Evaluation of an alkane yeast (Candida sp.) as a substitute for fish meal in Oregon Moist Pellet: Feeding trials with coho salmon (Oncorhynchus kisutch) and rainbow trout (Salmo gairdneri)

Up to 40% of the fish meal portion of the Oregon Moist Pellet (OMP) was replaced with up to 40% alkane yeast single cell protein (22% of dietary protein) in diets fed to rainbow trout in fresh water, and up to 100% of the fish meal portion was replaced with alkane yeast (54% of dietary protein) in OMP diets fed to coho salmon in salt water. Salmon diets were supplemented with DL-methionine to correct for a suspected deficiency in this essential amino acid. Alkane yeast was an acceptable substitute for fish meal at all levels tested in trout. Only 25% yeast substitution was judged to be acceptable in the OMP diet for marine-cultured coho salmon, causing less than 4% reduction in growth. In marine-cultured coho salmon, growth was depressed further at fish meal substitution levels greater than 25%, while supplementation with DL-methionine enhanced growth and feed conversion only slightly.     

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.     

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.     

Taurine Supplementation of All-plant Protein Diets for Rainbow Trout (Oncorhynchus mykiss)

Abstract.— Taurine has been demonstrated to be conditionally indispensable for several carnivorous fish species. Current trends in trout production include decreasing levels of fish-meal content in feeds, along with faster growing strains of fish. Taurine may be a limiting nutrient in support of elevated planes of growth for rainbow trout. A 9-wk feeding trial was conducted using a factorial treatment design with protein source (fish meal or plant) and taurine supplementation (four levels) as the main effects. The fish-meal diet series included 23% herring meal and contained 1.76% total sulfur amino acids (TSAA). The plant diet series did not contain any animal proteins and substituted protein from soy protein concentrate in place of the herring-meal protein and contained 1.5% TSAA. Taurine was supplemented at 0, 5, 10, and 15 g/kg dry diet to each of the diets in the plant series and the fish-meal series of diets. All diets were formulated to contain 43.8% crude protein and 20% lipid with an estimated physiological fuel value of 4.2 kcal/g. Fifteen fish were stocked in each of 24 tanks with a mean initial weight of approximately 26.8 g per fish. The unsupplemented fish-meal diet contained 2 g/kg taurine, and the unsupplemented plant diet had taurine levels below the detection limit of 0.1 g/kg diet. Taurine supplementation improved growth, feed conversion ratios, protein retention efficiencies, and energy retention efficiencies of fish fed the plant protein diets. No effects of taurine supplementation were observed for these response factors in fish fed the fish-meal series diets. This study demonstrates that taurine supplementation may be necessary for rainbow trout fed plant-protein-based feeds.     

Influence of multiple amino acid supplementation on the performance of rainbow trout, Oncorhynchus mykiss (Walbaum), fed soya based diets

Using rainbow trout, Oncorhynchus mykiss (Walbaum), of approximately 50 g, a 63 day feeding trial was undertaken to evaluate the efficacy of individual and multiple amino acid supplements in diets where soyabean meal was used as the principle protein source. Iso-nitrogenous diets (45% crude protein) were formulated where the control diet (F) contained fishmeal as the reference protein and a solvent extracted soyabean meal (S) replaced approximately 66% of this protein source. The soyabean containing diets were then supplemented with crystalline amino acids thus; methionine only, dual supplemented with two methionine and lysine levels and finally, a supplement comprising methionine, lysine, tryptophan, threonine, arginine and histidine. The results showed that soyabean meal (SBM) was inferior to the reference protein when SBM was used to replace 66% of the fishmeal and that no significant restoration in growth, feed efficiency and apparent net protein utilization was obtained by either methionine only or dual methionine and lysine supplementation. However, by comparison with the fish fed the unsupplemented, single and dual supplemented diets, multiple amino acid incorporation was associated with significantly improved percentage weight gain, specific growth rate and marginal improvements in apparent net protein utilization. However, performance was not equal to that of the fish fed the fishmeal based control diet. The results are discussed with respect to the level of each of the essential amino acids (EAA) as a proportion of the total EAAs (A/E index) of test diets by reference to the whole body tissue amino acid profile of rainbow trout.     

The Effects of Substituting Selected Oilseed Protein Concentrates for Fish Meal in Rainbow Trout Oncorhynchus mykiss Diets

Three oilseed protein concentrates (soybean, canola, and sunflower) were evaluated to determine their potential, when supplemented with deficient essential amino acids, to partially or completely replace fish meal in diets fed to rainbow trout Oncorhynchus mykiss . Triplicate aquaria of juvenile trout (average weight of 12 g) were fed the experimental diets for 10 wk, at which time the average weight of the fish was approximately sixfold higher than the initial weight. Average fish weight gains on diets in which the protein component was 100% fish meal; 75% fish meal, 25% soybean protein concentrate; 50% fish meal, 50% soybean protein concentrate; and 75% fish meal, 25% sunflowerseed protein concentrate were not significantly different ( P < 0.05). The average weight of fish fed a commercial feed was significantly lower than that of fish fed the 100% fish meal diet, but not significantly different from fish fed the three other formulations mentioned above. Fish fed diets containing 50% fish meal, 50% canola protein concentrate; and 25% fish meal, 75% sunflowerseed protein concentrate had significantly lower average final weights than those of fish fed the other diets. Feed conversion ratio patterns among the dietary treatment groups reflected those of weight gain. Fish survival exceeded 95% on all diets. Apparent protein digestibility coefficients ranged from 79.5% (75% soybean protein concentrate, 25% canola protein concentrate) to 90.6% (100% soybean protein concentrate). The results of this study demonstrated that certain oilseed protein concentrates have good potential as protein sources in rainbow trout feeds when properly supplemented with essential amino acids.     

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.     

Size-fractionated fish hydrolysate as feed ingredient for rainbow trout (Oncorhynchus mykiss) fed high plant protein diets. II: Flesh quality, absorption, retention and fillet levels of taurine and anserine

In the work to find replacement for fish meal in feed for fish, the inclusion of plant protein sources at high dietary level is an important issue. The present experiment was carried out to reveal how different feed ingredients affected the eating quality of the grown up fish with focus on nitrogen compounds as amino acids, taurine and anserine. Six experimental diets were fed to rainbow trout in triplicates for 90 d. All diets were composed to be equal in protein, lipid, energy and lysine. Three levels of a mixture of plant sources (full fat soy, extracted soy, soy protein concentrate, corn gluten) constituting 57.2%, 73.9% and 90.6% of total dietary protein were used. A small amount of fish meal was added in 5 diets constituting 9.4% of total protein. A fish hydrolysate that was high in free amino acids, taurine and anserine was tested at 16% and 32% dietary inclusion of total protein. Two other diets contained the same level of protein from the same hydrolysate that was ultra filtrated to remove low molecular weight compounds. Digestibility of taurine and anserine was found to be close to 99% for all groups, except for the group containing high level of plant sources. The levels of taurine in whole trout and fillets decreased during the feed experiment, but were about the same for all groups at the end of the feeding experiment and independent of dietary levels. The level of anserine in fish and fillets was equal from start to end of the experiment and independent of dietary inclusion. Taurine and anserine therefore seem to be homeostatic regulated in trout and independent on dietary levels. Amino acid content in fish and fillet was also equal for all groups and independent of protein sources used in the diets. The chemical composition showed higher lipid and dry matter levels in fish and fillet in fish that grew the fastest. In conclusion, plant protein sources may be included in diets for trout at high levels without affecting the eating quality as evaluated by amino acids, taurine and anserine levels.     

Effects of dietary supplements on the availability of minerals in fish meal; preliminary observations

Preliminary studies were conducted to determine if several feed supplements with the potential to improve dietary mineral availabilities in fish meal had any measurable effect in fish feeds. In the first study with rainbow trout, 11 supplements were tested: citric acid; sodium citrate; potassium chloride; sodium chloride; histamine dihydrochloride; EDTA disodium salt; sodium bicarbonate; a mixture of amino acids; ascorbic acid; a mixture of inositol and choline; and cholecalciferol. Apparent availability of calcium, phosphorus, magnesium, sodium, iron, manganese and strontium in fish meal-based diets was determined using both yttrium oxide (Y₂O₃) and chromium oxide (Cr₂O₃) as inert dietary markers. Apparent availability was expressed as the fractional net absorption (%) of minerals from diets. After a 7-day acclimation period with test diets, fecal samples were collected for five consecutive days using passive collection systems. Apparent availability of calcium, phosphorus, magnesium, iron, manganese and strontium was increased by citric acid supplementation. Apparent availability of manganese also was increased by EDTA and sodium citrate. The other supplements had no measurable effect on the apparent availability of minerals in fish meal. In the second study, the effect of supplemental citric acid was further investigated using monogastric (rainbow trout) and agastric fish (goldfish). Fish were fed for 5 weeks (rainbow trout) or 3 weeks (goldfish) with fish meal-based diets containing either 0% (control), 2% or 5% citric acid on a dry basis. Feces were collected by settling and by stripping. Apparent availabilities of calcium and phosphorus were greatly affected by citric acid supplementation in rainbow trout but not in goldfish. Phosphorus levels in feces of fish fed a diet with 5% citric acid were approximately half of that of fish fed the control diet (0% citric acid) in the rainbow trout trial. This pattern was consistent during the 5-week feeding trial. A dietary supplement of citric acid as high as 5% did not reduce feed intake or appetite of rainbow trout. Conversely, this level of dietary acidification led to a marked reduction of feed intake in goldfish. Dietary supplementation of citric acid at 2% level did not reduce feed intake of goldfish; however, this level of dietary acidification had little effect on the apparent availability of major minerals in fish meal-based diet. Levels of non-fecal excretion of calcium and phosphorus, inorganic phosphorus in urine, and citric acid in feces were increased in rainbow trout fed 5% citric acid. The pH values of the feces and urine were decreased in rainbow trout fed citric acid. Plasma bicarbonate, plasma calcium and phosphorus, and blood pH of rainbow trout tended to increase by a 5% dietary supplementation of citric acid. The soluble inorganic phosphorus content increased in the diets and decreased in the feces of rainbow trout by supplementing the diet with 5% citric acid. Feces samples of rainbow trout collected by stripping provided similar availability values to data collected by settling for most elements except sodium, which had negative values in all dietary treatments.     

Total fish meal replacement with rapeseed protein concentrate in diets fed to rainbow trout (Oncorhynchus mykiss Walbaum)

The potential of rapeseed protein concentrate as fish meal alternative in diets for rainbow trout (initial average weight 37.8?±?1.4?g) was evaluated. Nine experimental tanks of a freshwater flow-through system were stocked with 12 fish each. Triplicate groups of fish received isonitrogenous (47.9?±?0.5% CP) and isoenergetic (22.4?±?0.2?kJ?g^?1) experimental diets with 0, 66 and 100% of fish meal substituted with rapeseed protein concentrate (71.2% CP), thereby providing 0, 29 and 43% of dietary protein. As the amino acid profile of rapeseed protein concentrate was comparable to fish meal, there was no need to supplement experimental diets with synthetic amino acids. At the end of the 84?days of feeding period, fish growth performance, feed intake and feed efficiencies were not compromised, when 100% of fish meal in the control diet was replaced with rapeseed protein concentrate, revealing a SGR of 1.19 or 1.10, a FCR of 1.09 or 1.18 and a feed intake of 78.5 or 74.7?g in fish fed on the control diet or fed the diet devoid of fish meal, respectively. Intestinal morphology did not reveal any histological abnormalities in all dietary groups. Blood parameters including haematocrit and haemoglobin as well as glucose, triglycerides and total protein in the plasma were not different between treatment groups. Thus, the rapeseed protein concentrate tested here has great potential as an alternative to fish meal in rainbow trout diets.     

Partial substitution of fish meal and full-fat soya bean meal with wheat gluten and influence of lysine supplementation in diets for rainbow trout, Oncorhynchus mykiss (Walbaum)

A 65-day study was undertaken to evaluate the utilization of lysine-supplemented wheat gluten meal as a protein source for rainbow trout, Oncorhynchus mykiss (Walbaum). The performance of the trout fed wheat gluten was compared to that of trout where protein was principally supplied using fish meal and full-fat soyabean meal. Six isonitrogenous diets (approximately 45% crude protein) were formulated. Thus, the reference diet (FS) was based on fish meal and full-fat soya bean meal while a further five diets were formulated with a mixture of wheat gluten and wheat middlings used to isonitrogenously replace approximately 75% and 57% of the full-fat soya and fish meal respectively. Crystalline l -lysine representing 0.00%, 0.29%, 0.58%, 0.87% and 1.16% of the complete diet was then added to the wheat-gluten-based diets. Optimal performance in terms of weight gain and apparent net protein utilization was achieved by the fish fed a wheat-gluten-based diet supplemented with lysine (0.58%) yielding a digestible lysine level of 1.9% of the complete feed. Within the range of supplements provided, lysine digestibility was high. However, at the highest levels of supplemental lysine the relationship between uptake and supplement level was not linear. Additionally, arginine digestibility was not affected by the level of lysine supplementation. However, amongst the wheat-gluten-based diets, optimal performance was associated with a lysine: arginine ratio of 1.1: 1. Despite a lysine: arginine ratio of approximately 1.1: 1, the overall performance of the fish fed the fish-meal-soya-based reference diet was poorer than expected. The results are discussed with respect to optimal patterns of gross and digestible amino acids, lysine-arginine antagonism and the possible relationship between antinutritional factors and the poor performance of the fish fed the fish-meal-soya-based reference diet.     

Effects of Microbial Phytase Supplementation and Dosage on Apparent Digestibility Coefficients of Nutrients and Dry Matter in Soybean Product-Based Diets for Rainbow Trout Oncorhynchus mykiss

Three experiments were conducted to evaluate the effects of microbial phytase (Ronozyme P(L) and dosage on apparent digestibility coefficients of dry matter, crude protein, amino acids, and minerals in soybean product-based diets for rainbow trout Oncorhynchus mykiss. In experiments 1 and 2, fish were fed soy protein concentrate and soybean meal-based semi-purified diets, respectively. In experiment 3, fish were fed soybean meal-based practical diets. A total of 900 fish (average body weight 100.1 ± 7.4 g) were stocked into 30 150-L fiberglass tanks with 30 fish per tank and two tanks per diet. Phytase was supplemented into soybean product-based diets at 0, 500, 1,000, 2,000, and 4,000 FTU/kg diet. Yttrium oxide (0.01%) was used as inert marker. Feces were collected by hand stripping three times at 3-d intervals. Results of experiments 1 and 2 showed that phytase supplementation significantly increased apparent digestibility coefficients of minerals (except copper and iron), but not dry matter. Experiment 3 showed that phytase supplementation significantly increased apparent digestibility coefficients of dry matter, crude protein, amino acids (except tryptophan and tyrosine), and minerals (except copper and iron). The optimum level of phytase supplementation in rainbow trout diets was approximately 500 FTU/kg diet.     

Fishmeal alternative from renewable CO2 for rainbow trout feed

The rapid global growth in fish farming and limited supply of fish meal (FM) has consequently reduced FM inclusion levels in compound feeds leading to a higher reliance on alternative protein sources. Sasya is a single cell protein (SCP) product that has a similar amino acid profile as FM. The aim of this study was to evaluate the effects of replacing FM with SCP on in vivo digestibility, growth, feed efficiency, whole‐body proximate/amino acid composition and gene expression levels of various hepatic enzymes in rainbow trout (Oncorhynchus mykiss). Three isonitrogenous (470 g/kg crude protein) and isolipidic (18 g/kg crude lipid) diets were formulated as follows: Diet 1: control (30% FM); Diet 2:24% FM + 6% SCP and Diet 3:18% FM + 12% SCP. Each diet was hand‐fed to triplicate tanks containing 30 rainbow trout fingerlings (4.99 ± 0.20 g) for 9 weeks. Apparent digestibility coefficients of SCP for dry matter, crude protein, lipid and energy were 60, 80, 93 and 74% respectively. Growth performance (final weight: 69–71 g), feed conversion ratios (0.91–0.94) as well as whole‐body protein and amino acid composition were unaffected by diets. However, Diet 3 significantly increased whole‐body crude fat and energy. Fish fed the SCP‐based diets had significantly higher expression for carnitine palmitoyltransferase‐1b (CPT1b), fatty acid delta 6 desaturase (FADS6) and fatty acid elongase 5 compared to the control. Overall, the quality of the SCP was similar as FM. Therefore, this product could enlarge the portfolio of alternative protein sources that can be used in fish diets and thus open a new market opportunity for use of a new feed resource in the feed industry.     

Effect of Geotrichum candidum protein substitution in pelleted fish feed on the growth of rainbow trout (Salmo gairdneri Rich.) and on utilization of the diet

Three experiments were conducted with rainbow trout to determine if Geotrichum candidum GC single cell protein could replace 100, 75 or 50% of fish meal in a pelleted diet. When the fish meal was completely replaced by GC the fish growth was retarded after 3 weeks of the experiment. With the larger fish (individual weight 47–54 g) in the short trial there were significant differences between fish fed the control diet (fish meal) and those fed the 75% substitution of GC diet. The most remarkable differences in fish growth appeared in a 42-day trial with small fish (5 g individual weight) when fish groups fed diets with 0.50 and 75% replacement gave significantly different results (P < 0.05), being 93,9, 46.6 and 34.2% gain, with feed coefficients of 1.49, 2.77 and 3.67, respectively. With large fish fed diets with 0,50 and 75% GC replacement, apparent digestibility of protein was 64.7, 68.2 and 37.5%, but fat digestibility was 79.5, 91.1 and 81.0%, respectively. No significant differences in amounts of free plasma amino acid (PAA) were found between rainbow trout fed diets with 0 or 50% substitution, but there was a marked decrease in PAA in the group fed the diet with 75% GC substitution. Analysis of chosen heavy metals was made on diets, fish and faeces, and Cu in particular was found not to be accumulated in the fish body.     

Fly Prepupae as a Feedstuff for Rainbow Trout, Oncorhynchus mykiss

Fly larvae may provide an effective method to mitigate two large and growing global concerns: the use of fish meal derived from capture fisheries in aquaculture diets and manure management in livestock and poultry facilities. A 9‐wk feed trial was conducted to determine whether fly larvae could be used as a partial fish meal and fish oil replacement in rainbow trout, Oncorhynchus mykiss, diets. A trout diet was formulated to contain 40% crude protein and 15% fat. Sixty‐seven percent of the protein in the control diet was derived from fish meal, and all the fat was derived from fish oil. Two of the test diets included using the black soldier fly, Hermetia illucens, prepupae, which are 40% protein and 30% fat, as 25 and 50% replacement for the fish meal component of the control diet. The total protein derived from black soldier fly prepupae in these two test diets was 15 and 34%, respectively. A third test diet included using housefly, Musca domestica, pupae, which is 70% protein and 16% fat, as 25% replacement for the fish meal component of the control diet. Data suggest that a rainbow trout diet where black soldier fly prepupae or housefly pupae constitute 15% of the total protein has no adverse effect on the feed conversion ratio of fish over a 9‐wk feeding period. In addition, the diet with black soldier fly prepupae permitted a 38% reduction in fish oil (i.e., from 13 to 8%); however, fish fed black soldier fly diets low in fish oil had reduced levels of omega‐3 fatty acids in their muscle fillets. The findings from this study suggest that either the black soldier fly or the housefly may be a suitable feedstuff for rainbow trout diets.     

Preliminary study on effects of methionine hydroxy analog and taurine supplementation in a soy protein concentrate‐based diet on the biological performance and amino acid composition of rainbow trout [Oncorhynchus mykiss (Walbaum)]

A feeding trial was conducted on the effects of methionine hydroxy analog (MHA) and taurine supplementation in diets with high levels of soy protein concentrate (SPC) on the growth performance and amino acid composition of rainbow trout, Oncorhynchus mykiss (Walbaum) comparing with fish meal based diet. The control diet had 520 g kg^?1 fish meal. In the methionine deficient diets (5.1 g kg^?1), fish meal was replaced by 490 g kg^?1 of the SPC in the SPC49 diet. The SPC49 diet was supplemented with either MHA (6 g kg^?1) only or a combination of MHA and taurine (2 g kg^?1). Fish were fed isoproteic (460 g kg^?1) and isolipidic (130 g kg^?1) diets for 12 weeks. Growth performance (i.e. weight, feed conversion ratio, and thermal‐unit growth coefficient) was inferior in fish fed the SPC49 diet. MHA supplementation improved growth performance (P < 0.05). No difference was observed when taurine was added to the SPC49 and MHA diet (P > 0.05). Whole‐body taurine contents increased with taurine supplementation, whereas plasma methionine increased with MHA supplementation (P < 0.05). In conclusion, the substitution of fish meal with SPC supplemented with MHA did not negatively impact growth, and the addition of taurine did not improve growth performance in rainbow trout.     

Evaluation of Experimental and Practical Diets for Walleye Stizostedion vitreum

Culture of walleye Sfizostedion vitreum is one of the largest components of public sector aquaculture in the eastern U.S. and there is increasing interest in private sector culture. However, the nutritional requirements of walleye are unknown and experimental diets for use in quantifying nutritional requirements have not been identified. We formulated four experimental and four practical diets and fed those to triplicate groups of walleye with an initial weight of 13 g per fish. The experimental diets contained either casein (CAS), casein + gelatin (CG), casein + arginine (CA), or casein + gelatin + crystalline amino acids (CGAA) as sources of amino acids. The practical diets were formulated to mimic salmon grower (SG) and trout grower (TG) diets, a fish meal‐free diet for trout (TFMF), and a walleye grower (WG) diet. Fish were fed twice daily to satiation for 9 wk. Feed consumption, percent weight gain, specific growth rates, feed efficiency, protein efficiency ratio, and protein retention efficiency were not significantly different among fish fed CGAA, SG, and TG, but those values were significantly higher than in fish fed other diets. Weight gain of fish fed CGAA was approximately 80% of that in fish fed SG and 91% of that in fish fed TG. Protein retention efficiency of fish fed CGAA was approximately 69% and 81% of that observed for fish fed SG, and TG, respectively. In general, the carcasses of fish fed diets CGAA, SG and TG had significantly lower moisture and ash concentrations, and higher lipid levels than fish fed other diets. There were no significant differences in carcass protein concentration, muscle proximate composition, or liver lipid concentration among treatments. Livers from fish fed all diets were characterized by microvesicular degeneration and glycogen accumulation in hepatocytes. Results from the study indicate that CGAA can be used as a basal experimental diet in future nutritional research with juvenile walleye and confirms the benefits of trout and salmon grower diets. Fish meal‐free diets formulated around the requirements for rainbow trout were consumed at approximately 80% of the values in fish fed TG and SG, but weight gain was approximately 20% of that in fish fed TG and SG. It appears the nutritional requirements for walleye are different than those of rainbow trout.     

The nutritional evaluation of dried earthworm meal (Eisenia foetida, Savigny, 1826) included at low levels in production diets for rainbow trout, Salmo gairdneri Richardson

Abstract. Dried earthworm meal derived from the species Eisenia foetida was nutritionally evaluated as a replacement for herring meal in production diets from rainbow trout, Salmo gairdneri Richardson. Increasing levels of dried E. foetida meal, from 5 to 30% by weight, were included in the diet and the response of fish fed these diets was compared to fish fed a control diet without earthworm meal inclusion. There was no evidence of any adverse effect on the growth performance or feed utilization efficiency of fish fed diets containing these low levels of dried E. foetida meal. There was. however, a significant increase in the whole carcass lipid content of fish fed diets containing 5. 10 and 20% dried E. foetida meal. Concent rations of iron, zinc, lead, copper and cadmium within the whole fish carcass were not significantly elevated as a result of including these low levels of the dried E. foetida meal in diets for rainbow trout.     

Evaluation of 100% Fish Meal Substitution with Chicken Concentrate,Protein Poultry By‐Product Blend,and Chicken and Egg Concentrate on Growth and Disease Resistance of Juvenile Rainbow Trout,Oncorhynchus mykiss

The ability of poultry products to replace fish meal in diets for rainbow trout, Oncorhynchus mykiss, depends on their nutrient composition, cost, and consistency. The aim of this study was to assess the ability of three commercially available poultry products (chicken concentrate, CC, poultry by‐product blend, PBB; or chicken and egg concentrate, CE) to maintain growth and disease resistance when substituted for fish meal in a rainbow trout starter diet. A control diet was formulated to contain 48% crude protein and 18% crude lipid; 100% of the fish meal in test diets was replaced with CC, PBB, or CE. At stocking, fry were counted into groups (50 fish/tank) with six replicate tanks for each diet and fed their respective diets four times daily for 8 wk. All the poultry‐based diets supported growth (over 1600% increase over initial weight), nutrient retention, and feed conversion ratios of rainbow trout fry equal to or greater than those observed for fry fed with the fish meal‐based diet. No effect of diet on survival was observed following subcutaneous injection challenge with Flavobacterium psychrophilum. These data suggest that the examined products can be used in place of fish meal for rainbow trout fry without lowering growth and disease resistance.     

Effects of Microbial Phytase Supplementation in Corn Distiller's Dried Grain with Solubles on Nutrient Digestibility and Growth Performance of Rainbow Trout,Oncorhynchus mykiss

Abstract

Two experiments were conducted to evaluate the effects of microbial phytase in corn distiller's dried grain with solubles (DDGS) on apparent digestibility coefficients (ADCs) and growth performance of rainbow trout, Oncorhynchus mykiss. In experiment 1, DDGS was supplemented with phytase at 0,300,600,900, and 1200 FTU/kg diet. A total of 180 fish (129.1±9.3 g) were stocked into six 140-L tanks with 30 fish/tank. Fish were assigned randomly to a reference diet and each of the 5 diets containing DDGS. Yttrium oxide was used as an inert marker. Results showed that ADCs in DDGS supplemented with different dosages of phytase were: dry matter, 49.1-58.6%; crude fat, 78.9-88.9%; crude protein, 80.0-91.9%; gross energy, 50.5-66.6%; minerals, -7.3-99.7%; and amino acids: 73.9 to 96.8%. In experiment 2, abasal diet containing 15% DDGS supplemented with lysine and methionine was used to determine if trace mineral supplemental levels in rainbow trout diets could be reduced if microbial phytase was supplemented. Six diets were made with trace mineral premix supplementation at 0.1, 0.08, 0.06, 0.04, 0.02, and 0%. Phytase was not supplemented in the basal diet, but supplemented at 500 FTU/kg diet in all other diets. Ten-week results showed that there were no significant differences in fish weight gain, feed conversion ratio, and survival (P < 0.05). There were no significant differences in fish body composition and apparent nutrient retention among fish fed all diets, except that fish fed a diet without trace mineral supplementation had the lowest zinc level and the highest manganese retention. Results indicated that phytase was effective in releasing most of minerals, and that trace mineral supplementation level could be reduced when phytase was used in rainbow trout diets.