Dietary Zinc Requirement of Oreochromis aureus and Effects of Dietary Calcium and Phytate on Zinc Bioavailability

Two experiments were conducted to determine the dietary zinc requirement of fingerling blue tilapia ( Oreochromis aureus ) and the effects of dietary calcium and phytate on zinc bioavailability. Purified egg white diets containing graded levels of supplemental zinc were fed to fingerling tilapia in triplicate aquaria for 80 days. No overt signs of zinc deficiency were observed; however, scale and bone zinc concentrations of fish fed the various diets were significantly ( P < 0.05) affected and increased linearly as dietary zinc increased until plateauing at 20 mg Zn/kg diet and greater. Based on these data, 20 mg Zn/kg of dry diet was determined to be the minimum dietary zinc requirement of blue tilapia. Purified egg white diets containing 20 mg Zn/kg were also supplemented with 0.5 or 2.0% calcium and 0 or 1.5% phytate in a factorial arrangement to determine the effects of these dietary factors on zinc bioavailability. At this level of supplemental zinc, 1.5% phytate significantly ( P < 0.05) reduced zinc bioavailability as reflected in scale and bone zinc concentrations; whereas, dietary calcium did not affect zinc bioavailability. Results from this study establish the dietary zinc requirement of blue tilapia and indicate that higher levels of supplemental zinc should be included in practical feeds to compensate for reduced zinc bioavailability caused by dietary phytate.     

Optimal Dietary Protein Concentration for Hybrid Tilapia Oreochromis niloticus × O. aureus Fed All-Plant Diets

There are several estimates of the optimal dietary crude protein concentration for juvenile tilapia fed high quality animal proteins or mixtures of animal and plant derived feedstuffs. In the present study, the optimal dietary crude protein concentration for hybrid tilapia Oreochromis niloticus × O. aureus reared in glass aquaria was determined using diets free of fish meal. Further, initial weight of fish was approximately 21 g, which is the beginning of the growout phase of many commercial operations. The diets contained primarily corn co-products and soybean meal as the sources of amino acids, and were formulated to provide 24, 26, 28, 30, 32 or 34% crude protein. The diets were fed to quadruplicate groups of tilapia for 10 wk. Increasing concentrations of dietary crude protein resulted in proportional improvements in weight gain and feed efficiency up to 30% dietary crude protein. Fish fed 24% dietary crude protein exhibited significantly reduced weight gain compared to fish fed 28–34% dietary crude protein. Protein efficiency ratio (PER) of tilapia was unaffected by dietary crude protein concentration. However, fish fed 28% crude protein exhibited numerically higher PER (2.58) than fish fed other levels of crude protein. Muscle crude protein levels were lower in fish fed diets containing 24–28% crude protein than in fish fed 30% and higher concentrations. Quadratic regression analyses of weight gain and feed efficiency data indicated the optimal dietary crude protein concentration to be 29.65% and 28.33%, respectively, while broken line analyses indicated 27.5 and 27.3%, respectively. Based on weight gain, feed efficiency, PER, and proximate composition data, the authors recommend 28% dietary crude protein as the minimum for hybrid tilapia fed all-plant diets and reared in tanks.     

Dietary Zinc Requirement of Oreochromis aureus and Effects of Dietary Calcium and Phytate on Zinc Bioavailability

Two experiments were conducted to determine the dietary zinc requirement of fingerling blue tilapia ( Oreochromis oureus ) and the effects of dietary calcium and phytate on zinc bioavailability. Purified egg white diets containing graded levels of supplemental zinc were fed to fingerling tilapia in triplicate aquaria for 80 days. No overt signs of zinc deficiency were observed; however, scale and bone zinc concentrations of fish fed the various diets were significantly (P < 0.05) affected and increased linearly as dietary zinc increased until plateauing at 20 mg Zn/kg diet and greater. Based on these data, 20 mg Zn/kg of dry diet was determined to be the minimum dietary zinc requirement of blue tilapia. Purified egg white diets containing 20 mg Zn/kg were also supplemented with 0.5 or 2.0% calcium and 0 or 1.5% phytate in a factorial arrangement to determine the effects of these dietary factors on zinc bioavailability. At this level of supplemental zinc, 1.5% phytate significantly ( P < 0.05) reduced zinc bioavailability as reflected in scale and bone zinc concentrations; whereas, dietary calcium did not affect zinc bioavailability. Results from this study establish the dietary zinc requirement of blue tilapia and indicate that higher levels of supplemental zinc should be included in practical feeds to compensate for reduced zinc bioavailability caused by dietary phytate.     

Efficacy of Trenbolone Acetate in Sex Inversion of the Blue Tilapia Oreochromis aureus

Abstract.— Trenbolone acetate (TBA) is a synthetic anabolic androgenic steroid approved in the United States as a growth promoter for beef cattle. Pooled populations of blue tilapia Oreochromis aureus with more than 98% males were produced by feeding diets containing TBA. This hormone effectively inversed the sex of blue tilapia when doses of 25–100 mg/kg of diet were fed for 28 d. Fish treated with 60 mg of 17-alpha-methyltestosterone (MT)/kg of feed resulted in 88.7% males. The percentage of male tilapia masculinized with TBA was significantly higher (P < 0.05) than with MT. Intersex fish were found in both control and hormone-treated groups, and were significantly more common (P < 0.05) in the MT-treated batches. Survival, feed conversion ratio, and average weight of O. aureus fry fed diets containing either TBA, MT or no hormone were not different (P > 0.05) at the end of the 28-d treatment period.     

吉富罗非鱼对饲料中维生素B1的需要量

采用维生素B1(VB1)含量为0.08(对照组)、0.57、1.13、2.09、4.11和8.09 mg/kg的6种纯化饲料,分别饲养初始体质量为(64.4±1.5)g的吉富罗非鱼12周,研究VB1对其生长性能、部分血清生化指标、肝脏VB1蓄积量及转酮醇酶基因表达量的影响,以确定其对饲料VB1的需要量.结果显示,随着饲料中VB1含量增加,吉富罗非鱼增重率先呈线性增加后趋于稳定,当饲料中VB1含量为1.13、2.09、4.11、8.09 mg/kg时增重率达最大.吉富罗非鱼肝脏VB1含量随着饲料VB1含量增加不断增大,当增加到2.09 mg/kg后趋于稳定.饲料中缺乏VB1显著提高血清丙酮酸含量(P＜0.05),但对全鱼水分、粗脂肪、粗蛋白、灰分无显著性影响(P＞0.05).饲料中添加VB1显著提高血清高密度脂蛋白胆固醇和肝脏转酮醇酶基因表达量(P＜0.05).饲料中VB1含量大于1.13 mg/kg各组的肝脏转酮醇酶活性显著高于VB1含量小于0.57 mg/kg组(P＜0.05).折线回归分析表明,吉富罗非鱼(64 ～325 g)获得最佳生长时对饲料VB1需要量为1.16 mg/kg;肝脏VB1蓄积量达到最大时,对VB1的需要量为2.06mg/kg.     

Effect of dietary protein, lipid and carbohydrate ratio on growth, feed efficiency and body composition of pikeperch Sander lucioperca fingerlings

Pikeperch Sander lucioperca fingerlings were fed nine practical diets containing three levels of protein (P=34%, 43% and 50%), lipid (L=10%, 16% and 22%) and carbohydrate (C=10%, 15% and 20%) for 10 weeks in a recirculating water system at 23°C. Dietary treatments were distributed by orthogonal design with dietary energy content ranging from 15.5 to 23.1 MJ kg^?1 diet. Significant differences (P<0.05) in weight gain (%) and feed efficiency (FE) were observed after feeding trial. Relatively low growth and FE were found in fish fed diets containing 34% dietary protein level compared with that of fish fed diets with 43–50% protein levels, suggesting that 34% dietary protein probably is below the protein requirements of pikeperch fingerlings. Fish fed diets containing P43L10C15, P43L22C20 and P50L16C20 had significantly (P<0.05) higher weight gain and FE than fish fed the diets containing other dietary P/L/C ratios. There was no significant difference in weight gain and FE between fish fed diets of P43L10C15, P43L22C20 and P50L16C20. These results may indicate that pikeperch require at least 43% of dietary protein for adequate growth and FE, and considering the fish growth and feed ingredient cost P43L10C15 diet is more cost‐effective formulation for pikeperch fingerling. However, protein efficiency was not significantly affected by dietary P/L/C ratio.     

Replacement of Fishmeal with Soybean Meal in Male Tilapia (Oreochromis niloticusxO. aureus) Fingerling Diets at a Suboptimal Protein Level

A feeding trial was conducted to study the feasibility of using soybean meal (SBM) to replace fish meal (FM) as a protein source for tilapia feeds containing 24% dietary protein. Replacement levels were 0%, 33%, 67% and 100%. At each replacement level, methionine was either supplemented up to the amount that the 100% FM protein diet contained or not supplemented. The experiment was carried out for eight weeks in a recirculated water system. Fish fed diets in which 100% of the FM was replaced with SBM either with or without methionine supplementation had significantly ( P < 0.05) lower weight gain, feed conversion ratio, protein efficiency ratio and protein digestibility than that of the groups fed the diets containing FM as the sole source of protein. Also, fish fed diets in which 67% and 33% of the FM was replaced with SBM did not differ significantly ( P > 0.05) from that of the control group. These data suggest that when dietary protein level was suboptimal (24%), up to 67% of the FM protein in tilapin feeds can be replaced by hexane-extracted SBM protein without any adverse effect on tilapia growth and feed conversion ratio.     

The influence of carboxymethylcellulose on growth, digestion, gastric emptying time and body composition of tilapia

Carboxymethylcellulose (CMC) was incorporated into each of two experimental diets at one of four levels (2, 6, 10 and 14%). Each of the eight diets was fed to male tilapia hybrids (Oreochromis niloticus × O. aureus) for 9 weeks. The experiment was conducted in a closed, filtered and recirculated rearing system. The fish were fed the appropriate diets at a rate of 3% of body weight per day, 2 times a day, 6 days a week. The water temperature was maintained at 26°C. Tilapia fed diets containing, 6, 10 and 14% CMC showed significantly poorer (P<0.05) feed conversion rates than fish fed diets containing 2% CMC. The dry matter digestion coefficients of the diets did not differ significantly but generally declined as CMC level increased. Gastric emptying times decreased as the level of inclusion of CMC in the diets increased. Crude protein content and ash content of fish were similar in all dietary groups. Fish fed diets containing 6, 10 and 14% CMC had significantly lower (P<0.05) lipid content than fish fed diets with 2% CMC.     

Effect of diets containing gossypol on blood parameters and spleen structure in tilapia, Oreochromis sp., reared in a recirculating system

The high cost of fish meal in tilapia diets warrants the potential use of cottonseed meal (CSM) as an alternative source of high quality protein. The effects of varying levels of CSM (0, 25, 50, 75 and 100%) as fish meal protein replacement on growth, blood parameters, spleen characteristics, free and bound gossypol in blood plasma, haemoglobin and haematocrit were determined in tilapia. Gossypol (C(30)H(30)O(8)) is a polyphenolic substance found in cottonseed that has known toxic effects in fish. Tilapias (n = 219, average weight = 11.3 +/- 3.9 g) were randomly distributed into 15, 32-L glass aquaria, representing five dietary treatments and three replicates per treatment. Each aquarium containing 13-16 fish was supplied with thermoregulated, recirculating water (27 +/- 1 degrees C) at 1 L min(-1) flow rate and photoperiod was constant (12 h L/12 h D). Fish fed 25-50% CSM protein replacement showed similar body weights and total lengths as the controls at the completion of the 16-week trial. Fish fed 75 and 100% CSM protein replacement showed a significant decline in body weight and total length. Fish fed 25-100% CSM protein replacement had significantly lower haematocrit and haemoglobin (ANOVA/LSD, P < 0.05) compared with levels in controls. The decline was most prominent in groups fed diets with 50-100% CSM protein replacement. Total and free gossypol concentrations of blood plasma significantly increased with increasing levels of CSM replacement (P < 0.05). No gossypol was found in blood plasma of fish from the control group. The occurrence of immature and abnormal erythrocytes was significantly greater among fish fed 75 and 100% CSM diets compared with fish fed 0-50% CSM diets. Spleen-somatic index (spleen weight/body weight x 100) did not differ between control fish and fish fed 50-100% CSM diets. Spleen abnormalities, such as large depositions of haemosiderin and melanin pigments and proliferation of melano-macrophage centres, lymphocytic depletion of the white pulp areas (hypocellularity), and presence of vacuoles and necrotic areas were observed among fish fed 50-100% CSM protein diets. In general, the pathological effects of gossypol in tilapia (low haemoglobin and haematocrit levels, abundance of immature red blood cells or polychromatocytes, abnormal spleen morphology) were similar to the effects of vitamin E and/or vitamin C deficiencies observed in other studies.     

Nutritive value of palm kernel meal pretreated with enzyme or fermented with Trichoderma koningii (Oudemans) as a dietary ingredient for red hybrid tilapia (Oreochromis sp.)

The aim of this study was to evaluate whether pretreatment of palm kernel meal (PKM) with a commercial feed enzyme (Allzyme Vegpro?) or solid‐state fermentation of PKM with the cellulolytic fungus Trichoderma koningii (Oudemans) could improve the nutritive value of raw PKM in the diets of red hybrid tilapia, Oreochromis sp. Seven isonitrogenous (30% crude protein) and isoenergetic (15.1 kJ g^?1) practical diets were formulated and fed close to apparent satiation to triplicate groups of 14 fish (mean initial weight 5.1 ± 0.1 g) for 10 weeks. The diets consisted of a control diet which did not contain any PKM, raw PKM diets, enzyme‐treated PKM (EPKM) or fermented PKM (FPKM) diets at 20% and 40% (dry weight basis) inclusion rates. The growth performance and feed utilization efficiency of tilapia fed 20% PKM or 20% EPKM were not significantly different (P > 0.05) from those of fish fed the control diet. Fish fed diets containing 40% EPKM showed significantly higher growth and feed utilization efficiency than fish fed 40% raw PKM owing to the improved dry matter, protein, lipid and energy digestibility of the enzyme‐treated PKM diets. The apparent protein and lipid digestibility of the 20% EPKM and 40% EPKM diets were not significantly different, and nor was the growth and feed utilization efficiency of fish fed these two diets. Hybrid tilapia fed FPKM‐based diets at all dietary inclusions tested showed the poorest growth, and this might indicate the presence of antinutrients in the resultant fungal biomass. In conclusion, it is anticipated that, with further optimization of enzyme pretreatment of PKM, higher levels of PKM could be included in the diets of hybrid tilapia, thereby reducing the impact of rising costs to feed tilapia.     

Total and available tryptophan requirement of Nile tilapia,Oreochromis niloticus,fingerlings

The dietary total and available requirement of tryptophan of Nile tilapia fingerlings was determined using linear regression analysis. Six hundred fish (3.4 ± 0.0 g) were fed diets containing 296.4 g/kg of crude protein and 14.1 MJ/kg of digestible energy. Five extruded diets containing 2.5, 3.0, 3.4, 3.8 and 4.2 g/kg of total tryptophan were evaluated. Fish were fed four times a day during 45 days. Final body weight, weight gain, feed intake, feed conversion ratio and net protein utilization of fish fed Trp 3.4 and Trp 3.8 diets were improved compared to fish fed Trp 2.5 and Trp 4.2 diets. No significant differences in survival rate, whole‐body moisture and ash were observed. Whole‐body amino acid profile of fish fed different diets did not differ statistically (p > .05). Fish fed Trp 3.0 and Trp 3.4 diets showed higher tryptophan retention compared to fish fed Trp 2.5 and Trp 4.2 diets. Excepting blood glucose, no effects of dietary tryptophan on haematological parameters were observed. The dietary total tryptophan requirement of Nile tilapia fingerlings based on weight gain was estimated to be 3.4 g/kg (11.0 g/kg of dietary crude protein) or 3.0 g/kg of available tryptophan (11.0 g/kg of dietary digestible protein).     

Effects of dietary protein on growth and body composition of Nile tilapia, Oreochromis niloticus L.

The effects of dietary protein (25%, 30%, 35%, 40% and 45%) on growth, survival, feed conversion ratio (FCR), protein efficiency ratio (PER) and body composition were investigated for four sizes (0.51, 45, 96 and 264 g) of Nile tilapia, Oreochromis niloticus L. In all four experiments, there was a progressive increase in growth with increasing dietary protein. In fry (0.51 g), significantly higher growth, survival and feed conversion were recorded for fish fed 40–45% rather than 25–35% protein diets. Similar trends for growth and FCR were also noted in 45 g fish. For larger (96 and 264 g) tilapia, significant differences in growth and FCR were found only between fish fed 25% and 30–45% protein diets. FCR and PER decreased with increasing weight of fish, and both were found to be negatively correlated with dietary protein level. Whole-body composition of the smallest fish was significantly influenced by dietary protein content. Percentage body protein of the fish fed 40–45% protein was higher than that of fish fed 25–35% protein diets, whereas lipid content decreased with increasing dietary protein level. In 45 g fish, both protein and lipid contents were higher in fish fed 25% and 30% protein diets than in those fed 35–45% protein diets. In larger tilapia, no significant influence of dietary protein level on body protein content was found. Percentage lipid decreased with increasing dietary protein level, and no definite trends in ash content were found. The results of these studies indicate that O. niloticus fry (0.51 g) should be reared on a practical diet containing 40% protein, and larger tilapia (96–264 g) on a diet containing 30% protein.     

Replacement of Herring Fish Meal by Soybean Flour in Practical Diets for Red Tilapia,Oreochromis niloticus × O. mossambicus,Grown in Concrete Tanks

ABSTRACT

A feeding experiment was conducted for 100 days to evaluate the suitability of soybean flour (SBF) as a partial or complete substitute for the protein supplied by herring fish meal (HFM) in diets for growth of red tilapia, Oreochromis niloticus ×O. mossambicus, fingerlings (mean weight of 0.65 g/fish) grown outdoors in concrete tanks. Five isonitrogenous and isocaloric diets containing 35% crude protein and 3.36 kcal of digestible energy (DE)/g of diet were formulated in which SBF replaced 0%, 25%, 50%, 75% and 100% of the protein supplied by HFM. Results demonstrated that SBF has good potential as a substitute protein source for up to 75% of the protein supplied by HFM (diet 4) in red tilapia diets with no significant (P>0.05) adverse effects on growth, feed efficiency, body composition, and apparent digestibility of protein compared to the HFM-based control diet. The highest growth performance and best economic efficiency of fish weight gain were obtained with fish fed diet contained 50% of the protein from HFM and the other 50% from SBF. Fish fed this diet had the highest weight gain (11.95 g/fish), percent increase in weight (1838%) and growth rate (0.120 g/day) among fish fed all the other test diets. The lowest feed efficiency and growth performances were shown in the fish fed diet containing SBF as a complete substitute for protein supplied by HFM. Fish fed this diet had the lowest weight gain (4.70 g/fish), percent increase in weight (723%) and growth rate (0.047 g/day) among fish fed all the other test diets. Survival of fish was not statistically different (P>0.05) among all treatments. The apparent protein digestibility values showed wide variation between diets, ranging from 70.13% to 82.12% and the values were remarkably high in fish fed SBF-based diets. At the conclusion of the study, substituting HFM-protein with SBF-protein in diets for red tilapia did not affect the final fish protein, ash and moisture contents, but lipid content was significantly higher (P <0.05) in fish fed diets in which SBF substituted for 50% or more of the protein supplied by HFM. Hematological characteristics of red tilapia were examined at the end of the study and the results showed that all the blood parameter values were within normal values for fish. Economic analysis of diets suggested the possibility of using SBF as an alternative source of protein in red tilapia diets.     

Replacement of Fish Meal with Salicornia Meal in Feeds for Nile Tilapia Oreochromis niloticus

Abstract.— We investigated the use of the halophyte salicornia Sulicornia bigelovii as a replacement for fish meal in feeds containing 35% crude protein for Nile tilapia Oreochromis niloticus . Five isocaloric, isonitrogenous diets were formulated with salicornia meal to replace 0%. 20%. 40%. 60%. and 80% of the fish meal in the feed. Another diet was formulated entirely from salicornia meal. Diets were fed to three replicate groups of tilapia fingerlings (mean initial weight = 0.5 g/fish) for 6 wk in 40-L aquaria supplied with 22 C well water. Tilapia growth did not differ ( P < 0.05) for fish fed diets in which 0%. 20%. or 40% of the fish meal in the diet was replaced with salicornia meal. Weight gain was reduced when fish were fed diets with higher levels of salicornia meal, and growth was slowest for fish fed diets formulated entirely from salicornia meal. Body fat was reduced and body moisture content was increased ( P < 0.05) for fish fed diets in which more than 80% of the fish meal was replaced with salicornia meal. We conclude that salicornia meal can replace up to 40% of the fish meal in O. niloticus feeds without affecting growth or body composition.     

Optimum Dietary Level of L-ascorbic Acid for Japanese Eel, Anguilla japonica

A feeding experiment was conducted to determine the optimum dietary level of ascorbic acid (AsA) for Japanese eel juveniles using L-ascorbic acid Ca based on growth, AsA content in tissues, hematology, and bactericidal activity of serum with Escherichia coli . Test diets with six levels of AsA (3, 10, 27,126, 645, and 3,135-mg/kg diet) as Ca ascorbate were fed to juvenile Japanese eels (11.0 ± 0.2 g) once a day for 8 wk. High survival rates (> 80%) were observed among all dietary treatment groups. The specific growth rates of the fish fed diets containing 3 and 10-mg AsA/kg were significantly (P < 0.05) lower than those of other groups. Liver and brain AsA contents of the fish fed diets containing 3, 10, and 27-mg AsA/kg were significantly (P < 0.05) lower than those of the fish fed diets containing 645 and 3,135-mg AsA/kg. Hemoglobin content tended to be higher in the fish fed diets containing 645 and 3,135-mg AsA/kg than those of the fish fed other diets. Hematocrit value and total serum protein content of the fish fed diets containing 645 and 3135 mg AsA/kg were significantly (P < 0.05) higher than those of the other groups. The fish fed diets containing more than 27-mg AsAlkg showed a higher bactericidal activity of serum than the fish fed the diets containing 3-mg and 10-mg AsA/kg. The optimum dietary level of AsA for the Japanese eel juveniles growth was estimated to be more than 27-mg AsA/kg. Furthermore, the inclusion of 645-mg AsA/kg or more also increased the hematocrit, hemoglobin, total serum protein value, and liver and brain vitamin C concentrations.     

Use of duckweed, Spirodela polyrrhiza L. Schleiden, as a protein feedstuff in practical diets for tilapia, Oreochromis niloticus L.

The use of solar-dried duckweed, Spirodela polyrrhiza L. Schleiden, as a dietary protein component for tilapia, Oreochromis niloticus L., reared in glass tanks was evaluated. Six isonitrogenous diets (30% crude protein) were fed to all-male tilapia fingerlings for 56 days. The fish meal protein in the diets was substituted at a rate of 5%, 10%, 20%, 30% and 100% with duckweed. A diet without the duckweed served as a control. Growth performance and nutrient utilization of fish were based on daily weight gain, specific growth rate, feed conversion ratio, protein efficiency ratio and protein productive value. There were no significant differences (P > 0.05) in growth performance and nutrient utilization of fish fed on diets containing up to 20% duckweed inclusion and the control. However, increases in dietary duckweed inclusion resulted in progressively reduced growth performance and nutrient utilization of fish. Diet without fish meal (100% duckweed) gave the poorest result. The most cost-effective diet in terms of cost per unit gain in weight of fish was obtained with 30% duckweed dietary inclusion. The result showed that solar-dried up to 30% duckweed dietary inclusion as a replacement for fishmeal in practical diets supported fish growth and was cost-effective.     

Contamination of palm kernel meal with Aspergillus flavus affects its nutritive value in pelleted feed for tilapia, Oreochromis mossambicus

An assessment of the nutritive value of palm kernel meal (PKM) and aflatoxin‐contaminated PKM (obtained by fermenting PKM with Aspergillus flavus) as a dietary ingredient in pelleted feed for tilapia, Oreochromis mossambicus Peters, was carried out in a 12‐week feeding trial. Seven isonitrogenous (40% crude protein) and isoenergetic (15.1 kJ g^?1) practical diets were formulated and fed close to apparent satiation to triplicate groups of 12 fish (mean initial weight 8.4 ± 0.1 g). The control diet contained 30% fish meal and 10% soybean meal (SBM) proteins. Four other experimental diets containing 20% and 50% of the SBM protein replaced by either PKM or fermented PKM, respectively, were formulated. Two additional diets containing either PKM or fermented PKM supplemented with a commercial aflatoxin adsorber (0.5% Sorbatox^TM) were also formulated. Measured aflatoxin B₁ levels in the fermented PKM‐based diets ranged from 75 to 100 µg kg^?1 diet. The growth performance and feed utilization efficiency of tilapia fed fermented PKM‐based diets were significantly lower than in fish fed the control diet at all inclusion levels (P < 0.05). Despite a small reduction, weight gains of tilapia fed PKM‐based diets were not significantly different compared with fish fed the control diet. The addition of 0.5% Sorbatox did not produce any beneficial or negative effects to the growth of tilapia. Under the dietary conditions of the present experiment, it was concluded that PKM can substitute up to 50% SBM in practical diets for O. mossambicus without much adverse effect to fish growth. However, when PKM was contaminated with A. flavus, its' incorporation into tilapia diets resulted in growth depression as a result of decreased diet digestibility and also possibly because of the presence of anti‐nutrients found in the contaminated PKM.     

Growth Performance,Biochemical Responses,and Skeletal Muscle Development of Juvenile Nile Tilapia,Oreochromis niloticus,Fed with Increasing Levels of Arginine

Tilapia, Oreochromis niloticus, is among the fish species with high potential for aquaculture in intensive farming, and Brazil is among the largest producers worldwide. Some of the amino acid requirements in practical diets for tilapia are still unknown. Thus, this study determined the dietary arginine requirements for Nile tilapia juveniles based on growth performance, hematological and biochemical responses, and muscle growth. Three hundred Nile tilapia juveniles (2.95 ± 0.79 g) were distributed into 20–500 L fiberglass aquaria and fed five extruded isoproteic (28% crude protein) and isoenergetic (3160 kcal/kg) diets formulated to contain 0.95, 1.10, 1.25, 1.40, and 1.55% arginine. Based on the quadratic regression analysis, the best results in weight gain, feed conversion, protein efficiency ratio, and protein retention were estimated in fish fed diets containing 1.36, 1.34, 1.36, and 1.37% arginine, respectively. The best amino acid body retention values were estimated in fish fed diets containing 1.31–1.37% arginine. Muscle growth occurred mainly by hyperplasia in fish fed 0.95% arginine, whereas reduction in the hyperplasia time and signs of hypertrophy occurred in fish fed 1.10–1.55% arginine diets. It was concluded that a diet with 1.36% of arginine (with 1.53% lysine in diet) meets the requirements of Nile tilapia juveniles.     

Influence of Dietary Levels of Magnesium on Growth, Tissue Mineral Content, and Resistance of Channel Catfish Ictalurus punctatus Challenged with Edwardsiella ictaluri

Juvenile channel catfish were fed purified diets supplemented with magnesium (Mg) from Mg sulfate at levels of 0, 200, 400, 600, 800, and 1,000 mg/kg and 0, 200, 400, 600, and 800 mg/kg in two separate feeding studies. In study I, the effect of dietary levels of Mg on growth response, vertebral mineral content, and macrophage chemotaxis were evaluated. Study II had similar objectives except that whole body mineral content was measured, and resistance of channel catfish to Edwardsiella ictaluri challenge was also determined. Fish with an average weight of 10.89 g were stocked at a rate of 50 fish/110‐L aquarium (study I). In study II, fish with an average weight of 4.14 g were stocked at rates of 40 fish/110‐L aquarium. Prior to stocking, each batch of fish was acclimated to laboratory conditions and fed the basal diet for 2 wk. The concentration of Mg in rearing water was 1.8 mg/L. Each diet was fed to fish in quadruplicate and triplicate aquaria to apparent satiation for 10 wk for studies I and II, respectively. Fish fed the basal diet started to die as early as 3 d after the study began (17 d of feeding the diet without Mg supplementation). In both studies, weight gain, survival, and feed efficiency were lowest for fish fed the basal diet but increased with increasing dietary levels of Mg. However, the differences between the values of each of these parameters for fish fed diets containing supplemental Mg were not always significant. Magnesium‐deficiency signs observed were anorexia, sluggishness, convulsions, deformed snout, vertebral curvature, muscle flaccidity, and high mortality. Vertebral and whole body ash concentrations were high, but Mg content was low for fish fed the basal and the 200‐mg Mg diets. Bone Ca content did not differ among fish fed different diets (study I), but whole body Ca tended to increase for fish fed the basal diet, suggesting the possibility of calcification of soft tissues. Macrophage chemotaxis in the presence of exoantigen was highest for fish fed diets supplemented with Mg at 400 and 200 mgkg for studies I and II, respectively. When expressed in terms of chemotaxis index, however, maximum or near maximum value was observed at a dietary Mg level of 400 mg/kg. Thus, a dietary level of Mg of 400 mg/kg from Mg sulfate was required for optimum growth and survival, maintaining high tissue levels of Mg, prevention of muscle flaccidity and skeletal deformity, and stimulating macrophage chemotaxis. Dietary levels of Mg had no effect on the resistance of juvenile channel catfish to Edwarsiella. ictaluri challenge.     

Reevaluation of the Dietary Protein Requirement of Japanese Flounder Paralichthys olivaceus

An experiment was conducted to determine the dietary protein requirement by different analysis methods and to study the effects of dietary protein levels on growth performance and body composition in Japanese flounder Paralichthys olivaceus fed white fish meal and casein-based diets for 8 wk. After a 1-wk conditioning period, one of six isocaloric diets containing 30, 36, 42, 48, 54, and 60% crude protein (CP) was fed to fish at approximately 4–5% of wet body weight on a dry matter basis to triplicate groups of 15 fish averaging 13.3 ± 0.06 g (mean ± SD). After 8 wk of the feeding trial, weight gain (WG) and feed efficiency (FE) from fish fed 48% CP diet were similar to those from fish fed 42% and 54% CP diets, and were significantly higher than those from fish fed 30, 36 and 60% CP diets ( P < 0.05). Fish fed 48 and 54% CP diets had a significant higher specific growth rate (SGR) than did fish fed 30 and 36% CP diets ( P 0.05). Protein efficiency ratio (PER) was inversely related to the dietary protein level. No significant differences existed in hematocrit (PCV) and survival rate among the dietary treatments. Broken-line model analysis indicated that the optimum dietary protein level could be 44.0 ± 3.0% for maximum WG in Japanese flounder. Polynomial regression analysis of the dose-response showed that maximum WG occurred at 50.2% ( R² = 0.94) based on WG, and the second-order polynomial regression analysis with 95% confidence limits revealed that the range of minimum protein requirement was between 38.9% and 40.3% based on WG. Therefore, these findings suggest that the optimum dietary protein requirement for maximum growth of Japanese flounder is greater than 40%, but less than 44% CP in the fish meal and casein-based diets containing 17.0 kJ/g of energy.