (BUN) were increased significantly (p < 0.05) in fish exposed at 3 and 30 PSU. In contrast, opposite trends were observed for serum protein, lactate, and triglycerides content during cold exposure. Transaminase activities [glutamic-pyruvate transaminase (GPT), glutamic oxaloacetic transaminase (GOT), lactic acid dehydrogenase (LDH), gamma-glutamyl-transaminase (γGGT)] were significantly higher in fish exposed at 3 and 30 PSU on days 10 and 20. The abundance of heat shock protein 70 (HSP70), tumor necrosis factor-α (TNF-α), cystic fibrosis transmembrane conductance (CFTR) were significantly (p < 0.05) increased in fish exposed at 3 and 30 PSU during cold shock exposure. In contrast, insulin-like growth factor 1 (Igf1) expression was significantly lower in fish exposed at 3 and 30 PSU. Whereas, on day 20, Na+/K+ ATPase α1 and Na+/K+/Cl- cotransporter-1 (NKCC1) were significantly upregulated in fish exposed at 30 PSU, followed by 12, 6, and 3 PSU. Results demonstrated that ambient extreme winter cold events induce metabolic and physiological stress responses and provide a conceivable mechanism by which growth and physiological fitness are limited at cold thermal events. However, during ambient extreme cold (8 °C) exposure, European seabass exhibited better physiological fitness at 12 and 6 PSU water, providing possible insight into future aquaculture management options.

The Relationship between Hormones, Glucose, and Oxidative Damage Is Condition and Stress Dependent in a Free-Living Passerine Bird

AbstractPhysiological state is an emergent property of the interactions among physiological systems within an intricate network. Understanding the connections within this network is one of the goals in physiological ecology. Here, we studied the relationship between body condition, two neuroendocrine hormones (corticosterone and insulin-like growth factor 1 [IGF-1]) as physiological regulators, and two physiological systems related to resource metabolism (glucose) and oxidative balance (malondialdehyde). We measured these traits under baseline and stress-induced conditions in free-living house sparrows (Passer domesticus). We used path analysis to analyze different scenarios about the structure of the physiological network. Our data were most consistent with a model in which corticosterone was the major regulator under baseline conditions. This model shows that individuals in better condition have lower corticosterone levels; corticosterone and IGF-1 levels are positively associated; and oxidative damage is higher when levels of corticosterone, IGF-1, and glucose are elevated. After exposure to acute stress, these relationships were considerably reorganized. In response to acute stress, birds increased their corticosterone and glucose levels and decreased their IGF-1 levels. However, individuals in better condition increased their corticosterone levels more and better maintained their IGF-1 levels in response to acute stress. The acute stress-induced changes in corticosterone and IGF-1 levels were associated with an increase in glucose levels, which in turn was associated with a decrease in oxidative damage. We urge ecophysiologists to focus more on physiological networks, as the relationships between physiological traits are complex and dynamic during the organismal stress response.

Insulin-like growth factor 1 of wild vertebrates in a life-history context

Broad variation in intra- and interspecific life-history traits is largely shaped by resource limitation and the ensuing allocation trade-offs that animals are forced to make. Insulin-like growth factor 1 (IGF-1), a growth-hormone-dependent peptide, may be a key player in the regulation of allocation processes. In laboratory animals, the effects of IGF-1 on growth- and development (positive), reproduction (positive), and longevity (negative) are well established. We here review the evidence on these effects in wild vertebrates, where animals are more likely to face resource limitation and other challenges. We point out the similarities and dissimilarities in patterns of IGF-1 functions obtained in these two different study settings and discuss the knowledge we need to develop a comprehensive picture of the role of IGF-1 in mediating life-history variation of wild vertebrates.

Effects of feeding frequency on juvenile Chinese sturgeon Acipenser sinensis

In this study, the effects of different feeding frequencies on the growth and the expression of genes in the GH/IGF axis were assessed in juvenile Chinese sturgeon. The newly hatched Chinese sturgeons were bred for 38 days at three different feeding frequencies groups (feeding frequency of two times a day, TWD; three times a day, THD; and four times a day, FOD), and the expression levels of the GH/IGF axis responses to feeding frequency were determined by quantitative real-time PCR. In addition, the full-length of the Coding Sequences of IGF I and IGF II genes (489-bp and 660-bp, respectively), were cloned and analyzed from Chinese sturgeon the first time. Multiple sequence alignments of IGFs revealed that Chinese sturgeon are high sequence identity to IGFs from other species. The phylogenetic relationships based on the IGF I and IGF II amino acid sequences were consistent with the traditional classification. After 38 days of growth, the three different feeding frequencies groups of Chinese sturgeon had no significant difference of body length, body weight, specific growth rate, the survival rate, the rate of weight gain and the condition factor. However, the relative expression of Chinese sturgeon GH in the pituitary decreased with increasing feeding frequency. The relative expression of Chinese sturgeon GHR in liver and skeletal muscle was deceased with increasing feeding frequency, while the relative expression of GHR in stomach and intestines at THD group was significantly higher than that of at TWD group and FOD group (p < 0.05). The relative expression of Chinese sturgeon IGF I in liver increased significantly with increasing feeding frequency (p < 0.05). The relative expression of IGF I in stomach and skeletal muscle was similar at the three groups. The relative expression of IGF I in intestines was significantly higher at FOD group than at TWD group and THD group (p < 0.05). The relative expression of Chinese sturgeon IGF II in liver at TWD group was significantly higher than that at THD group and FOD group (p < 0.05). However, the relative expression of IGF II in stomach, intestines and skeletal muscle at THD group was higher than that at TWD group and FOD group. Based on these previous studies that liver IGF I is regarded as a biomarker of growth performance, this result suggested that the juvenile Chinese sturgeon is better for growth when feeding four times daily compared to twice and thrice daily.

Establishment of time-resolved fluoroimmunoassays for detection of growth hormone and insulin-like growth factor I in rainbow trout plasma

The GH/IGF-I axis influences many aspects of salmonid life history and is involved in a variety of physiological processes that are related to somatic growth (e.g., reproduction, smoltification, and the response to fasting and stress). As such, fisheries studies utilize GH/IGF-I axis components as indicators of growth and metabolic status. This study established time-resolved fluoroimmunoassays (TR-FIAs) for rainbow trout plasma GH and IGF-I using commercially available reagents. For the GH TR-FIA, the ED₈₀ and ED₂₀ were 0.6 and 28.1 ng/mL, the minimum detection limit was 0.2 ng/mL, and the intra- and inter-assay coefficients of variation (%CV) were 4.1% and 13.4%, respectively. Ethanol remaining from acid-ethanol cryoprecipitation (AEC) of plasma samples to remove IGF binding proteins reduced binding and increased variability in the IGF-I TR-FIA. Drying down and reconstituting extracted samples restored binding and reduced variability. The extraction efficiency of IGF-I standards through AEC, drying down, and reconstitution did not vary over the working range of the assay. For the IGF-I TR-FIA, the ED₈₀ and ED₂₀ were 0.2 and 6.5 ng/mL, the minimum detection limit was 0.03 ng/mL, and the intra- and inter-assay %CV were 3.0% and 6.5%, respectively. Biological validation was provided by GH injection and fasting studies in rainbow trout. Intraperitoneal injection with bovine GH increased plasma IGF-I levels. Four weeks of fasting decreased body weight, increased plasma GH levels, and decreased plasma IGF-I levels. The GH and IGF-I TR-FIAs established herein provide a cost-comparable, non-radioisotopic method for quantifying salmonid plasma GH and IGF-I using commercially available reagents.

Identification of the cDNA Encoding the Growth Hormone Receptor (GHR) and the Regulation of GHR and IGF-I Gene Expression by Nutritional Status in Reeves' Turtle (Chinemys reevesii)

Chinemys reevesii (Reeves’ turtle) is a slow-growing reptile that is distributed widely across China. Prior to this study, the cDNA sequence of the growth hormone receptor (GHR) in the Reeve’s turtle, or how periods of starvation might influence the gene expression of GHR and insulin-like growth factor I (IGF-I) in this species, were unknown. Here, we identified the full-length sequence of the cDNA encoding GHR in Reeves’ turtle by using RT-PCR and RACE. The full-length GHR cDNA was identified to be 3936 base-pairs in length, with a 1848 base-pair open reading frame (ORF) that encodes a 615 amino acid protein. Analysis showed that GHR mRNA was detectable in a wide range of tissues; the highest and lowest levels of expression were detected in the liver and the gonad, respectively. IGF-I was also expressed in a range of tissues, but not in the gonad; the highest levels of IGF-I expression were detected in the liver. After 4 weeks of fasting, the expression levels of GHR and IGF-I in the liver had decreased significantly; however, these gradually returned to normal after refeeding. We report the first cloned cDNA sequence for the GHR gene in the Reeve’s turtle. Our findings provide a foundation from which to investigate the specific function of the GHR in Reeve’s turtle, and serve as a reference for studying the effects of different nutrient levels on GHR expression in this species.

Growth and survival of Takifugu rubripes larvae cultured under different light conditions

We assessed the effects of light intensity and spectrum on the growth and survival of Takifugu rubripes larvae from 30 to 69 days after hatching. Five lighting regimes were applied using 0.5, 1.5, and 3.0 W m^-2 full spectrum white (W0.5, W1.5, W3.0), 0.5 W m^-2 yellow (Y0.5), and 0.5 W m^-2 blue light (B0.5). At the end of the experiment, body length, wet weight, and specific growth rate from day 0 to day 39 were significantly greater in larvae reared under W3.0 than under B0.5 (P ˂ 0.05). No significant differences were observed among W0.5, W1.5, and W3.0, or among W0.5, Y0.5, and B0.5 (P > 0.05). Survival rate was significantly higher in larvae reared under W1.5 than W0.5 (P ˂ 0.05), but no significant differences were observed among W0.5, Y0.5, and B0.5 (P > 0.05). Additionally, light conditioning did not affect the total thickness of the retina. Although the ratio of the thickness of the retinal pigment epithelium layer/total thickness (TT) was significantly higher in larvae exposed to W3.0 compared with those exposed to other light conditions, and the thickness of the outer nuclear layer/TT was significantly lower in larvae exposed to W3.0 compared with those exposed to W0.5 (P < 0.05), no relationship was confirmed between the structure of the retina and the growth performance of the T. rubripes larvae. Expression patterns of two stress-related and seven growth-related genes were also compared with the biometric parameters investigated in the experimental groups. No significant differences in the aanat1a, crh, ss1, igf1, or igf2 expression were observed among the five treatments. Pomc expression was significantly lower in larvae exposed to W1.5 than the larvae exposed to W0.5, and it was significantly lower in larvae exposed to Y0.5 than in larvae exposed to W0.5 or B0.5 (P < 0.05). Significant differences were also found in the expression of gh, with the highest levels being observed under W3.0, while the lowest levels were observed in B0.5 (P < 0.05). Ghrh expression was significantly higher in W3.0 (P < 0.05). These results should be considered when designing rearing protocols for fugu larvae in aquaculture systems.

Interactions of long-term food ration variation and short-term fasting on insulin-like growth factor-1 (IGF-1) pathways in copper rockfish (Sebastes caurinus)

Variation in food intake affects somatic growth by altering the expression of hormones in the somatotropic endocrine axis including insulin-like growth factor-1 (IGF-1). Here, we examined IGF-1 pathway responses to long- and short-term variation in food availability in copper rockfish (Sebastes caurinus), a nearshore Pacific rockfish important for commercial and recreational fisheries. Juvenile copper rockfish were raised under differing ration amounts (3% or 9% mass feed·g^-1 fish wet mass·day^-1) for 140 d to simulate 'long-term' feeding variation, after which some fish from both rations were fasted for 12 d to generate 'short-term' conditions of food deprivation. Rockfish on the 9% ration treatment grew more quickly than those on the 3% ration and were larger in mass, length, and body condition (k) after 152 d. Fish on the 9% ration had higher blood glucose than those on the 3% ration, with fasting decreasing blood glucose in both ration treatments, indicating that both long-term and short-term feed treatments altered energy status. Plasma IGF-1 was higher in rockfish from the 9% ration than those in the 3% ration and was also higher in fed fish than fasted fish. Additionally, plasma IGF-1 related positively to individual variation in specific growth rate (SGR). The positive association between IGF-1 and SGR showed discordance in fish that had experienced different levels of food and growth over the long-term but not short-term, suggesting that long-term nutritional experience can influence the relationship between IGF-1 and growth in this species. Rockfish on the 3% ration showed a lower relative abundance of gene transcripts encoding igf1 in the liver, but higher hepatic mRNAs for IGF binding proteins igfbp1a and igfbp1b. Fasting similarly decreased the abundance of igf1 mRNAs in the liver of fish reared under both the 9% and 3% rations, while concurrently increasing mRNAs encoding the IGF binding proteins igfbp1a, -1b, and -3a. Hepatic mRNAs for igfbp2b, -5a, and -5b were lower with long-term ration variation (3% ration) and fasting. Fish that experienced long-term reduced rations also had higher mRNA levels for igfbp3a, -3b, and IGF receptors isoforms A (igf1rA) and B (igf1rB) in skeletal muscle, but lower mRNA levels for igf1. Fasting increased muscle mRNA abundance for igfbp3a, igf1rA, and igf1rB, and decreased levels for igfbp2a and igf1. These data show that a positive relationship between circulating IGF-1 and individual growth rate is maintained in copper rockfish even when that growth variation relates to differences in food consumption across varying time scales, but that long- and short-term variation in food quantity can shift basal concentrations of circulating IGF-1 in this species.

Exploring the mechanistic link between corticosterone and insulin-like growth factor-1 in a wild passerine bird

Background

Physiological regulators of life history trade-offs need to be responsive to sudden changes of resource availability. When homeostasis is challenged by unpredictable stressors, vertebrates respond through a set of physiological reactions, which can promote organismal survival. Glucocorticoids have been traditionally recognized as one of the main regulators of the physiological stress response, but the role of an evolutionarily more conserved pathway, the hypothalamic-pituitary-somatotropic (HPS) axis producing insulin-like growth factor-1 (IGF-1) has received much less attention. Although IGF-1 is known to affect several life history traits, little is known about its role in the physiological stress response and it has never been studied directly in adult wild animals.

Methods

In this study, we combined field observations with a controlled experiment to investigate how circulating levels of IGF-1 change in response to stress and whether this change is due to concomitant change in glucocorticoids in a free-living songbird, the bearded reedling Panurus biarmicus. We used a standard capture-restraint protocol in field observation, in which we took first and second (stress induced: 15 minutes later) samples. In a follow-up experiment, we used a minimally invasive oral corticosterone manipulation.

Results

We showed that corticosterone levels significantly increased while IGF-1 levels significantly decreased during capture and handling stress. However, change in corticosterone levels were not related to change in IGF-1 levels. We found that experimentally elevated corticosterone levels did not affect IGF-1 levels.

Discussion

Our results are the first to highlight that circulating IGF-1 levels are responsive to stress independently from glucocorticoids and suggest that the HPS axis is an autonomous physiological pathway that may play an important role as regulator of life-history decisions.

Somatotropic Axis Regulation Unravels the Differential Effects of Nutritional and Environmental Factors in Growth Performance of Marine Farmed Fishes

The Gh/Prl/Sl family has evolved differentially through evolution, resulting in varying relationships between the somatotropic axis and growth rates within and across fish species. This is due to a wide range of endogenous and exogenous factors that make this association variable throughout season and life cycle, and the present minireview aims to better define the nutritional and environmental regulation of the endocrine growth cascade over precisely defined groups of fishes, focusing on Mediterranean farmed fishes. As a result, circulating Gh and Igf-i are revitalized as reliable growth markers, with a close association with growth rates of gilthead sea bream juveniles with deficiency signs in both macro- or micro-nutrients. This, together with other regulated responses, promotes the use of Gh and Igf-i as key performance indicators of growth, aerobic scope, and nutritional condition in gilthead sea bream. Moreover, the sirtuin-energy sensors might modulate the growth-promoting action of somatotropic axis. In this scenario, transcripts of igf-i and gh receptors mirror changes in plasma Gh and Igf-i levels, with the ghr-i/ghr-ii expression ratio mostly unaltered over season. However, this ratio is nutritionally regulated, and enriched plant-based diets or diets with specific nutrient deficiencies downregulate hepatic ghr-i, decreasing the ghr-i/ghr-ii ratio. The same trend, due to a ghr-ii increase, is found in skeletal muscle, whereas impaired growth during overwintering is related to increase in the ghr-i/ghr-ii and igf-ii/igf-i ratios in liver and skeletal muscle, respectively. Overall, expression of insulin receptors and igf receptors is less regulated, though the expression quotient is especially high in the liver and muscle of sea bream. Nutritional and environmental regulation of the full Igf binding protein 1-6 repertoire remains to be understood. However, tissue-specific expression profiling highlights an enhanced and nutritionally regulated expression of the igfbp-1/-2/-4 clade in liver, whereas the igfbp-3/-5/-6 clade is overexpressed and regulated in skeletal muscle. The somatotropic axis is, therefore, highly informative of a wide-range of growth-disturbing and stressful stimuli, and multivariate analysis supports its use as a reliable toolset for the assessment of growth potentiality and nutrient deficiencies and requirements, especially in combination with selected panels of other nutritionally regulated metabolic biomarkers.

Divergence of insulin superfamily ligands, receptors and Igf binding proteins in marine versus freshwater stickleback: Evidence of selection in known and novel genes

Three-spine stickleback (Gasterosteus aculeatus) is a teleost model for understanding genetic, physiological and morphological changes accompanying freshwater (FW) adaptation. There is growing evidence that the insulin superfamily plays important roles in traits involved in marine and FW adaptation. We performed a candidate gene analysis to look for evidence of selection on 33 insulin superfamily ligand-receptor genes and insulin-like growth factor binding proteins (Igfbp's) in stickleback. Using genotype data from 11 marine and 10 FW populations, we calculated the number of SNPs per site in regulatory and intronic regions, the number of synonymous and nonsynonymous mutations in coding regions, Wright's fixation index (Fst), and performed t-tests to identify SNPs with divergent genotype frequencies between marine/FW versus Atlantic/Pacific populations. Next, we analysed genome-wide transcriptome data from eight tissues to assess differential gene expression. Two Igfbp's (Igfbp2a and Igfbp5a) show evidence of divergent adaptation between life-history types, and a cluster of nonsynonymous mutations in Igfbp5a exhibit high Fst in exons apparently alternatively spliced in gill. We find evidence of selection on the relaxin family ligand-receptor gene pair, Insl3-Rxfp2, known to be involved in male spermatogenesis and bone metabolism, and in the 5' regulatory region of Igf2. We also confirmed the gene and coding sequence of two unannotated relaxin family ligands. These analyses underscore the utility of candidate gene studies and indicate directions for further exploration of the function of insulin superfamily genes in FW adaptation.

Expression of Hsp70, Igf1, and Three Oxidative Stress Biomarkers in Response to Handling and Salt Treatment at Different Water Temperatures in Yellow Perch, Perca flavescens

Stress is a major factor that causes diseases and mortality in the aquaculture industry. The goal was to analyze the expression of stress-related biomarkers in response to different stressors in yellow perch, which is an important aquaculture candidate in North America and highly sensitive to handling in captivity. Three fish groups were established, each having four replicates, and subjected to water temperatures of 14, 20, and 26°C and acute handling stress was performed followed by a salt treatment for 144h at a salinity of 5 ppt. Serum and hepatic mRNA levels of heat shock protein (hsp70), insulin-like growth factor 1 (Igf1), glutathione peroxidase (Gpx), superoxide dismutase 1 (Sod1), and glutathione reductase (Gsr) were quantified at seven times interval over 144 h using ELISA and RT-qPCR. Handling stress caused a significant down-regulation in Hsp70, Gpx, Sod1, and Gsr at a water temperature of 20°C compared to 14 and 26°C. Igf1 was significantly upregulated at 20°C and down-regulated at 14 and 26°C. Salt treatment had a transient reverse effect on the targeted biomarkers in all groups at 72 h, then caused an upregulation after 144 h, compared to the control groups. The data showed a negative strong regulatory linear relationship between igf1 with hsp70 and anti-oxidative gene expressions. These findings could provide valuable new insights into the stress responses that affect fish health and could be used to monitor the stress.

A comparative examination of cortisol effects on muscle myostatin and HSP90 gene expression in salmonids

Cortisol, the primary corticosteroid in teleost fishes, is released in response to stressors to elicit local functions, however little is understood regarding muscle-specific responses to cortisol in these fishes. In mammals, glucocorticoids strongly regulate the muscle growth inhibitor, myostatin, via glucocorticoid response elements (GREs) leading to muscle atrophy. Bioinformatics methods suggest that this regulatory mechanism is conserved among vertebrates, however recent evidence suggests some fishes exhibit divergent regulation. Therefore, the aim of this study was to evaluate the conserved actions of cortisol on myostatin and hsp90 expression to determine if variations in cortisol interactions have emerged in salmonid species. Representative salmonids; Chinook salmon (Oncorhynchus tshawytscha), cutthroat trout (Oncorhynchus clarki), brook trout (Salvelinus fontinalis), and Atlantic salmon (Salmo salar); were injected intraperitoneally with a cortisol implant (50μg/g body weight) and muscle gene expression was quantified after 48h. Plasma glucose and cortisol levels were significantly elevated by cortisol in all species, demonstrating physiological effectiveness of the treatment. HSP90 mRNA levels were elevated by cortisol in brook trout, Chinook salmon, and Atlantic salmon, but were decreased in cutthroat trout. Myostatin mRNA levels were affected in a species, tissue (muscle type), and paralog specific manner. Cortisol treatment increased myostatin expression in brook trout (Salvelinus) and Atlantic salmon (Salmo), but not in Chinook salmon (Oncorhynchus) or cutthroat trout (Oncorhynchus). Interestingly, the VC alone increased myostatin mRNA expression in Chinook and Atlantic salmon, while the addition of cortisol blocked the response. Taken together, these results suggest that cortisol affects muscle-specific gene expression in species-specific manners, with unique Oncorhynchus-specific divergence observed, that are not predictive solely based upon mammalian stress responses.

DNA damage and differential gene expression associated with physical stress in gilthead seabream (Sparus aurata)

Fish stress may result in inhibition of reproduction, development and growth. Thus, appropriate indices should be developed to accurately define the physiological plasticity of fish, in terms of coping with stress. Sea bream individuals were subjected to physical stress (fasting and confinement). DNA fragmentation of liver cells was assessed, in addition to gene expression of selected genes and plasma cortisol levels determination. Stress response was characterized with significant temporal alterations. Increased DNA fragmentation was observed as an aftereffect of physical stress and consequently gene expression of tp53 was stimulated. The expression pattern of glucocorticoid receptor (nr3c1) was directly correlated with plasma cortisol. Furthermore, glucokinase (gk) gene expression was considerably upregulated under acute stress, depicting putative energetic demands. Finally, igf1 downregulation during stress, reflects the suppression of the GH/IGF axis and the substantial stress effects on growth. To conclude, most of the indices described in the present study could be synergistically used, in order to robustly quantify physical stress in marine teleosts.

Hepatic insulin-like growth-factor binding protein (igfbp) responses to food restriction in Atlantic salmon smolts

The growth hormone (Gh)/insulin-like growth-factor (Igf) system plays a central role in the regulation of growth in fishes. However, the roles of Igf binding proteins (Igfbps) in coordinating responses to food availability are unresolved, especially in anadromous fishes preparing for seaward migration. We assayed plasma Gh, Igf1, thyroid hormones and cortisol along with igfbp mRNA levels in fasted and fed Atlantic salmon (Salmo salar). Fish were fasted for 3 or 10days near the peak of smoltification (late April to early May). Fasting reduced plasma glucose by 3days and condition factor by 10days. Plasma Gh, cortisol, and thyroxine (T4) were not altered in response to fasting, whereas Igf1 and 3,5,3'-triiodo-l-thyronine (T3) were slightly higher and lower than controls, respectively. Hepatic igfbp1b1, -1b2, -2a, -2b1 and -2b2 mRNA levels were not responsive to fasting, but there were marked increases in igfbp1a1 following 3 and 10days of fasting. Fasting did not alter hepatic igf1 or igf2; however, muscle igf1 was diminished by 10days of fasting. There were no signs that fasting compromised branchial ionoregulatory functions, as indicated by unchanged Na(+)/K(+)-ATPase activity and ion pump/transporter mRNA levels. We conclude that dynamic hepatic igfbp1a1 and muscle igf1 expression participate in the modulation of Gh/Igf signaling in smolts undergoing catabolism.

Comprehensive biometric, biochemical and histopathological assessment of nutrient deficiencies in gilthead sea bream fed semi-purified diets

Seven isoproteic and isolipidic semi-purified diets were formulated to assess specific nutrient deficiencies in sulphur amino acids (SAA), n-3 long-chain PUFA (n-3 LC-PUFA), phospholipids (PL), P, minerals (Min) and vitamins (Vit). The control diet (CTRL) contained these essential nutrients in adequate amounts. Each diet was allocated to triplicate groups of juvenile gilthead sea bream fed to satiety over an 11-week feeding trial period. Weight gain of n-3 LC-PUFA, P-Vit and PL-Min-SAA groups was 50, 60-75 and 80-85 % of the CTRL group, respectively. Fat retention was decreased by all nutrient deficiencies except by the Min diet. Strong effects on N retention were found in n-3 LC-PUFA and P fish. Combined anaemia and increased blood respiratory burst were observed in n-3 LC-PUFA fish. Hypoproteinaemia was found in SAA, n-3 LC-PUFA, PL and Vit fish. Derangements of lipid metabolism were also a common disorder, but the lipodystrophic phenotype of P fish was different from that of other groups. Changes in plasma levels of electrolytes (Ca, phosphate), metabolites (creatinine, choline) and enzyme activities (alkaline phosphatase) were related to specific nutrient deficiencies in PL, P, Min or Vit fish, whereas changes in circulating levels of growth hormone and insulin-like growth factor I primarily reflected the intensity of the nutritional stressor. Histopathological scoring of the liver and intestine segments showed specific nutrient-mediated changes in lipid cell vacuolisation, inflammation of intestinal submucosa, as well as the distribution and number of intestinal goblet and rodlet cells. These results contribute to define the normal range of variation for selected biometric, biochemical, haematological and histochemical markers.

Insulin-like growth factors I and II in starry flounder (Platichthys stellatus): molecular cloning and differential expression during embryonic development

In order to elucidate the possible roles of insulin-like growth factors I and II (IGF-I and IGF-II) in the embryonic development of Platichthys stellatus, their cDNAs were isolated and their spatial expression pattern in adult organs and temporal expression pattern throughout embryonic development were examined by quantitative real-time PCR assay. The IGF-I cDNA sequence was 1,268 bp in length and contained an open reading frame (ORF) of 558 bp, which encoded 185 amino acid residues. With respect to IGF-II, the full-length cDNA was 899 bp in length and contained a 648-bp ORF, which encoded 215 amino acid residues. The amino acid sequences of IGF-I and IGF-II exhibited high identities with their fish counterparts. The highest IGF-I mRNA level was found in the liver for both sexes, whereas the IGF-II gene was most abundantly expressed in female liver and male liver, gill, and brain. The sex-specific and spatial expression patterns of IGF-I and IGF-II mRNAs are thought to be related to the sexually dimorphic growth and development of starry flounder. Both IGF-I and IGF-II mRNAs were detected in unfertilized eggs, which indicated that IGF-I and IGF-II were parentally transmitted. Nineteen embryonic development stages were tested. IGF-I mRNA level remained high from unfertilized eggs to low blastula followed by a significant decrease at early gastrula and then maintained a lower level. In contrast, IGF-II mRNA level was low from unfertilized eggs to high blastula and peaked at low blastula followed by a gradual decrease. Moreover, higher levels of IGF-I mRNA than that of IGF-II were found from unfertilized eggs to high blastula, vice versa from low blastula to newly hatched larva, and the different expression pattern verified the differential roles of IGF-I and IGF-II in starry flounder embryonic development. These results could help in understanding the endocrine mechanism involved in the early development and growth of starry flounder.

Contribution of the autophagy-lysosomal and ubiquitin-proteasomal proteolytic systems to total proteolysis in rainbow trout (Oncorhynchus mykiss) myotubes

The ubiquitin-proteasome system (UPS) is recognized as the major contributor to total proteolysis in mammalian skeletal muscle, responsible for 50% or more of total protein degradation in skeletal muscle, whereas the autophagic-lysosome system (ALS) plays a more minor role. While the relative contribution of these systems to muscle loss is well documented in mammals, little is known in fish species. The current study uses myotubes derived from rainbow trout myogenic precursor cells as an in vitro model of white muscle tissue. Cells were incubated in complete or serum-deprived media or media supplemented with insulin-like growth factor-1 (IGF-1) and exposed to selective proteolytic inhibitors to determine the relative contribution of the ALS and UPS to total protein degradation in myotubes in different culture conditions. Results indicate that the ALS is responsible for 30-34% and 50% of total protein degradation in myotubes in complete and serum-deprived media, respectively. The UPS appears to contribute much less to total protein degradation at almost 4% in cells in complete media to nearly 17% in serum-deprived cells. IGF-1 decreases activity of both systems, as it inhibited the upregulation of both proteolytic systems induced by serum deprivation. The combined inhibition of both the ALS and UPS reduced degradation by a maximum of 55% in serum-deprived cells, suggesting an important contribution of other proteolytic systems to total protein degradation. Collectively, these data identify the ALS as a potential target for strategies aimed at improving muscle protein retention and fillet yield through reductions in protein degradation.

Acute physiological stress down-regulates mRNA expressions of growth-related genes in coho salmon

Growth and development in fish are regulated to a major extent by growth-related factors, such as liver-derived insulin-like growth factor (IGF) -1 in response to pituitary-secreted growth hormone (GH) binding to the GH receptor (GHR). Here, we report on the changes in the expressions of gh, ghr, and igf1 genes and the circulating levels of GH and IGF-1 proteins in juvenile coho salmon (Oncorhynchus kisutch) in response to handling as an acute physiological stressor. Plasma GH levels were not significantly different between stressed fish and prestressed control. Plasma IGF-1 concentrations in stressed fish 1.5 h post-stress were the same as in control fish, but levels in stressed fish decreased significantly 16 h post-stress. Real-time quantitative PCR (qPCR) analysis showed that ghr mRNA levels in pituitary, liver, and muscle decreased gradually in response to the stressor. After exposure to stress, hepatic igf1 expression transiently increased, whereas levels decreased 16 h post-stress. On the other hand, the pituitary gh mRNA level did not change in response to the stressor. These observations indicate that expression of gh, ghr, and igf1 responded differently to stress. Our results show that acute physiological stress can mainly down-regulate the expressions of growth-related genes in coho salmon in vivo. This study also suggests that a relationship between the neuroendocrine stress response and growth-related factors exists in fish.

Health of farmed fish: its relation to fish welfare and its utility as welfare indicator

This brief review focuses on health and biological function as cornerstones of fish welfare. From the function-based point of view, good welfare is reflected in the ability of the animal to cope with infectious and non-infectious stressors, thereby maintaining homeostasis and good health, whereas stressful husbandry conditions and protracted suffering will lead to the loss of the coping ability and, thus, to impaired health. In the first part of the review, the physiological processes through which stressful husbandry conditions modulate health of farmed fish are examined. If fish are subjected to unfavourable husbandry conditions, the resulting disruption of internal homeostasis necessitates energy-demanding physiological adjustments (allostasis/acclimation). The ensuing energy drain leads to trade-offs with other energy-demanding processes such as the functioning of the primary epithelial barriers (gut, skin, gills) and the immune system. Understanding of the relation between husbandry conditions, allostatic responses and fish health provides the basis for the second theme developed in this review, the potential use of biological function and health parameters as operational welfare indicators (OWIs). Advantages of function- and health-related parameters are that they are relatively straightforward to recognize and to measure and are routinely monitored in most aquaculture units, thereby providing feasible tools to assess fish welfare under practical farming conditions. As the efforts to improve fish welfare and environmental sustainability lead to increasingly diverse solutions, in particular integrated production, it is imperative that we have objective OWIs to compare with other production forms, such as high-density aquaculture. However, to receive the necessary acceptance for legislation, more robust scientific backing of the health- and function-related OWIs is urgently needed.

Whole body cortisol and expression of HSP70, IGF-I and MSTN in early development of sea bass subjected to heat shock

Whole body cortisol levels were determined during early larval developmental stages of sea bass (Dicentrarchus labrax) subjected to a heat shock with the aim to investigate the correlation between the stress event and the activation of the hypothalamic-pituitary-interrenal axis. Moreover, the mRNA expression of inducible heat shock protein 70 (HSP70), insulin-like growth factor I (IGF-I) and myostatin (MSTN) was also detected. Whole body cortisol was determined by a radio-immunoassay (RIA) technique whereas the expression of HSP70, IGF-I and MSTN mRNAs was quantified by Real-Time PCR. Cortisol was detectable in all the larvae from hatching but its level increased significantly in larvae submitted to heat shock from 2-day post hatching onwards. An effect of the sole transfer on cortisol levels was detectable at day 10, indicating an increase of the hypothalamic-pituitary-interrenal axis sensitivity from this stage of sea bass development. In animals exposed to heat shock, the expression of inducible HSP70 resulted in a marked increase of mRNA levels already at hatching. This increase was significantly higher from 6 days onwards if compared to controls. Moreover, heat shock resulted in a decrease (although not significant) in IGF-I mRNA expression of stressed larvae if compared to controls. On the contrary, heat shock did not influence the expression of MSTN mRNA in all groups. The results indicate a very early activation of the hypothalamic-pituitary-interrenal axis and in general of the stress response during the development of European sea bass. Moreover, these results suggest the importance of cortisol and inducible HSP70 as bioindicators of stress in aquaculture and confirm the role of IGF-I and MSTN as regulatory factors during development and growth of fish.

Correlation with larval body size of mRNA levels of growth hormone, growth hormone receptor I and insulin-like growth factor I in larval torafugu Takifugu rubripes

The full-length of insulin-like growth factor (IGF) complementary (c)DNAs encoded by igf-I and igf-II from torafugu pufferfish Takifugu rubripes were cloned in the present study. The deduced amino acid sequences of the two genes showed c. 80% identity each with those of Igf-I and Igf-II from other teleosts, respectively. Two growth hormone (GH) receptors, ghr1 and ghr2, were also cloned in silico using the T. rubripes Fugu genome database. The transcripts of T. rubripes igf-I were detected in slow muscle, heart, skin, gill, liver and intestine but not in fast muscle, spleen and testis of adult fish, whereas those of igf-II were found in all tissues examined. Subsequently, the accumulated messenger (m)RNA levels of igf-I and igf-II were investigated in an F(2) population derived from a male of an apparent fast-growing T. rubripes strain and a wild female T. rubripes together with those of other growth-related genes encoding Gh, Ghr1 and Ghr2, and with those of prolactin (Prl) and leptin (Lep) previously reported. The accumulated mRNA levels of igf-I, gh and ghr1 were significantly correlated to growth rate at larval stages in the population, but not for those of igf-II, prl, ghr2 and lep. Although it is unclear whether or not this phenotype is directly related to the heredity of the fast-growing strain, the findings suggest that the expression of igf-I, gh and ghr1 is involved in the regulation of growth rate at larval stages in T. rubripes.

Acute handling disturbance modulates plasma insulin-like growth factor binding proteins in rainbow trout (Oncorhynchus mykiss)

The effects of acute stressor exposure on proximal (growth hormone [GH]) and distal (insulin-like growth factor-I [IFG-I] and insulin-like growth factor-binding proteins [IFGBPs]) components of the somatotropic axis are poorly understood in finfish. Rainbow trout (Oncorhynchus mykiss) were exposed to a 5-min handling disturbance to mimic an acute stressor episode, and levels of plasma GH, IGF-I, and IGFBPs at 0, 1, 4, and 24 h post-stressor exposure were measured. An unstressed group was also sampled at the same clock times (09:00, 10:00, 13:00, and 08:00 [the following day]) as acute stress sampling to determine temporal changes in the above somatotropic axis components. The acute stressor transiently elevated plasma cortisol and glucose levels at 1 and 4 h post-stressor exposure, whereas no changes were seen in the unstressed group. Plasma GH levels were not affected by handling stress or sampling time in the unstressed animals. Plasma IGF-I levels were significantly depressed at 1 and 4 h post-stressor exposure, but no discernible temporal pattern was seen in the unstressed animals. Using a western ligand blotting technique, we detected plasma IGFBPs of 21, 32, 42, and 50 kDa in size. The plasma levels of the lower-molecular-weight IGFBPs (21 and 32 kDa) were unaffected by handling stressor, nor were there any discernible temporal patterns in the unstressed animals. By contrast, the higher-molecular-weight IGFBPs (42 and 50 kDa) were affected by stress or time of sampling. Levels of the 42-kDa IGFBP levels significantly decreased over the sampling period in unstressed control animals, but this temporal drop was eliminated in stressed animals. Levels of the 50-kDa IGFBPs also decreased significantly over the sampling time in unstressed trout, whereas handling disturbance transiently increased levels of this IGFBP at 1 h but not at 4 and 24 h post-stressor exposure compared with the control group. Overall, our results suggest that acute stress adaptation involves modulation of plasma IGF-1 and high-molecular-mass IGFBP levels (42 and 50 kDa) in rainbow trout.

Effects of short-term starvation on ghrelin, GH-IGF system, and IGF-binding proteins in Atlantic salmon

The effects of short-time fasting on appetite, growth, and nutrient were studied in Atlantic salmon (Salmo salar) smolts. Feed deprivation did change the energy metabolism with reduced plasma protein and muscle indispensible amino acid levels. Plasma levels of ghrelin were significantly higher in starved salmon compared with fed fish after 2 days, but no differences in circulating ghrelin were found between treatments after 14 days. Two mRNA sequences for ghrelin-1 and ghrelin-2, 430 and 533 bp long, respectively, were detected. In addition, the growth hormone secretagogues-receptor like receptor (GHSR-LR) 1a and 1b were identified. Ghrelin-1 but not ghrelin-2 mRNA levels were affected by starvation in the stomach. Lower ghrelin-1 mRNA levels were detected at day 2 in starved fish compared with fed fish. The mRNA levels of GHSR-LR1a were not affected by starvation. Fasting reduced the phenotypic growth and the transcription of insulin-like growth factor (IGF)-II together with IGF-IIR, but IGF-I mRNA were not regulated in fasted salmon after 14 days. Three IGF-binding proteins (IGFBP) at 23, 32, and 43 kDa were found in salmon, and circulating 23 kDa was significantly increased after 14 days of starvation compared with fed fish, indicating increased catabolism. The levels of IGFBP-1 mRNA were significantly higher in fed and starved fish after 14 days compared to those at the start of the experiment, but no significant difference was observed between the treatments. In conclusion, we have shown that circulating ghrelin and ghrelin-1 mRNA is related to changes in energy metabolism in Atlantic salmon.

Perspectives on concordant and discordant relations between insulin-like growth factor 1 (IGF1) and growth in fishes

Many physiological processes are modulated by the endocrine system, including growth. Insulin-like growth factor 1 is one of the primary hormones involved in growth regulation in vertebrates, including fishes. Current work on IGF1 in fishes is driven both by a desire to better understand mechanisms of growth as well as to develop a reliable index of growth rate. A review of studies relating IGF1 to growth broadly reveals positive and significant relations between IGF1 and growth; however, relations found in individual studies range from no correlation to highly significant correlations. Potential sources for this variation include both biological and methodological issues and range from differences in how growth is defined (changes in length or weight), the duration of growth assessed (weeks to months) and how growth is calculated (total change, rate, percent change); yet, these methodological concerns cannot account for all the variation found. A further review of the literature reveals a number of physiological conditions and environmental factors that might influence IGF1 level and the subsequent relation of that IGF1 level to growth rate. The term concordance is introduced to categorize factors that influence IGF1 and growth in a similar fashion, such that positive and significant relations between IGF1 and growth are maintained even though the factor stimulates changes in IGF1 level. Conversely, the term discordance is introduced to categorize factors that stimulate changes in the relations between IGF1 and growth, such that IGF1 is not an efficacious index of growth for both pre and post-stimulus fish combined. IGF1 and growth relations generally remain concordant after changes in nutrition (consumption rate or diet). Differences in IGF1 level of juvenile, maturing male and maturing female fish are common and IGF1-growth relations appear discordant between these groups. Acute changes in temperature and salinity induce discordant relations between IGF1 and growth but acclimation to persistent differences in environmental condition generally result in concordant relations. Overall, by discriminating between fish of differing physiological status and discerning and categorizing differences among environments one may effectively use IGF1 as a growth index for fishes.

Effects of repeated crowding on the stress response and growth performance in Atlantic salmon (Salmo salar)

A 64-day growth experiment was conducted in which two groups of Atlantic salmon parr were grown under either control conditions or subjected to a weekly crowding stressor. Subjecting fish to the stressor resulted in a 7.7% reduction in wet weight after 29 days, which was maintained at 7.9% by day 64. This reduction in weight was reflected in a 44% reduction in specific growth rate and 38% increase in feed conversion ratio over the first 29 days of the experiment. Elevation in plasma cortisol was observed in crowded fish on days 1, 29 and 64. Similarly, on days 1 and 29 an increase in both plasma glucose and lactate was detected. On day 64, however, no differences in plasma glucose and lactate were observed, with the magnitude of the cortisol response also significantly reduced. Overall, the relatively moderate impact on growth performance and reduction in magnitude of measured stress parameters at the end of the experiment suggests possible habituation to the applied stressor.

Molecular characterization of atrogin-1/F-box protein-32 (FBXO32) and F-box protein-25 (FBXO25) in rainbow trout (Oncorhynchus mykiss): Expression across tissues in response to feed deprivation

The characteristic increase in protein catabolism during muscle atrophy is largely the result of an increase in E3 ubiquitin ligase expression, specifically that of atrogin-1, or FBXO32, which functions to polyubiquitinate proteins. In rainbow trout, the cDNA sequences of two E3 ubiquitin ligase F-box proteins, FBXO32 and FBXO25, were characterized and their expression across tissues in response to feed deprivation was determined. The cDNA sequence for FBXO32 encodes a protein 355 amino acids long and is 97% identical to the homologous protein in salmon, 85% to zebrafish and 72% identical to both human and mouse. The cDNA for FBXO25 encodes a protein 356 amino acids in length that is 98% identical to the homologous protein in salmon, 84% to zebrafish, and 75% to human. After 28days of feed deprivation, FBXO32 expression increased by approximately 13-fold, 3-fold, and 5-fold in white muscle, red muscle, and intestine, respectively (P<0.05). Expression of FBXO32 and FBXO25 in kidney decreased 0.3-fold and 0.2-fold, respectively, and FBXO25 expression decreased by 0.2-fold in liver (P<0.05). These results indicate that these protein sequences are conserved and suggest that the up-regulation of FBXO32 is associated with skeletal and smooth muscle atrophy that occurs during fasting.

Influences of the environment on the endocrine and paracrine fish growth hormone-insulin-like growth factor-I system

Insulin-like growth factor-I (IGF-I) is a key component of the complex system that regulates differentiation, development, growth and reproduction of fishes. The IGF-I gene is mainly expressed in the liver that represents the principal source of endocrine IGF-I but also in numerous other organs where the hormone most probably acts in an autocrine-paracrine manner. The primary stimulus for synthesis and release of IGF-I is growth hormone (GH) from the anterior pituitary. Thus, in analogy to mammals, it is usual to speak of a fish 'GH-IGF-I axis'. The GH-IGF-I system is affected by changes in the environment and probably represents a target of endocrine disrupting compounds (EDC) that impair many physiological processes in fishes. Thus, the review deals with the influences of changes in different environmental factors, such as food availability, temperature, photoperiod, season, salinity and EDCs, on GH gene expression in pituitary, IGF-I gene expression in liver and extrahepatic sites and the physiological effects resulting from the evoked alterations in endocrine and local IGF-I. Environmental influences certainly interact with each other but for convenience of the reader they will be dealt with in separate sections. Current trends in GH-IGF-I research are analysed and future focuses are suggested at the end of the sections.

Effects of insulin-like growth factor-I, insulin, and leucine on protein turnover and ubiquitin ligase expression in rainbow trout primary myocytes

The effects of insulin-like growth factor-I (IGF-I), insulin, and leucine on protein turnover and pathways that regulate proteolytic gene expression and protein polyubiquitination were investigated in primary cultures of 4-day-old rainbow trout myocytes. Supplementing media with 100 nM IGF-I increased protein synthesis by 13% (P < 0.05) and decreased protein degradation by 14% (P < 0.05). Treatment with 1 microM insulin increased protein synthesis by 13% (P < 0.05) and decreased protein degradation by 17% (P < 0.05). Supplementing media containing 0.6 mM leucine with an additional 2.5 mM leucine did not increase protein synthesis rates but reduced rates of protein degradation by 8% (P < 0.05). IGF-I (1 nM-100 nM) and insulin (1 nM-1 microM) independently reduced the abundance of ubiquitin ligase mRNA in a dose-dependent manner, with maximal reductions of approximately 70% for muscle atrophy F-box (Fbx) 32, 40% for Fbx25, and 25% for muscle RING finger-1 (MuRF1, P < 0.05). IGF-I and insulin stimulated phosphorylation of FOXO1 and FOXO4 (P < 0.05), which was inhibited by the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor wortmannin, and decreased the abundance of polyubiquitinated proteins by 10-20% (P < 0.05). Supplementing media with leucine reduced Fbx32 expression by 25% (P < 0.05) but did not affect Fbx25 nor MuRF1 transcript abundance. Serum deprivation decreased rates of protein synthesis by 60% (P < 0.05), increased protein degradation by 40% (P < 0.05), and increased expression of all ubiquitin ligases. These data suggest that, similar to mammals, the inhibitory effects of IGF-I and insulin on proteolysis occur via P I3-kinase/protein kinase B signaling and are partially responsible for the ability of these compounds to promote protein accretion.

Ionoregulatory and endocrine responses to disturbed salt and water balance in Mozambique tilapia exposed to confinement and handling stress

This study assessed the endocrine and ionoregulatory responses by tilapia (Oreochromis mossambicus) to disturbances of hydromineral balance during confinement and handling. In fresh water (FW), confinement and handling for 0.5, 1, 2 and 6h produced elevations in plasma cortisol and glucose; a reduction in plasma osmolality was observed at 6h. Elevations in plasma prolactins (PRL(177) and PRL(188)) accompanied this fall in osmolality while no effect upon growth hormone (GH) was evident; an increase in insulin-like growth-factor I (IGF-I) occurred at 0.5h. In seawater (SW), confinement and handling increased plasma osmolality and glucose between 0.5 and 6h; no effect on plasma cortisol was seen due to variable control levels. Concurrently, both PRLs were reduced in stressed fish with only transient changes in the GH/IGF-I axis. Next, the branchial expression of Na(+)/K(+)/2Cl(-) cotransporter (NKCC) and Na(+)/Cl(-) cotransporter (NCC) was characterized following confinement and handling for 6h. In SW, NKCC mRNA levels increased in stressed fish concurrently with elevated plasma osmolality and diminished gill Na(+), K(+)-ATPase activity; NCC was unchanged in stressed fish irrespective of salinity. Taken together, PRL and NKCC participate in restoring osmotic balance during acute stress while the GH/IGF-I axis displays only modest responses.

Insulin-like growth factor-I and genetic effects on indexes of protein degradation in response to feed deprivation in rainbow trout (Oncorhynchus mykiss)

This study determined the effect of genetic variation, feed deprivation, and insulin-like growth factor-I (IGF-I) on weight loss, plasma IGF-I and growth hormone, and indexes of protein degradation in eight full-sibling families of rainbow trout. After 2 wk of feed deprivation, fish treated with IGF-I lost 16% less (P < 0.05) wet weight than untreated fish. Feed deprivation increased growth hormone (P < 0.05) and decreased IGF-I (P < 0.05), but hormone levels were not altered by IGF-I. Plasma 3-methylhistidine concentrations were not affected by IGF-I but were decreased after 2 wk (P < 0.05) and increased after 4 wk (P < 0.05) of feed deprivation. In white muscle, transcript abundance of genes in the ubiquitin-proteasome, lysosomal, and calpain- and caspase-dependent pathways were affected by feed deprivation (P < 0.05). IGF-I prevented the feed deprivation-induced upregulation of MAFbx (F-box) and cathepsin transcripts and reduced abundance of proteasomal mRNAs (P < 0.05), suggesting that reduction of protein degradation via these pathways may be partially responsible for the IGF-I-induced reduction of weight loss. Family variations in gene expression, IGF-I concentrations, and weight loss during fasting suggest genetic variation in the fasting response, with considerable impact on regulation of proteolytic pathways. These data indicate that nutrient availability, IGF-I, and genetic variation affect weight loss, in part through alterations of proteolytic pathways in rainbow trout, and that regulation of genes within these pathways is coordinated in a way that supports a similar physiological response.

Effects of fasting on IGF-I, IGF-II, and IGF-binding protein mRNA concentrations in channel catfish (Ictalurus punctatus)

The effects of fasting on insulin-like growth factor (IGF)-I, IGF-II, and IGF-binding protein (IGFBPs) mRNA in channel catfish were examined. Fed control fish (Fed) were compared to fish that had been fasted for 30 d followed by 15 d of additional feeding (Restricted). Sequence alignment and similarity to orthologous proteins in other vertebrates provided structural evidence that the 3 catfish sequences identified in the present research were IGFBP-1, -2, and -3. Prolonged fasting (30 d) reduced body weight approximately 60% (P<0.001) and decreased IGF-I mRNA in the liver and muscle (P<0.01). Fifteen days of re-feeding restored concentrations of hepatic and muscle IGF-I mRNA. Liver IGF-II mRNA was not affected by fasting but was increased 2.2-fold after 15 d of re-feeding (P<0.05). Abundance of muscle IGF-II mRNA was similar between the fed control group and the restricted group throughout the experimental period. Fasting also increased liver IGFBP-1 mRNA (P<0.05) and decreased IGFBP-3 mRNA (P<0.01), whereas abundance of IGFBP-2 mRNA was not significantly affected. Interestingly, re-feeding for 15 d did not restore concentrations of IGFBP-1 and IGFBP-3 mRNA relative to fed control concentrations. The IGF results suggest that IGF-I and IGF-II are differently regulated by nutritional status and probably have a differential effect in promoting muscle growth during recovery from fasting. Similar to mammals, IGFBP-1 mRNA in catfish is increased during catabolism, whereas IGFBP-3 mRNA is decreased during inhibited somatic growth. The IGFBP results provide additional evidence of the conserved nature of the IGF-IGFBP-growth axis in catfish.