Natural dietary additive yellow loess as potential antibiotic replacer in Japanese eel,Anguilla japonica: Effects on growth,immune responses,serological characteristics and disease resistance against Edwardsiella tarda

The present experiment was conducted to evaluate the efficacy of an additive derived from the nature as an alternative of dietary antibiotic in Japanese eel, Anguilla japonica. Six experimental diets were formulated to contain no antibiotics or additive (yellow loess/YL) (control/CON), three graded levels of yellow loess at 5 (YL₅), 10 (YL₁₀) and 20 g/kg (YL₂₀), oxytetracycline at 5 (OTC) and amoxicillin at 10 g/kg amoxicillin (AMX) of diet. Weight gain (WG) and specific growth rate (SGR) from fish fed CON or YL₅ diets were significantly lower than those of fish fed YL₂₀ or OTC diets. Among non‐specific enzyme, lysozyme activity of fish fed YL₂₀, OTC or AMX was detected to be significantly higher than that from fish fed CON or YL₅ diets, whereas superoxide dismutase (SOD) activity of the fish fed CON was significantly lower than that for fish fed other experimental diets. Challenge test with bacteria, Edwardsiella tarda, showed improved disease resistance among the fish fed different levels of natural additive without any statistical difference from those fed antibiotics (OTC and/or AMX) supplemented diets. Therefore, these results demonstrated the potential of natural feed additive, yellow loess to replace oxytetracycline and/or amoxicillin in Japanese eel, A. japonica.     

Evaluation of dietary natural mineral materials as an antibiotic replacer on growth performance,non‐specific immune responses and disease resistance in rainbow trout,Oncorhynchus mykiss

We evaluated the effects of some dietary natural mineral materials as an antibiotic replacer based on growth performance, non‐specific immune responses and disease resistance in juvenile and subadult rainbow trout, Oncorhynchus mykiss. First experiment, juvenile rainbow trout averaging 2.7 ± 0.02 g (mean ± SD) were fed one of the six experimental diets; a basal commercial diet as a control (CON), CON with oxytetracycline (OTC), with yellow loess (YL), with Macsumsuk^® (MS), with Song‐Gang^® stone (SG) and with barley stone (BS) at 0.4% of each diet. At the end of 8‐week feeding trial, weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and protein efficiency ratio (PER) of fish fed YL diet were significantly higher than those of fish fed CON diet. Non‐specific immune responses such as superoxide dismutase (SOD), myeloperoxidase (MPO), lysozyme (LYS) activity and oxidative radical production of fish fed YL diet were higher than those of fish fed CON diet. At the end of 15 days of challenge test with Aeromonas salmonicida, average cumulative survival rate of fish fed YL diet was significantly higher than that of fish fed BS and CON diets. However, there were no significant differences among fish fed YL, SG and OTC diets. Second experiment, subadult rainbow trout averaging 261.5 ± 3.5 g (mean ± SD) were fed one of the four experimental diets for 22 weeks: CON, and CON with OTC, YL or SG at 0.4% of each diet. At the end of feeding, growth performance of fish fed SG and YL diets was significantly higher than that of fish fed CON diet. Non‐specific immune responses in terms of SOD, MPO, LYS and NBT of fish fed SG and YL diets were significantly higher than those of fish fed CON diet. However, there were no significant differences among the fish fed YL, SG and OTC diets. The results indicate that dietary yellow loess or Song‐gang^® stone at 0.4% of diet could replace oxytetracycline in juvenile and subadult rainbow trout.     

A comparison of the effect of dietary fungal phytase and dicalcium phosphate supplementation on growth performances,feed and phosphorus utilization of tra catfish juveniles (Pangasianodon hypophthalmus Sauvage, 1878)

Six isonitrogenous (320 g kg^?1) and isolipidic (60 g kg^?1) diets were formulated with graded levels (0, 5, 10 and 15 g kg^?1) of dicalcium phosphate (DCP) and fungal phytase (750 and 1500 FTU kg^?1 diet). Tra catfish (Pangasianodon hypophthalmus), 9.6 g, were fed the diets for 12 weeks. Each experimental diet was fed to eight replicates of fish to apparent satiation. At the end of the trial, fish fed the diets containing 15 g kg^?1 DCP, 750 and 1500 FTU kg^?1 phytase had higher growth performances, protein efficiency ratio and phosphorus retention than those fed the control diet, 5 g kg^?1 DCP and 10 g kg^?1 DCP diets (P < 0.05). Whole body ash and phosphorus concentration of fish fed the 10 g kg^?1 DCP and 15 g kg^?1 DCP diets were significantly higher than those of fish fed the control diet. Higher apparent digestibility coefficient of phosphorus was observed in fish fed the phytase supplemented diets. The present results indicate that supplementation of phytase at 750 FTU kg^?1 and 1500 FTU kg^?1 improves growth performances, feed and phosphorus utilization. The supplementation can completely replace dicalcium phosphate or other phosphorus sources in tra catfish feed and reduce the phosphorus discharge into environment.     

Effects of dietary ethoxyquin on growth,feed utilization and residue in the muscle of juvenile Japanese seabass,Lateolabrax japonicus

Ethoxyquin (EQ) is the most common synthetic antioxidant used for preventing rancidity in fish foodstuffs. However, literature related to the effects of dietary EQ on performance of fish was limited. The present study was conducted to investigate the effects of EQ on performance and EQ residue in muscle of juvenile Japanese seabass Lateolabrax japonicus and to estimate the optimal EQ concentration in the diet. Graded levels [0 (control), 50, 150, 450 and 1350 mg EQ kg^?1 diet] of EQ were added to the basal diet, resulting in five dietary treatments in the experiment. Each diet was fed to triplicate groups of seabass (initial body weight 8.01 ± 0.76 g) for 12 weeks in floating sea cages (1.5 × 1.5 × 2.0 m, 30 fish per cage). Survival ranged from 78.9 to 86.7%, and was irrespective of dietary EQ levels. The specific growth rate (SGR) of fish fed diets supplemented with ≤50 mg kg^?1 EQ had significantly (P < 0.05) higher SGR than fish fed diets supplemented with ≥150 mg kg^?1 EQ, the highest SGR was observed in fish fed diet with 50 mg kg^?1 EQ supplementation. Feed intake (FI) and feed efficiency (FE) were not significantly (P > 0.05) different among dietary treatments. Fish fed diets with 50 and 1350 mg kg^?1 EQ had a significant (P < 0.05) lower body lipid content than fish in the control group. Muscle EQ level significantly increased when dietary EQ increased. Optimal EQ concentration estimated by polynomial regression based on maximum growth of juvenile Japanese seabass was 13.78 mg kg^?1 diet.     

The effect of dietary methionine on growth,antioxidant capacity,innate immune response and disease resistance of juvenile yellow catfish (Pelteobagrus fulvidraco)

An 11‐week feeding trial was conducted to evaluate the effect of dietary methionine on the growth, antioxidant status, innate immune response and disease resistance to Aeromonas hydrophila of juvenile yellow catfish. Six isonitrogenous and isolipidic practical diets were formulated to contain different graded methionine levels ranging from 6.1 to 16.4 g kg^?1 of dry weight. The results indicated that growth performance and feed utilization were significantly influenced by the dietary methionine levels; fish fed the diet containing 6.1 g kg^?1 methionine level had lower specific growth rate, percentage weight gain (PWG), feed efficiency and protein efficiency ratio than those fed the other diets (P < 0.05). Fish fed the diet containing 16.4 g kg^?1 methionine level had lowest protein contents in whole body and muscle among all treatments. Triacylglycerols, cholesterol, aspartate aminotransferase, alanine aminotransferase and haemoglobin (Hb) in plasma or whole blood were significantly affected by dietary methionine levels. Fish fed the diet containing 6.1 g kg^?1 methionine level had higher superoxide dismutase, glutathione peroxidase activities and malondialdehyde values than those fed other diets. Fish fed diets containing 9.7 and 11.8 g kg^?1 methionine levels had higher lysozyme activity, total immune globulin, phagocytic activity and respiratory burst than those fed other diets. The lowest survival after A. hydrophila challenge was observed in fish fed a diet containing 6.1 g kg^?1 methionine. Quadratic regression analysis of PWG against dietary methionine levels indicated that the optimal dietary methionine requirement for the maximum growth of juvenile yellow catfish was estimated to be 11.5 g kg^?1 of the diet in the presence of 4.0 g kg^?1 cystine (corresponding to 23.5 g kg^?1 of dietary protein on a dry weight basis).     

The effect of dietary methionine concentrations on growth performance of juvenile Nile tilapia (Oreochromis niloticus) fed diets with two different digestible energy levels

A growth trial was conducted to examine the effect of dietary digestible energy (DE) content on methionine (Met) utilization and requirement in juvenile Nile tilapia (Oreochromis niloticus). Ten iso‐nitrogenous (288 g kg^?1 protein) practical diets, with two DE levels (10.9 MJ kg^?1; 12.4 MJ kg^?1) and five methionine supplementation levels (0, 1, 2, 4 and 6 g kg^?1), were hand‐fed twice daily to triplicate groups of Nile tilapia (initial body weight 8.95 ± 0.06 g) for 8 weeks. Weight gain (WG) and specific growth rate (SGR) increased significantly with increasing dietary methionine concentration at the same DE content (P < 0.001). At the same dietary methionine level, WG and SGR of fish fed high‐DE diets were significantly higher than that of fish fed low‐DE diets (P = 0.0001), although no interaction was found between dietary DE and methionine supplementation. Based on quadratic regression analysis between dietary methionine concentration and weight gain, optimal methionine requirement for maximum growth, expressed as g Met required kg^?1 diet (low‐ versus high‐DE diets), increased as diet DE concentration increased (7.34 versus 9.90 g kg^?1 diet, respectively; with cysteine 4.70 g kg^?1 diet). The results indicated that diet DE content affects methionine utilization and requirement in juvenile Nile tilapia, fish fed high‐DE diets required more methionine for maximum growth.     

Dietary methionine requirement of juvenile Pseudobagrus ussuriensis

An 8‐week feeding trial was conducted to determine the optimum dietary methionine (Met) requirement of juvenile Pseudobagrus ussuriensis with an initial average weight of 0.60 g reared in indoor flow‐through and aerated aquaria. Six isonitrogenous (430 g kg^?1 protein) and isolipidic (50 g kg^?1 lipid) test diets were formulated to contain graded levels of crystalline L‐methionine (4.9, 9.0, 11.8, 14.2, 18.1 and 20.8 g kg^?1 dry diets, respectively) at a constant dietary cystine level of 2.5 g kg^?1 dry diets. Equal amino acid nitrogen was maintained by replacing methionine with non‐essential amino acid mixture. Fish were randomly allotted to 18 aquaria (1.0 × 0.5 × 0.8 m) with 50 fish to each glass aquarium. Fish were fed twice daily (08:00 and 16:00) to apparent satiation. No significant difference was observed in survival of fish (84.67–91.33%). Specific growth rate (SGR), weight gain (WG), feed conversion ratio (FCR), protein productive value (PPV) and protein efficiency ratio (PER) were significantly affected by different dietary methionine levels (P < 0.05). WG, SGR PPV and PER increased, while FCR decreased with increasing dietary methionine level from 4.9 to 11.8 g kg^?1 (P < 0.05). However, with further increase from 11.8 to 20.8 g kg^?1, WG, SGR PPV and PER significantly decreased, FCR increased (P < 0.05). The whole body and muscle composition were affected by different dietary methionine levels (P < 0.05). Condition factor (CF) increased with increasing dietary methionine levels up to 11.8 g kg^?1 (P < 0.05) and after 11.8 g kg^?1 methionine diet, but not significant, declines were observed (P > 0.05). Hepatosomatic index (HSI) of the 4.9, 9.0, 11.8 and 14.2 g kg^?1 Met diets was significantly higher than that of fish fed diets 18.1 and 20.8 g kg^?1 Met diets (P < 0.05). Viscerosomatic index (VSI) of the 4.9, 9.0 and 11.8 g kg^?1 Met diets was significantly higher than that of fish fed diets 14.2, 18.1 and 20.8 g kg^?1 Met diets (P < 0.05). Quadratic regression analysis of WG and PER against dietary methionine levels indicated that the optimal dietary methionine requirement for maximum growth and feed utilization of juvenile Pseudobagrus ussuriensis was 14.3 and 14.1 g kg^?1 dry diet (35.3 and 34.8 g kg^?1 dietary protein), respectively, in the presence of 2.5 g kg^?1 dry diets cystine.     

Effects of dietary phenylalanine on growth,digestive and brush border enzyme activities and antioxidant capacity in the hepatopancreas and intestine of young grass carp (Ctenopharyngodon idella)

This study investigated the effects of phenylalanine on growth, digestive and absorptive ability and antioxidant status of young grass carp (Ctenopharyngodon idella). Young grass carp were fed diets containing 3.4 (basal diet), 6.1, 9.1, 11.5, 14.0 and 16.8 g phenylalanine kg^?1 diet with a fixed of 10.7 g tyrosine kg^?1 diet for 8 weeks. Percent weight gain (PWG), feed efficiency and feed intake of fish were the lowest in fish fed the basal diet (P < 0.05). Trypsin, lipase and amylase activities in the hepatopancreas, and antioxidants including glutathione contents and glutathione reducase activities in the hepatopancreas and intestine were all the highest in fish fed 11.5 g phenylalanine kg^?1 diet (P < 0.05). Trypsin, chymotrypsin and amylase activities in whole intestine, and creatine kinase, Na⁺, K⁺‐ATPase and alkaline phosphatase activities in the proximal intestine, and superoxide dismutase activities in the hepatopancreas and intestine were all the highest when phenylalanine at level of 9.1 g kg^?1 diet (P < 0.05). In conclusion, phenylalanine improved growth, digestive and absorptive ability, and antioxidant capacity of young grass carp. The phenylalanine requirement of young grass carp (256–629 g) based on PWG was 10.4 g kg^?1 diet or 3.44 g 100 g^?1 protein.     

The effects of dietary vitamin C on growth performance,serum enzymes activities and resistance to Vibrio alginolyticus challenge of yellow drum Nibea albiflora

A 9‐week feeding trial was conducted to determine the optimal dietary vitamin C requirement and its effects on serum enzymes activities and bacterial resistance in the juvenile yellow drum Nibea albiflora (initial weight 33.2 ± 0.10 g). Six practical diets were formulated containing vitamin C 2.1, 45.3, 89.6, 132.4, 178.6 and 547.1 mg kg^?1 diet supplied as l ‐ascorbyl‐2‐monophosphate. The fish fed 547.1 mg kg^?1 diet showed a significantly higher survival than that fed 2.1 mg kg^?1 diet. The weight gains and specific growth rate of the fish fed 2.1 mg kg^?1 diet were significantly lower than those of the fish fed 89.6–547.1 mg kg^?1 diets. The liver vitamin C concentration firstly increased with increasing dietary vitamin C supply from 2.1 to 178.6 mg kg^?1 diet and then stabilized. The serum superoxide dismutase activities of the fish fed 547.1 mg kg^?1 diet were significantly lower than those of the fish fed 2.1–89.6 mg kg^?1 diet. The fish fed 2.1 mg kg^?1 diet had a significantly higher alkaline phosphatase activity than those in the other groups except the 45.3 mg kg^?1 group. Fish that received diets containing vitamin C at 547.1 mg kg^?1 had significantly higher nitro blue tetrazolium and lysozyme activity, and fish that received diets containing vitamin C at 45.3–547.1 mg kg^?1 exhibited resistance against Vibrio alginolyticus infection. The dietary vitamin C requirement of the juvenile yellow drum was established based on broken‐line model of weight gain to be 142.2 mg l ‐ascorbyl‐2‐monophosphate kg^?1 diet.     

Dietary selenium requirement for on‐growing gibel carp (Carassius auratus gibelio var. CAS III)

A 12‐week growth trial was conducted in a flow‐through system to determine dietary selenium (Se) requirement for on‐growing gibel carp (initial body weight: 76.2 ± 0.05 g, mean ± SEM). Selenomethionine was supplemented to the basal diet to formulate seven semi‐purified diets containing 0.26, 0.58, 0.72, 1.14, 1.34, 1.73 and 2.09 mg Se kg^?1 diet. The results showed that plasma superoxide dismutase (SOD) activity significantly increased when fish were fed with 0.58 mg Se kg^?1 diet (P < 0.05) and then decreased at 2.09 mg Se kg^?1 diet (P < 0.05). Plasma T‐AOC activity was higher in fish fed with 0.72 mg Se kg^?1 diet (P < 0.05) and plasma malondialdehyde (MDA) was higher in fish fed with 0.26 mg Se kg^?1 diet (P < 0.05). When fish were fed 1.14 mg Se kg^?1 diet, hepatic GSH‐Px, T‐AOC, GSH and CAT activities were significantly higher than those fed with 0.26 mg Se kg^?1 diet (P < 0.05). Hepatic superoxide dismutase (SOD) activity was higher at 1.34 mg Se kg^?1 diet (P < 0.05). Fish liver Se concentrations were significantly higher when fed with 0.72 mg Se kg^?1 diet (P < 0.05) and then kept constant when Se ≥ 0.72 mg kg^?1 (P > 0.05). Whole‐body and muscle Se concentrations were higher when fed with 1.34 mg Se kg^?1 diet (P < 0.05) and kept a plateau when Se ≥ 1.34 mg kg^?1 (P > 0.05). In conclusion, based on broken‐line regression of hepatic Se concentrations, hepatic SOD activity and hepatic T‐AOC activity, dietary Se requirements for on‐growing gibel carp was 0.73 mg kg^?1, 1.12 mg kg^?1 and 1.19 mg kg^?1 diet respectively.     

Effects of dietary glucose and starch levels on the growth,haematological indices and hepatic hexokinase and glucokinase mRNA expression of juvenile mirror carp (Cyprinus carpio)

The effect of the different dietary carbohydrate types and levels on growth performance, haematological indices and hepatic hexokinase (HK) and glucokinase (GK) genes expression involved in control of glucose metabolism, was studied in juvenile mirror carp (Cyprinus carpio). Two carbohydrates (glucose and starch) diets with two levels (250 and 500 g kg^?1) were fed to triplicate groups of 35 fish for 60 days. The best weight gain rate and specific growth rate were observed in fish fed with 250 g kg^?1 glucose diet and 500 g kg^?1 starch diet (P < 0.05). Fish fed with 500 g kg^?1 glucose showed low feed utilization, with the highest food conversion ratio and the lowest protein efficiency ratio (P < 0.05). Hepatosomatic index was significantly higher in fish fed with glucose diets and the 500 g kg^?1 starch diet compared to 250 g kg^?1 starch. CHOL, HDL‐C and LDL‐C were significantly highest in fish fed with 500 g kg^?1 starch than all other diets (P < 0.05). Hepatic GK mRNA expression level and activity were positively related to glucose and starch levels (P < 0.05). Correlation analysis showed that hepatic glycogen concentration was increased by dietary carbohydrate content (P < 0.05). These results suggest that GK may play a major role in the postprandial glucose utilization in juvenile mirror carp.     

Effects of dietary mannan oligosaccharide on growth,survival, physiological,immunological and gut morphological conditions of black tiger prawn (Penaeus monodon Fabricius 1798)

The aim of this experiment was to determine the effects of dietary inclusion with mannan oligosaccharide (Bio‐Mos, Alltech, Nicholasville, KY, USA) on growth, survival, physiological and immunological conditions and gut morphology of the black tiger prawn (Penaeus monodon). Five diets supplemented with MOS at 0 g kg^?1 (control diet), 1, 2, 4 and 8 g kg^?1 were fed to the prawn juveniles (0.4 ± 0.06 g, total weight) for the duration of 63 days. Growth was the highest (P < 0.05) when the prawns were fed the 1 g kg^?1 MOS included diet. Wet tail muscle index (Tw/B), dry tail muscle index (Td/B) and tail muscle protein (Tmp) were higher (P < 0.05) in the prawns fed MOS included diets MOS compared with the prawns fed the control diet. Total haemocyte counts (THCs) of the prawns fed MOS included diets were higher (P < 0.05) than THCs of the prawns fed the control diet. Epithelium layer and epidermal cell density of the gut of the prawns fed 1 g kg^?1 and 2 g kg^?1 MOS diets were better than the prawns fed the control and other MOS diets. The results imply a positive effect of dietary supplementation of 1–2 g kg^?1 MOS in the culture of black tiger prawns.     

Growth,digestive and absorptive abilities and antioxidative capacity in the hepatopancreas and intestine of young grass carp (Ctenopharyngodon idellus Val.) fed graded levels of dietary manganese

To study the effects of manganese on growth performance, digestive and absorptive abilities, as well as the antioxidative capacity in the hepatopancreas and intestine, young grass carp (Ctenopharyngodon idellus Val.) (264 ± 1 g) were fed diets containing graded levels of manganese at 3.65 (control), 8.62, 13.48, 18.24, 22.97 and 27.86 mg kg^?1 diet for 8 weeks. Per cent weight gain (PWG) and feed intake were the poorest in fish fed the basal diet (P < 0.05). The activities of trypsin, lipase and alkaline phosphatase in the intestine were significantly enhanced with dietary manganese level at 13.48 mg kg^?1 diet (P < 0.05). Additionally, in the hepatopancreas and intestine, the protein carbonyl and malondialdehyde contents were the lowest in fish fed the diet with dietary manganese level at 13.48 mg kg^?1 diet (P < 0.05), while the anti‐hydroxyl radical capacities, manganese superoxide dismutase (MnSOD), glutathione peroxidase and glutathione‐S‐transferase activities were significantly enhanced with dietary manganese level at 13.48 mg kg^?1 diet (P < 0.05). Moreover, the catalase activity and glutathione content in the intestine were the highest in fish fed the diet with dietary manganese level at 18.24 mg kg^?1 diet (P < 0.05). These results indicated that optimum dietary manganese promoted growth, enhanced the digestive and absorptive abilities, and improved the antioxidative capacity in young grass carp. Based on the quadratic regression analysis for PWG and intestinal MnSOD activity, the manganese requirements for young grass carp with the initial body weight of 264 g were 16.91 and 18.21 mg kg^?1 diet respectively.     

Growth,feed utilization and body composition of juvenile Manchurian trout,Brachymystax lenok (Pallas) fed different dietary protein and lipid levels

A 10‐week feeding trial with four dietary protein levels (400, 450, 500 and 550 g kg^?1 crude protein) and two dietary lipid levels (80 and 160 g kg^?1 crude lipid) was conducted to assess optimum dietary protein and lipid levels for the growth, feed utilization and body composition of juvenile Manchurian trout (initial weight 11.80 ± 0.15 g). Fish were fed twice daily (08:30 and 16:30 h) to apparent satiation. The results showed that fish fed the diet with 500 g kg^?1 protein and 80 g kg^?1 lipid had the highest growth and feed efficiency. However, fish fed the diet with 450 g kg^?1 protein and 160 g kg^?1 lipid showed comparable growth to that of the fish fed diet 5 (500/80) and had higher protein efficiency ratio (PER), nitrogen retention (NR) and energy retention (ER) than other groups (P < 0.05). Growth, PER, NR and ER of fish fed the 160 g kg^?1 lipid diet was significantly higher (P < 0.05) than that of fish fed the 80 g kg^?1 lipid diet at 400 and 450 g kg^?1 protein diet, whereas these values showed an opposite trend at 500 and 550 g kg^?1 protein diet, and the lowest PER, NR and ER was found by fish fed the 400 g kg^?1 protein diet with 80 g kg^?1 lipid. Fish fed diets with 400 g kg^?1 protein had lower feed intake (FI) than that of other groups. Feed intake of fish fed 80 g kg^?1 lipid level was significantly lower than that of fish fed 160 g kg^?1 lipid diet at 400 g kg^?1 protein (P < 0.05), while no significant differences were observed at 450, 500 and 550 g kg^?1 protein‐based diets. Contrary to moisture content, lipid content of whole body and muscle increased significantly (P < 0.05) with increasing lipid levels. The results of this study indicated that the diet containing 450 g kg^?1 protein and 160 g kg^?1 lipid, with a P/E ratio of 23.68 g protein MJ^?1 would be suitable for better growth and feed utilization of juvenile Manchurian trout under the experimental conditions and design level used in this study.     

Influence of digestible protein levels on growth and feed utilization of juvenile meagre Argyrosomus regius

This study investigates the effect of digestible protein levels in experimental diets for meagre (Argyrosomus regius). A group of 253 fish, 52 g of mean weight, was distributed in 12 tanks, three replicates per treatment. Four isolipidic diets (170 g kg^?1 crude lipid) with different digestible protein levels (350 g kg^?1, 430 g kg^?1, 490 g kg^?1 and 530 g kg^?1) were formulated using commercial ingredients. The trial lasted 62 days. Meagre fed diets 430, 490 and 530 g kg^?1 obtained higher TGC (2.47, 2.57, 2.69 × 10^?3, respectively) than fish fed diet 350 g kg^?1 (2.14 × 10^?3). Group of fish fed diet with 350 g kg^?1 DP showed the lowest ammonia excretion level. According to the in vitro digestibility trial diets with 350 and 430 g kg^?1 DP released less amino acids in comparison with diet with 49% DP, although in vivo digestibility test did not show significant differences among diets 430, 490 and 530 g kg^?1 DP. Using the quadratic regression, optimal digestible protein intake according to the ECR for rearing juvenile meagre was recorded in 0.8 g DP/100 g fish and day.     

Use of probiotics to enhance growth,stimulate immunity and confer disease resistance to Aeromonas salmonicida in rainbow trout (Oncorhynchus mykiss)

An 8‐week feeding trial was conducted to evaluate the effects of dietary probiotics on growth, non‐specific immune responses and disease resistance in juvenile rainbow trout, Oncorhynchus mykiss. Fish averaging 5.8 ± 0.8 g (mean ± SD) were fed one of the five experimental diets; one control (Cont), and four other diets were prepared by supplementing single probiotics 1 (Bacillus subtilis; SP₁, 0.5%), single probiotics 2 (Bacillus licheniformis; SP₂, 0.5%), multi‐probiotics (B. subtilis + B. licheniformis; MP, 0.5%) and oxytetracycline (OTC) at 5 g OTC kg^?1 diet. After 8 weeks of the feeding trial, weight gain and specific growth rate of fish fed SP₁, SP₂ and OTC diets were significantly higher than those of fish fed Cont diet (P < 0.05). Superoxide dismutase (SOD) and lysozyme activities of fish fed SP₁, SP₂ and MP diets were significantly higher than those of fish fed Cont diet (P < 0.05). There were no significant differences in SOD and lysozyme activities among fish fed SP₁, SP₂, MP and OTC diets. In challenge test with Aeromonas salmonicida for 15 days, fish fed SP₁, SP₂ and MP diets showed significantly higher cumulative survival rate than those of fish fed Cont diet (P < 0.05). However, there were no significant differences in cumulative survival rate among fish fed SP₁, SP₂, MP and OTC diets. Although there was a little advantage in fish fed MP diet in terms of non‐specific immune responses, single or multi‐probiotics are equally effective statistically. These results indicate that single or multi‐probiotics had equal beneficial effects as an antibiotic replacer on growth performance, non‐specific immune responses and disease resistance in juvenile rainbow trout.     

Effects of dietary copper sources on growth,tissue copper accumulation and physiological responses of Japanese sea bass (Lateolabrax japonicus) (Cuvier, 1828) fed semipurified or practical diets

An 8‐week trial was conducted to compare the efficacy of a chelated copper (Cu) with the inorganic Cu (CuSO₄), in the diet of Japanese sea bass (Lateolabrax japonicus). Six diets were prepared based on two basal diets (semi‐purified or practical) at two Cu inclusion levels (0 and 4 mg kg^?1 from or chelated‐Cu), accordingly named as S0, SI4, SM4, P0, PI4 and PM4 respectively. Each diet was fed to quadruplicate groups of Japanese sea bass (initial weight: 65.0 ± 0.03 g) during the trial. Fish fed practical diets had higher feed intake, specific growth rate, protein efficiency rate (PER), liver Cu accumulation, liver Na⁺K⁺‐ATPase and plasma alkaline phosphatase, but lower hepatosomatic index than the groups fed semi‐purified diets (P < 0.05). Higher PER was exhibited by fish fed chelated‐Cu diets than that of fish fed CuSO₄ diets (P < 0.05). Although liver Cu accumulation was significantly higher in fish fed practical diets,, liver Cu content increased significantly with increasing dietary copper levels only in fish fed semipurified diets. Chelated‐Cu has higher efficiency than CuSO₄ when fed in practical diets. Poor growth performance of fish fed semipurified diets might induce underestimating the nutrient requirement of Japanese sea bass.     

Effects of dietary inorganic copper on growth performance and immune responses of juvenile beluga,Huso huso

A 12‐week feeding trial was conducted to evaluate the optimum dietary inorganic copper (copper sulphate) in juvenile beluga, Huso huso. Eight semi‐purified diets containing 1.1 (Cu_1.0), 3.5 (Cu_4.0), 7.1 (Cu_7.0), 9.7 (Cu₁₀), 13.1 (Cu₁₃), 25.1 (Cu₂₅), 49.9 (Cu₅₀) and 195 (Cu₁₉₅) mg Cu kg^?1 diet in the form of CuSO₄.5H₂O were fed to fish of initial body weight 8.49 ± 0.32 g and length 11.85 ± 0.66 cm (mean ± SD) in triplicate groups in a flow‐through system. Weight gain (WG) of fish fed Cu₁₀ and Cu₁₃ diets was significantly higher than that of fish fed Cu_1.0, Cu_4.0, Cu₂₅, Cu₅₀ and Cu₁₉₅ diets (P < 0.05). Whole‐body and muscle crude protein increased with dietary Cu up to the supplementation level of 13.1 mg kg^?1 diet and then decreased. Whole‐body lipid content was negatively correlated, while whole‐body ash was positively correlated with dietary copper concentration. Hepatic copper–zinc superoxide dismutase activity of fish fed Cu₁₀ and Cu₁₃ diets was significantly higher than that of fish fed Cu_1.0, Cu_4.0 and Cu₁₉₅ diets. Hepatic thiobarbituric acid‐reactive substances of fish fed Cu₁₃ diet was significantly lower than those of fish fed the other diets except for that of fish fed Cu₁₀ diet. Aspartate aminotransferase, alanine aminotransferase and copper accumulation in tissues increased with dietary copper. Broken‐line analysis of WG suggested that the optimum dietary Cu level was 10.3 mg Cu kg^?1 diet. Therefore, these results may indicate that the optimum dietary Cu levels could be greater than 10.3 mg Cu kg^?1 diet but less than 13.1 mg Cu kg^?1 diet in juvenile beluga, when copper sulphate is used as the dietary source of inorganic copper.     

Growth performance,oxidative stress indices and hepatic carbohydrate metabolic enzymes activities of juvenile Nile tilapia,Oreochromis niloticus L., in response to dietary starch to protein ratios

The effect of various dietary starch to proteins ratios (STA/P) on growth performance, oxidative status and liver enzyme activities involved in intermediary metabolism in juvenile Nile tilapia was evaluated. Four isocaloric‐practical diets (12.73 MJ kg^?1 digestible energy) with increasing STA/CP ratios were formulated. These were designated D₀ (344 g crude protein (CP) and 163.5 g starch (STA) kg^?1), D₁ (310 g CP and 243 g STA kg^?1), D₂ (258 g CP and 322 g STA kg^?1) and D₃ (214 g CP and 401 g STA kg^?1). Each diet was fed to triplicate groups of 60 fish (2.7 g) for 45 days. Compared with the control diet (D₀), significantly (P < 0.05) depressed growth and feed efficiency were observed only in the groups fed on diet D₃. The activities of hepatic enzymes involved in glycolysis and lipogenesis pathways were significantly enhanced in groups fed on diet D₃ compared with other diets. A significant (P < 0.05) increase in catalase activity was detected only in groups fed on diet D₃. Similarly, a significant (P < 0.05) enhancement in superoxyde dismutase, glutathione S‐transferases and glutathione peroxidise was observed in groups fed on diets D₂ and D₃ compared with other diets. Results demonstrate the ability of juvenile Nile tilapia to spare protein by dietary carbohydrate.     

Effect of dietary protein levels on reproductive development and distribution of amino acids in the body tissues of female Pangasianodon hypophthalmus (Sauvage, 1878) broodstock in captivity

The present study investigated the optimum dietary protein level for the maturation of adult Pangasianodon hypophthalmus broodstock. Four isocaloric diets containing 250, 300, 350 and 400 g kg^?1 of protein levels were prepared and presented to triplicate groups of fish. The fish (mean weight 770 ± 17.23 g and 712 ± 23.42 g for females and males respectively) were stocked in outdoor canvas tanks (4 m × 1 m × 1 m) at a stocking density of 20 fish/tank with a male: female ratio of 1:4. The fish were fed the test diets to satiation twice daily for 6 months. Gonadosomatic index (GSI) and fecundity were similar among fish fed dietary protein levels, higher than those fed on the 250 g kg^?1. Final weight, weight gain, oocyte weight were significantly highest (P < 0.05) for the fish fed 350 and 400 g kg^?1 dietary protein treatments. Only the 350 g kg^?1 dietary protein treatment resulted in significantly best ovipositor diameter and % ripe egg. Amino acid levels were highest in the muscle followed by the oocyte and liver of fish fed 350 and 400 g kg^?1 dietary protein levels. The present results suggested that a dietary protein level of 350 g kg^?1 can be recommended for the development of P. hypophthalmus broodstock.