Dietary lysine requirement of juvenile Pseudobagrus ussuriensis

An 8‐week feeding trial was conducted to determine dietary lysine requirement of juvenile Pseudobagrus ussuriensis (initial body weight: 0.60 g). Six isonitrogenous (crude protein, 400 g/kg) and isolipidic (crude lipid, 50 g/kg) diets were formulated to contain graded levels of dietary lysine (12.8, 19.9, 26.5, 34.0, 40.8 and 44.1 g/kg dry diets, respectively). The results indicated that weight gain, specific growth rate, productive protein value and protein efficiency ratio increased, while feed conversion ratio decreased with increasing dietary lysine level up to 34.0 g/kg dry diet and then levelled off. Fish fed diet with 12.8 g/kg lysine had the lowest lysine content (58.6 g/kg dry matter) in muscle, while fish fed diet with 34.0 g/kg lysine had the highest value (61.6 g/kg dry matter; p < .05). Broken‐line analysis on the basis of weight gain showed that the optimal dietary lysine requirement for maximum growth of juvenile Pseudobagras ussuriensis is 33.5 g/kg dry diet (82.4 g/kg dietary protein). Quadratic regression analysis of protein efficiency ratio against dietary lysine levels indicated that the optimal dietary lysine requirement of juvenile Pseudobagras ussuriensis is 36.4 g/kg dry diet (89.5 g/kg dietary protein).     

Cholesterol requirement and phytosterols efficiency in semi‐purified diets of juvenile Pacific white shrimp Litopenaeus vannamei

Studies pertaining to cholesterol requirement are limited based on the levels evaluated and statistical analysis. Two trials were conducted to refine cholesterol requirement in Pacific white shrimp Litopenaeus vannamei feeds. The basal diet was supplemented with graded levels of cholesterol (ranging from 0.48 to 1.85 g/kg) in trial 1. Since the shrimp (initial weight: 0.24 g) growth response was very linear without reaching a plateau, it was not clear whether the requirement was met. Hence, a second trial was designed using eight diets designed with an increased range of cholesterol levels from 0.45 to 4.57 g/kg of diets. The shrimp (0.38 g initial weight) reached a final weight of (4.31–7.43 g) or per cent weight gain from 1,014%–1,874% (n = 4) after 6 weeks. Saturation kinetic model and broken‐line models with linear or quadratic ascending portions were used to evaluate dose–response relationships of feed efficiency (FE), thermal‐unit growth coefficient (TGC), whole‐body cholesterol (CHOL) and cholesterol deposition (CHOLD) against dietary cholesterol. The cholesterol requirement of shrimp was estimated at 1.9 (1.1–4.3) g/kg, 1.7 (1.1–3.4) g/kg, 2.5 (2.3–2.9) g/kg and 2.7 (2.4–3.1) g/kg of shrimp diet for FE, TGC, CHOL and CHOLD, respectively. Additionally, based on improved growth, the inclusion of phytosterol can serve as a partial replacement for cholesterol.     

The optimum dietary isoleucine requirement of juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

A six‐week growth trial was conducted to evaluate the optimum dietary isoleucine requirement of juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂). Seven isoenergetic (3,400 kcal/kg of dry matter), isoproteic (496 g/kg of dry matter) and isolipidic (70 g/kg of dry matter) diets were formulated to contain graded Ile levels (7.3, 11.3, 15.7, 19.6, 23.5, 26.8 and 30.8 g/kg, dry‐matter basis). Each experimental diet was fed to triplicate groups of 12 hybrid grouper juveniles (average initial body weight: 6.00 ± 0.01 g/fish). Experimental fish were randomly distributed into 21 glass tanks (L 60 × W 45 × H 50 cm) connected to mechanical and biological water filters as a recycling system. Fish were fed twice daily (08:00 and 16:00) to apparent satiation. After the sampling of the growth trial, the remaining fish in each group were fed their corresponding diets for 2 d and then exposed to 4 mg Cu²⁺ · L^?1 water for 24 hr. Results showed that growth performance and feed utilization were significantly affected by different dietary Ile levels (p < .05). Weight gain percentage (WG%), protein productive value (PPV), protein efficiency ratio (PER) and feed efficiency (FE) were increased as dietary Ile level increased, reaching a peak value at 19.6 g/kg dietary Ile, and thereafter, these four parameters declined as dietary Ile level continued to increase. Daily feed intake (DFI) showed an opposite tendency of variations as FE. The quadratic regression analysis of WG%, PPV, PER and FE against dietary Ile levels indicated that the optimum dietary Ile requirement for hybrid grouper was estimated to be 19.8, 20.8, 19.4 and 19.1 g/kg dry matter, respectively. Among all experimental treatments, fish fed 19.6 g/kg dietary Ile had the highest expression of growth and protein synthesis‐related genes, including growth hormone (GH) in pituitary, insulin‐like growth factor 1 (IGF‐1), growth hormone receptor 1 (GHR1), target of rapamycin (TOR) and S6‐kinase 1 (S6K1) in liver. Gut micromorphology was significantly influenced by dietary Ile levels. After the exposure to 4 mg Cu²⁺ · L^?1 water for 24 hr, fish fed 19.6 g/kg dietary Ile had the highest survival and the best immunologic manifestation among all experimental treatments. Generally, the optimum dietary Ile requirement for maximum growth of hybrid grouper was estimated to be 19.8 g/kg dry matter, corresponding to 39.9 g/kg dietary protein.     

Determination of dietary phosphorus requirement of stinging catfish Heteropneustes fossilis based on feed conversion,growth, vertebrae phosphorus,whole body phosphorus,haematology and antioxidant status

A 12‐week feeding trial was conducted to determine the dietary phosphorus requirement of Heteropneustes fossilis fingerlings (7.7 ± 0.04 g). Fish were fed casein–gelatine‐based purified diets in triplicate groups near satiation with seven different levels of dietary phosphorus (3.2, 5.2, 7.2, 9.2, 11.2, 13.2 and 15.2 g/kg dry diet). All diets were formulated to be isoproteic (400 g/kg) and isoenergetic (17.89 kJ/g). Highest absolute weight gain (68.38 g/fish), best feed conversion ratio (1.48), protein retention efficiency (30.74%), protein gain (12.44 g/fish), haemoglobin (11.19 g/dL), RBCs (3.12 x10⁶/mm³), haematocrit (33.44%) and serum phosphate (2.82 mg/L) were found at 9.2 g/kg phosphorus. Hepatic superoxide dismutase and catalase activity were also significantly influenced by the dietary phosphorus levels. Whole body and vertebrae phosphorus concentrations increased significantly as the amount of dietary phosphorus increased from 3.2 to 11.2 g/kg dry diet and then plateaued. More accurate information on dietary phosphorus requirement was obtained by subjecting the AWG, FCR, vertebrae phosphorus and whole body phosphorus concentrations data against various levels of dietary phosphorus to broken‐line analysis, which yielded the requirement in the range of 9.0–11.0 g/kg for optimum growth and mineralization of H. fossilis.     

Effects of dietary carbohydrate to lipid ratio on growth,feed utilization,body composition and digestive enzyme activities of golden pompano (Trachinotus ovatus)

An 8‐week feeding trial was conducted to investigate the effects of dietary carbohydrate to lipid ratio (CHO: L) on growth, feed utilization, body composition and digestive enzyme activities of golden pompano, Trachinotus ovatus. Five iso‐nitrogenous (450 g/kg protein) and iso‐energetic (19 MJ/kg gross energy) diets with varying CHO: L ratios of 0.68, 1.02, 1.62, 2.61 and 4.35, respectively, were fed to triplicate groups of 30 fish (average 13.8 ± 0.1 g). Results showed that dietary CHO: L ratios did not show any significant influence on survival of golden pompano (p > .05) but significantly affected its growth performance and feed utilization (p < .05). Fish fed diets with CHO: L ratios at 1.62 and 2.61 exhibited the highest final body weight, weight gain ratio, specific growth rate, feed efficiency ratio and protein efficiency ratio. Fish body lipid and liver glycogen contents were also significantly influenced by CHO: L ratio (p < .05). Hepatic amylase activity increased firstly and then decreased as the dietary CHO: L ratio increased, while lipases activity decreased with increasing dietary CHO:L level. The regression model analysis showed that the most suitable dietary CHO: L ratio (protein 450 g/kg) to reach the highest weight gain ratio is 2.38.     

Quantitative Dietary Taurine Requirement for California Yellowtail,Seriola lalandi

Although taurine has been identified as a required nutrient in several Seriola species, there are no available quantitative data on dietary taurine requirements for these commercially important species and recommendations are highly variable. Therefore, juvenile Seriola lalandi were fed one of eight practical diets supplemented with graded levels of taurine (0.11–1.08% of the dry diet, analyzed) to estimate their taurine requirement. Response in growth rate, feed efficiency, and nutrient deposition were evaluated using a broken‐quadratic model and 4‐ and 5‐parameter saturation kinetic models (4‐SKM and 5‐SKM) Blood serum composition was analyzed using linear models. Requirement estimates based on growth rates (thermal‐unit growth coefficient) and protein deposition were similar at 0.26% (95% confidence interval [CI]: 0.23–0.28) and 0.29% (95% CI: 0.25–0.34) dietary taurine, respectively. Feed and protein deposition efficiencies were optimized at 0.26–1.02% and 0.26–1.00% dietary taurine, respectively. Taurine deposition in the animal was maximized at higher dietary levels (0.64%). Levels of serum taurine increased in response to dietary levels and peaked at around 0.80% dietary taurine. Concomitantly, serum urea and total amino acid levels decreased with increasing dietary taurine levels, suggesting a reduced amino acid catabolism relative to the aforementioned improvement in protein deposition efficiency.     

Dietary histidine requirement of juvenile blunt snout bream (Megalobrama amblycephala)

An eight‐week feeding trial was conducted to determine the dietary histidine requirement of juvenile blunt snout bream. The results showed that final body weight, weight gain rate and specific growth rate significantly increased with increasing dietary histidine levels up to 9.9 g/kg (p < .05) and decreased gradually thereafter, while feed conversion ratio showed a converse trend. The survival rate, condition factor, viscerosomatic and hepatosomatic index were not significantly affected by the graded dietary histidine levels (p > .05). About 9.9 g/kg dietary histidine level significantly improved whole‐body protein and lowered moisture content. The contents of plasma total protein, cholesterol, urea and triglyceride levels were not significantly affected by dietary histidine levels. About 9.9 g/kg dietary histidine level significantly upregulated target of rapamycin and insulin‐like growth factor mRNA levels (p < .05), and 12.1 g/kg and 14.2 g/kg dietary histidine levels significantly upregulated eukaryotic translation initiation factor 4E‐binding protein 2 and ribosomal protein S6 kinase‐polypeptide 1 mRNA levels (p < .05). Based on second‐degree polynomial regression analysis of weight gain rate, and specific growth rate against dietary histidine levels, the dietary histidine requirement for juvenile blunt snout bream was estimated to be 11.2 g/kg of diet, corresponding to 36.1 g/kg of dietary protein.     

Effects of dietary tryptophan levels on growth performance,whole body composition and gene expression levels related to glycometabolism for juvenile blunt snout bream,Megalobrama amblycephala

To investigate the effects of dietary tryptophan on growth and glycometabolism in juvenile blunt snout bream, 450 fish (initial weight 23.33 ± 0.03 g) were fed six practical diets with graded levels of tryptophan (from 0.79 g/kg to 5.96 g/kg dry matter) for 8 weeks. Results showed that final weight, per cent weight gain (PWG), protein efficiency rate, feed intake and feed conversion ratio (FCR) were significantly improved by 2.80 g/kg diet. The maximum values of protein and ash were observed in 2.80 g/kg diet, while moisture was minimum. Lipid content of fish fed 3.95 g/kg diet was significantly higher than other diets. The highest plasma insulin‐like growth factor‐1 (IGF‐1) content was observed in 0.79 g/kg diet. In the liver, IGF‐1 mRNA levels were significantly downregulated by 2.80 g/kg dietary tryptophan, while glucokinase levels were by 3.95 g/kg, while glucose‐6‐phosphatase and phosphoenolpyruvate carboxykinase mRNA levels showed a converse trend compared with IGF‐1. Based on PWG and FCR, the optimal dietary tryptophan level was determined to be 1.99 g/kg (6.20 g/kg of dietary protein) and 1.96 g/kg (6.11 g/kg of dietary protein), respectively, using broken‐line regression analysis.     

Optimum dietary taurine level in casein-based diet for juvenile red sea bream Pagrus major

ABSTRACT:   This study was conducted to investigate the effect of dietary taurine and cholyltaurine (C-tau) on growth and body composition of juvenile red sea bream Pagrus major . Semi-purified casein-based diets supplemented with 0 (control diet), 0.1, 0.3, 0.5 and 0.7% taurine and 0.5% C-tau were fed to red sea bream (average body weight 4.7 g) for 6 weeks at 20°C. The growth and feed efficiency were the lowest in fish fed the control diet. Taurine supplementation improved the growth and feed efficiency of fish dose-dependently, and the taurine requirement was estimated as 0.52% in terms of optimizing growth and 0.48% in terms of optimizing feed efficiency. Taurine content in the whole body and liver increased with the dietary taurine level. Supplemental C-tau at the 0.5% level had limited effects on the growth and no effect on body taurine, biliary bile salt and liver fat contents. From these results it can be inferred that the optimal dietary taurine requirement of juvenile red sea bream is 0.5% on a dry weight basis, and that the supplementation of taurine in the diet not only improves the growth but also increases hepatic lipid levels of red sea bream juveniles.     

Optimal dietary methionine + cystine requirement for finishing lambari,Astyanax altiparanae (Garutti and Britski, 2000)

A 95‐day feeding trial was conducted to quantify the methionine + cystine requirement for finishing lambari, Astyanax altiparanae (6.10 ± 0.11 g). Six extruded isoproteic (310.14 g/kg crude protein) and isoenergetic (19.76 MJ/kg gross energy) diets were prepared to contain 6.71, 8.31, 11.31, 13.12, 15.59 and 19.74 g/kg dry diet of methionine + cystine. Quadruplicate groups of female lambari were randomly assigned to 24 aquaria (70 L each) and fed to apparent satiety six times daily. The methionine + cystine requirement was determined by quadratic regression analysis of growth performance, whole body composition, muscle development, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activity against dietary methionine + cystine concentrations, at 5% significance. Fish fed 6.71–11.31 g/kg dry diet of methionine + cystine showed increased weight gain, per cent weight gain, specific growth rate and protein efficiency ratio. There were no significant differences in whole body composition, muscle growth and activity of AST and ALT in fish fed the dietary treatments. In conclusion, according to the second‐order polynomial analysis of weight gain, the optimum dietary methionine + cystine requirements for finishing lambari were estimated to be 13.66 g/kg dry diet (4.40% dietary protein).     

Dietary available phosphorus requirement of crucian carp,Carassius auratus

This study was carried out to evaluate the dietary available phosphorus (AP) requirement for crucian carp (Carassius auratus). Triplicate groups were fed diets containing five graded levels of AP in 15 recirculating tanks. After a 9‐week feeding experiment, weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and whole‐body and vertebrae P contents were significantly increased as dietary AP increased from 1.1 to 7.6 g/kg (p < .05) and then levelled off. N and P retention was also significantly increased as dietary AP increased to 5.5 g/kg (p < .05). Condition factor, viscerosomatic index, hepatosomatic index, whole‐body moisture, muscle P content and plasma total cholesterol were not affected by dietary P levels (p > .05). Protein and ash contents of the whole body increased linearly as the dietary P level increased, but the lipid content, plasma alkaline phosphatase activities and triacylglycerol contents showed an inverse relationship. Based on WG, FE, whole‐body P content and vertebrae P content, the optimum requirement of dietary AP for crucian carp was estimated to be 8.3, 8.3, 8.0 and 7.8 g/Kg, respectively.     

Assessment of total dietary phosphorus requirement of juvenile largemouth bass,Micropterus salmoides,using soybean meal‐based diets: Effects on production performance,tissue mineralization,physiological parameters in plasma and intestine and expression of head‐kidney genes

A 9‐week feeding trial was conducted to evaluate effects of supplemental phosphorus (P) in soybean meal (SBM)‐based diets for largemouth bass (LMB). Six isonitrogenous (~400 g/kg crude protein) and isolipidic (~130 g/kg crude lipid) diets containing non‐phytic acid phosphorus (nPA‐P) ranging from 4.1 to 10.5 g/kg were fed twice daily to triplicate groups of 20 feed‐trained LMB (9.5g). Upon conclusion of the feeding trial, regression analyses showed that growth, feed efficiency and survival of LMB were unaffected by diet. Intraperitoneal fat index and whole‐body lipid content of LMB decreased linearly as dietary nPA‐P increased from 4.1 to ~7.0 g/kg, while protein retention efficiency increased quadratically over the dietary range of nPA‐P. Regressions on whole‐body P and skeletal mineral (P, Ca, Mg and Zn) concentrations of LMB revealed optimal levels when dietary nPA‐P was ~7.0 g/kg. Increasing trends of MDA concentration and ALT activity in plasma and GP_x activity in intestine in response to dietary nPA‐P were observed. Head‐kidney genes responded to dietary treatments and expression of GH, IGF‐1 and TGF‐β1 were highest and that of TNF‐α was lowest when dietary nPA‐P was 6.9 g/kg. Based on our results, practical diets for juvenile LMB should contain a minimum of 7.0 g/kg total nPA‐P.     

Dietary lysine requirement of juvenile gilthead seabream Sparus aurata L.*

The dietary lysine requirement of juvenile gilthead seabream was determined by the growth response of duplicate groups of fish (3.5 g initial weight) fed on six isonitrogenous (427 g kg^?1) and isolipidic (135 g kg^?1) diets containing graded levels of crystalline l ‐lysine HCl, with dietary lysine content ranging from 36.3 to 79.7 g kg^?1 of protein. The final indispensable amino acid profile of the diets except for lysine was formulated so as to resemble that of wild seabream whole body. Except for the reduced growth performance of fish groups fed the lysine‐deficient diets no other deficiency signs were apparent. Survival observed throughout the feeding period of 6 weeks was excellent. Weight gain (in %), specific growth rate, feed efficiency and daily protein deposition (DPD) were significantly improved in response to the increasing levels of dietary lysine up to 52.7 g kg^?1 of protein and remained nearly constant thereafter. Whole‐body protein content followed a similar pattern as growth parameters in relation to dietary lysine level. Non‐linear regression analysis of DPD against dietary lysine level using the four‐parameter saturation kinetic model indicated a lysine requirement of 50.4 g kg^?1 of protein for this species to support growth.     

Effect of dietary valine levels on the growth performance,feed utilization and immune function of juvenile golden pompano,Trachinotus ovatus

This experiment was designed to investigate the effects of dietary valine on the growth performance, feed utilization, digestive enzymes, serum antioxidant and immune indices of juvenile Trachinotus ovatus and determine its valine requirement. Six diets with different concentrations of L‐valine (15.0, 16.6, 18.6, 20.7, 23.5 and 25.4 g/kg dry diet, defined as diet Val‐1 to Val‐6.), were formulated to contain 430 g/kg crude protein with fish meal, soybean meal, peanut meal and precoated crystalline amino acids. Each diet was randomly assigned to triplicate treatments of 20 fish (the initial body weight was 5.34 ± 0.03 g) for 8 weeks. The results indicated that the final body weight and percent weight gain (PWG) increased with increasing valine concentration up to 18.6 g/kg (diet Val‐3), whereas the diets containing higher valine concentration reduced the growth performance significantly (p < .05). Moreover, the protein efficiency ratio, body protein deposition (BPD), muscle protein content, intestinal amylase and pepsin activities, serum T‐AOC, LZM activities, IgM, complement 3 and complement 4 concentration had a similar trend with PWG, and the trend of feed conversion ratio, serum AST, ALT activities, urea and MDA content was opposite. Meanwhile, the lipid contents of whole fish and muscle in diet Val‐6 were particularly lower than other diets (p < .05). The survival rate of diet Val‐1 was lowest in this study and was significantly lower than diet Val‐2 (p < .05). The results of polynomial regression based on PWG and BPD indicated that the optimal dietary valine requirement for Trachinotus ovatus reared in seawater‐floating net cages was 19.87–20.17 g/kg valine of dry diet, correspondingly 46.22–46.91 g/kg of dietary protein.     

Dietary Phosphorus Requirement of Fingerling Indian Major Carp,Labeo rohita (Hamilton)

Dietary phosphorus requirement of fingerling Labeo rohita (6.1 ± 0.13 cm; 1.88 ± 0.05 g) was quantified by feeding seven isonitrogenous (350 g/kg crude protein) and isocaloric (16.72 kJ/g gross energy) purified diets with different levels of phosphorus as 3.5 (basal diet), 4.6, 5.7, 6.5, 7.8, 8.9, and 10.1 g/kg. Triplicate groups of fish were fed at 0800, 1200, and 1600 h to apparent satiation for 8 wk. Live weight gain (LWG; 494.68%), specific growth rate (3.18%/d), feed conversion ratio (1.54), feed efficiency (0.65), protein gain (PG; 1.26 g/fish), protein efficiency ratio (1.86), and phosphorus utilization efficiency (98.78%) improved significantly (P < 0.05), with increasing dietary phosphorus level up to 6.5 g/kg. However, phosphorus contents of vertebrae and scale increased significantly up to 7.8 g/kg. Dietary phosphorus levels significantly affected serum phosphorus concentration and alkaline phosphatase activity. Broken‐line analysis based on LWG; PG; and whole‐body, vertebrae, and scale phosphorus against dietary phosphorus indicated the optimal phosphorus requirement of fingerling L. rohita at 6.56, 6.58, 6.56, 8.02, and 8.44 g/kg diet, respectively. In order to restrict superfluous phosphorus in the diet, inclusion of 6.56 g/kg phosphorus is recommended for optimal growth of fingerling L. rohita.     

Metabolic responses of juvenile GIFT strain of Nile tilapia (Oreochromis niloticus) to dietary L‐tryptophan supplementation

A 60‐day indoor feeding trial was conducted to evaluate the effects of dietary tryptophan supplementation on growth performances, whole‐body chemical composition, expression of muscle growth‐related genes (MyoD, myogenin and myostatin), and haematological and biochemical responses of juvenile genetically improved farmed tilapia (GIFT). Five corn–soy‐based isonitrogenous and isoenergetic diets were formulated to contain graded levels of dietary tryptophan (2.6, 3.2, 3.7, 4.2 and 4.8 g/kg of diet). Each diet was randomly assigned to triplicate groups of 30 fish (5.3 ± 0.1 g) per experimental unit, which were fed thrice a day (9:00, 13:00 and 17:00 hr). Maximum growth performances and feed utilization were observed in fish fed tryptophan at 3.7 g/kg of diet. There was no significant (p > .05) effect on whole‐body composition and amino acid profile by dietary tryptophan supplementation. However, significant (p < .05) differences were observed in plasma metabolites and the mRNA expression of MyoD, myogenin and myostatin. Serum cortisol level was found significantly lowest in fish fed tryptophan at 3.7 g/kg of diet. Second‐order polynomial regression analysis of weight gain and nitrogen gain against dietary tryptophan levels indicated that the optimum dietary tryptophan requirement for maximum growth and feed utilization of juvenile GIFT tilapia was 3.8 g/kg of diet.     

Effects of increasing protein level on the performance,enzyme activity and body composition of the Brazilian sardine,Sardinella brasiliensis (Steindachner, 1879)

A six‐week growth trial was performed to estimate the dietary protein requirements for maximum growth of juvenile Brazilian sardine (Sardinella brasiliensis) based on growth performance, feed utilization, body composition and digestive enzyme activity. Six isoenergetic diets were formulated to contain protein levels that increased from 250 to 500 g/kg. Each diet was randomly assigned to triplicate groups of 160 fish with mean initial body weight of 0.93 ± 0.13 g, which were fed four times a day to apparent satiation. Growth tended to increase with the increase in the dietary protein level up to 400 g/kg. Total protein intake was indirectly correlated to apparent protein utilization. No significant differences in whole‐body composition were found between fish fed the different protein levels. Acid protease and neutral lipase activities did not show significant differences among the different protein dietary groups. Alkaline protease activity increased in fish fed up to 350 g/kg of protein and amylase activity in fish fed up to 400 g/kg. Using polynomial regression, 367 g/kg was estimated to be the optimum dietary protein requirement for maximum weight gain of juvenile Brazilian sardines.     

Dietary protein/carbohydrate ratio in low‐lipid diets for Senegalese sole (Solea senegalensis,Kaup 1858) juveniles. Influence on growth performance,nutrient utilization and flesh quality

Four isoenergetic (21 kJ/g dry matter, DM) and isolipidic (65 g/kg DM) diets containing different crude protein/total carbohydrate (CHO) ratios: 60/26, 56/30, 52/34 and 48/38, were tested in 22 g Senegalese sole for 104 days. Apparent digestibility coefficients (ADC) were not affected by the treatments, and all groups presented extremely low starch ADC values (22.8%–36.5%). Replacement of dietary protein by CHO did not affect daily growth index (0.9–1.0), but significantly increased voluntary feed intake of fish. Regression analyses demonstrated that digestible protein content, rather than digestible energy, was the main dietary factor influencing such feeding activity (R² = .952). A significantly increased feed conversion ratio was observed in sole fed increasing CHO contents. The dietary protein/CHO ratio did not influence whole‐body composition. Sole fed the 48/38 diet showed the lowest efficiency in terms of N and energy utilization. PUFA were the most represented fatty acid fraction in fillet, regardless of the dietary protein/CHO ratio, mainly due to the high content of DHA. Senegalese sole increase feed intake under low dietary protein/CHO ratios to ensure an adequate N intake. Such compensatory mechanism seems to be triggered to satisfy a specific protein metabolic requirement for energy purposes as tissue accretion remained unchanged.     

Effect of dietary leucine on growth performance,hemolymph and hepatopancreas enzyme activities of swimming crab,Portunus trituberculatus

An 8‐week feeding trial was conducted to determine the dietary leucine requirement for juvenile swimming crabs reared in cement pools. Six isonitrogenous and isolipidic practical diets (430 g/kg crude protein and 70 g/kg crude lipid) were formulated to contain graded leucine levels which ranged from 16.7 to 26.7 g/kg (dry weight). Each diet was randomly assigned to triplicate groups of 60 juvenile swimming crabs (initial average weight 3.75 ± 0.12 g) that were stocked in rectangle plastic baskets. The results of the present study indicated that dietary leucine levels significantly influenced weight gain (WG) and specific growth ratio (SGR) (p < .05), crab fed the diet containing 22.7 g/kg leucine had significantly higher WG and SGR than those fed the other diets. Feed efficiency and protein efficiency ratio were not significantly affected by the dietary leucine levels (p > .05). Total protein, cholesterol, triglyceride and glucose in serum were significantly affected by the dietary leucine levels. Aspartate aminotransferase (AST) and alanine aminotransferase activities in hemolymph, AST and superoxide dismutase activities in hepatopancreas were significantly affected by dietary leucine levels; moreover, crab fed the 16.7 g/kg leucine diet had higher malondialdehyde in hemolymph and hepatopancreas than those fed the other diets. Crab fed the diet containing 24.9 g/kg leucine had higher phenoloxidase activity in hemolymph than those fed the other diets. Based on two‐slope broken‐line model of SGR against dietary leucine levels, the optimal dietary leucine requirement for growth was estimated to be 22.1 g/kg of the dry diet (corresponding to 51.4 g/kg of dietary protein on a dry weight basis). In summary, findings of this study indicated that dietary leucine could improve growth performance and antioxidant status.     

Beef tallow is suitable as a primary lipid source in juvenile Florida pompano feeds

It is assumed that Florida pompano have dietary EPA (20:5n‐3) and DHA (22:6n‐3) requirements. However, it is unclear whether both are equally important in meeting demand for n‐3 long‐chain polyunsaturated fatty acids (LC‐PUFAs) or whether the requirement(s) can be influenced by other fatty acids. Accordingly, we assessed production performance and tissue composition of juvenile Florida pompano (41.0 ± 0.5 g) fed diets containing fish oil; beef tallow; or beef tallow partially or fully supplemented with EPA, DHA or both. After 8 weeks, no signs of fatty acid deficiency were observed. Although fish performance did not vary significantly among the dietary treatments, fish fed the DHA‐supplemented feeds exhibited numerically superior growth than those fed the other diets. Fillets of fish fed the beef tallow‐based diets contained reduced levels of n‐3 fatty acids and LC‐PUFAs and elevated levels of MUFAs and n‐6 fatty acids, although dietary supplementation with EPA and/or DHA attenuated these effects somewhat. Our results suggest that beef tallow is suitable as a primary lipid source in Florida pompano feeds and n‐3 LC‐PUFA requirements may be met by as little as 4 g/kg EPA and 4 g/kg DHA. However, there may be value in supplementing tallow‐based diets with DHA to enhance tissue levels and possibly growth.