The effects of swimming exercise and dissolved oxygen on growth performance,fin condition and precocious maturation of early‐rearing Atlantic salmon Salmo salar

Swimming exercise, typically measured in body‐lengths per second (BL/s), and dissolved oxygen (DO), are important environmental variables in fish culture. While there is an obvious physiological association between these two parameters, their interaction has not been adequately studied in Atlantic salmon Salmo salar. Because exercise and DO are variables that can be easily manipulated in modern aquaculture systems, we sought to assess the impact of these parameters, alone and in combination, on the performance, health and welfare of juvenile Atlantic salmon. In our study, Atlantic salmon fry were stocked into 12 circular 0.5 m³ tanks in a flow‐through system and exposed to either high (1.5–2 BL/s) or low (<0.5 BL/s) swimming speeding and high (100% saturation) or low (70% saturation) DO while being raised from 10 g to approximately 350 g in weight. Throughout the study period, we assessed the impacts of exercise and DO concentration on growth, feed conversion, survival and fin condition. By study's end, both increased swimming speed and higher DO were independently associated with a statistically significant increase in growth performance (p < .05); however, no significant differences were noted in survival and feed conversion. Caudal fin damage was associated with low DO, while right pectoral fin damage was associated with higher swimming speed. Finally, precocious male sexual maturation was associated with low swimming speed. These results suggest that providing exercise and dissolved oxygen at saturation during Atlantic salmon early rearing can result in improved growth performance and a lower incidence of precocious parr.     

Cholesterolaemia and triacylglycerolaemia in farmed rainbow trout,Oncorhynchus mykiss

Physiological (reference) value intervals determined by the lower 2.5% and upper 97.5% quantiles were calculated for blood plasma cholesterol (CHOL) and triacylglycerol (TGL) in farmed rainbow trout, Oncorhynchus mykiss, in raceway culture. The fish were given dry pelleted diets that contained 37–47% crude protein and 7–14% crude fat and were kept at a stocking density of 50 kg m^?3 in tanks provided with running freshwater at an ambient temperature of 3–16°C and dissolved oxygen, 8.4–11.5 mg L^?1. Blood was sampled between September and November at a photoperiod of 9:00–13:00 hours: 11:00–15:00 hours (light:dark). Cholesterol levels were significantly (P = 0.0001) greater in males (4.7–12.1 mmol L^?1, n = 34, mean weight 406 ± 138 g) than immature females (3.2–9.7 mmol L^?1, n = 386, mean weight 416 ± 147 g). Physiological range for TGL in immature females and males was 2.4–14.4 mmol L^?1 (n = 249, mean weight 418 ± 149 g). The distribution and density of the quantiles in the tested reference group were made possible by the use of histograms, which showed normal distributions for CHOL in males and in females, but not for TGL, in which a sinistral asymmetry was found. Correlation and regression analyses indicated significant (P = 0.0000) dependence between the CHOL and total protein (r² = 76.2%), CHOL and Fulton's condition factor (r² = 43.3%) and CHOL and absolute weight of liver (r² = 45.5%). Fluctuation in cholesterolaemia and triacylglycerolaemia, depending on nutrition and the aquaculture method is discussed below.     

Insulin stimulates hepatic lipogenesis in rainbow trout,Oncorhynchus mykiss

The effects of the pancreatic hormones, insulin and glucagon, on rates of lipid biosynthesis in liver removed from rainbow trout, Oncorhynchus mykiss, were evaluated in vitro. Livers were removed from animals fasted for 30–36h, cut into ca. 1 mm³ pieces, and incubated in the presence of various concentrations of salmon insulin (sINS), bovine insulin (bINS), or a combination of BINS and bovine/porcine glucagon (GLU). Lipid synthesis was evaluated by total lipid concentration, ³H₂O incorporation into total lipid, and by fatty acid synthetase activity. Both mammalian and sINS tended to increase tissue total lipid concentration in hepatic tissue incubated for 5h. Insulin also stimulated ³H₂O incorporation into total lipid in a dose-dependent manner. Bovine INS (2 × 10^?6 M) stimulated de novo synthesis nearly 6-fold over control rates; sINS (2 × 10^?6 M) stimulated label incorporation more than 7-fold over control rates. Glucagon inhibited INS-stimulated ³H₂O incorporation; whereas, GLU alone had no effect on lipid synthesis in liver pieces incubated 5h. Lipid class analysis indicated that bINS significantly stimulated ³H₂O incorporation into phospholipids, fatty acids, and triacylglycerols. The greatest accumulation of label was in the triacylglycerol fraction, where incorporation was stimulated 17-fold over control levels. Hepatic enzymatic analysis indicated that bINS also significantly stimulated lipogenic enzyme activity 9-fold above control levels. These results indicate that INS is an important regulator of lipid synthesis in the liver of trout.     

Nutritional regulation of somatostatin expression in rainbow trout, Oncorhynchus mykiss

Previously we characterized three DNAs from the endocrine pancreas (Brockmann body) of rainbow trout (Oncorhynchus mykiss) that encode for distinct preprosomatostatin (PPSS) molecules: one containing somatostatin-14 and its C-terminus (PPSS I) and two containing [Tyr⁷, Gly¹⁰]-somatostatin-14 at their C-termini (PPSS II′ and PPSS II″). In the present study, the regulation of PPSS expression was studied in rainbow trout placed on varying nutritional regimes (fed continuously, fasted, fasted then refed). Fish that were fasted for one week displayed reduced growth compared to their fed counterparts, but no alteration in pancreatic PPSS expression was noted between the two groups. Fish fasted for 4 and 6 weeks also were growth retarded and displayed increased levels of PPSS I mRNA and PPSS II″ mRNA compared to fed animals; PPSS II′ mRNA levels were not affected by food deprivation. Refeeding fish for two weeks following 4 weeks of food deprivation restored growth and reduced PPSS I and PPSS II″ mRNA expression to levels similar to those displayed by continuously fed fish. Changes in PPSS expression were correlated with increases in plasma SS. These results indicate that nutritional state modulates differential expression of PPSSs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Arginine effects on biochemical composition of sperm in rainbow trout,Oncorhynchus mykiss

The present study investigated the effect of arginine on seminal plasma composition in rainbow trout. Male rainbow trout broodstocks (2500 ± 200 g) were fed five practical diets (each consisting of three triplicates) supplemented with Arginine at 0.50%, 1.50% and 2.00%. The control group were fed without arginine. Broodstock feeding lasted for 90 days, and then fish semen was sampled. Results indicated no significant differences in LDH, ALP, Fe²⁺ and phosphorous content among the different treatments. The lowest levels of AST and ALT and the highest levels of Ca²⁺ and Mg²⁺ ions were observed in the treatment fed with 1.50% arginine, which showed significant differences from other treatments (P < 0.05). Moreover, the amount of Cl^?, Na⁺ and K⁺ ions was significantly increased in the seminal plasma in fish fed diets containing arginine in comparison with the control. As the amount of arginine was increased, the levels of uric acid became significantly greater in contrast to urea and glucose levels. The highest amounts of cholesterol, fructose and total protein were observed in treatments fed on 2.00%, 0.50% and 1.00% arginine, respectively, showing significant differences from other treatments (P < 0.05). The highest pH value was assayed in the 1.50% arginine treatment. Results indicated that arginine had a potential efficacy on semen quality in rainbow trout broodstocks.     

Effects of traditional rainbow trout (Oncorhynchus mykiss) breeding on dissolved organic nitrogen pools and microbial activity in the water

Seasonal effects of rainbow trout (Oncorhynchus mykiss) breeding in traditional, flow‐through ponds on abundance and activity of bacteria, and on pools and cycling of dissolved free and combined amino acids (DFAA and DCAA), were studied in three aquaculture systems in Denmark. The fish breeding was found to increase both abundance and production of bacteria by about 60% (annual average of all three systems). The bacterial production correlated positively with temperature, and was 10 to 60‐fold higher in summer than winter. Concentrations of DFAA (range: 45–690 nM) increased by 40–350% (mean of 89%) during passage in the systems. The bacterial uptake of DFAA was stimulated by 42% (annual average value of the three systems) between inlets and outlets. Uptake of DFAA was estimated to sustain from 45% (C) and 70% (N) of the bacterial C and N demand. Concentrations of DCAA, e.g., proteins and peptides, varied from 600 to 3900 nM, and increased on average 89% during passage in the three systems. Bacterial capacity for utilization of DCAA was determined as leucine peptidase activity and related to the bacterial density. The cell‐specific peptidase activity was, on average, 103% higher at outlets than inlets. Changes in the peptidase activity did not correlate with variations in DCAA pools or the bacterial production. Concentrations of ammonium, urea and phosphate increased on average by 88%, 103% and 66%, respectively, during passage in the three systems, whereas no changes were observed for nitrate. Our study shows that traditional fish breeding impacts pools and cycling of dissolved organic N, as well as bacterial dynamics. The short residence time of water in the ponds (3–6 h) implies that most of the nutrients produced in the systems were discharged into the downstream water, rather than assimilated by bacteria within the systems.     

Effect of acute and chronic toxicity of paraquat on immune system and growth performance in rainbow trout,Oncorhynchus mykiss

In this study, the impact of paraquat (1, 1‐dimethyl 4, 4‐bipyridiniumdicholoride) on rainbow trout immune system and growth parameters was evaluated. In acute exposure, fish were distributed into four groups and exposed to 0, 54, 90 and 150 mg L^?1 of paraquat for 96 h. In chronic trial, fish were allocated into six groups and exposed to 0, 1.25, 2.5, 5, 10 and 20 mg L^?1 of paraquat for 30 days. Growth performance (percentage weight gain, condition factor and specific growth rate) and innate immune parameters (lysozyme, haemolytic complement activity and total immunoglobulin) were evaluated. Experimental data showed a LD₅₀ about 48.2 mg of paraquat per litre. Immunotoxic proprieties of paraquat especially in higher doses were shown in both trials. Total weight was also significantly decreased in chronic exposure when fish was subjected to 10 and 20 mg L^?1 paraquat whereas other growth parameters were not affected in this experiment. In general, these results suggest that paraquat exposure in rainbow trout could suppress the immunological and growth parameters.     

Relationships between growth and disease resistance in rainbow trout,Oncorhynchus mykiss (Walbaum)

Rainbow trout from 23 families were evaluated for growth and resistance to the bacterial coldwater disease (BCWD) caused by Flavobacterium psychrophilum and infectious haematopoietic necrosis (IHN) caused by IHN virus. Average family weights were between 161 and 263 g with an average of 225 g at 213 days post‐fertilization with specific growth rates ranging from 2.37 to 2.88. Per cent survival of fish challenged with F. psychrophilum was between 18% and 100%, while for those challenged with IHNV, the range was between 12% and 93%. Significant positive correlations were found for end body weight and resistance to IHN (P < 0.05) and for early body weight and resistance to BCWD (P < 0.1). However, no significant correlations were detected between resistance to both pathogens or disease resistance and overall genetic diversity or diversity within the major histocompatibility locus.     

Feeding behaviour of fast- and slow-growing strains of rainbow trout, Oncorhynchus mykiss (Walbaum), during first feeding

The development of feeding behaviour in two rainbow trout strains and their hybrid was compared at the transition from endogenous nutrition to exogenous feeding. After 60 min of acclimatization, the swimming pattern, spatial distribution, agonistic behaviour and snapping of fish were quantified by making 5-min observations on groups of five fish. Behavioural patterns were recorded in four replicate groups per treatment, before and after the introduction of dry trout feed or Artemia nauplii (actometric tests) or extracts of these (olfactometric tests). Fish of the slow growing strain were less active than those of the other two strains. Greater swimming activity observed in the fish of the fast growing strain was associated with more rapid feeding and a higher number of snapping responses. Such behavioural precocity is of interest because it could provide the basis for the growth differences between the fast and slow growing strains.     

Glucose-stimulated lipolysis in rainbow trout,Oncorhynchus mykiss,liver

Rainbow trout, Oncorhynchus mykiss, were used to characterize further the influence of glucose on hepatic lipolysis. Liver was removed from fed fish, cut into 1 mm³ pieces and incubated for up to 5 h in Hanks medium containing either 2 mM, 5.5 mM, 10 mM, or 25 mM glucose. Glucose-stimulated lipolysis was indicated by tissue triacylglycerol (TG) lipase activity and by medium concentrations of glycerol and fatty acids (FA). Triacylglycerol lipase activity in liver pieces incubated in the presence of higher concentrations (25 mM) of glucose was significantly higher than that in liver pieces incubated in lower concentrations (2 mM) of glucose, rising from 0.075 ± 0.002 (mean ± SEM) nmol FA released/h/mg protein to 0.092 ± 0.004 units. Similarly, higher concentrations of glucose stimulated significantly more FA release and glycerol release from liver pieces than that stimulated by lower concentrations of glucose. Glycerol release from liver pieces incubated in the presence of 10 mM glucose and 25 mM glucose was ca. 2-fold to 2.8-fold, respectively, higher than that from liver pieces incubated in the presence of either 2 mM or 5.5 mM glucose. Fatty acid release from liver pieces incubated in the presence of 10 mM or 25 mM glucose was ca. 1.8-fold higher than that from liver pieces incubated in the presence of either 2 mM or 5.5 mM glucose. Notably, increased glycerol release was not accompanied by a parallel increase in FA. Fatty acid reesterification was more pronounced in liver pieces exposed to higher glucose (10 mM and 25 mM) than in liver pieces exposed to lower glucose (2 mM and 5.5 mM). ¹⁴C-incorporation studies indicated that glucose serves as a carbon source for reesterified FA in trout liver. The route of reesterification appears to be from glucose to glycerophosphate to phosphatidic acid to diacylglycerol to TG. Increasing concentrations of glucose did not affect glycerol kinase activity, indicating that glucose-stimulated lipolysis was not accompanied by increased glycerol recycling within the liver. These results suggest that glucose stimulates fatty acid reesterification and directly enhances net lipolysis in trout liver incubated in vitro.A part of this study was presented at the Annual Meeting of the American Society of Zoologists, December 26–30, 1991, Atlanta, GA.     

Identification of a novel gill-specific calpain from rainbow trout (Oncorhynchus mykiss)

Calpains are calcium-dependent neutral proteases responsible for many cellular functions. The two forms of calpain ubiquitously expressed in mammalian tissues are known as μ-calpain and m-calpain. We report here the identification of a novel calpain that is similar to but distinct from the μ- and m-calpains in rainbow trout. The cDNA of the novel gene is 2623 bp in length with a single open reading frame. The predicted protein (676 amino acids) contains the conserved calpain characteristic domains that include: domain I (pro peptide), II (cysteine catalytic site), III (electrostatic switch), and IV (calmodulin-like) with five Ca²⁺-binding EF hands. Northern blot and RT-PCR analyses demonstrated that the novel calpain gene is predominantly expressed in rainbow trout gills. Comparison of the novel protein with the ubiquitously expressed calpains and several mammalian tissue-specific calpains revealed that the novel calpain is an orthologue of the mammalian digestive tract specific calpain (calpain 9).     

Effect of dietary inclusion of lysozyme on growth performance and plasma biochemical parameters of rainbow trout (Oncorhynchus mykiss)

This study was conducted to evaluate the effect of dietary lysozyme supplementation on growth performance and plasma biochemical parameters of rainbow trout (Oncorhynchus mykiss). Graded levels of lysozyme [0 (control), 150, 300, 450 and 600 mg kg^?1 diet] were fed to fish (initial average weight 7.76 g) for 10 weeks. Dietary lysozyme supplementation regardless of inclusion level generally improved the growth, feed utilization and nutrient retention, but significant differences were mainly observed between the 450 or 600 mg kg^?1 lysozyme group and the control group. Lysozyme supplementation generally decreased the plasma aspartate aminotransferase and alanine aminotransferase (ALT) activities, but significant difference was only observed in the ALT activity between the 450 mg kg^?1 lysozyme group and the control group. In contrast, lysozyme supplementation generally increased the plasma alkaline phosphatase and lysozyme activities, but significant difference was only observed in the lysozyme activity between the 600 mg kg^?1 lysozyme group and the control group. Lysozyme supplementation generally increased the plasma antioxidant activities of enzymes (including superoxide dismutase, glutathione peroxidase and catalase) and total antioxidant capacity, but decreased the plasma malondialdehyde level. These results suggest that dietary 450–600 mg kg^?1 lysozyme inclusion may improve the growth and non‐specific immune response of rainbow trout.     

Effects of unilateral ovariectomy on recruitment and growth of follicles in the rainbow trout,Oncorhynchus mykiss

Virgin female rainbow trout, Oncorhynchus mykiss, were unilaterally ovariectomised at various stages of ovarian development to investigate the effect of the removal of one ovary on subsequent recruitment and growth of follicles in the remaining ovary. The right ovary was removed from groups of 12–15 fish, 12, 7 and 4 months before they were due to ovulate, and the gonadosomatic index and follicle number and size determined just prior to ovulation. There were no differences in fecundity or follicle size in fish unilaterally ovariectomised at 12 and 7 months prior to ovulation compared to the controls. However, in the females unilaterally ovariectomised 4 months prior to ovulation, the remaining ovary either had the normal number of follicles for a single ovary but of a significantly larger size than follicles in the controls, or alternatively had almost 70% more than the normal number of vitellogenic follicles but comprising two distinctly different size populations. Differences in plasma oestradiol-17β concentrations at the final sample were seen only in females unilaterally ovariectomised 4 months prior to ovulation, where the levels were significantly lower than both the sham operated and control fish (p < 0.05). These data show that in the rainbow trout, complete compensatory ovarian hypertrophy following unilateral ovariectomy can occur throughout a major part of ovarian development, but that follicle recruitment is limited to stages up to (and therefore fecundity is determined by) mid-vitellogenesis.     

The use of AquaMats® to enhance growth and improve fin condition among raceway cultured rainbow trout Oncorhynchus mykiss (Walbaum)

AquaMats® are a type of artificial seaweed designed to provide structure in ponds used for fish culture and as a substrate for the growth of aquatic plants and invertebrates which in turn are a source of nutrition to cultured species. In two separate tests AquaMats® were placed into raceways used to rear rainbow trout Oncorhynchus mykiss (Walbaum) to evaluate their effect on fish growth and fin condition. In the first test, the AquaMats® were placed perpendicular to the raceway length similar to a baffle design. One treatment consisted of AquaMats® that were cleaned on a regular basis, and the other treatment consisted of AquaMats® that were not cleaned throughout the test. By the end of the test no differences were found between treatments with respect to final fish weight, specific growth rate, or feed conversion ratio. The use of AquaMats® did not improve fin condition, in fact several fins measured were significantly better among control fish. In the second test AquaMats® were placed on the raceway bottom parallel to their length and to the water flow. AquaMats® were also hung from the side of the raceway to provide cover. At the conclusion of this test no differences were found between treatments with respect to final fish weight, specific growth rate, or feed conversion ratio. The placement of AquaMats® did have a transitory impact on fin condition. Mid‐way through the test, treatment fish generally exhibited longer fins compared with the controls. However, by the end of the test, these differences were no longer detectable. The results from both tests indicate that fish were not provided with additional nutrition to the extent it improved growth. However, the use of AquaMats® did make a significant, albeit transitory, impact on fin condition.     

Effect of different plant oils on growth performance,fatty acid composition and flesh quality of rainbow trout (Oncorhynchus mykiss)

This experiment intended to assess the effect of sesame (SO), sunflower (SFO) and linseed (LO) oils on growth performance, fatty acid composition of fillet and liver or flesh quality traits of rainbow trout. Fish fed different four iso‐nitrogenous and iso‐lipidic experimental feeds. The control feed contained only fish oil as the primary lipid source. The fillet eicosapentaenoic acid and docosahexaenoic acid levels were the highest in fish fed control feed. In contrast, the liver eicosapentaenoic acid level was the highest in fish fed LO feed. Fish fed SFO feed had the highest level of total n?6 fatty acids in fillet and liver. Fish fed SO feed had the highest level of 18:1 n?9 fatty acid in fillet and liver. During the 12 days refrigerated storage period at 1°C, thiobarbituric acid (TBA) and pH values gradually increased in all dietary groups. However, trimethylamin nitrogen (TMA‐N) values increased in all dietary groups between days 0 and 9 during the storage period. Generally, pH value in fillets of control group was slightly higher than the other fish groups during 12 days refrigerated storage. Nevertheless, the chemical indicators of spoilage, TBA, TMA‐N and pH values were in the limit of acceptability for human consumption. Results of growth performance and chemical tests in the present study showed that sesame, linseed and sunflower oils could be used in feeds for rainbow trout. Moreover, we concluded that further researches should be carried out on the partial replacement of fish oil by sesame oil in rainbow trout nutrition.     

Lipid-stimulated somatostatin secretion in rainbow trout,Oncorhynchus mykiss

Previous work has shown that somatostatins (SS) affect teleost lipid metabolism indirectly by inhibition of insulin (INS) and directly by stimulation of hepatic lipolysis. In the present study, rainbow trout (Oncorhynchus mykiss) were used to characterize further the lipid-SS relationship by evaluating how lipid, contributes to SS secretion bothin vivo andin vitro. In vivo hyperlipidemia was induced for up to 3 h by short-term (2 min) infusion of a triacylglycerol (TG)-rich lipid emulsion (20% Intralipid^®). Plasma total lipid concentration increased 118 and 155% over control levels 1 h and 3 h, respectively, after infusion; much of this increase was due to elevated plasma fatty acids (FA), which increased 39 and 520%, respectively, over the same time-frame. The hyperlipidemic pattern was attended by a significant increase in the plasma concentration of SS. The specific effects of fatty acids were evaluated on isolated Brockmann bodies. Palmitic acid and oleic acid stimulated SS release 378 and 82%, respectively, over baseline levels. These results indicate that lipids, and in particular fatty acids, modulate SS secretion in rainbow trout.     

Granulomatous enteritis in rainbow trout (Oncorhynchus mykiss) associated with soya bean meal regardless of water dissolved oxygen level

This study investigated morphological changes associated with soya bean meal‐induced enteritis (SBMIE) in distal intestine (DI) of rainbow trout (Oncorhynchus mykiss) fed a soya bean meal (SBM)‐based diet and exposed to normoxia or hypoxia created by optimal and low water flow rates, respectively. A 28‐day adaption period was followed by a 42‐day challenge period where 600 fish were subjected to dietary challenge and/or hypoxia. Twelve tanks each containing 50 juvenile trout were assigned randomly in triplicate to each treatment. Histopathological and immunohistochemical evaluation revealed pathological features that have not previously been described in association with SBMIE. Vacuolar degeneration of epithelial cells mainly at the base of mucosal folds, epithelial cysts, epithelial dysplasia, necrosis, shedding of necrotic cells, and granulomatous inflammation including infiltration of enlarged, sometimes finely vacuolated or “foamy” macrophages, multinucleated giant cells and increased proliferation of fibroblasts were observed. Acid‐fast bacteria were not detected in enlarged macrophages; however, these cells contained AB‐PAS‐ and sometimes cytokeratin‐positive material, which was interpreted to be of epithelial/goblet cell origin. Hypoxia did not affect the morphological changes in DI. These results suggest that SBM was associated with a granulomatous form of enteritis in DI of rainbow trout regardless of water oxygen level.     

Probiotic applications for rainbow trout (Oncorhynchus mykiss Walbaum) I. Effects on growth performance,feed utilization,intestinal microbiota and related health criteria

The effect of dietary probiotics (Bacillus subtilis, Bacillus licheniformis and Enterococcus faecium) used singularly and synergistically on the growth performance, intestinal microbiota and health status of rainbow trout (Oncorhynchus mykiss Walbaum) were assessed after 10 weeks feeding on supplemented diets. No significant improvements of weight gain or specific growth rate were observed in the probiotic fed groups. However, a significant improvement of feed conversion ratio was observed in the group fed E. faecium. High levels of probiotic species were observed in the posterior gastrointestinal tract as transient digesta‐associated populations and potentially resident mucosal populations. Bacillus subtilis and B. licheniformis levels accounted for 36% of the total culturable microbial population adhered to the mucosa and 62% in the digesta. E. faecium levels accounted for 45% of the mucosal population and 89% of the population in the digesta. An increase of serum lysozyme activity was observed in the fish fed diets containing the Bacillus probionts and elevated leukocyte levels were observed in fish fed diets containing Bacillus + E. faecium synergistically. The results of the current study demonstrate potential for B. subtilis, B. licheniformis and E. faecium to improve feed utilization, modulate intestinal microbiota and the health status of rainbow trout.