Role of the GH-IGF-1 system in Atlantic salmon and rainbow trout postsmolts at elevated water temperature

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.

Impact of stress phenotype, elevated temperature, and bacterin exposure on male Atlantic salmon (Salmo salar) growth, stress, and immune biomarker gene expression

In this study, postsmolt male Atlantic salmon, previously identified as low responders (LRs) or high responders (HRs) based on poststress cortisol levels, had their head kidney and liver sampled at 12°C and 20°C before injection (time 0) and after injection (i.e., at 12- and 24-h postinjection, respectively) with either Forte Micro (a multivalent vaccine containing bacterin, to capture peak antibacterial responses) or an equal volume of PBS. Quantitative real-time PCR (qPCR) was then used to measure the expression of 15 biomarker genes in the head kidney and 12 genes in the liver at each temperature/sampling point. Target transcripts were chosen that were related to growth, stress, and innate antibacterial immune responses. Many temperature, phenotype, and injection effects were found for individual genes within these three broad categories, and multivariate statistical analyses (i.e., principal component analysis and permutational multivariate analysis of variance) were used to look for overall patterns in transcript expression. These analyses revealed that HR salmon at 20°C mounted a more robust response (P < 0.05) for the 10 head kidney immune-related transcripts when injected with Forte Micro than LR salmon. In contrast, the seven liver stress-related transcripts displayed a greater response (P = 0.057) in LR versus HR fish with Forte Micro at 12°C. Overall, although this research did find some differences between LR and HR fish, it does not provide strong (conclusive) evidence that the selection of a particular phenotype would have major implications for the health of salmon over the temperature range examined.NEW & NOTEWORTHY This is the first paper to describe the impact of both temperature and bacterial stimulation on head kidney and liver transcript expression in Atlantic salmon characterized as LRs versus HRs. Notably, we found that HR salmon at 20°C mounted a more robust innate antibacterial immune response than LR salmon. In addition, LR fish at 12°C may (P = 0.057) exhibit higher expression of stress-related transcripts in response to vaccine injection relative to HR fish.

Seasonal Changes in Photoperiod: Effects on Growth and Redox Signaling Patterns in Atlantic Salmon Postsmolts

Farmed Atlantic salmon reared under natural seasonal changes in sea-cages had an elevated consumption of antioxidants during spring. It is, however, unclear if this response was caused by the increase in day length, temperature, or both. The present study examined redox processes in Atlantic salmon that were reared in indoor tanks at constant temperature (9 °C) under a simulated natural photoperiod. The experiment lasted for 6 months, from vernal to autumnal equinoxes, with the associated increase and subsequent decrease in day length. We found that intracellular antioxidants were depleted, and there was an increase in malondialdehyde (MDA) levels in the liver and muscle of Atlantic salmon with increasing day length. Antioxidant enzyme activity in liver and muscle and their related gene profiles was also affected, with a distinct upregulation of genes involved in maintaining redox homeostasis, such as peroxiredoxins in the brain in April. This study also revealed a nuclear factor-erythroid 2-related factor 2 (Nrf2)-mediated oxidative stress response in muscle and liver, suggesting that fish integrate environmental signals through redox signaling pathways. Furthermore, growth and expression profiles implicated in growth hormone (GH) signaling and cell cycle regulation coincided with stress patterns. The results demonstrate that a change in photoperiod without the concomitant increase in temperature is sufficient to stimulate growth and change the tissue oxidative state in Atlantic salmon during spring and early summer. These findings provide new insights into redox regulation mechanisms underlying the response to the changing photoperiod, and highlight a link between oxidative status and physiological function.

Effects of the short-term fasting and refeeding on growth-related genes in Japanese eel (Anguilla japonica) larvae

The Japanese eel (Anguilla japonica) spends a long period as the leptocephalus larval form under current rearing conditions. The duration of the larval stage until metamorphosis is influenced by body size and growth; however, little knowledge exists of the regulatory mechanism of growth in eel larvae. The present study focused on growth hormone (GH), insulin-like growth factors (IGFs), and IGF binding protein (IGFBP) as the central regulators of growth in teleost fishes and transforming growth factor-beta 3 (TGF-β3) as a possible key modulator of muscle growth and body component synthesis. Japanese eel IGFBP-1a and TGF-β3, comprising 264 and 411 amino acids, respectively, were cloned. Short-term (5-day) fasting and refeeding experiments were performed to understand changes in growth-related genes affected by nutritional status. The relative expression of gh increased with fasting and subsequently decreased with refeeding to the basal levels of the fed control. Relative igf-1 and igf-2 expression levels were high in the fasted group. Relative igf-1 was reduced after 2-day refeeding, whereas igf-2 decreased to the basal level after 1-day refeeding, suggesting that IGF-1 and IGF-2 might be regulated independently and contribute to postnatal growth in eel larvae. Relative igfbp-1a expression was sharply increased by fasting, whereas tgf-β3 showed high and low values in the fed and fasted groups, respectively. Relative igfbp-1a and tgf-β3 levels were negatively and positively correlated with body size, respectively. These results suggest that igfbp-1a and tgf-β3 are potential indices of growth for exploring optimal rearing conditions to shorten the larval stage in Japanese eels.

Swimming energetics of Atlantic salmon in relation to extended fasting at different temperatures

Predicted future warming of aquatic environments could make fish vulnerable to naturally occurring fasting periods during migration between feeding and spawning sites, as these endeavours become energetically more expensive. In this study, Atlantic salmon (Salmo salar) acclimated to midrange (9°C) or elevated suboptimal (18°C) temperatures were subjected to critical (U_crit) and sustained (4 hours at 80% U_crit) swimming trials before and after 4 weeks of fasting. Fasting caused weight losses of 7.3% and 8.3% at 9°C and 18°C, respectively. The U_crit was unaffected by fasting, but higher at 18°C. Fatigue was associated with higher plasma cortisol, osmolality, Na⁺ and Cl^- at 18°C, and ionic disturbances were higher in fasted fish. All fish completed the sustained swim trials while maintaining constant oxygen uptake rates (ṀO₂), indicating strictly aerobic swimming efforts. At low swimming speeds ṀO₂ was downregulated in fasted fish by 23.8% and 15.6% at 9°C and 18°C, respectively, likely as an adaptation to preserve resources. However, at higher speeds ṀO₂ became similar to fed fish showing that maximum metabolic rates were maintained. The changes in ṀO₂ lowered costs of transport and optimal swimming speeds in fasted fish at both temperatures, but these energetic alterations were smaller at 18°C while routine ṀO₂ was 57% higher than at 9°C. As such, this study shows that Atlantic salmon maintain both glycolytic and aerobic swimming capacities after extended fasting, even at elevated suboptimal temperatures, and adaptive metabolic downregulation provides increased swimming efficiency in fasted fish. Although, improved swimming energetics were smaller when fasting at the higher temperature while metabolism becomes elevated. This could affect migration success in warming climates, especially when considering interactions with other costly activities such as coping with parasites obtained when passing aquaculture sites during seaward travel or gonad development while being voluntarily anorexic during upriver travel to spawning grounds.

Evaluation of circulating insulin-like growth factor (IGF)-I and IGF-binding proteins as growth indices in rainbow trout (Oncorhynchus mykiss)

Circulating insulin-like growth factor (IGF)-I has been proposed as a growth index in several teleosts, including salmonids, and its level in circulation is stabilized by multiple IGF-binding proteins (IGFBPs). Three IGFBPs, IGFBP-2b, -1a, and -1b, are consistently detected in salmonid blood and are suggested to be indices of positive or negative growth, although their applicability to rainbow trout (Oncorhynchus mykiss) is unclear. The present study examined the usefulness of IGFBPs along with IGF-I as a physiological indicator of growth rate in rainbow trout through a rearing experiment. Two groups of underyearling rainbow trout were pit-tagged and either fed or fasted for 33 days. A third group was fasted for 22 days, followed by refeeding for 11 days. Serum IGF-I levels were reduced after fasting for 22 days, but refeeding did not retore its levels to those of the fed control. Nevertheless, there was a positive relationship between serum IGF-I levels and individual growth rates over 33 days of experimentation, confirming its validity as a growth index. Ligand blotting using labeled human IGF-I revealed two IGFBP bands at 43 and 32 kDa, which corresponded to IGFBP-2b and an unidentified form, respectively. In contrast, bands corresponding to IGFBP-1a and -1b, which usually increase after fasting, were hardly detected, even in the fasted fish. The responses of circulating IGFBP-2b to fasting and refeeding were similar to those of circulating IGF-I and positively correlated with growth rate and IGF-I levels. The intensity of the serum 32-kDa IGFBP band was higher in constantly fed fish than in the fasted fish; however, its correlation with growth rate was weaker than those of IGF-I and IGFBP-2b. The present study shows that IGF-I and IGFBP-2b can be used as growth indices for rainbow trout. In contrast, circulating IGFBP-1a and -1b may not serve as negative growth indices in rainbow trout under regular aquaculture conditions because they are rarely detected by ligand blotting or respond to fasting/refeeding.

Potential for Coastal and Offshore Aquaculture in Portugal: Insights from Physico-Chemical and Oceanographic Conditions

Physico-chemical and biological parameters along the Portuguese coast were analyzed to evaluate the potential to produce aquatic species of economic interest. Water samples were collected in 2018 and 2019 in five different areas of the Portuguese coast. Currents data were collected between 2018 and 2020 and historical waves height data from 1988 to 2019. According to the results, there is a wide variety of species that can be considered for production. The northernmost area presented the lowest temperature, as well as the highest levels of chlorophyll a, and nitrate. Under such conditions, the rearing of salmon Salmo salar, mussel Mytilus edulis, scallop Pecten maximus, macroalgae Porphyra umbilicalis, and Undaria pinnatifida can be considered. Regarding the southernmost area, due to the highest temperature, this area seems appropriate for the production of meager Argyrosomus regius, sea bream Sparus aurata, sea bass Dicentrarchus labrax, and greater amberjack Seriola dumerili. This study highlights the challenges in deploying aquaculture structures on the Atlantic coast due to its oceanographic conditions. Site selection for aquaculture is a complex process and pilot studies are essential to analyze the feasibility of developing offshore aquaculture along the coast of Portugal.

Combined effects of elevated rearing temperature and dietary energy level on heart morphology and growth performance of Tasmanian Atlantic salmon (Salmo salar L.)

Cardiac abnormalities may pose a threat to salmonid aquaculture due to their potential detrimental effect on fish health and welfare. The teleost heart is an extremely plastic organ with important morphological differences between wild and farmed fish that include ventricular shape, alignment of the bulbus arteriosus and epicardial fat deposition. However, little is known about how different factors and interactions among them may affect cardiac morphology of Atlantic salmon. To determine whether rearing temperature could induce cardiac malformations in large Tasmanian Atlantic salmon, we examined a range of cardiac morphology indicators and growth parameters in a population of 1-2 kg seawater salmon (n = 60 temperature^-1 diet^-1 ) exposed to control and elevated temperatures of 15 and 19°C, respectively, while fed one of two commercial feeds with different dietary energy levels. Most fish possessed conspicuous fat around the heart with a tendency towards a rounded ventricle and a more obtuse angle of the bulbus arteriosus. However, fish showed no significant differences in heart shape and bulbus alignment in relation to water temperature and dietary energy. These results suggest that cardiac morphology of large Atlantic salmon is unlikely to be affected by rearing temperature and dietary energy during the grow-out phase.

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.

Acclimation to warm temperatures has important implications for mitochondrial function in Atlantic salmon (Salmo salar)

In fish, the capacity of thermal acclimation to preserve cardiac mitochondrial function under future warming scenarios is important to understand given the central roles that cardiac energy metabolism and performance play in this taxa's thermal tolerance. We acclimated Atlantic salmon to 12 and 20°C (for >2 months), and investigated the effects of acute and chronic warming on cardiac mitochondrial respiration and reactive oxygen species (ROS) production (release rate) using high-resolution fluorespirometry. Further, we compared the sensitivity of mitochondrial respiration to nitric oxide (i.e. the NO IC50), and assessed the mitochondrial response to anoxia-reoxygenation (AR). Acute exposure to 20°C increased maximal mitochondrial respiration by ∼55%; however, the mitochondria's complex I respiratory control ratio was 17% lower and ROS production was increased by ≥60%. Acclimation to 20°C: (1) preserved mitochondrial coupling and aerobic capacity; (2) decreased the mitochondria's ROS production by ∼30%; (3) increased the mitochondria's NO IC50 by ∼23%; and (4) improved mitochondrial membrane integrity at 20°C. AR did not affect mitochondrial function at 12°C, but acute exposure to 20°C and AR depressed maximal mitochondrial respiration (by ∼9%) and coupling (by ∼16%) without impacting ROS production. Finally, warm acclimation did not improve the capacity of mitochondria to recover from AR, indicating that there was no 'cross-tolerance' between these challenges. Our findings provide compelling evidence that thermal plasticity of cardiac mitochondrial function contributes to the Atlantic salmon's capability to survive at ≥20°C for prolonged periods, but call into question whether this plasticity may allow them to withstand high temperatures when combined with other stressors.

Physiological and molecular responses to thermal stress in red cusk-eel (Genypterus chilensis) juveniles reveals atrophy and oxidative damage in skeletal muscle

The red cusk-eel (Genypterus chilensis) is a native species with strong potential to support Chilean aquaculture diversification. Environmental stressors, such as temperature, may generate important effects in fish physiology with negative impact. However, no information exists on the effects of thermal stress in Genypterus species or how this stressor affects the skeletal muscle. The present study evaluated for the first time the effect of high temperature stress in red cusk-eel juveniles to determine changes in plasmatic markers of stress (cortisol, glucose and lactate dehydrogenase (LDH)), the transcriptional effect in skeletal muscle genes related to (i) heat shock protein response (hsp60 and hsp70), (ii) muscle atrophy and growth (foxo1, foxo3, fbxo32, murf-1, myod1 and ddit4), and (iii) oxidative stress (cat, sod1 and gpx1), and evaluate the DNA damage (AP sites) and peroxidative damage (lipid peroxidation (HNE proteins)) in this tissue. Thermal stress generates a significant increase in plasmatic levels of cortisol, glucose and LDH activity and induced heat shock protein transcripts in muscle. We also observed an upregulation of atrophy-related genes (foxo1, foxo3 and fbxo32) and a significant modulation of growth-related genes (myod1 and ddit4). Thermal stress induced oxidative stress in skeletal muscle, as represented by the upregulation of antioxidant genes (cat and sod1) and a significant increase in DNA damage and lipid peroxidation. The present study provides the first physiological and molecular information of the effects of thermal stress on skeletal muscle in a Genypterus species, which should be considered in a climate change scenario.

Optimum feeding frequency of juvenile largemouth bass (Micropterus salmoides) reared in in-pond raceway recirculating culture system

This study was conducted to determine the effects of feeding frequency on the growth, serum biochemical parameters, antioxidant status and hepatic growth hormone (GH), insulin-like growth factor I (IGF-I), lipoprotein lipase (LPL) and hepatic lipase (HL) gene expression levels of juvenile largemouth bass (Micropterus salmoides) reared in an in-pond raceway recirculating culture system (IPRS). Fish (initial body weight 5.0 ± 0.4 g) were hand-fed with a commercial diet under one of three different feeding frequency treatments (2, 3 or 4 meals/day) for 120 days. The results indicated that no significant differences were observed in the final body weight, weight gain and specific growth rate of fish fed different feeding frequencies on 30 days and 60 days (P > 0.05). Fish fed 2 times/day had higher growth than that fed 4 times/day on 90 days but had higher growth than those fed 3 and 4 times/day on 120 days. No significant differences were found in serum alanine aminotransferase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP) activities, total protein (TP), lysozyme and triglyceride (TG) content, hepatic total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-PX) activities and malondialdehyde (MDA) content among fish fed different feeding frequency (P > 0.05). Serum glucose (Glu) content and catalase (CAT) activity decreased, while total cholesterol (TC) content increased with increasing feeding frequency. Fish fed 2 times/day had higher hepatic total superoxide dismutase (T-SOD) than that fed 4 times/day on 60 days, 90 days and 120 days (P < 0.05). Fish fed 2 times/day had higher IGF-1 gene mRNA expression on 30 days, 60 days and 120 days (P < 0.05), while no significant difference on 90 days. No significant difference was found in GH gene mRNA expression on 30 days and 60 days, while fish fed 4 times/day had lower values than that fed 2 times/day on 90 days and 120 days (P < 0.05). Fish fed 2 times/day had significantly higher LPL mRNA expression level than that fed 4 times/day on 60 days and 90 days and had significantly higher HL mRNA expression level on 60 days, 90 days and 120 days (P < 0.05). Based on growth, physiology, hepatic gene expression levels, labour costs and intensity, the optimal feeding frequency of largemouth bass (average body weight 5.0 ± 0.4 g) reared in IPRS is 2 times/day. These data are very necessary for the optimizing of culture conditions and feeding management strategy in IPRS culture operations.

Diets supplemented with Saccharina latissima influence the expression of genes related to lipid metabolism and oxidative stress modulating rainbow trout (Oncorhynchus mykiss) fillet composition

This study aimed to evaluate the impact of diets including increasing amounts (1, 2 and 4%) of an iodine-rich macroalgae, Saccharina latissima, on gene expression and fillet composition of commercial-sized rainbow trout. Liver and muscle expression of genes related to growth, iodine, oxidative stress, and lipid metabolism, and the fillet content of fatty acids, cholesterol, and vitamin D3 were assessed. The highest kelp inclusion led to lower final body weight and HSI, without significant differences in mRNA transcription of genes involved in growth (ghr1, ghr2 and igf1) or iodine metabolism (dio1, thra, and thrb). A significant downregulation of an oxidative stress marker, gpx1b2, was observed in fish fed 2% S. latissima, which might suggest the need for less endogenous antioxidants. Dietary inclusion of kelp impacted lipid metabolism, with a downregulation of fatty acid synthase, accompanied by a general decrease of fatty acids in fillet. The present study demonstrated that supplementation of diets with 1 or 2% S. latissima can be achieved without detrimental effects on rainbow trout final weight. Evidence suggest a lipid-lowering effect of diets that did not compromise fillet EPA and DHA concentrations, being 3.7 times above the recommended levels for human consumption.

Environmental hypoxia causes growth retardation, osteoclast differentiation and calcium dyshomeostasis in juvenile rainbow trout (Oncorhynchus mykiss)

Hypoxia generally refers to a dissolved oxygen (DO) level that is less than 2-3 mg/L. With ongoing global warming and environment pollution, environmental or geological studies showed hypoxia frequently occurs in global aquatic systems including ocean, river, estuaries and coasts. A preliminary study was performed to evaluate hypoxia tolerant of rainbow trout (Oncorhynchus mykiss) with parameters of mortality, behavior, endocrine and metabolite, identifying three DO levels including normoxia (Ctrl, 7.0 mg/L), non-lethal hypoxia (NH, 4.5 mg/L) and lethal hypoxia (LH, 3.0 mg/L). Furthermore, trout was treated by Ctrl, NH and LH for six hours to mimic the acute hypoxia in wild and/or farming conditions. A significantly higher mortality was observed in LH group. Trout of NH and LH showed stressful responses with unnormal swimming, increased serum cortisol and up-regulated gill hif1α transcription. Despite trout of NH and LH increased the oxygen delivery abilities by increasing the serum hemoglobin levels, the anerobic metabolism were inevitably observed with increased lactate. This study also showed a prolonged influence of NH and LH on growth after 30-days' recovery. Based on RNA-Seq data, different expression genes (DEGs) associated with stress, apoptosis, antioxidant, chaperone, growth, calcium and vitamin D metabolism were identified. Enrichment analysis showed DEGs were clustered in osteoclast differentiation, apoptosis and intracellular signaling transduction pathways. Results further showed NH and LH significantly decreased bone calcium content and disrupted the growth hormone-insulin-like growth factor (GH-IGF) axis. Our study might contribute to a better understanding of the effects of hypoxia on rainbow trout.

A temperature shift on the migratory route similarly impairs hypo-osmoregulatory capacities in two strains of Atlantic salmon (Salmo salar L.) smolts

Anthropogenic use of water systems may cause temperature fluctuations between tributaries and large rivers for which physiological population related-effects on osmoregulatory capacity of Atlantic salmon are not well described. We simulated the downstream route in the case of the River Meuse basin to investigate the impact of a 5 °C temperature shift during smoltification on hypo-osmoregulatory capacities of smolts. Three temperature regimes were tested: control temperature-treatment (T1) without temperature shift, early (T2) or late (T3) temperature shift-treatment. Moreover, fish were subjected to seawater challenge during and after the downstream migration peak time. Two allochtonous strains were used: Loire-Allier (LA) and Cong (CG). Without temperature shift (T1), significant differences between the strains were noticed in the peak date and maximum activity of gill Na⁺/K⁺ATPase as well as in plasma sodium and potassium concentrations. For early (T2) and late (T3) temperature shift-treatments, gill Na⁺/K⁺ATPase activity, plasma osmolality and ion concentrations were negatively influenced in both strains. After salinity challenge, the highest osmolality was measured in smolts subjected to the temperature shift. Predictably circulating levels of GH and IGF-1 changed over the smolting period but they did not explain the observed modifications in hypo-osmoregulatory abilities whatever the population. The results show a negative impact of a temperature shift on hypo-osmoregulatory capacities of smolts regardless of population differences in smoltification timing under conditions without temperature shift. The resilience of such physiological impact was sustained at least for 1 week, comforting the role of high temperature in influencing the rate of changes occurring during smoltification. Therefore, favouring the downstream migration to help smolts reach the sea faster may mitigate the impact of a rapid temperature increase.

Comparison between Atlantic salmon Salmo salar post-smolts reared in open sea cages and in the Preline raceway semi-closed containment aquaculture system

The use of closed containment (CCS) or semi-closed containment systems (S-CCS) for Atlantic salmon Salmo salar aquaculture is under evaluation in Norway. One such system is the Preline S-CCS, a floating raceway system that pumps water from 35 m depth creating a constant current through the system. Exposing fish to moderate water currents is considered aerobic exercise and it is often perceived as positive for fish welfare, growth, food utilization, muscle development and cardiac health. The present study compared fish reared in the Preline S-CCS and in a reference open pen. Samples were taken in fresh water before being transferred to the seawater systems and after 1, 2 and 4 months in seawater and analysed for growth, mortality, muscle development and plasma insulin-like growth factor I (IGF-I) levels. Moreover, gene transcription were determined in the skeletal muscle [igf-I, insulin-like growth factor 1 receptor a (igf1ra) and insulin-like growth factor 1 binding protein 1a (igf1bp1a)] and cardiac transcription factors [myocyte-specific enhancer factor 2C (mef2c), gata4 and vascular endothelial growth factor (vegf)]. While the results suggest that post-smolts in Preline S-CCS were smaller than reference fish, fish from Preline S-CCS have less accumulated mortality at the end of the experiment and showed 2.44 times more small muscle fibres than the reference group fish after 4 months in seawater. These results confirmed what was previously observed in the second generation of Preline. Similar levels of big muscle fibres between Preline S-CCS and reference suggest a similar hypertrophy of muscle fibres even with lower IGF-I expression in the Preline S-CCS. Cardiac gene transcription suggests cardiac hypertrophy was observed after 4 months in seawater in the Preline S-CCS group. Altogether, Preline S-CCS is a promising technology able to produce more robust S. salar with a faster growth and lower mortality in the subsequent standard open cage system growth period.

Circulating insulin-like growth factor binding proteins in fish: Their identities and physiological regulation

Insulin-like growth factor binding proteins (IGFBPs) play crucial roles in regulating the availability of IGFs to receptors and prolong the half-lives of IGFs. There are six IGFBPs present in the mammalian circulation with IGFBP-3 being most abundant. In mammals IGFBP-3 is the major carrier of circulating IGFs, facilitated by forming a ternary complex with IGF and an acid-labile subunit (ALS). IGFBP-1 is generally inhibitory to IGF action by preventing it from interacting with its receptors. In teleosts, the third-round of vertebrate whole genome duplication created paralogs of each IGFBP, except IGFBP-4. In the fish circulation, three major IGFBPs are typically detected at molecular ranges of 20-25, 28-32 and 40-50kDa. However, their identities are not well established. Three major circulating IGFBPs in Chinook salmon have been identified through protein purification and cDNA cloning. Salmon 28- and 22-kDa IGFBPs are co-orthologs of IGFBP-1, termed IGFBP-1a and -1b, respectively. They are induced under catabolic conditions such as stress and fasting but their responses are somewhat different, with IGFBP-1b being the most sensitive of the two. Cortisol stimulates production and secretion of these IGFBP-1 subtypes while, unlike in mammals, insulin may not be a primary suppressor. Salmon 41-kDa IGFBP, a major carrier of IGF-I, is not IGFBP-3, as might be expected extrapolating from mammals, but is in fact IGFBP-2b. Salmon IGFBP-2b levels in plasma are high when fish are fed, and GH treatment increases its circulating levels similar to mammalian IGFBP-3. These findings suggest that salmon IGFBP-2b acquired the role and regulation similar to mammalian IGFBP-3. Multiple replications of fish IGFBPs offer a unique opportunity to investigate molecular evolution of IGFBPs.

The effect of thermal acclimation on aerobic scope and critical swimming speed in Atlantic salmon, Salmo salar

The Atlantic salmon is extensively studied owing to conservation concerns and its economic importance in aquaculture. However, a thorough report of their aerobic capacity throughout their entire thermal niche has not been described. In this study, Atlantic salmon (∼450 g) were acclimated for 4 weeks at 3, 8, 13, 18 or 23°C, and then tested in a large Brett-type swimming respirometer in groups of 10 per trial. Both standard metabolic rate and active metabolic rate continued to increase with temperature, which resulted in an aerobic scope that also increased with temperature, but was statistically similar between 13, 18 and 23°C. The critical swimming speed peaked at 18°C (93.1±1.2 cm s^-1), and decreased significantly at the extreme temperatures to 74.8±0.5 and 84.8±1.6 cm s^-1 at 3 and 23°C, respectively. At 23°C, the accumulated mortality reached 20% over 4 weeks, while no fish died during acclimation at colder temperatures. Furthermore, fish at 23°C had poor appetite and lower condition factor despite still having a high aerobic scope, suggesting that oxygen uptake was not the limiting factor in the upper thermal niche boundary. In conclusion, Atlantic salmon were able to maintain a high aerobic capacity and good swimming capabilities throughout the entire thermal interval tested, thus demonstrating a high level of flexibility in respiratory capacity towards different temperature exposures.

Lens metabolomic profiling as a tool to understand cataractogenesis in Atlantic salmon and rainbow trout reared at optimum and high temperature

Periods of high or fluctuating seawater temperatures result in several physiological challenges for farmed salmonids, including an increased prevalence and severity of cataracts. The aim of the present study was to compare cataractogenesis in Atlantic salmon (Salmo salar L.) and rainbow trout (Oncorhynchus mykiss) reared at two temperatures, and investigate whether temperature influences lens metabolism and cataract development. Atlantic salmon (101±2 g) and rainbow trout (125±3 g) were reared in seawater at either 13°C (optimum for growth) or 19°C during the 35 days experiment (n = 4 tanks for each treatment). At the end of the experiment, the prevalence of cataracts was nearly 100% for Atlantic salmon compared to ~50% for rainbow trout, irrespective of temperature. The severity of the cataracts, as evaluated by slit-lamp inspection of the lens, was almost three fold higher in Atlantic salmon compared to rainbow trout. The global metabolic profile revealed differences in lens composition and metabolism between the two species, which may explain the observed differences in cataract susceptibility between the species. The largest differences were seen in the metabolism of amino acids, especially the histidine metabolism, and this was confirmed by a separate quantitative analysis. The global metabolic profile showed temperature dependent differences in the lens carbohydrate metabolism, osmoregulation and redox homeostasis. The results from the present study give new insight in cataractogenesis in Atlantic salmon and rainbow trout reared at high temperature, in addition to identifying metabolic markers for cataract development.