Requirements of vitamin C (L-ascorbyl-2-monophosphate-Mg and L-ascorbyl-2-monophosphate-Na) and its effects on immune responses of grouper, Epinephelus malabaricus

An 8‐week feeding trial was conducted to evaluate two vitamin C derivatives, L‐ascorbyl‐2‐monophosphate‐Mg (C2MP‐Mg) and L‐ascorbyl‐2‐monophosphate‐Na (C2MP‐Na), to satisfy the vitamin C requirement and to test their effects on the immune responses of juvenile grouper, Epinephelus malabaricus. C2MP‐Mg and C2MP‐Na were each supplemented at 20, 50, 80, 150, 250, and 400 mg kg^?1 diet in the basal diet providing of 7, 18, 31, 51, 93, 145 mg ascorbic acid (AA) equivalent of C2MP‐Mg kg^?1 diet and 4, 10, 17, 31, 47, 77 mg ascorbic acid (AA) equivalent of C2MP‐Na kg^?1 diet, respectively. Basal diet without AA supplementation was included as control. Each diet was fed to triplicate groups of grouper (mean initial weight 3.20 ± 0.05 g). Fish fed diets supplemented with either C2MP‐Mg or C2MP‐Na had significantly (P < 0.05) greater weight gain (WG), feed efficiency and survival than those fed the unsupplemented control diet. Liver ascorbate concentrations in fish generally increased as dietary C2MP‐Mg or C2MP‐Na supplementation level increased. Haemolytic complement activity was higher in fish fed diets supplemented with 92 mg AA equivalent of C2MP‐Mg kg^?1 or 10–17 mg AA equivalent of C2MP‐Na kg^?1 than fish fed the unsupplemented control diet. Lysozyme activity was higher in fish fed ≥51 mg AA equivalent of C2MP‐Mg kg^?1 or ≥47 mg AA equivalent of C2MP‐Na kg^?1 than fish fed the unsupplemented control diet. Analysis by broken‐line regression of WG indicated that the adequate dietary vitamin C concentration from each vitamin C derivative in growing grouper is 17.9 mg AA equivalent of 2MP‐Mg kg^?1 and 8.3 mg AA equivalent of C2MP‐Na kg^?1, and it also indicated that C2MP‐Mg is about 46% as effective as C2MP‐Na in meeting the vitamin C requirement of grouper.     

Requirements of vitamin C (l-ascorbyl-2-sulphate and l-ascorbyl-2-polyphosphate) and its effects on non-specific immune responses of grouper, Epinephelus malabaricus

An 8‐week feeding trial was conducted to determine two vitamin C derivatives, l ‐ascorbyl‐2‐sulphate (C2S) and l ‐ascorbyl‐2‐polyphosphate (C2PP), to satisfy vitamin C requirement and to test their effects on the non‐specific humoral immune responses of juvenile grouper, Epinephelus malabaricus. C2S and C2PP were each supplemented at 20, 50, 80, 150, 250 and 400 mg kg^?1 diet in the semi‐purified basal diet providing of 7, 16, 28, 55, 86, 142 mg ascorbic acid (AA) equivalent of C2S kg^?1 diet and 4, 9, 15, 31, 49, 75 mg AA equivalent of C2PP kg^?1 diet, respectively. Basal diet without AA supplemented was included as a control. Each diet was fed to triplicate groups of grouper (mean initial weight: 6.69 ± 0.07 g). Fish fed diets with ≥28 mg AA equivalent of C2S or ≥4 mg AA equivalent of C2PP kg^?1 had significantly (P < 0.05) greater weight gain (WG) than fish fed the unsupplemented control diet. Liver AA concentrations were higher in fish fed diets with ≥16 mg AA equivalent of C2S or ≥9 mg AA equivalent of C2PP kg^?1 than fish fed the control diet. Alternative pathway of complement activation (ACP) was higher in fish fed diets with ≥55 mg AA equivalent of C2S or ≥15 mg AA equivalent of C2PP kg^?1 than fish fed the control diet. Lysozyme activity was higher in fish fed ≥86 mg AA equivalent of C2S or ≥15 mg AA equivalent of C2PP kg^?1 than fish fed the control diet. Analysis by broken‐line regression of WG indicated that the adequate dietary vitamin C concentration from each vitamin C derivative in growing grouper is 46.2 mg AA equivalent of C2S kg^?1 diet and 17.8 mg AA equivalent of C2PP kg^?1 diet, and it also indicated that C2S is approximately 39% as effective as C2PP in meeting the vitamin C requirement for grouper. The data suggest that both C2S and C2PP supplementation support non‐specific immune responses of grouper.     

Nucleotide promotes feed intake and protein utilization via regulating the gene expression of feeding and nitrogen metabolism in juvenile Chinese perch (Siniperca chuatsi)

Nucleotide (NT) could enhance growth, feeding and immunity in higher vertebrate and fish. Chinese perch (Siniperca chuatsi) refuse artificial diet in natural water, whereas the NT might promote its feeding of domestication diet. The present study was designed to investigate the effect of dietary NT on growth, feed intake, feed utilization, body composition, serum biochemistry and nitrogen metabolism in juvenile Siniperca chuatsi. 0, 0.5, 1.0, 1.5, 2.0 and 4.0 g NT kg^?1 diet were supplemented in each diet, respectively. Triplicate groups of Chinese perch (36.21 ± 0.98 g) were fed twice a day to apparent satiation for 8 weeks. The results showed that fish fed with 1.5 g NT kg^?1 diet had the highest weight gain (WG), specific growth rate, feed efficiency, feed intake, protein efficiency ratio and protein retention efficiency. The crude protein content in whole body was highest in fish fed the diet containing 1.5 g NT kg^?1 diet. Dietary NT supplementation significantly increased the neuropeptide Y gene expression and significantly decreased the agouti‐related protein and pro‐opiomelanocortin gene expressions in brain. NT supplementation decreased urea nitrogen content, aspartate aminotransferase (AST) and alanine aminotransferase activities in serum. The hepatic AST activity was increased first and then decreased, and the highest activity was observed in fish fed with 1 g NT kg^?1 diet. Inversely, the activity of glutamate dehydrogenase (GDH) in liver and adenosine 5′‐monophosphate deaminase in muscle decreased first and then increased, and the lowest activity was observed in fish fed with 1.5 g NT kg^?1 diet. Similarly, the gene expression levels of GDH and arginase in liver were lowest in fish fed with 1.5 g NT kg^?1 diet. Based on the broken‐line regression analysis of WG in the present experimental condition, 1.44 g NT kg^?1 diet was the optimum supplementation level in juvenile Siniperca chuatsi.     

Effectiveness of l‐ascorbyl‐2‐monophosphate Na/Ca as a vitamin C source for yellowtail Seriola quinqueradiata juveniles

A feeding experiment was conducted to examine the efficacy of a vitamin C (L‐ascorbic acid, AsA) derivative, l ‐ascorbyl‐2‐monophosphate Na/Ca (AMP‐Na/Ca) by comparing to l ‐ascorbyl‐2‐monophosphate‐Mg (AMP‐Mg) in terms of growth, AsA content in tissues, and hematology in yellowtail Seriola quinqueradiata juvenile (1.10 ± 0.01 g). Furthermore, a stress resistance test for the species fed AMP‐Na/Ca was also conducted. In experiment 1, 11 test pellet diets with different levels of AMP‐Na/Ca (0, 12, 43, 88, 440 and 881 mg AsA kg^?1diet) and AMP‐Mg (0, 16, 52, 106, 595 and 1164 mg AsA kg^?1 diet) were formulated and fed to the yellowtail three times per day for 50 days. In both the vitamin C sources, the survival rates of the fish fed diets without supplemental AsA were lower than 50% at day 20, and more than 50% mortality occurred in fish that fed the diets containing 12 or 16 mg AsA kg^?1 after day 30. However, no significant differences were detected in survival and growth among fish that fed the diets containing more than 43 mg AsA kg^?1. Liver and brain AsA concentrations generally increased with increasing dietary AsA level in both sources. In experiment 2, test diets were formulated to contain 43, 88, 440 and 881 mg AsA kg^?1 using AMP‐Na/Ca, and after 60 days of feeding, yellowtail juveniles were subjected to low salinity and air exposure stress. The fish that received diets with 440 mg AsA kg^?1 showed significantly higher tolerance to low salinity stress and higher survival rate in air exposure stress than those of other groups. The present study demonstrated that yellowtail juveniles could utilize AMP‐Na/Ca as an AsA source like AMP‐Mg, and that supplementation of 43–52 mg AsA kg^?1 diet was optimum for normal growth. However, this study showed that dietary inclusion of 440 mg AsA kg^?1 would be necessary to improve stress resistance of this species.     

Optimal dietary protein requirement of grouper Epinephelus coioides juveniles fed isoenergetic diets in floating net cages

An experiment to determine the optimal protein requirement of grouper Epinephelus coioides juveniles was conducted in floating net cages (1.5 m × 1 m × 1.5 m). Six isoenergetic fishmeal–casein‐based experimental diets containing 350–600 g kg^?1 crude protein (CP) were fed to triplicate groups of 20 fish (10.7 ± 0.2 g) for 56 days. Weight gain (WG) and specific growth rate (SGR) increased with increasing dietary protein level from 350 to 450 g kg^?1 and then plateaued above these levels. Feed intake (FI) showed no significant difference among fish fed more than 350 g kg^?1 CP. Lowest feed conversion ratio (FCR) was found for fish fed 500 g kg^?1 CP but this was not significantly different from that of fish fed the 450 and 600 g kg^?1 CP. Lowest protein efficiency ratio (PER) was found for fish fed 550 and 600 g kg^?1 CP. Fish fed the 600 g kg^?1 CP had the highest body protein and moisture contents but the lowest body lipid content. Body ash content was unaffected by protein level for fish fed >400 g kg^?1 CP. Dietary protein level had no significant effect on hepatosomatic index (HSI). Fish fed the 350 g kg^?1 CP had significantly lower condition factor (CF) and viscerosomatic index (VSI). Based on broken‐line regression analysis of SGR the optimal dietary protein requirement for E. coioides juveniles was determined to be close to 480 g kg^?1.     

Vitamin C requirement of kuruma shrimp postlarvae, Marsupenaeus japonicus (Bate), using l-ascorbyl-2-monophosphate-Na/Ca

l ‐ascorbyl‐2‐monophosphate‐Na/Ca (AMP‐Na/Ca) was used as a vitamin C source to investigate the ascorbic acid (AsA) requirements on growth performance and stress resistance of the post‐larval kuruma shrimp, Marsupenaeus japonicus. Purified carrageenan‐microbound diets with six levels of AMP‐Na/Ca, AsA equivalent to 0, 20, 56, 87, 759 and 1697 mg kg^?1 diet were fed to triplicate groups of M. japonicus (mean initial weight 16±0.3 mg) for 30 days. The diets with AsA 0, 20 and 56 mg kg^?1 showed high cumulative mortality after 10 days of feeding. After the 30‐day trial, the shrimp fed these diets had significantly lower survival and weight gain (WG, %) than those fed the 87, 759 and 1697 mg AsA kg^?1 diets. Specific growth rate and individual dry weight showed the same pattern as WG (%). There were no significant differences in growth performance among the groups fed the AsA levels at 87, 759 and 1697 mg kg^?1 at the termination of feeding trial. Broken‐line regression analysis indicated that 91.8 mg AsA kg^?1 in the diet was the optimum for post‐larval shrimp. On the other hand, dietary level of more than 800 mg AsA kg^?1 was needed to ensure high resistance to stressful conditions such as osmotic and formalin stressors.     

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.     

Effects of dietary L‐carnitine level on growth performance,body composition and antioxidant status in beluga (Huso huso L. 1758)

A 17‐week feeding trial was carried out to evaluate the effects of dietary L‐carnitine level in beluga, Huso huso. A total of fish averaging 1247 ± 15.6 g (mean ± SD) were randomly distributed into 18 fibreglass tanks, and each tank holding 10 fish was then randomly assigned to one of three replicates of six diets with 50, 150, 350, 650, 950 and 1250 mg L‐carnitine kg^?1 diet. At the end of 17 weeks of feeding trial, average weight gain (WG), feed efficiency (FE), protein efficiency ratio (PER) and condition factor (CF) of fish fed 350 mg kg^?1 diet were significantly (P < 0.05) higher than those of fish fed 50, 150, 950 and 1250 mg kg^?1 diets. WG, FE, PER and CF of beluga fed 650 mg kg^?1 diet were also significantly higher than those of fish fed 50, 950 and 1250 mg kg^?1 diets. Whole body and muscle protein were significantly improved by the elevation of dietary L‐carnitine level up to 350 mg kg^?1. Liver superoxide dismutase and glutathione peroxidase activities of fish fed 350 and 650 mg kg^?1 diets were significantly higher than those of fish fed 50, 950 and 1250 mg kg^?1 diets. The dietary L‐carnitine level of 350–650 mg kg^?1 diet could improve growth performance, feed utilization, protein‐sparing effects of lipid, antioxidant defence system and reproductive success. Polynomial regression of WG suggested that the optimum dietary L‐carnitine level was 480 mg kg^?1 diet. Therefore, these results may indicate that the optimum dietary L‐carnitine could be higher than 350 but <650 mg kg^?1 diet in beluga reared in intensive culture conditions.     

Evaluation of l-ascorbyl-2-glucose as the source of vitamin C for juvenile Korean rockfish Sebastes schlegeli (Hilgendorf)

This study was conducted to compare l ‐ascorbyl‐2‐glucose (AA2G) with l ‐ascorbyl‐2‐monophosphate‐Na/Ca (AMP‐Na/Ca) for supplying the dietary vitamin C for juvenile Korean rockfish Sebastes schlegeli (Hilgendorf). Fish were fed one of seven semi‐purified diets containing equivalents of 0, 50, 100 and 200 mg ascorbic acid (AA) kg^?1 diet in the form of AA2G or AMP‐Na/Ca for 12 weeks. After 12 weeks of feeding, weight gain, feed efficiency ratio and survival of fish fed the vitamin C‐free diet were significantly lower than those of fish fed the vitamin C‐supplemented diets in either form. The hepatosomatic index, condition factor and survival of fish fed AMP‐Na/Ca₁₀₀, AMP‐Na/Ca₂₀₀, AA2G₁₀₀ and AA2G₂₀₀ diets were significantly higher than fish fed the vitamin C‐free diet. After 9 weeks of feeding, fish fed the vitamin C‐free diet began to show vitamin C deficiency signs such as anorexia and lethargy. At the end of the 12‐week feeding trial, fish fed the vitamin C‐free diet exhibited vitamin C deficiency signs, e.g., anorexia, scoliosis, exophthalmia and fin haemorrhage. Vitamin C retention in the muscle and liver was similar to those of fish fed AA2G‐ or AMP‐Na/Ca‐supplemented diets. In general, there was no significant difference in the muscle and liver vitamin C concen‐tration in fish fed the AA2G and AMP‐Na/Ca diets at the same supplementation levels.     

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 nucleotides improve the growth performance,antioxidative capacity and intestinal morphology of turbot (Scophthalmus maximus)

A growth trial was conducted to evaluate the effects and safety of nucleotides in low fish meal diets on the growth performance, antioxidative capacity and intestinal morphology of turbot (Scophthalmus maximus). High fish meal control diet was formulated with 500 g kg^?1 fish meal. Seven levels (0.075, 0.15, 0.225, 0.300, 1.5 and 3.0 g kg^?1, respectively) of nucleotides were added to a low fish meal basal diet, which was formulated with 400 g kg^?1 fish meal. The eight experimental diets were fed to groups of juvenile turbot (initial weight: 6.0 ± 0.03 g) for 60 days. Results showed that compared with high fish meal control diet, low fish meal basal diet treatment had lower total antioxidative capacity (T‐AOC), glutathione peroxidase activity, fold height of proximal and distal intestine, enterocyte height of all evaluated enteric section and microvillus height of mid‐intestine and distal intestine (P < 0.05). However, supplemented nucleotides in diets could significantly improve growth (specific growth rate, SGR), feed utilization, antioxidative capacity and intestinal morphology of turbot (P < 0.05). Broken‐line regression analysis of SGR and T‐AOC showed that the optimal supplemental levels of dietary nucleotide for juvenile turbot were 0.366 and 0.188 g kg^?1, respectively. In summary, 0.300 g kg^?1 of dietary nucleotides was helpful in improving growth, feed utilization, antioxidative capacity and intestinal morphology of turbot fed with low fish meal diet. Excessive dietary nucleotides (3.0 g kg^?1) might cause oxidative stress and morphological damage in intestine and then reduce the growth of turbot.     

Polka-dot grouper, Cromileptes altivelis, can utilize dietary fat efficiently

Polka‐dot grouper, Cromileptes altivelis, a highly‐prized fish in Asian live fish markets, is a slow‐growing species. Long‐chain (LCF) or medium‐chain fatty acids (MCF) were fed to polka‐dot grouper (14 g initial weight) for 8 weeks to see if growth could be stimulated. Five dietary treatments were compared: a control diet with low fat (56 g kg^?1) or diets that contained either moderate (150 g kg^?1) or high (300 g kg^?1) supplements of fat that were added either as olive oil for the LCF or coconut oil for the MCF. Control fish performed well; they grew at 2.2 g week^?1, had a dry matter feed conversion ratio of 1.0 and deposited dietary protein and energy at efficiencies of 25 and 26%. Fish fed LCF at moderate levels performed better than controls but, when fed LCF at high levels or MCF at any level, their performance was inferior to controls. We conclude that dietary supplementation with 150 g kg^?1 of LCF stimulates growth and improves protein retention of polka‐dot grouper whereas higher levels, or the same or higher levels of MCF, depress performance.     

Effects of different dietary levels of L-ascorbyl-2-polyphosphate on growth and tissue vitamin C concentrations in juvenile olive flounder, Paralichthys olivaceus (Temminck et Schlegel)

This experiment was conducted to study the effects of different dietary levels of vitamin C, L‐ascorbyl‐2‐polyphosphate (ASPP), on growth and tissue vitamin C concentrations in juvenile olive flounder, Paralichthys olivaceus (Temminck et Schlegel). Fish were fed one of six semi‐purified diets containing an equivalent of 0, 25, 50, 75, 150, or 1500 mg ascorbic acid (AA) kg^?1 diet (C₀, C₂₅, C₅₀, C₇₅, C₁₅₀ or C₁₅₀₀) in the form of ASPP for 12 weeks. Weight gain (WG) and protein efficiency ratio (PER) of fish fed the C₀ diet were significantly lower than those of fish fed the other diets (P < 0.05), and WG and PER of fish fed the C₂₅, C₅₀ and C₇₅ diets were significantly lower than those of fish fed the C₁₅₀₀ diet (P < 0.05). Fish fed the C₀ diet exhibited vitamin C deficiency symptoms such as anorexia, scoliosis, cataract, exophthalmia and fin hemorrhage at the end of the 12‐week test. After 12 weeks of the feeding trial, AA concentrations from gill, kidney, and liver of fish fed the C₀, C₂₅, C₅₀ and C₇₅ diets were significantly lower than those of fish fed the C₁₅₀ and C₁₅₀₀ diets (P < 0.05). Based on broken line analyses for WG and PER, the optimum dietary levels of vitamin C were 91 and 93 mg AA kg^?1 diet respectively. These findings suggest that the dietary vitamin C requirement could be 93 mg AA kg^?1 diet to support reasonable growth, and greater than 150 mg AA kg^?1 diet may be required for AA saturation of major tissues for juvenile olive flounder under experimental conditions.     

Dietary ascorbic acid requirement of cobia,Rachycentron canadum Linneaus

A 10‐week feeding trial was conducted to determine the optimal requirement of cobia (Rachycentron canadum Linneaus) for dietary ascorbic acid (AA). Graded levels of L‐ascorbyl‐2‐polyphosphate (LAPP) were supplemented in basal diet to formulate six semi‐purified diets containing 2.70 (the control diet), 8.47, 28.3, 80.6, 241 and 733 mg AA equivalent kg^?1 diet, respectively. Each diet was randomly fed to triplicate groups of fish in flow‐through plastic tanks (300 L), and each tank was stocked with 25 fish with average initial weight of 4.59 ± 0.36 g. Observed deficiency signs included poor growth, higher mortality and lower feeding rate (FR) in the fish of the control group. Fish fed the control diet had significantly lower weight gain (WG), lower feed efficiency ratio (FER) and lower tissue AA concentrations in fish liver and muscle. With the increase of dietary AA, the survival, WG, FER, hepatic and muscular AA concentrations of cobia significantly increased and then levelled off. The dietary AA requirement of cobia was estimated to be 44.7 mg kg^?1 based on WG, 53.9 mg kg^?1 or 104 mg kg^?1 based on either hepatic or muscular AA concentration, respectively.     

Evaluation of dietary yellow loess as an antibiotic replacer on growth,immune responses,serological characteristics and disease resistance in rainbow trout,Oncorhynchus mykiss

A 12 weeks of feeding trial was conducted to evaluate the effects of different levels of dietary yellow loess as an antibiotic (oxytetracycline) replacer in rainbow trout, Oncorhynchus mykiss. Five experimental diets were formulated to contain no antibiotics or yellow loess (control/CON), three graded levels of yellow loess 5 (YL₅), 10 (YL₁₀) and 20 g YL kg^?1 diet (YL₂₀) and oxytetracycline at 5 g OTC kg^?1 diet. Forty‐five fish averaging 39.4 ± 1.6 g (mean ± SD) were randomly distributed in to 15 aquaria. Triplicate groups of fish were fed one of the experimental diets at 1.5 ~ 1.9% of wet body weight per day. At the end of the feeding trial, average weight gain (WG) and specific growth rate (SGR) from fish fed CON diet were significantly lower than those from fish fed YL₁₀, YL₂₀ or OTC diets (P < 0.05). Lysozyme activity from fish fed YL₂₀ was detected to be significantly higher than that from fish fed CON diet (P < 0.05). While, superoxide dismutase (SOD) activity from fish fed YL₁₀ and YL₂₀ was recorded to be significantly higher than that from fish fed CON diet (P < 0.05). Fourteen days of challenge test with bacteria A. salmonicida showed significantly lower survival rate for CON than those of fish fed other experimental diets. Therefore, these results indicated that dietary yellow loess at 10–20 g kg^?1 could be a promising alternative of oxytetracycline in rainbow trout.     

Dietary digestible lysine requirement and essential amino acid to lysine ratio for pacu Piaractus mesopotamicus

To determine the digestible lysine requirement for pacu juveniles, a dose–response feeding trial was carried out. The fish (8.66 ± 1.13 g) were fed six diets containing the digestible lysine levels: 6.8, 9.1, 11.4, 13.2, 16.1 and 19.6 g kg^?1 dry diet. The gradual increase of dietary digestible lysine levels from 6.8 to 13.2 g kg^?1 did not influence the average values of the parameters evaluated (P > 0.05). The increase of dietary digestible lysine level to 16.1 g kg^?1 significantly improved weight gain (WG), specific growth rate (SGR), protein productive value (PPV), protein efficiency rate (PER), and apparent feed conversion rate (FCR), but was not different from fish fed diets containing 19.6 g kg^?1 lysine. Fish fed diets containing 16.1 and 19.6 g kg^?1 digestible lysine showed lower body lipid contents than fish in the other treatments. The digestible lysine requirement as determined by the broken‐line model, based on average WG values, was 16.4 g kg^?1. The other essential amino acid requirements were estimated based on the ideal protein concept and the value determined for lysine.     

Use of turkey meal as partial and total replacement of fish meal in practical diets for sunshine bass (Morone chrysops × Morone saxatilis) grown in tanks

Economical, nutritious diets for hybrid striped bass (HSTB) are required for the continued expansion and sustainability of this industry. Turkey meal (TM) is a by‐product of the US turkey industry and is a potentially‐valuable local, alternative protein source for use in aquaculture diets because of its excellent nutritional composition and quality. TM may substitute for more expensive fish meal (FM)‐based diets; however, there are no published data with regard to using this ingredient in sunshine bass diets. Therefore, a 16‐week feeding trial was conducted with juvenile (36 g) sunshine bass (Morone chrysops × Morone saxatilis) to evaluate growth, feed conversion and body composition when fed diets with decreasing levels of FM (300, 200, 100 and 0 g kg^?1) and increasing levels of turkey meal (0, 97, 175 and 264 g kg^?1). Four practical diets were formulated to contain 400 g kg^?1 protein and similar energy levels. Twenty fish were stocked into each of the 12, 1200‐L circular tanks and were fed twice daily ad libitum. At the conclusion of the feeding trial, there were no significant (P > 0.05) differences in final mean weight, percentage weight gain, specific growth rate and feed conversion ratio among treatments, which averaged 363.7 g, 904.3%, 2.02% day^?1 and 1.73, respectively. Percentage survival of fish fed diet 4 (0 g kg^?1 FM and 264 g kg^?1 TM) was significantly (P > 0.05) lower (survival = 88.3%) than fish fed diet 3 (100 g kg^?1 FM and 175 g kg^?1 TM; survival = 95%), but not different from fish fed diet 1 (survival = 92.5%) and fish fed diet 2 (survival = 93.3%). Fillet weight and amount of abdominal fat were not significantly different among all treatments and averaged 258 and 58 g kg^?1, respectively. Fish fed diet 1 (300 g kg^?1 FM, 0 g kg^?1 TM) and diet 2 (200 g kg^?1 FM and 970 g kg^?1 TM) had a significantly (P < 0.05) lower hepatosomatic index (2.83 and 3.01, respectively) than fish fed diet 4 (3.33), but not different (P > 0.05) compared to fish fed diet 3 (3.14). Lipid in the fillet of fish fed diet 2 (197 g kg^?1) was significantly (P < 0.05) higher than fish fed all other diets; and the percentage lipid in the fillet of fish fed diet 1 (126 g kg^?1) was significantly lower than fish fed diets 2 and 4, but not different (P >0.05) compared to fish fed diet 3. Fillet moisture, protein and ash were similar among fish fed all diets and averaged 748, 798 g kg^?1 and 51.0 g kg^?1 (dry‐matter basis), respectively. The amino acid composition of fillets was similar among all treatments with a few slight significant differences. Results from the present study indicate that tank‐grown sunshine bass can be fed a diet containing 264 g kg^?1 TM with 0 g kg^?1 FM, compared to diets containing up to 300 g kg^?1 FM, without adverse effects on weight gain, growth rate, feed conversion and body composition. Further research should be conducted using lower‐protein diets to determine minimum protein level for tank‐grown sunshine bass.     

Quantitative l-lysine requirement of juvenile grouper Epinephelus coioides

An 8‐week feeding trial was conducted to determine the quantitative lysine requirement of juvenile grouper Epinephelus coioides (initial mean weight: 15.84 ± 0.23 g, mean ± SD) in eighteen 500‐L indoors flow‐through circular fibreglass tanks provided with sand‐filtered aerated seawater by feeding diets containing six levels of l ‐lysine ranging from 19.2 to 39.5 g kg^?1 dry diet in 4 g kg^?1 increments. The diets, in which 250 g crude protein kg^?1 diet came from fish meal and soybean protein concentrate, and 230 g kg^?1 from crystalline amino acids, were formulated to simulate the amino acid profile of 480 g kg^?1 whole chicken egg protein except for lysine. Each diet was assigned to three tanks in a completely randomized design. Grouper were fed to apparent satiation twice daily during the week and once daily on weekends. Weight gain and specific growth rate increased with increasing levels of dietary lysine up to 27.2 g kg^?1 (P < 0.05) and remained nearly the same thereafter (P > 0.05). Feed efficiency was the poorest for fish fed the lowest lysine diet (P < 0.05) and showed no significant differences among other treatments (P > 0.05). Survival could not be related to dietary treatments. Body composition remained relatively constant except for lipid contents in muscle and liver. Total essential amino acid contents in liver increased with dietary lysine level although there was a slight decline for fish fed the highest lysine level of diet. Plasma protein content increased with increasing dietary lysine level (P < 0.05), but cholesterol, triacylglycerol and glucose contents were more variable and could not be related to dietary treatments. Dietary lysine level significantly influenced morphometrical parameters (condition factor, hepatosomatic index and intraperitoneal fat ratio) of juvenile grouper (P > 0.05). Broken‐line analysis of weight gain indicated the dietary lysine requirement of juvenile grouper to be 28.3 g kg^?1 diet or 55.6 g kg^?1 dietary protein.     

Effects of various corn distillers by‐products on growth,feed efficiency,and body composition of channel catfish,Ictalurus punctatus

A study was conducted to examine the use of corn distillers’ by‐products in diets and the effects of additional dietary fat on channel catfish, Ictalurus punctatus, performance. Juvenile channel catfish (initial weight: 12.6 g per fish) were stocked in flow‐through aquaria and fed one of six practical diets for 9 weeks. Fish fed the control + fat diet consumed more diet and had higher feed efficiency ratio (FER) than fish fed the control diet, but weight gain was not significantly different between fish fed these two diets. Fish fed the diet containing 300 g kg^?1 distillers dried grains with solubles (DDGS) consumed more diet and gained more weight, but had similar FER compared with fish fed the control + fat diet. The diet containing 200 g kg^?1 high‐protein distillers grains (HPDDG) resulted in similar diet consumption, weight gain and FER as the control + fat diet. Fish fed the diet containing 100 g kg^?1 distillers solubles (DS) consumed more diet, but had similar weight gain and FER compared with fish fed the 300 g kg^?1 DDGS diet. The presence of distillers solubles in the diet (300 g kg^?1 DDGS, 100 g kg^?1 DS, 100 g kg^?1 EDS diets) appears to increase diet consumption, weight gain, and FER over the control diets with or without additional fat.     

Dietary myo‐inositol requirement for juvenile gibel carp (Carassius auratus gibelio)

An 11‐week growth trial was conducted to determine dietary myo‐inositol (MI) requirement for juvenile gibel carp (Carassius auratus gibelio). Myo‐inositol was supplemented to the basal diet to formulate six purified diets containing 1, 56, 107, 146, 194 and 247 mg MI kg^?1 diet, respectively. Each diet was fed to triplicate groups of juvenile gibel carp (initial body weight 3.38 ± 0.27 g, mean ± SD) in a flow‐through system. The diets were randomly assigned to different fish tanks. Fish fed ≥ 107 mg MI kg^?1 diet had significantly higher weight gain (WG), feed efficiency (FE) and protein efficiency ratio than those fed 1 mg MI kg^?1 diet. Fish fed ≥ 56 mg MI kg^?1 diet had higher feeding rate and survival compared with fish fed 1 mg MI kg^?1 diet. Dietary supplemental inositol did not affect fish liver inositol concentration. Fish fed ≥ 56 mg MI kg^?1 diet had higher body dry matter, crude protein and gross energy and lower hepatosomatic index than fish fed 1 mg MI kg^?1 diet. Dietary inositol supplementation decreased fish body ash. Quadratic regression of weight gain indicated that the myo‐inositol requirement to maximum growth for juvenile gibel carp was 165.3 mg MI kg^?1 diet.