Evaluation of dietary natural mineral materials as an antibiotic replacer on growth performance,non‐specific immune responses and disease resistance in rainbow trout,Oncorhynchus mykiss

We evaluated the effects of some dietary natural mineral materials as an antibiotic replacer based on growth performance, non‐specific immune responses and disease resistance in juvenile and subadult rainbow trout, Oncorhynchus mykiss. First experiment, juvenile rainbow trout averaging 2.7 ± 0.02 g (mean ± SD) were fed one of the six experimental diets; a basal commercial diet as a control (CON), CON with oxytetracycline (OTC), with yellow loess (YL), with Macsumsuk^® (MS), with Song‐Gang^® stone (SG) and with barley stone (BS) at 0.4% of each diet. At the end of 8‐week feeding trial, weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and protein efficiency ratio (PER) of fish fed YL diet were significantly higher than those of fish fed CON diet. Non‐specific immune responses such as superoxide dismutase (SOD), myeloperoxidase (MPO), lysozyme (LYS) activity and oxidative radical production of fish fed YL diet were higher than those of fish fed CON diet. At the end of 15 days of challenge test with Aeromonas salmonicida, average cumulative survival rate of fish fed YL diet was significantly higher than that of fish fed BS and CON diets. However, there were no significant differences among fish fed YL, SG and OTC diets. Second experiment, subadult rainbow trout averaging 261.5 ± 3.5 g (mean ± SD) were fed one of the four experimental diets for 22 weeks: CON, and CON with OTC, YL or SG at 0.4% of each diet. At the end of feeding, growth performance of fish fed SG and YL diets was significantly higher than that of fish fed CON diet. Non‐specific immune responses in terms of SOD, MPO, LYS and NBT of fish fed SG and YL diets were significantly higher than those of fish fed CON diet. However, there were no significant differences among the fish fed YL, SG and OTC diets. The results indicate that dietary yellow loess or Song‐gang^® stone at 0.4% of diet could replace oxytetracycline in juvenile and subadult rainbow trout.     

Effect of nucleotides supplementation to low‐fish meal feed on long‐chain polyunsaturated fatty acid composition of juvenile rainbow trout Oncorhynchus mykiss

A feeding trial was conducted to evaluate the effect of nucleotides supplementation to low‐fish meal feed on growth and fatty acid composition of rainbow trout. Six isonitrogenous (42% crude protein) and isolipidic (18% crude lipid) diets were formulated containing fish meal and plant ingredients as main protein sources. The control diet was a basal diet without supplementation of nucleotides, and five experimental diets were prepared by supplementing one of the five different nucleotides in the form of 5′‐monophosphate (0.15%), that is inosine (IMP), adenosine (AMP), guanosine (GMP), uridine (UMP) and cytidine (CMP) onto basal diet. Two hundred forty juvenile rainbow trout with an initial average body weight 9.8 g were randomly distributed into twelve aquaria. After 15 weeks of feeding period, growth performance and feed utilization of rainbow trout were not significantly different among dietary treatments. Dietary GMP, UMP and CMP tended to accumulate crude lipid in the muscle and whole fish body. Moreover, dietary GMP, UMP and CMP significantly increased hepatic 18:3n‐3 and long‐chain homologue 18:4n‐3 and 20:4n‐3 contents. Hepatic 18:2n‐6 content showed also increase in fish fed GMP, UMP and CMP diets, but decreased in long‐chain homologue 20:3n‐6 and 20:4n‐6 contents. Decrease in 20:4n‐6, 20:5n‐3 and 22:6n‐3 contents was also found in the muscle of fish fed IMP, GMP and CMP diets. The present study clearly showed that there was no positive effect of dietary nucleotides on growth of fish, but dietary nucleotides particularly GMP, UMP and CMP altered polyunsaturated fatty acid composition of rainbow trout.     

High dietary incorporation levels of rendered animal protein ingredients on performance of rainbow trout Oncorhynchus mykiss (Walbaum, 1972)

Two growth trials were conducted using spray-dried blood meal (BM), feather meal (FEM), meat and bone meal (MBM) and poultry by-product meal (PBM) as major protein sources in the diet of rainbow trout. In the first trial, five diets were formulated to examine the nutritive value of spray-dried BM and PBM. Increasing levels of BM (6, 12%) or PBM (10, 20, and 30%) replaced fish meal and corn gluten meal in the diet. For the second trial, eight diets were formulated to contain the following combinations: FEM + MBM, FEM + PBM or MBM + PBM. The diets containing FEM + MBM and FEM + PBM were supplemented with either L-lysine or DL-methionine, the amino acids predicted to be the two most limiting in these diets. Each experimental diet was allocated to three tanks of fish and fed for 20 weeks in the first trial or 16 weeks in the second trial. All the experimental diets were readily consumed by the fish and high growth and good feed efficiency ratio (FER) were achieved for all diets. In the first trial, there were no significant differences (P > 0.05) in weight gain or FER of fish fed the five experimental diets, suggesting that BM and PBM had high nutritive values for rainbow trout. In the second trial, growth of the fish fed the diet containing the FEM + PBM combination was not statistically different from growth of fish fed the control diet. Growth of fish fed diets with FEM + MBM or PBM + MBM combinations were slightly lower than that of fish fed the control diet. Supplementation of diets with either L-lysine or DL-methionine had no effect on the performance of the fish. The results from this study show that feather meal, poultry by-product meal, blood meal and meat and bone meal have good potential for use in rainbow trout diets at high levels of incorporation.     

Adverse and beneficial effects of long-term high-concentration ascorbic acid supplementation in rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

The present study examined the effects of high-concentration ascorbic acid (AsA) supplementation over a long period on growth, plasma components, nonspecific immune responses, and thermal tolerance in rainbow trout Oncorhynchus mykiss. Four commercial diets supplemented with 0, 100, 1000, and 5000 mg AsA per kg of diet (designated AsA0, AsA100, AsA1000, and AsA5000, respectively) were fed to rainbow trout (initial weight 1.85 g) for 100 days. AsA contents in liver increased with increasing dietary AsA levels. Feeding period, growth performance, and plasma components did not differ significantly between the AsA groups. On the other hand, the phagocytic assay [nitro-blue tetrazolium (NBT) assay] was significantly higher in fish fed AsA1000 and AsA5000 than those fed a diet without AsA (AsA0) at the end of feeding trial. Superoxide dismutase (SOD) activity in the intestines of fish fed AsA5000 was also significantly higher than that of fish fed AsA0. In the thermal tolerance test, fish fed AsA5000 only showed significantly lower cumulative mortality compared with the AsA0 group. In conclusion, high-concentration AsA supplementation such as AsA5000 over a long period does not induce any adverse effects and can enhance disease and stress resistance in rainbow trout.     

Partial replacement of soybean meal with Methylobacterium extorquens single‐cell protein in feeds for rainbow trout (Oncorhynchus mykiss Walbaum)

A feeding trial was conducted with juvenile rainbow trout (15–16 g initial weight) to assess the effects of including single‐cell protein (SCP) produced from Methylobacterium extorquens in trout feeds. Three isonitrogenous and isoenergetic diets were produced: a control diet and two experimental diets containing 5% or 10% bacterial protein meal replacing soybean meal. Triplicate tanks, each containing 35 fish, were fed each diet to apparent satiation in a constant‐temperature (15°C), flow‐through tank system for 12 weeks. No statistically significant differences in final fish weight or other fish growth parameters were observed. Similarly, feed efficiency parameters showed no significant differences among groups. Nutrient retention indices (protein, fat, energy) were relatively high and similar among fish in each dietary treatment group, as were whole body proximate compositions. Fish survival was high, with a small but statistically significant increase for the 10% SCP diet. Overall, results demonstrate that SCP from M. extorquens is a safe and effective alternative protein for rainbow trout diets at the low inclusion levels tested. Slightly lower weight gain in fish fed the 10% SCP diet was largely due to lower feed intake, suggesting that adding palatability‐enhancing ingredients to feeds may allow higher levels of M. extorquens SCP to be used without compromising fish growth.     

Partial replacement of fish meal with spray-dried blood powder to reduce phosphorus concentrations in diets for juvenile rainbow trout,Oncorhynchus mykiss (Walbaum)1

Feeds formulated with 5.7, 11.4 and 22.7% spray-dried blood powder, also called blood flour (88.1% protein, 0.2% total phosphorus), were compared with a control diet with 49% herring meal (64% protein, 2.1% total phosphorus) and no blood powder for rearing juvenile rainbow trout. Oncorhynchus my kiss (Walbaum). Diets with 5.7, 11.4 and 22.7% blood powder contained 1.22,1.03 and 0.84% phosphorus, respectively, compared with 1.36% phosphorus in the control diet. Over 12 weeks, differences in mean specific growth (range 2.23-2.35 day^?1) or feed conversion (range 1.04-1.09) among the four diets were not significant (P > 0.05). Apparent digestibility of phosphorus in the diet with 22.7% blood powder was greater (45.2%) than that in the control diet (31.6%). Increases in phosphorus concentrations in the water in which trout were fed diets with blood powder (range 16-20 μg^?1 total phosphorus) were 33-47% less (P<0.05) than in tanks where trout were fed the control diet (30μg^?1 total phosphorus). Feed formulations for rainbow trout prepared with 22.7% blood powder and 17.0% fish meal would contain 65.3% less fish meal and 38% less total phosphorus than present in the control diet, which was a representation of a modern feed formulation for rainbow trout.     

Influence of soya saponin, soya lectin, and cholyltaurine supplemented to a casein-based semipurified diet on intestinal morphology and biliary bile status in fingerling rainbow trout Oncorhynchus mykiss

To investigate the cause of the changes in intestinal morphology and biliary bile status of rainbow trout Oncorhynchus mykiss fed defatted soybean meal (SBM)-based diets, casein-based semipurified diets supplemented with soya saponin, soya lectin, and cholyltaurine were fed to rainbow trout for 6 weeks. An unsupplemented control diet and a SBM-based diet were also tested as references. Poor development of microvilli and pinocytotic vacuoles, and accumulation of large vacuoles in the epithelial cells were observed in the distal intestine of fish fed diets containing saponin but not cholyltaurine. Hyperplastic connective tissue in the mucosal folds of the distal intestine was observed in fish fed a diet containing both saponin and lectin but not cholyltaurine. However, intestinal histological features in fish fed diet supplemented with cholyltaurine and lectin and/or saponin were similar to those in the control diet group. Liver morphology and biliary bile status were not affected by saponin and lectin. These results suggest that the abnormal features of the distal intestine of rainbow trout fed SBM-based diets are caused by the combination of soya saponin and soya lectin, and that supplemental cholyltaurine plays certain roles in normalizing the intestinal abnormalities caused by the saponin and lectin.     

Purified deoxynivalenol or feed restriction reduces mortality in rainbow trout,Oncorhynchus mykiss (Walbaum), with experimental bacterial coldwater disease but biologically relevant concentrations of deoxynivalenol do not impair the growth of Flavobacterium psychrophilum

Diets containing deoxynivalenol (DON) were fed to rainbow trout Oncorhynchus mykiss (Walbaum) for 4 weeks followed by experimental infection (intraperitoneal) with Flavobacterium psychrophilum (4.1 × 10⁶ colony‐forming units [CFU] mL⁻¹). Mortality of rainbow trout fed either 6.4 mg kg⁻¹ DON or trout pair‐fed the control diet was significantly reduced (P < 0.05) in comparison with trout fed the control diet to apparent satiation (<0.1 mg kg⁻¹ DON). In a second experiment, trout were fed one of three experimental diets; a control diet, a diet produced with corn naturally contaminated with DON (3.3 mg kg⁻¹ DON) or a diet containing purified DON (3.8 mg kg⁻¹); however, these fish were not experimentally infected. The presence of DON resulted in significant reduction (P < 0.0001) in feed intake as well as weight gain after 4 weeks. Respiratory burst of head‐kidney leucocytes isolated from rainbow trout fed diets containing purified DON (3.8 mg kg⁻¹) was significantly higher (P < 0.05) at 35 day post‐exposure compared with controls. The antimicrobial activity of DON was examined by subjecting F. psychrophilum in vitro to serial dilutions of the chemical. Complete inhibition occurred at a concentration of 75 mg L⁻¹ DON, but no effect was observed below this concentration (0–30 mg L⁻¹).     

Growth performance,haematological and serum biochemical profiles in rainbow trout (Oncorhynchus mykiss) fed diets with varying levels of lupin (Lupinus albus) meal

A feeding experiment was conducted to study the response of rainbow trout juveniles fed different levels of lupin meal in diets for rainbow trout juveniles. Very limited information is available on the relationship between dietary lupin meal in rainbow trout health status. Therefore, this study aimed to determine the effects of lupin meal inclusion levels (0%, 15%, 30%, 45%, and 60%) on growth performance and health status of rainbow trout juveniles. The experimental diets (LM₀, LM₁₅, LM₃₀, LM₄₅, and LM₆₀) were formulated iso‐nitrogenous (41% crude protein) and iso‐calorific (18% crude lipid). The fish were fed twice a day. As a result, the best growth performance was observed in fish fed with LM₁₅ and LM₃₀ diets. No significant differences were detected among experimental groups in terms of body compositions. The haematological values showed significantly (p < 0.05) lower heamatocrit and mean cellular volume (MCV) in the group of LM₆₀ compared with the other groups. For the other haematological parameters such as haemoglobin, red blood cell and mean cellular haemoglobin studied in the present study no significant differences were observed (p < 0.05). The lupin meal included groups showed significant reduction in total protein (TPROT), triglyceride (TROG), cholesterol (CHOL), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH) compared with the control group (p < 0.05). The inclusion of lupin meal did not cause any changes in glucose (GLU), glutamic oxaloacetic transaminase (GOT), and glutamic pyruvic transaminase (GPT) between the treatment groups (p < 0.05). In conclusion, lupin meal might be used in rainbow trout diets up to 30% without any malnutrition effect on growth performance, haemotological and serum biochemical parameters.     

Evaluation of Experimental and Practical Diets for Bluegill Lepomis macrochirus and Hybrid Bluegill L. cyanellus × L. macrochirus

Two experiments were conducted to identify appropriate experimental and practical diets for bluegill Lepomis macrochirus and hybrid bluegill L. cyanellus × L. macrochirus reared in aquaria. In the first study, four experimental diets and five commercial diets were evaluated in juvenile hybrid bluegill initially weighing 4.8 g/fish. The experimental diets contained casein (CAS), casein + gelatin (CAWGEL), casein + L‐arginine‐HCI (CAS/ARG), or casein + gelatin + crystalline amino acids (CAS/AA) as sources of crude protein. The commercial diets included three diets formulated to meet the nutritional requirements of rainbow trout Oncorhynchus mykiss and two diets formulated to meet the nutritional requirements of channel catfish Ictalurus punctatus. Each diet was fed twice daily at a rate of 4% of body weigh/d to triplicate groups of fish. At the end of the 8‐wk feeding trial, weight gain was significantly higher in fish fed the best commercial rainbow trout diets (205–217%) compared to fish fed diets formulated for channel catfish (87–104%). Weight gain and feed efficiency (FE) of fish fed the experimental diets (5346% and 0.19–0.32, respectively) were significantly lower than those of fish fed the commercial rainbow trout diets (143–217% and 0.49–0.64, respectively). In the second experiment, the same dietary treatments were fed for 8 wk to juvenile bluegill initially weighing 3.7 g/fish. Each diet was fed twice daily at a rate of 4% of body weight/d to triplicate groups of fish. Weight gain was significantly higher in fish fed commercial trout diets (291–402%) compared to fish fed diets formulated for channel catfish (164–191%). Weight gain and FE of fish fed CAS/ARG were significantly higher than those of fish fed the commercial catfish diets, but significantly lower than those of fish fed the best commercial trout diets. Results of this study indicate that commercial rainbow trout diets are preferable to commercial channel catfish diets for culture of bluegill and hybrid bluegill. More research is needed to identify appropriate experimental diets for this group of fishes.     

Effects of diets containing a bacterial protein meal on growth and feed utilisation in rainbow trout (Oncorhynchus mykiss)

Triplicate groups of rainbow trout with initial weight 361 g were fed either a fish meal based control diet or diets containing 9, 18 or 27% bacterial protein meal (BPM) or 9% of an autolysate (AU) of the BPM. No significant treatment effects were found on specific growth rates (SGR), feed intake, feed efficiency ratio (FER), or retention of nitrogen, amino acids or energy. The apparent digestibility coefficients (ADC) of nitrogen, energy and most indispensable amino acids decreased when BPM was included in the diet. The ADC of lipid, sum of amino acids, arginine, lysine, threonine and most of the dispensable amino acids were reduced at 27% BPM inclusion compared to the control, 9% and 18% BPM diets. None of the ADC estimated was different in the 9% AU diet compared to the 9% BPM diet. The loss of nitrogen and energy in faeces per kg gain increased as the dietary BPM or AU levels increased, and the energy used for activity and maintenance was higher in fish fed the 27% BPM diet than in fish fed the other diets (P < 0.05). There were no significant differences in the urea concentrations in plasma, liver and muscle, whereas the uric acid level in plasma was elevated in trout fed the 27% BPM diet. Histological evaluation of tissue from the stomach, pyloric caeca, mid-intestine and distal intestine did not reveal any diet-related morphological changes.In conclusion, no significant differences in growth and feed efficiency were found in the rainbow trout fed diets containing up to 27% BPM, and the AU did not increase fish performance compared to the BPM. Based on the data from this study, at levels up to 27% dietary inclusion, BPM is a good replacement for fish meal in diets for rainbow trout.     

The effect of plant‐based diet and suboptimal environmental conditions on digestive function and diet‐induced enteropathy in rainbow trout (Oncorhynchus mykiss)

This experiment investigated intestinal enteropathy and digestive function of rainbow trout challenged with soybean meal‐based diet (SBM) at optimal or suboptimal environments created by normal or reduced water flow, respectively. Oxygen level remained above 7 mg L^‐1 for optimal environment and between 4 and 5 mg L^‐1 for suboptimal environment. Triplicate groups of fish (mean body weight 74 g) were fed fishmeal‐based diet (FM) or SBM at optimal environment in period 1 (28 days). In period 2 (42 days), fish were subjected to a change from FM to SBM or remained on the same diet as used in period 1. The fish were also exposed to change from optimal to suboptimal environment or remained under optimal conditions. The fish subjected to change from FM to SBM, regardless of their environment, showed similar degree of enteropathy from day 14. Lipid and starch digestibility was lower in SBM‐fed fish at suboptimal environment compared to fish fed the same diet at optimal environment. Crude protein digestibility, however, was highest in SBM‐fed fish at suboptimal environment throughout period 2. In conclusion, in SBM‐fed rainbow trout, exposure to suboptimal environment did not change the degree of enteropathy; however, lipid and starch digestibility were further reduced.     

Dietary Spirulina (Arthrospira platensis,Gomont, 1892) improved the flesh quality and shelf life of rainbow trout (Oncorhynchus mykiss,Walbaum, 1792) fed fish meal or plant‐based diet

This study was carried out to determine the effects of fish meal or plant‐based diets with supplementation of dietary Spirulina (4%) on shelf life of rainbow trout, Oncorhynchus mykiss. Rainbow trout (initial weight: ~135 g) were fed four experimental diets (fish meal‐based FM, plant meal‐based‐PM, Spirulina included at 4% of fish meal‐based‐FM/S or plant meal‐based PM/S) for 12 weeks. After the feeding trial, trout were stored on ice at 4°C for 0, 5, 10, 15 and 20 days. The chemical, microbiological and sensory analyses of fish were subjected to each sampling days for flesh quality evaluation. TBA of supplemented dietary Spirulina was lower than that non‐supplemented dietary Spirulina. pH values of all groups decreased significantly between days 0 and 20 during the storage period (p < 0.05). Luminosity (L*) value of all groups increased with time in storage period. Fish fed Spirulina supplemented diets showed an increased red/green tonality (a*) (p < 0.05) compared with fish fed non‐Spirulina supplemented diets. In the end of the storage period, the total coliforms values of fish fed with PM/S diet lower than that of other all diets. In conclusion, dietary Spirulina could be allowed the shelf life of the rainbow trout to be extended.     

Supra-nutritional dietary intake of selenite and selenium yeast in normal and stressed rainbow trout (Oncorhynchus mykiss): Implications on selenium status and health responses

Commercial salmonid diets are not typically supplemented with selenium (Se) as they naturally contain relatively high levels of this essential trace element; however supplementation may be necessary to meet requirements during physical stress. Adopting an integrated approach by simultaneously determining Se status, various health parameters and interactions with other trace elements, this study aimed to determine the role of supra-supplemented selenite and Se-yeast (Selplex^®) on the growth and health of rainbow trout (Oncorhynchus mykiss), both under normal conditions and after exposure to chronic physical stress. Fish were fed one of seven diets; a basal un-supplemented diet (0.73 mg kg^− 1 Se) or diets supplemented with Se-yeast or sodium selenite to provide 2, 4, or 8 mg kg^− 1 Se for 10 weeks prior to subjection of daily handling and confinement stressors for seven days. Net whole body Se retention was significantly greater for Se-yeast than selenite at all levels. In normal conditions activities of hepatic glutathione peroxidase (GSH-Px) and thioredoxin reductase (Trx-R) indicate that Se requirements were met by the basal diet. Similarly, pre-stress supra-supplementation of selenite and Se-yeast did not affect oxidative status (total antioxidant capacity of serum and hepatic malondialdehyde), immuno-competence (respiratory burst activity, serum lysozyme, and leukocyte counts) or other haematological and growth parameters (nuclear abnormalities in erythrocytes, and specific growth rate). In contrast, the trend towards a higher GSH-Px post-stress in Se supplemented diets over the basal diet, particularly in Se-yeast fed fish, indicates that Se requirements may not be met by the un-supplemented practical diet in stressed fish. Seven days of chronic physical stress decreased whole body Se and increased GSH-Px activity signifying an increased Se utilisation. During stress Se status was more effectively maintained by Se-yeast than selenite. Increased hepatic lipid peroxidation in stressed fish fed 8 mg kg^− 1 selenite indicates a possible pro-oxidant effect of selenite. A positive interaction was observed between dietary selenite and whole body copper, but no such interaction was observed with Se-yeast. This study concludes that physical stressors can result in an elevated Se utilisation and consequently supplementation of commercial diets may be necessary such that Se reserves are available as a contingency for stress.     

Urea and trimethylamine oxide in diets for seawater farmed rainbow trout: effect on fat belching,skin vesicle,winter ulcer and quality grading

Three experiments were conducted in order to evaluate the effects of urea and trimethylamine oxide (TMAO) supplementation in diets for seawater‐farmed rainbow trout Oncorhynchus mykiss. In all experiments, commercial extruded feed was used as basal control diet, whereas experimental diets were the basal diet supplemented with either 10 g kg^–1 TMAO, 10 g kg^–1 urea or 10 g kg^–1 TMAO and 10 g kg^–1 urea. The experiments were conducted both in research units and in a commercial fish farm. Quality was evaluated in three different commercial slaughterhouses, sorting the rainbow trout into superior, ordinary or processing grade. Significantly more TMAO was observed in muscle of rainbow trout given dietary supplementation of TMAO. However, the levels were low compared with levels in marine fish in general. Trimethylamine (TMA) was not found. No increase in muscle urea content was observed in trout fed urea in the diet. Significantly reduced fat belching, seen as reduced number of fat droplets surfacing in the net pen, was observed in groups given TMAO‐supplemented feeds. At least twice as many rainbow trout with skin vesicles were observed in the control group as in the group fed urea‐supplemented diet. In addition, skin vesicles developed into open sores in the winter only in rainbow trout fed control diet. In a large‐scale trial, quality grading of almost 200 000 market‐sized rainbow trout showed significantly more (88 vs. 83%) trout of superior grade in the group fed dietary urea compared with fish fed control diet. The main reason for downgrading from superior to ordinary and processing grade was skin lesions, supporting the observations made in the experimental units.     

Evaluation of fish-meal free diets for rainbow trout, Oncorhynchus mykiss

Eight experimental diets were formulated for rainbow trout using agricultural byproducts as major ingredients. Each experimental diet contained varying amounts of corn grain, corn gluten meal, corn gluten feed and one of the following: 200 g kg^?1 peanut meal, 200 or 400 g kg^?1 soybean meal (SBM), 390 g kg^?1 low-allergen soy flour, 310 g kg^?1 soy protein concentrate, 300 g kg^?1 low-allergen soy protein concentrate or 200 g kg^?1 SBM + 110 g kg^?1 blood meal. One diet contained 200 g kg^?1 SBM and canola oil as the main lipid source. The remaining diets contained 95 g kg^?1 menhaden oil. Fish fed a commercial trout diet exhibited significantly greater weight gain (322%), and a lower feed conversion ratio (0.89) but significantly lower protein efficiency ratio (2.18) than fish fed the experimental diets. Within the experimental diets, fish fed the 400 g kg^?1 soy flour diet and the 400 g kg^?1 soybean meal diet had significantly higher weight gains (276% and 268%) and protein efficiency ratios (2.58 and 2.52), and lower feed conversion ratios (1.02 and 1.03) than fish fed other experimental diets. Fillet flavour varied between treatments. Most notable was the lower fishy flavour and higher chicken flavour of fish fed the diet that contained canola oil rather than menhaden oil. Microscopic evaluation of the liver and five sections of the gastrointestinal tract failed to demonstrate any differences between treatment groups. The ingredient costs of several experimental diets were lower than the estimated cost of a standard commercial trout diet. However, the superior feed conversion ratios of fish fed the control diet resulted in lower feed costs per unit of fish produced.     

Growth performance,nutrient digestibility and intestinal morphology of rainbow trout (Oncorhynchus mykiss) fed graded levels of the yeasts Saccharomyces cerevisiae and Wickerhamomyces anomalus

In a 10‐week study, we evaluated the effects of replacing 20%, 40% or 60% of fishmeal (present in control diet at 300 g/kg) on a digestible protein basis with yeast Saccharomyces cerevisiae or a yeast mixture of Wickerhamomyces anomalus and S. cerevisiae on growth performance, nutrient digestibility, nutrient retention and intestinal health of rainbow trout (Oncorhynchus mykiss). Triplicate tanks with 35 rainbow trout (144.7 ± 25.1 g mean ± SEM) were fed rations of 1.5% of total biomass per tank. Replacement of 60% of fishmeal with yeast mixture resulted in lower specific growth rate of 1.0% versus 1.2%/day for other diets. Apparent digestibility coefficients for crude protein and most amino acids were highest in fish fed fishmeal‐based diet, with similar values for fish fed the diet with 20% replacement with yeast mixture. Diet with 20% replacement with yeast mixture resulted in highest phosphorus digestibility. Replacement of 60% of fishmeal with S. cerevisiae resulted in oedematous mucosal fold tips in the proximal intestine. The results of this study suggest that these yeasts can replace up to 40% of fishmeal under current inclusion levels in diets for rainbow trout without compromising growth performance, nutrient digestibility or intestinal health.     

High‐oil residue camelina meal,a viable source of protein at low levels in diets for juvenile salmonids

The oilseed Camelina sativa has been studied as a lipid source for farmed salmonids, but recommended inclusion as a protein source has not been determined. This study evaluated low inclusion of camelina high‐oil residue meal (HORM) at 20, 40 and 60 g/kg of the diet, to determine an adequate level for Atlantic salmon parr (Salmo salar) and rainbow trout (Oncorhynchus mykiss). Salmon and trout were fed experimental diets containing up to 60 g/kg HORM for 16 weeks. At 40 g/kg HORM, trout and salmon growth performance were similar to those fed a control diet. However, at 60 g/kg HORM, trout showed lower final weight, weight gain and feed intake than those fed the control diet. Rainbow trout fed 40 and 60 g/kg HORM showed significantly lower whole body ash (p = .005), slightly lower whole body protein levels and higher fat than the control. In salmon fed 60 g/kg HORM diets, whole body ash (p = .024), and the submucosal layer of the intestine was thicker than the control (p = .007). Current results indicate that up to 40 g/kg HORM can be included in diets for rainbow trout and salmon juveniles.     

Supplemental effect of cholyltaurine and soybean lecithin to a soybean meal-based fish meal-free diet on hepatic and intestinal morphology of rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

The supplemental effects of cholyltaurine and soybean lecithin to a defatted soybean meal (SBM)-based fish meal-free diet on the hepatic and intestinal morphology of rainbow trout Oncorhynchus mykiss were investigated. A fish meal-based diet (FM), three fish meal-free diets supplemented either with soybean lecithin (SL), bovine gall powder (BG) or cholyltaurine (C-tau) and an unsupplemented fish meal-free diet (NFM), were given to fish (−11 g) for 10 weeks. The growth was the lowest in fish fed diet NFM, intermediate in fish fed diet SL and the highest in fish fed diet FM, BG and C-tau. Hepatocytes of fish fed diet NFM were atrophied, and the distal intestine of these fish showed abnormal features: disintegrated microvilli and fatty degeneration in epithelial cells and increased amount of connective tissue in the submucosa. Hepatic and intestinal histological features in fish fed diets SL, BG and C-tau were similar to those in fish fed diet FM. These results indicate that soybean lecithin, bovine bile salts and cholyltaurine have similar effects on normalizing the hepatic and intestinal morphologies of rainbow trout fed the SBM-based diet, although growth promotion effect was limited in the soybean lecithin.     

Salmon testes meal as a functional feed additive in fish meal and plant protein‐based diets for rainbow trout (Oncorhynchus mykiss Walbaum) and Nile tilapia (Oreochromis niloticus L.) fry

Fishery processing by‐products are a large resource from which to produce fishmeal and other products for a variety of uses. In this study, testes meal (TM) produced from pink salmon processing by‐product was evaluated as a functional ingredient in aquafeeds. Nile tilapia and rainbow trout fry were fed five isonitrogenous and isoenergetic experimental diets for 4 and 9 weeks respectively. Two diets were fishmeal‐based (FM) and three were plant protein‐based (PP). Salmon TM was added to the FM and PP diets at 7% to replace 20% of fishmeal protein (FMTM and PPTM respectively). An additional control diet was prepared in which fishmeal was added to the PP diet to supply an equivalent amount of protein as supplied by TM (PPFM). Inclusion of TM in both the FM‐ and PP‐based diets resulted in higher final body weights, although differences were only significant between rainbow trout fed FM or FMTM diets. Similar differences were calculated for other indices of fish performance, e.g. specific growth rate, feed conversion ratio, protein efficiency ratio and protein retention efficiency. Feed intake was significantly higher for fish fed FMTM compared with FM in rainbow trout. For tilapia, final weights were numerically higher, but not significantly different for fish fed diets containing TM compared with non‐TM diets (FM vs. FMTM; PP vs. PPTM). Performance of trout or tilapia fed the PPFM diet did not increase compared with the PP diet. The results indicate that TM addition to both FM and PP diets increased feed intake and also increased metabolic efficiency, demonstrating that TM can be a functional ingredient in aquafeeds.