Effects of Replacing Fish Meal with Soybean Meal in Diets for Red Drum Sciaenops ocellatus and Potential for Palatability Enhancement

Two 8-wk feeding trials were conducted with juvenile red drum to determine the maximum levels of soybean meal that may replace fish meal in diets containing 38% crude protein, without reducing weight gain. In the first experiment, fish fed diets containing up to 90% of the protein from soybean meal gained as much weight as fish fed a diet with 100% of protein from fish meal, but fish fed the diet with 100% of its protein from soybean meal gained significantly (P < 0.05) less. Supplementation of glycine and fish solubles individually at 2% (as-fed basis) in diets containing 90% of their protein from soybean meal tended to increase weight gain of fish compared to those fed a similar diet without supplementation. Similar results were obtained in the second experiment, as fish fed diets containing 90% of their protein from soybean meal gained as much weight as fish fed a diet with 100% of its protein from fish meal. Fish fed diets with 95% and 100% of their protein from soybean meal gained significantly less weight than those fed the diet with all of its protein from fish meal. Supplementation of glycine at 2% in the diet containing 95% of its protein from soybean meal significantly improved weight gain of fish relative to those fed a similar unsupplemented diet. Supplementation of fish solubles at 5% of diet on a dry-matter basis provided a nonsignificant increase in weight gain compared to that of fish fed a similar unsupplemented diet. In both experiments there was greater observed consumption of the soybean-meal-based diets than diets with all of their protein from fish meal. A minimum of 10% of protein from fish meal appears necessary in practical diets containing most of their protein from soybean meal to prevent impaired growth and feed efficiency of red drum.     

Tolerance of Juvenile Red Drum Sciaenops ocellatus to Rapidly Decreasing Water Temperatures

This study assessed the potential mortality of pond-reared juvenile red drum Sciaenops ocellatus subjected to rapid declines in water temperature simulating cold front activity. Fish acclimated in an earthen pond at ambient temperature and photoperiod were introduced into a recirculating aquarium and biofiltration system when pond water temperatures decreased to 20, 18, 16, 14, 12, and 10 C. Fish were stocked according to size group into 10 aquaria containing filtered pond water at 9 ± 1‰ salinity and temperature matching the acclimation temperature. Fish were acclimated to the aquaria for 3 d, subjected to a 6 C decrease over 24 h, and then held for 72 h. No mortalities were observed in any trial. The results suggest that if juvenile red drum are maintained in water with salinity around 9‰, they should survive the passage of most cold fronts.     

Evaluation of Soybean Proteins as Replacements for Menhaden Fish Meal in Practical Diets for the Red Drum Sciaenops ocellatus

A series of growth trials was conducted to evaluate the use of soy protein as a replacement for fish protein in isonitrogenous practical diets for juvenile red drum Sciacnops ocellatus. Feeds were offered at or in excess of satiation to juvenile red drum maintained at 26–28 C and a salinity of 25–35 ppt. In the first growth trial, red drum were offered one of four diets containing graded levels of menhaden fish meal, replacing solvent-extracted soybean meal and soy-protein isolates. Differences in weight gain, survival and feed efficiency ratios of the fish corresponded to increases in fish meal content of the diets. Due to poor performance of the fish maintained on the low (15%) fish meal diet, a methionine supplement was introduced into this diet at the midpoint of the growth trial. A positive increase in growth indicated a dietary deficiency of methionine and/or total sulfur amino acids in the unsupplemented diet. A positive response to dietary fish meal also occurred in the second growth trial despite the supplementation of L-methionine in the test diets. In low fish meal diets the utilization of solvent extracted soybean meal or a soy-protein isolate resulted in similar growth responses. Hence, the presence of an antinutrient did not likely cause reduced growth rates. In the third feeding trial, weight gain also increased with increasing fish meal content of the diet despite the equalization of digestible protein and selected amino acids. There were no significant differences in whole-body compositions which indicated similar biological value of the diets (protein digestibility, amino acid balance and energy availability). The singular deletion of fish-solubles, glycine, lysine and methionine from the diet containing the lowest level of fish meal (10 g/100 g diet) did not result in significant changes in weight gain. This indicated that these components did not add to the nutritive value and/or palatability of this formulation. The final experiment was designed to evaluate the response of red drum to a control diet (high fish meal) as compared to a low fish meal diet with and without potential attractants/palatability enhancers. Weight gain and feed efficiency ratios of fish offered the low fish meal diet supplemented with seafood flavor or fish flavor #2 were not significantly different from the control (high fish meal diet). Based on the results of this study, with suitable formulation restrictions, soy protein is acceptable for inclusion in practical diet formulations for red drum. However, soy protein itself does not appear replete in sulfur-containing amino acids and does not have acceptable palatability properties. Consequently, feeds containing reduced levels of marine proteins could require suitable attractants and/or amino acid supplements.     

Effects of Various Levels of Silica Ash in the Diet of Juvenile Red Drum,Sciaenops ocellatus

The demand for alternative feedstuffs to fish meal is anticipated to continue increasing due to fish meal's limited supply and escalating price. One group of alternative feedstuffs includes lipid‐extracted algae (LEA) by‐products from algae production for biofuels. Most LEA by‐products are known to contain relatively high levels of ash ranging from 20 to 30% of dry weight. Thus, inclusion of LEA by‐products in aquafeeds may contribute a substantial amount of ash, which potentially could have negative effects on utilization of other nutrients. To study the ash component of LEA by‐products, diatomaceous earth (DE) was used as a homogeneous source of silica ash. Therefore, two feeding trials were conducted with red drum, Sciaenops ocellatus, in a closed, recirculating system to evaluate the effects of graded levels of dietary silica ash. In Experiment 1, semi‐purified diets were formulated to contain 35% crude protein, with DE included at 0, 5, 10, 20, or 30% of dry weight in place of cellulose to provide diets with analyzed ash levels of 8.6, 12.4, 16.7, 25.5, and 33.8% of dry weight in a regression design. Similar diets were fed in Experiment 2 but DE and cellulose were restricted to no more than 20% of diet. Each diet was fed to triplicate groups of juvenile fish (initial average weight of 1.4 ± 0.2 and 2.3 ± 0.1 g) for 8 wk. In both experiments it was apparent that red drum did not respond negatively to even the highest dietary ash levels based on weight gain, feed efficiency, survival, or body composition. No apparent histological changes in the gastrointestinal tract of fish fed the graded levels of ash were observed. Therefore, inclusion of algae by‐products in diets of red drum will not be limited due to their contribution of ash.     

Effects of the Prebiotics GroBiotic®‐A and Inulin on the Intestinal Microbiota of Red Drum,Sciaenops ocellatus

Two separate feeding trials examined the effects of dietary supplementation of the prebiotics GroBiotic^®‐A and inulin on growth performance and gastrointestinal tract microbiota of the red drum, Sciaenops ocellatus. In the first feeding trial, fish meal‐based diets without prebiotics or supplemented with either GroBiotic^®‐A or inulin at 1% of dry weight were fed to triplicate groups of juvenile red drum (initial weight of 2.6 g) in 110‐L aquaria operated as a brackish water (7 ppt) recirculating system for 8 wk. In the second feeding trial, soybean meal/fish meal‐based diets supplemented with either GroBiotic^®‐A or inulin at 1% of dry weight were fed to triplicate groups of red drum (initial weight of 15.8 g) in 110‐L aquaria operated as either a common recirculating water system or closed system with individual biofilters (independent aquaria) for 6 wk. Supplementation of the prebiotics in either feeding trial did not alter weight gain, feed efficiency ratio, or protein efficiency ratio of red drum fed the various diets. In the second feeding trial, the culture system significantly affected weight gain, feed efficiency ratio, and protein efficiency ratio although there were no effects of dietary treatments on fish performance or whole‐body protein, lipid, moisture, or ash. Denaturing gradient gel electrophoresis (DGGE) analysis of the gastrointestinal tract microbial community showed no effect of the dietary prebiotics as the microbial community appeared to be dominated by a single organism with very low diversity when compared with other livestock and fish species. DGGE of the microbial community in the biofilters of the independent aquariums showed a diverse microbial community that was not affected by the dietary prebiotics.     

Effects of Phase-Feeding Decreasing Levels of Dietary Protein on Growth and Diet Utilization of the Red Drum,Sciaenops ocellatus

Abstract

Two experiments were conducted to evaluate phase-feeding strategies on growth and nutrient retention of red drum, Sciaenops ocellatus. The first experiment was conducted over a 17-week period, utilizing sub-adult (initial mean weight, 70.8 g/fish) red drum. Treatments included three fixed-feeding regimes in which the fish were offered diets containing either 44, 40 or 36% protein throughout the growth trial (F44, F40, F36, respectively) and two phased-feeding regimes. The phased-feeding regimes included feeding the 44% protein diet the first 8 weeks after which the fish were switched to the 40 (P44/40) or 36% (P44/36) protein diets. At the conclusion of the experiment, final mean weights ranged from 592.8 to 543.3 g/fish (F44 and F36, respectively). Although statistical differences were not found in final weights (P = 0.1015) of the fish, percent weight gain was significantly reduced as the protein content of the diet was reduced. Similarly, feed efficiency (FE) values decreased as the protein content of the diet was reduced. Although protein conversion efficiency (PCE) values generally decreased with protein content of the diet, there were no statistical differences. The second experiment was initiated with 281 g mean weight fish and was conducted over a 14-week period. Three fixed-feeding regimes (FF44, F40 and F36) and three phased-feeding regimes were evaluated. After six weeks some of the fish (mean weight 448 g) were switched from 44% protein diet to diets containing 40, 36 and 32% protein (P44/40, P44/36, P44/28, respectively). Results of this feeding trial were similar to the first in that performance followed protein intake which in turn paralleled protein content of the diet. In both experiments, considerable differences in final weight were observed, but due to variation in the data statistical differences were minimal but the same ranking occurred. Overall, it would appear that fish up to about 450 g will perform best on a 44% protein diet but minimal reduction in growth occurs after this point if the protein content of the diet is reduced to as low as 36%.     

Evaluation of Elevated Dietary Aluminum and Iron on Red Drum,Sciaenops ocellatus

This study was conducted to determine if relatively high dietary levels of aluminum and iron might affect growth, mortality, and mineral content of red drum, Sciaenops ocellatus, because algae coproduct may have rather high aluminum and iron levels due to the algae harvesting and extracting processes. Experimental diets were prepared by supplementing different levels of aluminum (1000, 2000, 4000, 8000, and 3000 mg/kg diet) from aluminum sulfate, or iron (1000, 2000, 4000, and 8000 mg/kg diet) from ferric sulfate, or a combination of aluminum and iron (4000 mg Al/kg and 4000 mg Fe/kg) to a basal diet which was formulated from practical ingredients and analyzed to contain an average of 526 mg Fe/kg and 1940 mg Al/kg diet. The feeding trial was conducted in a recirculating system consisting of 38‐L aquaria maintained at 7 ppt salinity with synthetic seawater and sodium chloride. Each diet was fed to triplicate groups of 12 juvenile red drum initially averaging 4.5 g/fish for 7 wk. At the end of the feeding period, there were no significant differences in average weight gain, feed efficiency, or hepatosomatic index of fish fed the various diets. Significant differences were found in liver iron concentration (P = 0.045) but not iron concentration of whole body or muscle tissues. In regard to aluminum content of the liver, whole body, and muscle tissues, detectable levels were not recorded. Based on these results, it does not appear that extremely high levels of aluminum or iron adversely affect juvenile red drum, and thus elevated levels of these minerals should not limit the use of algal coproducts in diet formulations.     

Acute Toxicity of Nitrite to Red Drum Sciaenops ocellatus: Effect of Salinity1

Acute toxicity of nitrite to red drum fingerlings was investigated under static conditions in environments containing 36.0 to 0.6 g/L salinity. The 48 h median lethal concentrations ranged from 85.7 mg/L nitrite-N (36.0 g/L salinity) to 2.8 mg/L nitrite-N (0.6 g/L salinity). Plasma nitrite concentrations increased with exposure time during a 48 h study and exceeded environmental concentrations in fish exposed to 9.1 and 5.1 mg/L nitrite-N (1.4 g/L salinity). During 24 h of exposure, methemoglobin levels increased with increasing environmental nitrite conditions in fish exposed to 3, 6 and 9 mg/L nitrite-N for 24 h (1.4 g/L salinity). The chloride component of salinity was not as effective in preventing nitrite toxicity as in other species of fish, indicating a potential problem for the culture of red drum in low-salinity waters.     

Toxicity of Ammonia to Red Drum Sciaenops ocellatus Fingerlings with Information on Uptake and Depuration1

Median lethal concentrations of un-ionized ammonia-nitrogen to red drum (Sciuenops ocellarus) were 0.9 ± 0.14 mg/L (mean ± SE) after 24 h and 0.8 ± 0.16 mg/L after 48 h (salinity = 4.0%, temperature = 20 C, pH = 6.8–7.1). Ammonia moved quickly from the environment into the plasma with 90% of steady state concentrations being reached after 33 minutes. When ammonia-exposed fish were moved to ammonia-free water, 90% of the ammonia which had accumulated in the plasma was no longer present after 3.3 minutes. The sensitivity of red drum to environmental ammonia appears to be similar to that of most other fishes tested. Based on the median lethal concentrations for red drum observed in this study and the acute-chronic concentration ratios for other species of fish, it is suggested that red drum fingerlings be chronically exposed to no more than 0.05 mg/L un-ionized ammonia-nitrogen.     

Replacement of Fish Meal with Soybean Meal in the Production Diets of Juvenile Red Snapper, Lutjanus campechanus

The replacement of fish meal with soybean meal in fish diets has met with varying degrees of success. Quite often, poor responses to high soybean meal diets are either due to shifts in the nutrient profile or a reduced palatability of the diet when fish meal is removed. The present research was designed to evaluate the replacement of menhaden fish meal with solvent-extracted soybean meal in practical diets containing 10% poultry by-product meal and formulated to contain 40% protein, 8% lipid, and a total sulfur amino acid content of > 3.0% of the protein. The response of red snapper (mean initial weight 10.9 g) to diets containing graded levels of fish meal (30,20, 10, 0%) as well as the response to a low fish meal diet (10%) without poultry by-product meal were evaluated over a 6-wk growth period. Significant ( P ± 0.05) differences in final mean weight, percent weight gain, and feed conversion were observed. Final weights (percent gain) ranged from 30.9 g (185.5%) for fish offered diets with 30% fish meal to 12.6 g (16.3%) for fish offered diets with 0% fish meal. Corresponding feed conversion efficiencies ranged from 60.1% to 7.7%. No significant differences were observed for survival between treatment means. Although there was a clear reduction in performance as the fish meal was replaced with soybean meal, the use of 10% poultry by-product meal or 10% fish meal resulted in similar performance of the fish. This is a good indication that poultry by-product meal does not have palatability problems and could be used as a substitute. The present findings suggest that replacing fish meal with high levels of soybean meal appears to reduce the palatability of the diet. While the cost reducing benefit, with respect to the replacement of fish meal, has been shown with other species, before high levels of inclusion can be efficiently utilized further research is needed to address the palatability problems observed with red snapper.     

Effects of Dietary Nutrient Density on Water Quality and Growth of Red Drum Sciaenops ocellatus in Closed Systems

A 10-wk growth trial was conducted to determine the effects of dietary nutrient density (protein and energy) on the growth of red drum Sciaenops ocellatus and on water quality in closed recirculating systems. Four test diets, with increasing nutrient density, were formulated to contain 32%, 36%, 40%, and 44% protein and 3.4, 3.5, 3.6 and 3.8 kcal/kg energy, respectively. In addition to growth, total ammonia-nitrogen (TAN), nitrite-nitrogen, nitratenitrogen, biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), total suspended solids, net solids accumulated and total phosphorus were measured periodically throughout the study. Significant differences in weight gain and total biomass corresponded to increasing dietary nutrient density. Feed efficiency ratios and protein conversion efficiencies increased with increasing nutrient density of the diet indicating the production of fewer waste products per unit gain. Accumulated waste (net solids accumulated expressed as g/kg of fish) decreased with increasing dietary nutrient density. Additionally, there was a significant decrease in COD and suspended phosphorus with increasing dietary nutrient density. TAN, nitrate-N and BOD₅ showed no significant trends presumably due to the ability of the biological filter to process these nutrients. Based on the observed results, manipulation of dietary nutrient density can reduce metabolic wastes and at the same time improve fish growth in an aquaculture system.     

Replacement of Fish Meal by Plant Proteins in the Diet of Nile Tilapia: Digestibility and Growth Performance

Apparent digestibility coefficient (ADC) values for a number of ingredients of plant or animal origin were obtained in order to formulate diets based on such values and to evaluate growth performance of Nile tilapia Oreochromis niloticus fed four experimental diets in which fish meal was gradually replaced by a mixture of other ingredients.The digestibility of various diet components was measured by using an inert marker in the feed and by using the Guelph faeces collecting system. ADC values of the ingredients tested were generally high, especially for fish meal. It was found that extruded pea seed meal (92.6%), defatted soybean meal (94.4%), full-fat toasted soybean (90.0%) and micronized wheat (88.6%) were the best vegetable proteins tested. Lupin seed meal and faba bean meal had similar ADC values for protein and energy.Groups of tilapia, initial mean body weight (SD) 6.7 (0.1) g, were fed experimental diets with the same digestible protein (DP) and digestible energy (DE) containing graded levels of a mixture of vegetable ingredients as partial or total replacement of fish meal protein. A growth trial was conducted over 12 weeks as partial or total replacement of fish meal protein. A growth trial was conducted over 12 weeks at a water temperature of 25 °C. Significant differences were observed for weight gain among tilapia fed diets D0, D33, D66 and D100 (containing only animal protein, 33, 66, and 100% of plant protein, respectively). No significant differences were observed for voluntary intake among tilapia fed diets D0, D33 and D66. These values were significantly lower than those observed for tilapia fed plant protein based diet (D100) and suggest the possibility of partial replacement of fish meal by vegetable proteins without negative effects.     

Use of Plant Proteins in Catfish Feeds: Replacement of Soybean Meal with Cottonseed Meal and Replacement of Fish Meal with Soybean Meal and Cottonseed Meal

Plant protein sources were evaluated in 32% protein grow-out feeds for channel catfish (initial weight: 180 g/fish) stocked at high densities (24,700 fish/ha) in 0.04 ha earthen ponds. Each of the eight practical-type feeds was assigned for five replicate ponds. The fish were fed to satiation once daily for 170 d. Specifically, cottonseed meal and cottonseed meal plus supplemental lysine were evaluated as replacements for soybean meal. Soybean meal, a combination of soybean meal and cottonseed meal, or a combination of soybean meal and cottonseed meal plus supplemental lysine were evaluated as a substitute for animal protein sources. Based on weight pin, feed conversion ratio, body composition, percentage visceral fat, and dressed yield, the data indicated that cottonseed meal plus lysine can be used as a total substitute for soybean meal in catfish feeds. However, it is not recommended that more than 30% cottonseed meal be used in catfish feeds until additional data are available on the effects of gossypol on reproduction in catfish. Also, data indicated that plant proteins can be used as a total replacement for animal protein without detrimental effects. Reduced weight gain was observed in fish fed a feed that contained 68% of the established available lysine requirement. However, fish fed feeds estimated to contain only 76 or 82% of the available lysine requirement did not show reduced weight gain. This suggests that lysine may be more highly available from cottonseed meal than previously estimated, or that natural food organisms in the pond contributed nutrients including lysine, or that fish were able to consume enough of the marginally deficient feeds to meet their requirement for lysine. This study was conducted with large catfish fed a 32% protein feed to satiation once daily. If smaller fish, a lower protein fed, or a restricted feeding regimen had been used, the results may have been different.     

Effect of Total Water Hardness and Chloride on Survival, Growth, and Feed Conversion of Juvenile Red Drum Sciaenops ocellatus

Juvenile red drum Sciaenops ocellatus were tank-reared in two, separate 30-d trials to assess effects of total water hardness and chloride concentratlon on growth, survival, and feed conversion. Two levels of total hardness and chloride were used in 2 × 2 factorial designs to obtain total hardness and chloride levels in trial one of 100 and 200mg/L CaCO₃ and 125 and 250mg/L Cl⁻, and hardness and chloride levels of 100 and 400mg/L CaCO₃ and 150 and 500mg/L Cl⁻ in trial two. In trial one, average daily growth and feed conversion were significantly ( P ≤ 0.05) improved at 100mg/L hardness levels compared to 200mg/L at both chloride levels. Average daily growth was 0.11 ± 0.02g/d at 100mg/L hardness and 125mg/L Cl⁻ compared to 0.06 ± 0.01g/d at 200 mg/L hardness and 125mg/L chlorides. No significant ( P ≥ 0.05) difference in survival could be attributed to levels of total hardness or chloride. In trial two, 500 mg/L Cl⁻ treatments produced significantly ( P ≤ 0.01) better growth, survival and feed conversion than 150mg/L Cl⁻ at either level of total hardness (100 and 400mg/L). Survival at 150mg/L chloride and 100mg/L hardness was 48.8 ± 18.7%, while at 500mg/L chloride and 400mg/L hardness survival increased to 96.6 ± 2.1%. Growth also increased from 0.14 ± 0.03 to 0.27 ± 0.01g/d and feed conversion improved from 5.77 ± 1.56 to 1.87 ± 0.06 at the same levels. No interactions between levels of hardness or chlorides were shown to affect red drum growth, survival, or feed conversion in either trial.     

Demonstration that Feeds Containing <1% Fishmeal Can Support Grow‐out of Large Juvenile Red Drum,Sciaenops ocellatus,and Reduce Nutrient Waste

We conducted a 16‐wk feeding trial with large juvenile red drum, Sciaenops ocellatus. Four diets were randomly assigned to six replicate tanks per treatment. Three isonitrogenous (ca. 44.5% protein) and isolipidic (ca. 14.1% lipid) extruded diets were formulated to compare a fishmeal‐based diet with diets using alternative protein sources. Diet 1 contained 19.60% fishmeal and 21.42% poultry meals as primary protein sources. Two alternative diets were formulated reducing the fishmeal to 0.61% by substituting poultry meals (33.85%) and soybean protein concentrate (11.55% in Diet 2 and 11.70% in Diet 3). Diet 3 also included Allzyme Vegpro® and Allzyme® SSF at 0.04%. Diet 4, a natural diet consisting of chopped cigar minnows, squid, and shrimp, was used as a positive control to compare growth rates of formulated feeds to near maximum growth under these culture conditions. We found that reducing the amount of fishmeal to <1% by using alternative protein sources did not affect the growth rate, survival, or health of red drum but improved assimilation of phosphorus, reduced potential release of P to the environment, and significantly lowered the amount of feeder fish needed in feed. The control diet identified performance benchmarks for future feeds development work.     

The Effects of Enriching Live Foods With Highly Unsaturated Fatty Acids on the Growth and Fatty Acid Composition of Larval Red Drum Sciaenops ocellatus

Three experiments were carried out to test the effects of enrichment of live food (rotifers) with varying levels of n-3 highly unsaturated fatty acids (HUFA) on the growth rate and fatty acid composition of red drum larvae. Additionally, the fatty acid compositions of red drum eggs and day-1 larvae were compared. The enrichment techniques were successful in that the levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were elevated in the rotifers fed the enrichment diet. Red drum larvae fed the control rotifers produced the highest growth rate of the three experiments. Larvae fed rotifers with no HUFA supplement (NHUFA) had a significantly lower growth rate than the controls for that experiment. The fatty acid compositions of the eggs and day-1 larvae did not vary significantly and contained high levels of 16:0, 16:1 n-7 and DHA (22:6 n-3). Based on these data, the lack of DHA in the diet significantly reduced the growth rates of larval red drum. The 10-day-old red drum larvae had similar fatty acid profiles at the end of the experiments regardless of the diet they were fed, indicating that dietary inputs have little effect on the fatty acid composition of larvae during the first ten days of growth. Red drum larvae appear to have the ability, though limited, to bioconvert EPA to DHA since there was a significant increase in the levels of DHA from day 1 to day 10 in the NHUFA larvae. However, the efficiency of this bioconversion is not sufficient for optimal growth and supplemental DHA at least to the level found in the control rotifers (0.3–0.4mg/100mg tissue) is necessary to maximize growth. The exact role of EPA could not be determined from this study due to the inability to produce an EPA-free rotifer.     

Replacement of Dietary Fish Meal with Poultry By‐product Meal and Soybean Meal for Golden Pompano,Trachinotus ovatus,Reared in Net Pens

Two 8‐wk feeding trials were conducted to examine the effect of replacing dietary fish meal with poultry by‐product meal (PBM) and soybean meal (SBM) on growth, feed utilization, body composition, and wastes output of juvenile golden pompano, Trachinotus ovatus (initial body weight 16.7 g), reared in net pens. A control diet (C) was formulated to contain 35% fish meal. In Trial I, dietary fish meal level was reduced to 21, 14, 7, and 0% by replacing 40, 60, 80, and 100% of the fish meal in diet C with PBM. The weight gain (WG), nitrogen retention efficiency (NRE), and energy retention efficiency (ERE) decreased, while the feed conversion ratio (FCR) and total waste output of nitrogen (TNW) increased, with the fish meal level reducing from 35 to 21%. No significant differences were found in the hepatosomatic index, viscersomatic index, and body composition between fish fed diet C and test diets. In Trial II, a 2 × 2 layout was established, and 40 and 60% of the fish meal in diet C was replaced by either PBM or SBM. At the same fish meal replacement level, the WG and NRE were higher and the FCR and TNW were lower in fish fed the diets with fish meal replaced by PBM than in fish fed the diets with fish meal replaced by SBM. The results of this study indicate that more than 21% fish meal must be retained in diets for golden pompano when PBM or SBM is used alone as a fish meal substitute.     

Partial Replacement of Fish Meal with Poultry By‐product Meal in Diets for Snakehead,Channa striata (Bloch, 1793), Fingerlings

A 12‐wk feeding trial was carried out to examine the response of snakehead, Channa striata, fingerlings to diets containing poultry by‐product meal (PBM) protein as replacement to fish meal (FM) protein. Fish (mean initial weight 3.98 ± 0.01) were reared in 15 tanks and fed one of five isocaloric (18.5 kJ/g gross energy) diets, in triplicates. Each diet was formulated to contain 45% crude protein and 6.5% crude fat and utilizing protein from PBM to replace that of defatted FM in the following decreasing order; 40, 30, 20, 10, and 0%, respectively. Fish were fed assigned diets to apparent satiation twice daily during the trial, for 12 wk. Water quality parameters (temperature, pH, and dissolved oxygen) were monitored and ranged between 28.5–30.5 C, 6.1–6.6, and 4.61–6.34 mg/L, respectively. Fish survival and growth performance were not significantly (P < 0.05) different among all the treatments. Dietary PBM level did not significantly (P > 0.05) affect the hepatosomatic (HSI) and viserosomatic indices (VSI) in fish and the carcass protein and ash compositions. Muscle lipid was significantly the highest in the 30PBM compared to 0PBM, 10PBM and 20PBM groups, but similar to the 40PBM treatment. The result of this trial indicates that protein from PBM could be used to successfully replace minimum 40% of defatted FM protein in diets for snakehead fingerlings without negative effects on growth and feed utilization.