Phosphorus retention efficiency in rainbow trout fed diets with low fish meal and alternative protein ingredients

ABSTRACT:   Two experiments were conducted to evaluate feed quality and body phosphorus (P) and nitrogen (N) retention by rainbow trout fed test diets with low amounts of fish meal content and alternative low-P protein sources. A fish meal (FM) diet was used as control. Fish weighing 2.0 g and 134.7 g on average were reared with the experimental diets for 30 weeks and 15 weeks, respectively. The experimental diets had a good growth rate and feed utilization. In the first experiment the P retention was higher in the group of fish fed test diets (56 and 69%) compared to the FM-based diet (36%); N retention rates were similar for all groups. In the second experiment, fish were fed the test diet that had the best P retention in the earlier experiment. The P retention was lower than the values obtained in the first experiment (smaller fish), but still higher in the group of fish fed the low FM diet in comparison with the control group (36.0% and 22.2%, respectively). This represents a P loading into the water of 5.9 kg/t and 12.8 kg/t production for the test and the control diet, respectively. Therefore, low-P-loading diets for rainbow trout can be developed through the appropriate combination of alternative protein sources.     

Different combinations of protein ingredients in carp diets for reducing phosphorus loading

ABSTRACT: This study was conducted to gather data on the reduction of environmental phosphorus (P) loading through the formulation of carp diets with different combinations of protein ingredients. Five experimental diets were formulated by substituting fishmeal (FM; 10–20%) with alternative protein sources such as meat meal (MM; 5–15%), blood meal (BM; 5–7%), and defatted soybean meal (dSBM; 6–10%). The control diet used was a commercial carp diet selected based on earlier experiments. Each diet was fed to duplicate groups of juvenile carp three times a day, until satiation for 12 weeks. Feed performance was proportional to the increase in dietary FM levels. Phosphorus absorption ranged between 41.6% and 52.0% among the experimental groups and was 42.6% for the control group, but there were no marked differences in nitrogen (N) absorption rates. Phosphorus retention ranged from 31.4% to 35.7% for the test diets, whereas N retention increased proportionally with dietary FM levels and ranged from 34.7% to 41.7%. The P and N retention values of the control diet were 27.6% and 41.2%, respectively. The total P loading (T-P) increased at the higher FM levels (9.1–10.7 kg/t production), whereas lower FM levels produced higher total N loading (T-N, 34.6–43.1 kg/t production), the figures for the control being 13.9 T-P kg/t production and 35.6 T-N kg/t production. These results indicate that the reduction of FM levels to 10–20% by replacing it with MM, BM, and dSBM in carp diets was effective in reducing the loading of P and N.     

Replacing Fish Meal with Rendered Animal Protein Ingredients in Diets for Malabar Grouper,Epinephelus malabaricus,Reared in Net Pens

The potential of using rendered animal protein ingredients, poultry by‐products meal (PBM), meat and bone meal (MBM), and feather meal (FM), to replace fish meal in diets for malabar grouper, Epinephelus malabaricus, was evaluated in a 10‐week net pen experiment. Triplicate groups of fish (initial body weight 50.2 g) were fed eight isonitrogenous and isocaloric diets formulated to contain 52% crude protein and 9% crude lipid. The control diet contained 50% herring meal, whereas in the remaining seven diets, PBM was incorporated at 11.9 (PM1), 23.8 (PM2), and 35.7% (PM3) to replace 25, 50, and 75% of the fish meal; MBM was incorporated at 14.5 (MM1) and 29.0% (MM2) to replace 25 and 50% of the fish meal; and FM was incorporated at 9.4 (FM1) and 18.8% (FM2) to replace 25 and 50% of the fish meal. A raw fish (RF) diet was used as comparison to assess growth performance of fish fed the formulated diets. Feed intake was lower in fish fed the diets PM3 and FM2 than fish fed the control diet. There were no significant differences in weight gain (WG), final body weight (FBW), nitrogen retention efficiency (NRE), energy retention efficiency (ERE), and total nitrogen waste output (TNW) between fish fed the control diet and the diets PM1, PM2, PM3, MM1, MM2, and FM1. Fish fed the diet FM2 had lower WG, FBW, NRE, and ERE but higher TNW than that of fish fed the control diet. Feed conversion ratio (FCR) was higher in fish fed the diets MM2, FM1, and FM2 than fish fed the control diet. At the end of the experiment, there were no significant differences in whole‐body content of moisture, crude protein, and crude lipid among fish fed the formulated diets. WG, FBW, and TNW of fish fed the diet RF were higher, while FCR and NRE were lower than that of fish fed the control diet. No significant differences were found in feed intake, ERE, and whole‐body composition between fish fed the diet RF and the control diet. Results of the present study suggest that dietary fish meal level for malabar grouper can be lowered from 50 to 38% by incorporating PBM, MBM, or FM.     

Effect of monocalcium phosphate supplementation in a low fish meal diet for rainbow trout based on growth,feed utilization,and total phosphorus loading

ABSTRACT:   In order to verify methods for minimizing waste output of phosphorus (P) into the water and preserve an adequate growth rate in rainbow trout, a succession of two feeding trials were performed employing three test diets that were formulated with a low proportion of fish meal (FM), low-P ingredients (defatted soybean meal, corn gluten meal, feather meal, and blood meal), and varying levels of monocalcium phosphate (MCP) as a P supplement (0, 0.5 and 1% of diet which represent 0, 1 and 2 mg/g of available P, respectively). Total P concentrations achieved were 6.2, 8.7 and 9.6 mg/g, respectively. A control diet was formulated with FM as the main protein source and without MCP (total P content was 17.0 mg/g). Diets were fed until apparent satiation to duplicate groups of 50 (1.5 g) and 15 fish (147.8 g) during 24 and 14 weeks, respectively. In both cases, the lowest growth was observed in fish fed the basal diet without MCP. The test diet supplemented with 0.5% MCP provided growth and feed performance comparable to that obtained in fish fed the control diet. These results suggest that diets formulated with low-P ingredients should be supplemented with an adequate amount of P in order to meet the fish requirements and reduced diet-related P loading.     

Replacement of Fishmeal with a Blend of Poultry Byproduct Meal and Soybean Meal in Diets for Largemouth Bass,Micropterus salmoides

A feeding trial was conducted to evaluate the potential of replacing fishmeal with poultry byproduct meal (PBM) and soybean meal in diets for largemouth bass, Micropterus salmoides. A reference diet (C) contained 400 g/kg fishmeal, and 40 or 60% of the fishmeal was replaced with a blend of pet‐food‐grade PBM and soybean meal (diets PP1 and PP2) or a blend of feed‐grade PBM and soybean meal (diets PF1 and PF2). No significant differences were found in weight gain, nitrogen retention efficiency (NRE), condition factor, and body composition among fish fed diets PP1, PP2, PF1, and PF2. Feed intake and feed conversion ratio (FCR) were higher in fish fed diet PF1 than in fish fed diet PP1. No significant differences were found in weight gain, NRE, condition factor, and body composition between fish fed diet C and diets PP1, PP2, PF1, and PF2. The feed intake and FCR were lower in fish fed diet C than in fish fed diets PP2, PF1, and PF2. This study reveals that dietary fishmeal level for largemouth bass could be reduced to 160 g/kg by inclusion of PBM and soybean meal in combination.     

Partial replacement of fish meal by soybean meal with or without methionine and phytase supplement in diets for juvenile Chinese sucker,Myxocyprinus asiaticus

This study was designed to evaluate the effects of using soybean meal supplemented with or without methionine (M) and graded levels of phytase (P) to replace high‐level (60%) fish meal in the diets for juvenile Chinese sucker. Seven experimental diets (about 430 g kg^?1 crude protein on dry matter basis) were formulated from practical ingredients. The control diet (FM) was formulated to contain 400 g kg^?1 white fish meal (FM), whereas in the other six diets (diets 2–7), soybean meal (SBM) was used to replace 60% fish meal with or without methionine (3 g kg ^?1) and 0,500, 1000, 1500 and 2000 U kg^?1 phytase (designated as SBM, SM, SMP500, SMP1000, SMP1500 and SMP2000, respectively). Results from the feeding trial indicated that SBM without any methionine or phytase supplement replacing about 60% FM significantly affected the growth of fish (P < 0.05). Weight gain of fish fed diet SM was significantly higher than the fish fed diet SBM, but still much lower than fish fed the control diet (P < 0.05). SBM with methionine and phytase supplement significantly improved the growth of fish and apparent digestibility coefficients of phosphorus compared with the groups which fed diet SBM and diet SM (P < 0.05). Weight gain of fish fed SMP1000, SMP1500 and SMP2000 had no significant difference than fish fed control diet. Furthermore, fish fed SMP1500 showed optimum weight gain and ADC of phosphorus between these three groups. This suggested that soybean meal with 3 g kg^?1 methionine and 1500 U kg^?1 phytase supplement could successfully replace 60% fish meal in the diet for juvenile Chinese sucker without affecting growth and enhanced the apparent digestibility coefficient of phosphorus.     

The effect of dietary protein replacement by crystalline amino acid on growth and nitrogen utilization of turbot Scophthalmus maximus juveniles

A study was conducted to evaluate the effect of partial replacement of dietary fish meal by crystalline amino acids on growth performance, feed utilization, body composition and nitrogen utilization of turbot juveniles.

Four diets were formulated to be isolipidic (12% DM) and isonitrogenous (8% DM). A fish meal based diet was used as control. In the experimental diets, a crystalline amino acid (AA) mixture was used to partially replace fish meal, corresponding to a non-protein nitrogen content of 19, 37 and 56%, respectively (diets 19AA, 37AA and 56AA, respectively). The overall amino acid profile of the experimental diets resembled that of the whole-body protein of turbot. Each experimental diet was fed to triplicate groups of 20 fish (initial body weight of 31.8 g) twice daily to apparent satiation for 42 days. During the trial water temperature averaged 18 °C.

Final body weight, weight gain (g kg ABW^− 1 day^− 1) and specific growth rate were not different between the control and 19AA diet but significantly decreased with the increase of crystalline-AA inclusion from 19 to 56%. Feed intake and feed efficiency of fish fed the control and diet 19AA were similar and significantly higher than those of fish fed the 56AA diet. At the end of the growth trial, there were no significant differences in whole-body composition among groups. Hepatosomatic index was also unaffected by dietary treatments.

Nitrogen retention (g kg ABW^− 1 day^− 1) of fish fed the control and the 19AA diets were similar and significantly higher than that of fish fed the other diets. Expressed as a percentage of the nitrogen intake, N retention was significantly higher with the control than with the 37AA and 56AA diets.

Daily ammonia excretion (mg kg ABW^− 1 day^− 1) of fish fed the control diet was significantly higher than that of fish fed the 37AA and 56AA diets, while daily urea excretion (mg kg ABW^− 1 day^− 1) did not significantly differ among treatments. Non-fecal nitrogen (ammonia + urea) excretion (mg kg ABW^− 1 day^− 1) was significantly higher for fish fed the control diet than in those fed the 37AA and 56AA diets. However, as percent of N intake, ammonia excretion and non-fecal N excretion were significantly higher in fish fed the 56AA diet than in those fed the control and 19AA diets.

Specific activity of glutamate dehydrogenase, alanine and aspartate aminotransferases did not significantly differ among experimental groups.

In conclusion, in diets with an overall amino acid profile resembling that of the whole-body protein of turbot, crystalline-AA may replace 19% of dietary protein without negatively affecting growth performances or feed utilization efficiency. However, higher protein replacement levels of protein-bound-AA by crystalline-AA severely depressed growth performance.     

Growth, uptake and retention of nitrogen and phosphorus, and absorption of other minerals in Atlantic salmon Salmo salar fed diets with fish meal and soy–protein concentrate as the main sources of protein

An experiment with 0.2‐kg Atlantic salmon, Salmo salar in saltwater was conducted to determine if the fish could grow normally, and maintain normal nitrogen (N) and mineral balance when fed a diet with the majority of the protein (75%) derived from soy‐protein concentrate (SPC). The two diets contained 50% SPC and 15% fish meal (FM) or 60% FM as the sources of protein. No calcium phosphate was added to the diets in order to assess the availability of P from the ingredients. A second aim was to investigate if whole‐body concentrations of essential elements and growth were related in individual salmon. Growth (SGR=0.88–0.89) was similar in salmon fed the two diets, and the fish nearly doubled their body weights during the 84 days of feeding. Feed conversion was more efficient for the FM diet (0.81 kg intake kg^?1 gain) than for the SPC diet (0.89 kg kg^?1). The intake of N was similar, faecal loss of N was lower, while the metabolic N excretion was greater in the fish fed the FM than the SPC diet. This resulted in a total excretion of 35.4 g N kg^?1 gain for the salmon fed the FM diet and 35.5 g N for the fish fed the SPC diet. Both the intake, faecal and metabolic excretion of P were higher in the fish fed the FM diet than the SPC diet, resulting in a total excretion of 10.5 g P kg^?1 gain for the FM diet and 7.2 g P for the SPC diet. Whole‐body concentrations of Ca, Mg, P and Zn were lower in the fish fed the SPC diet, while the Ca–P ratio was decreased, both when compared with the fish at the start of the experiment, and the fish fed the FM diet. The differences in elemental composition were ascribed to a combination of reduced availability of elements due to phytic acid and lower concentration of elements in the SPC than in the FM. No reduction in growth of individual fish, which could be ascribed to reduced availability of essential elements, was seen.     

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.     

Fisheries By-Catch and By-Product Meals as Protein Sources For Rainbow Trout Oncorhynchus mykiss

Abstract— Fisheries by-catch and by-product meals are portrayed as ingredients having a great potential as ingredients in aquaculture feeds. The present study was designed to evaluate the nutritional value of shrimp by-catch meal, shrimp processing waste meal, and two fish meals made from Pacific whiting (meal with and without solubles) for rainbow trout by determining apparent digestibilityof these ingredients and conducting a 12-wk feeding trial with juvenile fish (average initial weight 20 g/fish). Apparent digestibility coefficients (ADCs) for protein in diets containing by-catch and processing by-products were 76% for shrimp by-catch meal, 79% for shrimp processing waste meal, 88% for Pacific whiting meal without solubles, and 92% for Pacific whiting meal with solubles. ADCs for lipid were higher than 94% for all the diets. ADCs for energy were 57% for shrimp by-catch meal, 73% for shrimp processing waste meal, 70% for Pacific whiting meal without solubles, and 73% for Pacific whiting meal with solubles. Growth performance was significantly affected by dietary protein source. Fish fed the shrimp by-catch meal diet had weight gain and feed conversion ratios similar to that of fish fed the control diet with anchovy fish meal. Fish fed diets containing shrimp processing waste and Pacific whiting meal with solubles had significantly lower weight gain and higher feed conversion ratios than the control diet. Growth was significantly lower in fish fed the Pacific whiting meal diet compared to fish fed the anchovy fish meal. The lower growth of fish fed diets containing Pacific whiting meal appeared to be a result of lower feed intake, indicating perhaps a lower palatability of this ingredient. Additional research addressing processing methods, nutritional manipulations, and palatability enhancement is needed to improve potential of some fisheries byproduct meals as ingredients in the diets of rainbow trout.     

Improved carp diets based on plant protein sources reduceenvironmental phosphorus loading

ABSTRACT:   As part of on-going efforts to reduce environmental phosphorus(P) and nitrogen (N) loading from culture systems, five experimentaldiets were formulated containing 5–15% of fishmeal (FM) and different levels of soy protein concentrate (10–20%),corn gluten meal (3–5%) and defatted soybean meal(2.0–8.5%). These diets had total P ranging between1.04 and 1.29% and available P between 0.62 and 0.63%.A FM-based (43%) commercial diet was used as the controland this diet had total P of 1.87% and available P of 0.82%.Waste loading was calculated after feeding the diets to 3.4 gcarp for 10 weeks. Feed gain ratios were not significantly differentfor fish fed control and experimental diets having 10–15% FM,but the protein efficiency ratio was lower for the control group.The rates of P absorption and retention in the experimental dietgroups were significantly higher than those of the control group.The lowest N retention was obtained for the control group, althoughabsorption was not markedly different among the treatment groups.Total P and N loading (kg/ton production) produced fromthe experimental diets ranged from 7.1 to 8.9 and from 36.1 to 41.3,respectively, whereas the corresponding values for the control dietwere 15.2 and 48.1.     

Almost total replacement of fish meal by plant protein sources in the diet of a marine teleost, the European seabass, Dicentrarchus labrax

Five practical diets in which the supply of protein from fish meal was decreased gradually from 100% to about 2% and replaced by plant protein sources were formulated. European seabass weighing about 190 g were fed these diets for 12 weeks at a water temperature of 22 °C. Feed was dispensed using automatic self-feeders and voluntary feed intake (VFI) was closely monitored. We did not find any significant difference among diets in the apparent digestibility coefficients (ADC) of dry matter (80–82%), protein (94–96%), energy (88–92%) or phosphorus (49–58%). Replacement of fish meal by plant protein ingredients did not influence VFI. All groups had very good growth rates (DGI above 1.3%/day) and there were no significant differences in growth rate, feed efficiency or in daily nitrogen gains among groups. There was, however, a slight increase in fat deposition in fish fed diets with plant protein sources. Ammonia nitrogen and soluble phosphorus excretion rates were measured. Nitrogen and phosphorus balance studies indicated that fish meal replacement by plant ingredients led to a slight increase in nitrogen losses (from 83 to 103 g N/kg weight gain) but led to a significant reduction in total phosphorus losses (from 13 to 5 g P/kg weight gain). These results combined with the remarkable acceptability of diets containing high levels of plant protein ingredients with identical growth performances of European seabass show clearly that dietary fish meal levels can be considerably reduced without any adverse consequence in terms of somatic growth or nitrogen utilisation.     

Incorporation of plant protein feedstuffs into fish meal diets for rainbow trout increases phosphorus availability

Individual plant protein feedstuffs were incorporated into a diet containing fish meal and fed to rainbow trout to determine apparent and true phosphorus availability (APA and TPA, respectively). The plant protein feedstuffs evaluated were soybean, canola and peanut meals; each was incorporated at 200 g kg^–1 of dry matter. The average initial weight of fish was 68 g and the water temperature was maintained at 15°C. Concentrations of macronutrients were constant in diets. Incorporation of plant protein feedstuffs significantly increased APA and TPA values. The APA values were 19.5% for fish meal and 39.5%, 40.2%, and 38.5% for the diets containing soybean meal, canola meal, and peanut meal, respectively. Similarly, the TPA values for the combination of fish meal and plant protein feedstuff were 43.4%, 42.1% and 40.6% for diets containing soybean, canola and peanut meals, respectively, which were significantly higher than values for fish meal (21.5%). Calculation of APA and TPA values for individual feedstuffs resulted in values for the plant protein ingredients of over 100%. We speculate that the increased APA and TPA values were the result of decreasing total dietary phosphorus concentrations or dilution of the calcium concentrations from bone in fish meal.     

Effects of dietary phosphorus and lipid levels on utilization and excretion of phosphorus and nitrogen by rainbow trout (Oncorhynchus mykiss). 1. Laboratory-scale study

Nutritional strategies to reduce both phosphorus (P) and nitrogen (N) excretion relative to growth of rainbow trout were tested in a 2 × 3 factorial experiment. The two factors were `dietary P level' and `dietary lipid level.' Reduction in dietary P from 14 to 8 g kg^–1 dry diet was achieved by partial substitution of dietary fish meal with a combination of full-fat soyabean meal, corn gluten and spray-dried blood meal. Triplicate tanks of 35 rainbow trout per tank were fed experimental diets for 16 weeks and grew from approximately 40 to 250 g, in 15 °C spring water. All tanks were fed the same percent biomass per day. Diets were isonitrogenous, and dietary energy varied with dietary lipid. Diet digestibility data and results of the experiment were used to construct N and P budgets for the fish fed the various diets. A reduction in dietary fish meal from 500 to 200 g kg^–1 dry diet, corresponding to a reduction in dietary P from 14 to 8 g kg^–1 dry diet, resulted in >50% reductions in both solid and dissolved P waste, but did not affect growth, feed efficiency ratio (FER) or sensory characteristics of rainbow trout. Increasing dietary lipid from 170 to 310 g kg^–1 dry diet led to higher growth rate and FER, and lower total N waste relative to weight gain, but did not change protein retention. Increasing dietary lipid level increased deposition of lipid in whole bodies of rainbow trout, and resulted in discernible differences in sensory characteristics of trout fillets.     

The nutritional properties of co-dried fish silage in rainbow trout (Salmo gairdneri) dry diets

Feed ingredients containing fish silage and liquefied fish made from ground, whole Pacific whiting and co-dried in a vacuum dryer with mixtures of soybean meal and feather meal to facilitate drying were prepared. An additional batch of fish silage was co-dried with the other dry ingredients in the diet formulation that was used, Abernathy diet S8-1. Fish meal, made by vacuum drying Pacific whiting, was used in the control diet. Co-dried fish meal was made by co-drying Pacific whiting with a soybean meal-feather meal mixture. Fish meal was entirely replaced by the co-dried products in the experimental diets, which were fed to rainbow trout (Salmo gairdneri) for 32 weeks. The best growth and food conversion values were obtained by feeding the fish meal control diet or the diet in which the fish meal was replaced with co-dried liquefied fish. No significant differences in final weights were found between trout fed diets containing co-dried fish meal or co-dried fish silage (fish products were 25% of the diet), but these fish were significantly smaller than fish fed the fish meal control or the co-dried liquefied fish diets. Reducing the fish silage to 12.5% or increasing it to 50% further reduced weight gains in the trout. Food conversion values, protein efficiency ratios, and net protein utilization values generally followed the same trends between diets as did the final weight values. Apparent digestibility coefficients for the co-dried products were lower than for the fish meal, possibly because they contained soybean meal-feather meal mixtures. Organoleptic properties of the fish were not affected by diet.     

Evaluation of Poultry By‐product Meal in Commercial Diets for Hybrid Striped Bass,Morone chrysops ♀ × Morone saxatilis ♂, in Pond Production

The efficacy of replacing fish meal with petfood‐grade poultry by‐product meal (PBM) on an ideal protein basis in commercial diets for hybrid striped bass (HSB) was evaluated under production conditions in pond culture. A generic production diet (GEN) for HSB was formulated to contain 45% protein, 12% lipid, and 3.7 kcal/kg. Protein in the generic diet was supplied by a mix of animal and plant sources typically used by the industry that included more than 20% select menhaden fish meal and less than 10% PBM. A positive control diet (GEN + AA) was formulated by supplementing the generic diet with feed‐grade Met and Lys to match the level of those amino acids in HSB muscle at 40% digestible protein. Substitution diets were formulated by replacing 35, 70, or 100% of fish meal in the GEN diet with PBM on a digestible protein basis and then supplementing with Met and Lys (designated 35PBM, 70PBM, and 100PBM, respectively) as needed to maintain concentrations equal to those in the GEN + AA diet. Diet formulation and extrusion were conducted by a commercial mill, and all diets met or exceeded known nutritional requirements for HSB. Twenty 0.10‐ha ponds (4 ponds/diet) were randomly stocked with juvenile HSB (76 ± 10 g; mean ± SD) at a density of 7400/ha and fed for 600 d (October 2004 to May 2006). Diets were fed once daily to apparent satiation to a maximum of 95 kg feed/ha. Total weight and number of fish in each pond were determined at harvest. Weight distributions in each pond were estimated by selecting every 15th fish during harvest. Subsets of ten fish from each of these samples were selected randomly for the determination of body composition and nutrient and energy retention. The availability of indispensable amino acids as well as ammonia production from the commercial test diets were determined in separate tank trials. Most production characteristics were not statistically different (P > 0.10) among dietary treatments. Distributions of individual fish weights from each of the ponds were not affected by poultry by‐product level in the diet. Multivariate analysis of body compositional indices grouped diets into two clusters composed of GEN, GEN + AA, 35PBM vs. 70PBM, and 100PBM mainly because fish fed the 70PBM and 100PBM diets had greater (P = 0.001) body fat (visceral somatic indices) than fish fed the other diets. Ammonia production in tanks was not different among diets and peaked 6–8 h after feeding when fish were fed at 1.5% of body weight; ammonia‐N excretion ranged from 197 to 212 mg/kg/d and 18.5–21.5% of nitrogen intake. Some imbalances in the levels and ratios of selected amino acids to Lys were found in the diets containing higher amounts of PBM and were attributed to a lack of accurate availability coefficients during formulation for some dietary proteins. These imbalances in essential amino acids may have been the predominant factor in the somewhat fattier fish observed fed diets containing the two highest levels of PBM. Nevertheless, these results from fish stocked at commercial densities and raised to market size in ponds suggest that formulating diets on an available amino acid basis for all protein sources while balancing limiting amino acids, particularly Met, Lys, Thr, and Trp, on an ideal protein basis will yield significant improvements in HSB performance when fed commercial diets in which all fish meal is replaced with PBM.     

Effect of protein source and nutrient density on growth efficiency, histology and plasma amino acid concentration of rainbow trout (Oncorhynchus mykiss Walbaum)

The effects of protein source and nutrient density on growth efficiency, nutrient digestibility and plasma amino acid concentrations of rainbow trout were evaluated. A 3 by 2 factorial treatment design with three protein sources, fish meal–barley (F–B), plant concentrates (PC) and plant meals (PM), and two nutrient densities were used. A commercial reference diet was also fed. Triplicate tanks of 30 fish (initial wt. 28 g) were fed each diet, and the final weight averaged 240 g fish⁻¹. Protein source and nutrient density affected feed intake, weight gain and feed conversion ratio. Weight gain of trout fed the PC and PM diets was approximately 10% less than fish fed the F–B diets. Protein retention was affected by protein source, but not nutrient density, and was the highest for the fish fed diets containing fish meal and the lowest for the fish fed PM diets. Apparent digestibility coefficients and apparent amino acid availabilities of the diets corresponded with differences in weight gain. This study provides further evidence that growth rates of trout fed fish meal‐free diets, using conventional and concentrated plant protein ingredients, are good but some limitation to growth exists in the fish meal‐free diets.     

The Effects of Plant-protein-based Diets Supplemented with Yucca on Growth, Digestibility, and Chemical Composition of Nile Tilapia (Oreochromis niloticus, L) Fingerlings

Replacement of fish meal (FM) protein with dehulled and solvent‐extracted plant by‐products, soybean meal, cottonseed meal, sunflower meal, and linseed meal was tested in diets for juvenile Nile tilapia, Oreochromis niloticus. Fish averaging (±SD) 14.2 ± 2.9 g were divided into 18 groups and fed for 6 mo on pelleted feed containing each of the plant protein meal supplemented with Yucca schidigera powder extract at 750 mg/kg. Methionine (1%) and lysine (0.5%) were added to each diet except the control diet (FMC), while diet FMC + Y was supplemented with yucca only. Three groups of fish were fed each of six isonitrogenous (25% crude protein) and isocaloric (4.3 kcal/g) diets replacing 100% of FM protein and performance compared against a nutritionally balanced control and a commercial tilapia feed. After 6 mo of feeding, the fish fed plant protein diets supplemented with yucca exhibited growth performance not differing significantly from that of fish fed FMC + Y, while differing significantly from the control FMC and diet linseed meal (LSM). The highest apparent protein digestibility coefficient was observed for diets treated with yucca, which was significantly higher than that observed for the control diet FMC. No significant differences were found in whole‐body moisture of fish fed different experimental diets. An increase in the whole‐body protein content was observed in fish fed diets supplemented with yucca, which was significantly different from that of the diet FMC. The whole‐body fat content of Nile tilapia was low and showed significant differences among treatments supplemented with yucca compared with the control diet FMC. The whole‐body energy content showed the same trend as whole‐body fat content.     

Replacement of fishmeal by soy protein concentrate with taurine supplementation in diets for golden pompano (Trachinotus ovatus)

Two 7‐week feeding trials were conducted to evaluate the capacity of golden pompano (Trachinotus ovatus) to use soy protein concentrate (SPC) as a dietary fish meal substitute. In trial I, fish were fed with a control diet (C) containing 400 g kg^?1 fish meal and other four diets in which the fish meal in diet C was replaced by SPC at 20 (R20), 40 (R40), 60 (R60) and 80% (R80). In trial II, a 3 × 2 design was used, and 40 and 80% of the fish meal in diet C were replaced by SPC, with or without 5 g kg^?1 taurine supplementation (six diets, C + T, R40 + T, R80 + T, C, R40 and R80, were formulated). In trial I, no significant difference was found in the feed intake between feeding treatments. The weight gain and nitrogen retention efficiency (NRE) decreased, whereas the feed conversion ratio (FCR) and phosphorus retention efficiency (PRE) increased, with decreasing dietary levels of fish meal. No significant differences were found in the weight gain, FCR and NRE between fish fed diets C and R20, whereas fish fed diets C and R20 had higher weight gain than those fed diets R40, R60 and R80. In trial II, no significant differences were found in the feed intake, weight gain, FCR, NRE and PRE between fish fed diets C + T and C. No significant differences were found in the feed intake, weight gain and NRE between fish fed diets R40 and R40 + T or between fish fed diets R80 and R80 + T. At the end of trial II, no significant differences were found in the condition factor, hepatosomatic index and body composition between fish fed diets C and C + T, or between fish diets R40 and R40 + T, or between fish fed diets R80 and R80 + T, except that fish fed diet R40 had lower body protein content than that of fish fed diet R40 + T. The present study reveals that taurine supplementation can elevate fish meal replacement level by SPC in the golden pompano diets. Fish meal can be reduced from 400 to 320 g kg^?1, if fish meal is substituted by SPC without taurine supplementation, and can be further reduced to 240 g kg^?1, if fish meal is substituted by SPC with 5 g kg^?1 taurine supplementation.     

Apparent digestibility coefficients of four feed ingredients for Synechogobius hasta

Apparent digestibility coefficients (ADCs) of dry matter, crude protein, lipid, energy, phosphorus and amino acids in white fish meal, soybean meal, rapeseed meal and peanut meal were determined for Synechogobius hasta (28.65 ± 0.43 g, mean ± SD), using a reference diet with chromic oxide indicator and test diets that contained 70% reference diet, by weight, and 30% of feed ingredients. The juvenile S. hasta were held in 300 L tanks at a density of 30 fish per tank respectively. Faeces were collected from three replicate groups of fish by siphoning. The ADCs of dry matter and energy were the highest in white fish meal and the lowest in rapeseed meal ( P <0.05). Crude protein ADC was the lowest in rapeseed meal ( P <0.05) and showed no significant differences among other treatments ( P >0.05). The highest phosphorus ADC was observed in white fish meal and differences were not marked for other treatments ( P >0.05). Lipid ADC were above 90% and showed no significant differences among the treatments ( P >0.05). Amino acid availability values for the test ingredients followed similar trend to values of protein digestibility. All amino acids were more available from fish meal than from plant protein ingredients. Among three plant meals, the availability of amino acids was higher in peanut meal and lower in rapeseed meal.