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This study assessed the flesh proximate and lipid composition of two year classes and sizes of non-transgenic (NT) and transgenic (T) coho salmon (Oncorhynchus kisutch) that were grown to market size in the same rearing environment and on similar commercial feeds. The data also assessed land-based commercially raised farmed coho salmon, as well as two other species of ocean-raised farmed salmonids, and four species of wild Pacific salmon. The largest differences in nutritional content were seen between wild and farmed salmon. Farmed salmon contained higher muscle lipid levels and had higher levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) relative to wild counterparts. Moreover, the farmed fish also contained higher levels of n-6 poly-unsaturated fatty acids (PUFAs) and a lower omega-3 to omega-6 ratios (n-3/n-6). There were small differences in nutritional content between NT and T coho salmon, but most of these differences were due to the lower body weight and consequently lower lipid content in the small T coho salmon group. The larger NT coho salmon were very similar in nutritional content to their T counterparts. Overall, fish diet composition and rearing location (commercial feeds in culture vs. natural prey in the wild) had a much larger influence on the flesh nutritional content than did effects of the transgene, and all salmon, regardless of source, were found to be rich sources of EPA and DHA.

Reductions in flesh contaminant concentrations were evaluated in a 36-week feeding trial examining several dietary techniques. Atlantic salmon were fed one of seven dietary treatments for 24 weeks. These diets included a fishmeal, fish oil control diet, an industry control diet, three diets that examined a 75% replacement level of anchovy oil (AO) with flaxseed oil, canola oil and poultry fat, and two diets formulated to be low in contaminants formulated with canola oil, activated carbon-treated anchovy oil and canola protein concentrate or soy protein concentrate. Following this initial 24-week feeding interval, a 12-week finishing diet was utilized to restore the levels of omega-3 highly unsaturated fatty acids (n-3 HUFAs). The salmon had marked reductions in their flesh concentrations of total polychlorinated biphenyls (PCBs), dioxin-like PCBs and total toxic equivalents by the end of the grow-out phase, but also exhibited significant depressions in their flesh concentrations of n-3 HUFAs relative to 100AO-fed fish. The 12-week finishing diet period was effective in partially re-instating omega-3 levels to those present in the flesh lipids of fish fed 100AO while concurrently maintaining lower flesh contaminant concentrations.

The objective of this study was to access the suitability of using poultry fat (PF) or blends of PF with flaxseed oil (FO) to replace 75% of the supplemental anchovy oil (AO) in the diet of juvenile sablefish (Anoplopoma fimbria), a relatively new marine species to aquaculture. Sablefish were fed one of four diets twice daily to satiation for 15 weeks. The test diets were identical in composition except for the source of supplemental lipid which was either 100% AO (100AO), or had 75% of the supplemental AO replaced with 50% FO:25% PF, 25% FO:50% PF or 75% PF. Sablefish growth parameters, whole body and fillet proximate constituent concentrations, and apparent digestibility coefficients were uninfluenced by diet treatment. There were also no adverse effects of the diet treatments on fish health, as determined from analysis of various haematological and innate immunological parameters. Terminal fillet fatty acid compositions generally reflected the dietary fatty acid compositions. Results indicated that PF or blends of PF and FO may comprise 75% of the supplemental lipid in a grower diet for sablefish and are an economic alternative to AO while still providing humans with a rich dietary source of highly unsaturated fatty acids.

This study was undertaken to determine the suitability of using cold-pressed flaxseed oil (FO) as a major source of lipid in place of anchovy oil (AO) in the diet of juvenile sablefish (Anoplopoma fimbria), a relatively new marine species to aquaculture. Sablefish were fed one of four diets twice daily to satiation for 15 weeks. The test diets were identical in composition, except for the source of supplemental lipid which was either 100% AO (100AO), or increasing replacement of AO with FO i.e., 75AO:25FO, 50AO:50 FO or 25AO:75FO. Sablefish growth parameters, whole body and fillet proximate constituent concentrations and apparent digestibility coefficients were uninfluenced by diet treatment. There were also no adverse effects of the diet treatments on fish health, as determined from analysis of various haematological and innate immunological parameters. Terminal fillet fatty acid compositions generally reflected the dietary fatty acid compositions, while flesh contaminant concentration decreased with increasing dietary flaxseed oil content. Results indicated that FO may comprise up to 75% of the supplemental lipid in a grower diet for sablefish, while still providing humans with a rich dietary source of highly unsaturated fatty acids.

In the flesh (skinless fillet) of chinook, chum, coho, pink, and sockeye salmon (Oncorhynchus tshawytscha, O. keta, O. kisutch, O. gorbuscha, and O. nerka, respectively), sablefish (Anoplopoma fimbria) and walleye pollock (Theragra chalcogramma) from several sites in the northeast Pacific sampled between 2002 and 2008, tetra- and pentabrominated diphenyl ethers (BDEs) (BDE 47, 49, 99, and 100) dominated the congener distribution. Chinook and sablefish contained the highest concentrations, followed by sockeye, coho, and pink salmon, and pollock. In sockeye from the Bering Sea – Aleutians and from the Gulf of Alaska, total tri- to hepta-BDE concentrations fell significantly between 2002 and 2005; in sablefish from Gulf of Alaska, there was a steady but statistically nonsignificant decline in BDE concentrations between 2002 and 2008. Relative proportions of the main BDE congeners did not change appreciably over time, within species or location. All species except sockeye salmon showed a clear southeastward increase in BDE concentrations, implying an increasing gradient in general ecosystem contamination. In chinook, coho, and sablefish, especially, the southeastward trend in increasing total concentrations was associated with increasing proportions of BDEs 47 and 100. Chinook returning to western North American natal streams appeared to accumulate most of their PBDE burden towards the end of their migration. Fish from more northern sampling sites often had higher proportions of more highly brominated congeners than those from more southern sites, perhaps reflecting contamination from Asian sources where higher-brominated commercial PBDE formulations are used. In sablefish and pollock, the relative proportions of BDEs 99 and 47 varied inversely in almost a 1:1 ratio, implying debromination of BDE 99 to 47. Environ. Toxicol. Chem. 2011; 30:1261–1271. © 2011 SETAC

We assessed the effects of dietary fatty acid composition on sodium-potassium ATPase (Na(+)/K(+)-ATPase) activity and isoform expression in the gills of juvenile fall chinook salmon, Oncorhynchus tshawytscha by supplementing diets with either anchovy oil (AO) or AO blended with canola oil (CO) so that CO comprised 0% (0CO), 11% (11CO), 22% (22CO), 33% (33CO), 43% (43CO), or 54% (54CO) of the measured dietary lipid content. The effects of diet were assessed in freshwater (FW) following 104 days of diet manipulation, in response to 24-h seawater (SW) transfer at this time, and following an additional 35 days of SW acclimation. Gill Na(+)/K(+)-ATPase activity was not significantly affected by diet at any sampling time, and there were no consistent effects of diet on the expression of the Na(+)/K(+)-ATPase alpha1a isoform. As dietary CO increased, Na(+)/K(+)-ATPase alpha1b mRNA decreased in fish held in FW, with the 43CO and 54CO diet groups having significantly lower levels than fish fed the 0CO and 11CO diets. Twenty-four-hour SW challenge did not affect the expression of the Na(+)/K(+)-ATPase alpha1a isoform in any diet group, but this isoform was down-regulated in all diet groups following 35 days of SW acclimation. Na(+)/K(+)-ATPase alpha1b expression levels increased in response to 24-h SW transfer and SW acclimation only in fish fed the 54CO diet. The effects of the two extreme diets (0CO and 54CO) were also assessed at various time points during 104 days of rearing in FW. Na(+)/K(+)-ATPase alpha1b mRNA levels were greater in fish fed diet 0CO versus those fed diet 54CO at all times during the FW culture period. These data demonstrate that dietary fatty acid composition can influence the gill Na(+)/K(+)-ATPase isoform physiology of juvenile fall-run chinook salmon prior to SW transfer.

This study compared the ability of juvenile non-transgenic (NT) and transgenic growth hormone (T; gene construct OnMTGH1) coho salmon ( Oncorhynchus kisutch ) to metabolically utilize energy from lipid and carbohydrate for growth at two dietary protein concentrations. Triplicate groups of size-matched (initial weight, 28.2–29.1 g) NT and T salmon held in 10.5–10.8 °C well water on a natural phototocycle (12.25 h → 8.25 h) were each fed one of four isoenergetic (~ 17.5 MJ of digestible energy (DE)/kg) dry diets twice daily to satiation for 83 days. These diets contained 340 g (LP) or 430 g (HP) of estimated digestible protein (DP)/kg and either 123 g (LL) or 164 g (HL) of estimated digestible lipid (DL)/kg at each DP level (dry weight basis). Estimated digestible carbohydrate (DCHO) concentrations ranged from 45 to 269 g/kg to equalize dietary DE. Under the preceding conditions 46–66% of NT and 18.7–27.5% of T coho, depending upon diet treatment, exhibited no growth or lost weight during the study. NT coho are known to grow slowly or lose weight between the fall equinox and winter solstice but this was unexpected for T coho. Considering all fish T coho, regardless of diet treatment, exhibited significantly higher specific growth rates (SGR) than NT fish due to enhanced feed intake, feed and protein (gross and available deposited) utilization and generally improved available energy utilization. Diet treatment did not affect the growth performance of T fish. Within NT fish, the HP diets supported best gross and available protein and energy utilization. SGR values for growing fish (F G ) only followed identical trends to those for all fish in relation to diet treatment. Regardless of fish genotype, terminal hepatosomatic indices for F G were directly related to dietary DCHO content and maximum values were noted in NT fish fed LP–LL (significantly higher than observed in NT or T fish fed HP–HL). Final whole body protein concentrations adjusted for dissimilar fish size were higher in T fish fed HP–HL than in T fish fed LP diets and NT fish fed LP–LL. This was also true for T fish fed HP–LL versus T fish fed the LP diets. Within HP groups, whole body lipid and energy contents were generally higher in NT versus T fish whereas within the LP groups energy content was significantly higher in T versus NT fish and was highest in T fish fed LP–LL. Terminal plasma titres for GH and IGF–1 (all fish) were significantly higher in T than in NT fish and were generally uninfluenced by diet treatment. Non-growing NT and T fish had elevated GH relative to NT and T fish that grew. Also, GH was higher in growing T fish relative to growing NT fish whereas the opposite was true in non-growing fish. Plasma IGF-1 levels were higher in growing NT and T fish than in their respective non-growing counterparts. Within F G only, IGF-1 levels were higher in T versus NT fish. It is concluded that T coho have enhanced ability to effectively utilize DE from DCHO relative to NT fish especially when DP is near the bottom of the optimal range and DL is concurrently suboptimal for NT fish. This is likely due to the elevated titres of GH, IGF-1 and 3,5,3′-triiodo- l -thyronine (measured in another study) in T fish. Also, the enhanced ability of T fish to store energy under these dietary conditions suggests enzymatic improvements in their anaerobic and aerobic metabolism of glucose.

This study assessed refined canola oil (CO) as a supplemental dietary lipid source for juvenile fall chinook salmon, Oncorhynchus tshawytscha , parr with respect to possible effects on their growth and osmoregulatory performance and body composition. Diets with equal protein (∼ 57%) and lipid (∼ 19%) content (dry weight basis) were supplemented with lipid from either anchovy oil (AO) or CO with AO so that CO comprised 0 (0CO), 11% (11CO), 22% (22CO), 33% (33CO), 43% (43CO) or 54% (54CO) of the dietary lipid content. Triplicate groups of juvenile chinook salmon were fed their prescribed diets for 104 days in freshwater (FW) and 31 days in seawater (SW) after a 4-day transition period. Dietary fatty acid compositions reflected the different proportions of AO and CO in the supplemental lipid. Diet treatment had no effect on fish growth, feed intake, feed efficiency, protein utilization, fish mortality or terminal whole body water and ash percentages. Whole body lipid percentages were higher in 11CO and 43CO fish than in 33CO fish and in 11CO fish versus 22CO fish. Whole body protein percentages were highest in 33CO, 43CO and 54CO fish and lowest in 0CO and 22CO fish. Terminal whole body fatty acid compositions were influenced strongly by the dietary fatty acid compositions. Haematocrit and muscle water percentages were not affected consistently and plasma Na + and Cl − concentrations were unaffected by diet treatment in FW or 24-h seawater challenges during FW residency. Also, diet treatment had no effect on the physiological parameters after SW residency. We conclude that dietary treatment had no effect on fish growth performance under our experimental conditions. Also, the dietary inclusion of CO neither facilitated nor impaired the transfer of chinook salmon parr to seawater. Thus, CO was found to be an excellent and cost-effective source of supplemental dietary lipid for culture of juvenile fall chinook salmon during freshwater residency.

Consumption of salmon, wild or farmed, has been encouraged by many scientists and by national and international health organizations due to the potential health benefits associated with their high contents of omega-3 (n-3) highly unsaturated fatty acids (n-3 HUFAs). In 2004, there was increased public concern regarding the safety of farmed Atlantic salmon following the publication of several studies that indicated higher levels of organohalogens in their flesh relative to those noted in the flesh of wild Pacific salmon. Farmed salmon obtain most of these contaminants from the consumption of marine fish oil (MFO) present in salmon feed. In both a laboratory feeding trial and an on-farm field study, partial replacement of MFO in aquaculture feeds with economical and abundant lipids of terrestrial origin resulted in farmed Atlantic salmon with reduced flesh polychlorinated biphenyl and polychlorinated dibenzodioxin and furan concentrations. Flesh levels of n-3 HUFAs (g/(100 g serving)) were lower in farmed Atlantic salmon fed diets with alternative lipids relative to farmed salmon fed more traditional MFO-based diets. However, the former salmon were found to have higher flesh levels of n-3 HUFAs and also similar or lower flesh levels of organic contaminants than some species of market-size wild Pacific salmon. These findings showthat consumption of either farmed Atlantic salmon or wild Pacific salmon can meet recommended weekly n-3 HUFA levels with minimal concurrent intake of flesh organohalogens.

This study assessed the potential of refined canola oil (CO) as a source of supplemental dietary lipid for pre-smolt spring chinook salmon (Oncorhynchus tshawytscha) over a period of 30 weeks. Triplicate groups of 320 fry (∼ 0.80 g), reared in flow-through well water (8–11.5 °C), were fed one of four steam-pelleted dry diets with equivalent gross energy (24.3 MJ/kg), protein (∼ 51.3%) and lipid (∼ 21.6%) content on a dry-weight basis. CO furnished either 0%, 33%, 67%, or 100% of the supplemental dietary lipid, with the remainder from a commercial blend of 1:1 anchovy oil and poultry fat (APF). Thus, CO comprised either 0% (dAPF), 25% (CO25), 49% (CO49), or 72% (CO72) of total dietary lipid content. Overall fish growth rate, feed intake, feed efficiency, protein utilization, percent survival, and terminal whole body proximate constituents were unaffected by diet treatment. Dietary lipid compositions reflected the ratios of CO and APF in the supplemental lipid and their respective fatty acid compositions. Whole body fatty acid compositions mirrored those of diet treatments. However, some essential fatty acids, namely, arachidonic acid (20:4n-6; AA), and docosahexaenoic acid (22:6n-3; DHA) were conserved in fish regardless of dietary CO level. Direct relationships were found between dietary and whole body concentrations of: 18:2n-6 (R2 = 0.94; slope = 0.72), 18:3n-3 (R2 = 0.99; slope = 0.58), 20:4n-6 (R2 = 0.84; slope = 0.42), 20:5n-3 (R2 = 0.99; slope = 0.43) and 22:6n-3 (R2 = 0.82; slope = 1.25). High dietary levels of 18:3n-3, 18:2n-6, and 20:5n-3 may have been utilized for energy or converted to more unsaturated derivatives. Overall development of ionoregulatory ability, as assessed by 24-h seawater challenge tests, was unaffected by diet. However, whole body chloride content was generally inversely related to dietary CO level during early development. Our findings suggest that there is excellent potential for long-term replacement of fish oil with canola oil in the diet of pre-smolt spring chinook salmon, provided that some marine oil is present to ensure that the essential fatty acid needs of the fish are met.

The effect of different dietary lipid sources on the athletic health of five groups of Atlantic salmon (Salmo salar) was tested by measuring oxygen consumption rates, prolonged swimming performance, and recovery from exhaustive exercise in a closed circuit respirometer. These groups of fish differed from each other in the source of the supplemental lipid in their diet. The control diet contained 100% anchovy oil, while in the test diets, poultry fat, de-gummed canola oil, or flaxseed oil were used to replace up to 75% fish oil. The composition of the industry diet was a 1:1 blend of anchovy oil and poultry fat, also 50% of the fishmeal protein in this diet was replaced with protein from poultry by-product meal. Despite major differences in dietary lipid and protein composition that altered the lipid composition of the fish, all of our treatment groups performed equally well with respect to their oxygen consumption, swimming performance and recovery ability. Since these swim tests integrated many physiological functions, and collectively represented a sensitive measure of the athletic health of the fish, we concluded that our alternative lipid and protein-based diets represented viable possibilities for salmon farming.

This study was undertaken to evaluate the suitability of using refined canola oil as a source of supplemental dietary lipid for juvenile red sea bream (Pagrus major). Triplicate groups of 25 red sea bream fingerlings held under identical culture conditions (25 °C, aerated, re-circulated artificial seawater, 30 g/L; 12-h light/12-h dark photoperiod) were fed three times daily to satiation one of four diets with equivalent protein (∼ 46%), energy (∼ 21.9 MJ/kg) and lipid (∼ 15%) content on a dry weight basis for 12 weeks. The diets were identical in composition except refined canola oil (CO) replaced either 0%, 33%, 67%, or 100% of the supplemental dietary lipid content with the remainder originating from pollock liver oil (FO). Thus CO comprised either 0% (diet FO), 25% (CO25), 48% (CO48), or 70% (CO70) of total dietary lipid content. Fish weight gain, specific growth rate, feed intake, feed efficiency, protein and gross energy utilization, and percent survival were not affected by diet treatment. Except for percent moisture which was depressed in CO48 and CO70-fed fish, concentrations of terminal whole body proximate constituents were similarly uninfluenced by diet treatment. Dietary lipid compositions reflected the proportions of CO and FO in supplemental lipid and their respective fatty acid compositions. Whole body fatty acid compositions mirrored those of diet treatments. However, liver polar lipids of the fish suggested, some essential fatty acids such as eicosapentaenoic acid, docosahexaenoic acid and arachidonic acid were preferentially incorporated and regulated, which resulted in a relatively lower degree of difference between diet treatments compared to what was found in whole body lipid. Our findings suggest that refined canola oil is a suitable dietary lipid source for juvenile red sea bream under our test conditions. However, chronic assessments of CO as a supplemental dietary lipid source for red sea bream are warranted to ensure that similar results are obtained without adverse effects on fish health.

Duplicate groups of size-matched (range in initial mean weight, 23.5–27.2 g) growth-hormone-transgenic (T; construct OnMTGH1) and non-transgenic (NT) juvenile coho salmon from wild (W) and commercial (COM) sources, were fed a high nutritive value steam pelleted dry diet by hand four times daily for 63 days to maximum ration (R) viz., T-R T , NT-W-R W , and NT-COM-R COM , or they were pair-fed the maximum ration ingested by NT-W fish (NT-COM-R W and T-R W ) or that consumed by NT-COM fish (T-R COM ). The pair-fed rations were below the maximum rations of NT-COM and T fish. All groups were provided with running (6–8 L/min), aerated (dissolved oxygen, 6.8–10.3 mg/L), 10.5–11.0 °C well water and a natural photoperiod during the study. T-R T coho had significantly higher growth rates (1.9 fold) and dry feed (2.2 fold) and digestible protein and energy intakes (1.7 fold) than noted for NT-W-R W and NT-COM-R COM fish. Moreover T-R T coho, unlike pair-fed T coho and all NT groups, did not show a body weight or seasonal decline in growth rate during the study. Feed and protein utilization, but not energy utilization, were enhanced significantly in T fish relative to NT-COM fish regardless of ration level. NT-W fish were not included in the two-way ANOVA of the performance results where genotype and ration level were the factors. Nevertheless, randomized block ANOVA of performance parameters for all treatment groups followed by Tukey's test with P = 0.05 indicated that NT-W-R W and NT-COM-R COM fish generally performed similarly. NT-W-R W , T-R W and T-R COM groups had lowest condition factors whereas those for NT-COM-R COM and NT-COM-R W were highest. Viscera-somatic indices were significantly enhanced in T fish relative to NT-COM fish (data analyzed by two-way ANOVA). Fish size-corrected terminal whole body proximate compositions were uninfluenced by treatment even though the initial moisture and lipid concentrations in T fish were respectively lower and higher than noted in NT fish. Fish mortality was uninfluenced by treatment. It is concluded that dramatic growth enhancement in T coho is mainly due to enhanced dietary intakes of protein and energy and to a small (∼ 17%) but nevertheless significant improvement in utilization of dietary protein for body protein synthesis. The latter occurred at high and reduced rations and may have been due to high and unregulated plasma growth hormone levels accompanied by increased titres of insulin-like growth factor (found elevated in this transgenic strain in other studies) and 3, 5, 3′ triiodo- l -thyronine. Collectively, these hormones likely directly stimulated tissue protein synthesis. Also, the former two hormones probably spared protein (amino acids) for growth by promoting fatty acid catabolism for energy. The latter effect, in turn, probably played a major role in appetite stimulation of T-R T fish while simultaneously protecting their tissues from excessive lipid deposition.

This study compared the flesh quality of farmed and wild sources of British Columbia (BC) salmon with respect to concentrations of polychlorinated biphenyl compounds, polychlorinated dibenzodioxins/dibenzofurans and their associated toxic equivalents, total mercury (THg), methylmercury (MeHg), and selected fatty acids of known importance for human health viz., omega-3 (n-3) highly unsaturated fatty acids (n-3 HUFAs) and (n-6) fatty acids. Skinned fillets from known sources of farmed Atlantic, coho, and chinook salmon (n = 110) and wild coho, chinook, chum, sockeye, and pink salmon (n = 91) were examined. Atlantic salmon contained higher PCB concentrations (means, 28-38 ng/g) than farmed coho or chinook salmon, and levels in these latter species were similar to those in wild counterparts (means, 2.8-13.7 ng/g). PCB levels in Atlantic salmon flesh were, nevertheless, 53-71-fold less than the level of concern for human consumption of fish, i.e., 2000 ng/g as established by Health Canada and the U.S. Food and Drug Administration (US-FDA). Similarly, THg and MeHg levels in all samples were well below the Health Canada guideline (0.5 microg/g) and the US-FDA action level (1.0 microg/g). On average, THg in farmed salmon (0.021 microg/g) was similar to or lower than wild salmon (0.013-0.077 microg/g). Atlantic salmon were a richer source (mean, 2.34 g/100 g fillet) of n-3 HUFAs than the other farmed and wild sources of salmon examined (means, 0.39-1.17 g/100 g). The present findings support the recommended weekly consumption guidelines for oily fish species (includes all BC salmon sources) for cardio-protective benefits as made by the American Heart Association and the UK Food Standards Agency.

Juvenile Atlantic salmon (Salmo salar) held in 11.6–13.0 °C sea water were fed to satiation for 126 days, 1 of 12 diets formulated to contain equivalent crude protein (500 g/kg) and gross energy contents (21.2–21.6 MJ/kg). The diets contained two different supplemental levels of copper (10 or 35 mg/kg; determined levels ranged from 7 to 14 or 24 to 40 mg/kg) and iron (333 or 1000 mg/kg; determined levels ranged from 667 to 760 or 1405 to 1557 mg/kg) and either unoxidized or actively oxidizing (+) supplemental herring oil (145.7 g/kg) as measured by the initial peroxide value (PV

Twelve previously unpigmented Atlantic salmon with a body weight of 545 ± 39 (SE) g were kept individually and fed a diet containing 69 mg·kg− 1 astaxanthin for 63 days. On day 35 each fish was fitted with a dorsal aorta cannula. During the last 28 days blood levels of astaxanthin were measured on three separate occasions. At 63 days the fish were slaughtered and muscle content of astaxanthin was analysed. The fish had grown by an average of 171 ± 29 g, with an SGR of 0.61 ± 0.08, with a feed conversion ratio of 0.84 ± 0.10 and astaxanthin retention of 7–10%, during the 63-day period. The average blood concentration of astaxanthin was 0.65 ± 0.09 μg·g− 1 and muscle content was 0.68 ± 0.12 mg·kg− 1. Muscle content and retention of astaxanthin varied closely with that of blood concentration (R2 = 0.92, p 0.05) related to either astaxanthin blood or muscle level. On the basis of the data and provided that feed intake and fish is included in the analysis, we concluded that the level of astaxanthin in blood is indicative of long-term muscle deposition and can be used as a rapid scanning method to distinguish between the effects of different dietary treatments on long-term deposition of astaxanthin in muscle.

This study assessed the potential for using dietary phytase to improve the nutritive value of canola protein concentrate (CPC) for rainbow trout, and to concomitantly minimize phosphorus discharge into the environment. Eight diets were prepared. LT-anchovy meal (AM) provided 89% of the protein in the basal diet, whereas in the remaining diets, 59% of the protein originated from CPC by replacement of AM protein. Four CPC diets were supplemented with phytase (Natuphos®) at levels of either 0, 500, 1500 or 4500 phytase units (FTU)/kg diet together with 4505 mg/kg phosphorus. Two CPC diets contained 1500 FTU/kg and either 0 or 2253 mg/kg of supplemental phosphorus. The seventh CPC diet contained no phytase or supplemental phosphorus. A commercial trout feed served as an industry control. All diets were fed to triplicate groups of rainbow trout (initial weight, 17.9 g) to satiation daily for 84 days. Mean water temperature was 11.0°C. The level of phytic acid degradation and the apparent availability of dietary phosphorus were ascertained for all groups. Fish fed the CPC diets, regardless of their phytase and phosphorus levels, exhibited growth rates, feed efficiencies and protein utilization comparable to those of control fish. There was, however, a clear positive dose-response of phytase on dietary phytate digestibility and phosphorus availability was improved significantly by the highest level of phytase. We conclude that dietary phytase has potential to improve the nutritive quality of CPC for rainbow trout and the availability of phytate phosphorus.

The acute (3 days) and chronic (21 days) effects of dietary protein quality on thyroid function and growth parameters were studied in immature rainbow trout held at 12°C on a LD 12:12 light cycle. Five isocaloric (∼17.2 MJ digestible energy/kg dry diet) and isonitrogenous (45.1% protein) diets varying in amino acid composition were fed by hand once daily. The ration across all groups was consistent and varied between 1.0 and 1.5% of wet body wt. The dietary amino acid profiles mimicked that within the rainbow trout egg protein (EP), or whole-body protein (WBP), or they were varied widely by altering the proportions of casein and gelatin, i.e. HC/LG (high casein/low gelatin); MC/MG (medium casein/medium gelatin); LC/HG (low casein/high gelatin). Since these diets contained a chemo-attractant (FinnStim) to enhance food intake, a sixth diet, EP/NF (EP but lacking FinnStim), was used to ascertain FinnStim effects. Thyroid function was assessed from plasma levels of T 4 (L-thyroxine) and T 3 (3,5,3′-triiodo-L-thyronine), and from the activity of the hepatic microsomal T 4 5′-monodeiodinase (5′D) which converts T 4 to the more active T 3 form. After 3 days, plasma T 3 and T 4 titres were unaffected by diet, but 5′D activity was depressed by FinnStim and lowered in fish fed diets WBP and LC/HG relative to those fed diet MC/MG. After 21 days, plasma T 3 was uninfluenced by diet, but plasma T 4 was elevated in trout ingesting diet MC/MG. The 5′D activity was lower in fish fed diet WBP than in those receiving diets MC/MG and LC/HG. Final body weight was greater for fish fed diet EP/NF than for those fed diet LC/HG. Fork length was uninfluenced by diet, but the condition factor was depressed in fish fed diet LC/HG. Feed efficiency and percent protein deposited were depressed, whereas hepatosomatic index was elevated in fish fed diet LC/HG. It is concluded that thyroidal status, as judged primarily by hepatic 5′D activity, is influenced in trout both acutely and chronically by the profile of dietary amino acids. The diet high in gelatin content exerted the most consistent effects by depressing growth, condition factor, feed efficiency, and protein conversion into body protein, while simultaneously increasing both the mass of the liver and its 5′D specific activity. Further study is required to identify the particular amino acid(s) responsible for increasing hepatic 5′D potential under conditions of reduced growth.

To assess the effect of diet composition on the anabolic efficacy of orally administered, 3,5,3′-triiodo-L-thyronine (T3), juvenile steelhead trout (Salmo gairdneri) were fed either a commercial dry diet (Silvercup) or an experimental dry diet with similar protein and gross energy contents. Lipid provided the major part of available non-protein energy in the former diet whereas carbohydrate (dextrin and glucose monohydrate) was the predominant source in the latter. After an initial 42-day period growth rate, appetite and protein efficiency ratios (PER) were similar for groups fed the two basal diets without hormone supplements. Terminal moisture content was significantly reduced and lipid content increased in fish fed the experimental diet. These fish also had a significantly elevated hepatosomatic index (HSI) and histological examination indicated a high degree of hepatic lipid or glycogen deposition. Supplementing the Silvercup diet with 1 or 5 ppm of T3 did not significantly affect growth rate, appetite, PER, protein conversion efficiency (PCE) or energy conversion efficiency (ECE). However, 25 ppm of T3 induced a small but statistically significant increase in weight. Fish fed the experimental diet, on the other hand, responded to T3 supplementation (1, 5 and 25 ppm) with significant increases in weight and length. PER increased in proportion to the T3 dose. Increases were also noted in PCE and ECE. Whole body protein and moisture content increased but lipid content and HSI decreased in the 25 ppm group. A highly variable enlargement of thyroid follicle epithelial cells was noted in all fish administered T3. Dietary T3 affected external morphology to a degree proportional to the T3 dose. We conclude that diet composition has a pronouced influence on the anabolic efficacy of oral T3. Also, our data suggest that oral T3 stimulates growth of steelhead trout through increased carbohydrate utilization.