Dietary arginine requirement of juvenile hybrid sturgeon (Acipenser schrenckii♀ × Acipenser baerii♂)

An 8‐week feeding trial was conducted to evaluate the dietary arginine requirement of juvenile hybrid sturgeon. Seven isonitrogenous and isolipidic diets were formulated to contain graded levels of dietary arginine ranging from 1.74% to 3.54% (dry weight). The results indicated that the fish fed with 1.76% arginine diet had lower specific growth rate (SGR) and feed efficiency ratio (FER) than the fish fed the 2.64% to 3.24% arginine diets (p < .05), and the fish fed the 2.64% arginine diet presented the highest SGR. The fish fed with 1.76% arginine diet had lower whole‐body crude protein content than the fish fed the 2.64% or 2.93% arginine diets (p < .05). Compared with the 1.76% arginine diet, 2.36% to 2.93% arginine diets significantly increased the total amino acid (TAA) concentration and total nonessential amino acid (TNEAA) of carcasses. The fish fed with 1.76% arginine diet had lower activity of nitric oxide synthase (T‐NOS) and content of nitric oxide (NO) than the fish fed the 2.05% to 2.93% arginine diets in the liver. The fish fed with 1.76%, 2.05% or 2.36% arginine diets had lower gene expression of growth hormone (GH) and insulin‐like growth factor I (IGF‐I) in the liver than the fish fed the 2.64% to 3.53% arginine diets in the liver (p < .05). A broken‐line analysis between SGR against the dietary arginine levels provided estimates for the optimal dietary arginine requirement of 2.47% corresponding to 6.18% of the dietary protein on a dry weight basis.     

Effect of dietary carbohydrate level on growth performance,body composition,apparent digestibility coefficient and digestive enzyme activities of juvenile cobia,Rachycentron canadum L

A 9‐week feeding trial was conducted to investigate the effect of dietary carbohydrate level on the growth performance, body composition and apparent digestibility coefficient and digestive enzyme activities of juvenile cobia. Six isonitrogenous and isolipidic diets containing graded levels of starch (1.3%, 6.5%, 12.5%, 18.4%, 24.2% and 30.4%) were fed to juvenile cobia. Specific growth rate (SGR), feed efficiency ratio (FER) and protein efficiency ratio (PER) increased with increasing dietary starch up to 18.4% (P<0.05), and thereafter SGR declined but FER and PER remained nearly the same. Apparent digestibility coefficient of starch reduced significantly when dietary starch up to 30.4%. Fish fed the diets with starch from 18.4% to 30.4% showed higher amylase activities in intestinal tract than those fed diets containing starch 1.3% and 6.5% (P<0.05). Significantly higher whole‐body lipid contents were observed in fish fed the diets containing higher starch. Whole‐body moisture content was inversely correlated with whole‐body lipid content, while protein and ash showed no significant differences. Plasma glucose, hepatosomatic index, liver glycogen and liver lipid increased with an increasing dietary starch. Based on SGR and FER, the appropriate dietary starch supplementations of juvenile cobia were estimated to be 21.1% and 18.0 % of diet respectively.     

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.     

Dietary selenium requirement for juvenile cobia,Rachycentron canadum L.

A 10‐week feeding trial was conducted to estimate the optimum dietary selenium (Se) requirement for juvenile cobia, Rachycentron canadum L. The basal diet was formulated to contain 50.6% crude protein from vitamin‐free casein, gelatin. A control diet (no added seleno‐dl ‐methionine) and five experimental diets containing 0.20, 0.40, 0.60, 0.80 and 1.00 mg seleno‐dl ‐methionine kg^?1 were prepared. Each diet was randomly fed to triplicate groups of juvenile cobia with initial weight 6.27±0.03 g in a flow‐through system. The Se concentration in rearing water was monitored during the feeding period, and was not detectable. The dietary Se level significantly influenced the survival, specific growth rate (SGR), feed efficiency and the Se concentrations in the whole body and vertebra of cobia. The Se‐dependent glutathione peroxidase (EC 1.11.119) activity increased with an increase in the dietary Se levels (P<0.05). Hepatic glutathione reductase (EC 1.6.4.2) activity was the highest in fish fed the diet with 0.21 mg Se kg^?1, and declined with an increase in the dietary Se levels. Based on broke‐line regression of SGR, the Se concentration in the whole body and vertebra, the Se requirements of juvenile cobia were 0.788, 0.811 and 0.793 mg Se kg^?1 diet in the form of seleno‐dl ‐methionine respectively.     

Dietary threonine requirement of juvenile large yellow croaker,Larmichthys crocea

A feeding trial was conducted to determine the dietary threonine requirement of juvenile large yellow croaker (Larmichthys crocea). Six diets were formulated containing 45% crude protein with six graded levels of threonine (0.71–2.46% in about 0.35% increment). Each diet was randomly assigned to triplicate groups of 60 juvenile fish (initial body weight 6.00 ± 0.10 g). Fish were fed twice daily (05:00 and 16:30) to apparent satiation for 8 weeks. The result indicated that significant difference was observed in the weight gain among all treatments. Specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER) and nitrogen retention (NR) increased with increasing levels of threonine up to 1.75% diet (P < 0.05), and thereafter, declined. No significant differences in body dry matter, crude protein, crude lipid or ash content were found among dietary treatments. Theronine contents of fish muscle were significantly affected by dietary threonine levels (P < 0.05). Fish fed the diet with 0.71% threonine showed the lowest threonine content (2.94%) in fish muscle, while fish fed the diet with 1.75% threonine had the highest value (3.16%). Other essential amino acid contents of muscle were not significantly different among the dietary treatments. On the basis of SGR, FE or NR, the optimum dietary threonine requirements of juvenile L. crocea were estimated to be 1.86% of diet (4.13% of dietary protein), 1.90% of diet (4.22% of dietary protein) and 2.06% of diet (4.58% of dietary protein), respectively, using second‐order polynomial regression analysis.     

Effects of phospholipid addition to diets with different inclusion levels of fish oil on growth and fatty acid body composition of juvenile swimming crab Portunus trituberculatus

Six experimental diets were designed with two phospholipid (PL; 0% and 1.5%) and three fish oil levels (0%, 1% and 3%) to evaluate the effects of dietary fish oil and PL levels on growth, survival and fatty acid composition of juvenile swimming crab, Portunus trituberculatus. Diets were iso‐energetic and iso‐nitrogenous and each diet was fed to triplicate groups (initially weight, 24.88 ± 0.04 g per crab) for 59 days. Weight gain (WG) and specific growth rate (SGR) increased with dietary PL addition to 0% fish oil‐supplemented diets (P < 0.05). On the other hand, WG and SGR decreased with dietary PL addition to 3% fish oil diets (P < 0.05). Crabs fed PL supplemented diets had higher haemolymph low‐density lipoprotein cholesterol concentrations and muscle crude lipid levels (P < 0.05) than crabs fed a none PL supplemented diet. The percentage of highly unsaturated fatty acids (HUFA; % total FA) in both polar and neutral lipids fractions of muscle tissue only increased in case of PL addition to 0% and 1% fish oil‐supplemented diets (P < 0.05). HUFA levels in the neutral lipids fraction of the hepatopancreas increased by dietary PL addition at each dietary fish oil level (P < 0.05). In this study, both dietary fish oil and PL addition contributed to a high n‐3/n‐6 ratio in muscle and hepatopancreas of P. trituberculatus. In conclusion, PL addition is only meaningful with fish oil‐deficient diets, in which case it enhanced lipid transport and HUFA absorption efficiency, hence improving the nutritional value of the diet.     

Replacement of fishmeal in cobia (<Emphasis Type="Italic">Rachycentron canadum</Emphasis>) diets using poultry by-product meal

An 8-week feeding trial was conducted to evaluate the use of local poultry by-product meal (PBM) in replacement of imported fishmeal in the diets of cobia, Rachycentron canadum. Six isolipidic (12%) and isoproteic (45%) experimental diets were formulated using PBM to replace fishmeal at 20, 40, 60, 80 and 100% dietary protein. Eleven juvenile cobia (initial mean weight of 30.7 ± 0.78 g) were randomly stocked in 300-L circular fibreglass tanks and hand-fed based on the total biomass of each tank, twice a day at 0900 h and 1500 h. The fish were group weighed at 2-week intervals to monitor their growth performance in order to adjust the feeding ratio. At the end of the feeding trial, weight gains (WGs) ranging from 221 to 322% were obtained. The specific growth rate (SGR), WG and protein efficiency ratio (PER) for fish fed with PBM-based diets were not significantly different (P > 0.05) when compared to fish fed the control diet. The best SGR was recorded for fish fed with 60PBM diet, which was significantly higher (P < 0.05) than those fed the control diet with values at 2.40 ± 0.01 and 1.97 ± 0.26%/day, respectively. The FCR of 1.83 ± 0.05 for fish fed the 60PBM diet was not significantly different (P > 0.05) when compared to those fed the control diet. The PBM source and dietary level did not significantly (P > 0.05) affect the hepatosomatic index of the fish. The results from this study suggested that PBM could replace 100% dietary fishmeal without adversely affecting the growth performance, but an optimal replacement level at approximately 60% was recommended for better growth performance and efficient feed utilization.     

Compensatory growth of juvenile black sea bream,Acanthopagrus schlegelii with cyclical feed deprivation and refeeding

An 8‐week feeding trial was conducted to evaluate compensatory growth of juvenile black sea bream, Acanthopagrus schlegelii (initial weight 9.56 ± 0.12 g) in fifteen 300 L indoors flow‐through circular fibreglass tanks. Feeding regimes was designed as follows: the control group (fed continuously), and S1, S2, S3 and S4 groups experienced 1, 2, 3 and 4 days of feed deprivation and then refeeding for the remaining days per week respectively. Changes in body weight, specific growth rate (SGR), feed intake (FI) and feed efficiency ratio (FER) were examined biweekly during the trial. At the end of the cyclical feeding periods, survival was not significantly affected by feeding strategy (P > 0.05). Final body weight of fish in S1 group was significantly higher than the control group (P < 0.05) after an 8 weeks trial, and fish in the S2 group reached the same body weight of the control fish (P > 0.05), however, the growth data in the S3 and S4 groups could not catch‐up with the control treatment (P < 0.05). In the first 4 weeks, SGR values of fish with feed deprivation more than 2 days per week were inferior to those of control group (P < 0.05); however, no significant differences of SGR were observed among the groups for the last 4 weeks (P > 0.05). FI increased significantly with the starvation days increasing during the whole feeding trial (P < 0.05). At the periods 2, 4 and 6 weeks, FER values increased significantly with increasing feed‐deprivation days up to S2 group and then levelled off (P < 0.05); however, FER in S2 group was only higher than that in S0 and S1, but no significant differences were found among the other treatments at the end of week 8. Significant differences were found in apparent digestibility coefficients (ADCs) of dry matter and crude protein among the treatments, while ADCs of crude lipid were unaffected. Protein and lipid contents in whole body and dorsal muscle showed declining tendency with increasing food deprivation days, while moisture contents tended to increase (P < 0.05). Serum parameters were markedly affected by feeding regimes except for total protein concentration and thyroxine level. The present results indicated that starvation for 1 and 2 days per week of juvenile black sea bream could achieve over‐compensation and complete compensation respectively. However, in case of longer term feed restriction regime, fish failed to obtain good growth performance.     

Effects of dietary supplementation of glycyrrhizic acid on growth performance,survival, innate immune response and parasite resistance in juvenile large yellow croaker,Larimichthys crocea (Richardson)

An 8‐week feeding experiment was conducted to investigate the effects of dietary glycyrrhizic acid (GA) on growth, survival and immune response of juvenile large yellow croaker, in seawater floating net cages. GA was supplemented into the basal diet to formulate four isonitrogenous and isoenergetic practical diets containing 0.00% (the control diet), 0.01%, 0.02% and 0.04% GA of dry weight, respectively. Triplicate groups of 60 fish were fed to apparent satiation by hand twice daily. The results showed that the specific growth rate, survival rate and feed efficiency ratio revealed no significant differences among dietary treatments (P > 0.05). The phagocytic index of head kidney macrophage was significantly increased by the supplementation of 0.04% dietary GA compared to the control group (P < 0.05). Fish fed 0.04% dietary GA also showed significantly higher serum lysozyme activity than fish fed the control diet and diet with 0.01% GA (P < 0.05). The cumulative mortality rate after natural infestation of parasites (protozoan, Cryptocaryon irritans Brown) showed no significant differences among dietary treatments. These results suggested that dietary glycyrrhizic acid improved certain non‐specific immunological parameters of juvenile large yellow croaker. However, GA was not able to protect juvenile large yellow croaker effectively from protozoan infection.     

Evaluation of Enteromorpha prolifera as a feed component in large yellow croaker (Pseudosciaena crocea,Richardson, 1846) diets

A 9‐week feeding trial was conducted to investigate the effects of dietary Enteromorpha prolifera on the growth performance and body composition of juvenile large yellow croaker (Pseudosciaena crocea) (Richardson, 1846) (11.41 ± 1.59 g) in floating sea cages (1.5 × 1.5 × 2.0 m). Four isonitrogenous and isoenergetic diets were formulated to contain graded levels (0%, 5%, 10% and 15%) of E. prolifera. Survival ranged from 98.7% to 99.7%, and was independent of dietary treatment (P>0.05). There were no significant differences in the feeding rate among dietary treatments (P>0.05). The specific growth rate (SGR) increased with increasing levels of E. prolifera. When the supplementation of E. prolifera was >5%, SGR was significantly higher compared with the control group (0%). The feed efficiency ratio (FER) in fish fed the diet with 5%E. prolifera (diet 2) was higher than that of the other groups, while in fish fed the diet with 10%E. prolifera (diet 3), it was the lowest (P<0.05). The protein retention (PR) decreased as the level of E. prolifera increased in diets (5%, 10% and 15%). The protein body content displayed a trend similar to that of PR. No significant difference was observed in body moisture and ash among the dietary treatments. An increase in minerals of potassium, magnesium and sodium in body was observed with an increase in dietary seaweed concentrations. On basis of the SGR and FER, supplementation levels of E. prolifera can reach at least 15% without affecting the growth and still maintain a high survival rate for juvenile large yellow croaker.     

Dietary manganese requirement for juvenile cobia,Rachycentron canadum L

A 10‐week feeding trial was conducted to estimate the optimum dietary manganese requirement for juvenile cobia, Rachycentron canadum L. The basal diet was formulated to contain 501 g kg^?1 crude protein from vitamin‐free casein, gelatin and fish protein concentrate. Manganese sulphate was added to the basal diet at 0 (control group), 6, 12, 18, 24 and 36 mg Mn kg^?1 diet providing 5.98, 7.23, 16.05, 23.87, 28.87 and 41.29 mg Mn kg^?1 diet, respectively. Each diet was randomly fed to three replicate groups of cobia for 10 weeks, and each tank was stocked with 30 fish (initial weight, 6.27 ± 0.03 g). The manganese concentration in rearing water was monitored during the feeding period and was < 0.01 mg L^?1. Dietary manganese level significantly influenced survival ratio (SR), specific growth ratio (SGR), feed efficiency ratio (FER) and the manganese concentrations in the whole body, vertebra and liver of cobia. When the dietary manganese level rose from 5.98 mg kg^?1 to 23.87 mg kg^?1, the superoxide dismutase (SOD; EC 1.15.1.1) activities in liver also increased (P < 0.05). But there was no significant change in SOD activities for the groups fed with diets containing manganese level higher than 23.87 mg kg^?1. On the basis of broken‐line regression of SGR, manganese concentration in whole body and vertebra the manganese requirements of juvenile cobia were 21.72 mg kg^?1, 22.38 mg kg^?1 and 24.93 mg kg^?1 diet in the form of manganese sulphate, respectively.     

Optimum arginine requirement of juvenile black sea bream,Sparus macrocephalus

An 8‐week feeding trial was conducted to determine the dietary arginine requirement of juvenile black sea bream Sparus macrocephalus in 18 350 L indoors flow‐through circular fibreglass tanks. Six isonitrogenous and isoenergetic diets were formulated to contain graded levels of l ‐arginine (1.85%, 2.23%, 2.51%, 2.86%, 3.20% and 3.46% dry diet) from dietary ingredients and crystalline arginine. Each diet was randomly assigned to triplicate groups of 25 juvenile fish (10.51±0.15 g) twice daily (08:00 and 16:00 hours) to apparent satiation. Results showed that the specific growth rate (SGR) increased with increasing dietary arginine levels up to 2.51% and remained nearly the same thereafter. Feed efficiency ratio, protein efficiency ratio (PER) and protein productive value all showed an increasing tendency and then levelled off. Apparent digestibility coefficients of dry matter, crude protein and gross energy significantly improved up to 2.86% arginine diet and decreased at different extents thereafter. Fish fed 1.85% arginine diet had significantly lower protein content in the whole body and dorsal muscle than those fed diets supplemented with or >2.86% of arginine. Lipid content decreased and lower value occurred at 3.46% of dietary arginine. The dietary essential amino acid composition in the whole body of the black sea bream was significantly influenced by dietary arginine. Arginine retention increased with an increasing dietary arginine level from 1.85% to 3.20%, then declined slightly at 3.46% arginine diet. Serum biochemical parameters were significantly affected by the dietary arginine level except for the cholesterol content. Broken‐line regression based on SGR and second‐order polynomial regression based on PER indicated that the optimum dietary arginine requirements for juvenile black sea bream were 2.79% and 3.09% diet, corresponding to 7.74% and 8.13% of the dietary protein respectively.     

Quantitative dietary copper requirement of juvenile Siberian sturgeon,Acipenser baerii,and effects on muscle composition and some enzymatic activities

An 8‐week feeding trial was conducted to quantify dietary copper (Cu) requirement of juvenile Siberian sturgeon, Acipenser baerii. Five isonitrogenous diets were formulated to provide actual dietary copper values of 1.8, 5.7, 10.1, 15.9 and 28.3 mg Cu per kg diet. Experimental diets were fed to the Siberian sturgeon (27.57 ± 0.24 g) in triplicate to apparent satiation for 8 weeks. At the end of experiment, weight gain (WG), specific growth rate (SGR) and protein efficiency ratio (PER) were significantly increased with increasing dietary Cu level up to 10.1 mg/kg and then decreased with further increases in dietary Cu level (p < .05). The Cu concentration in the liver and cartilage was positively correlated with the respective concentrations in the diet (p < .05), while muscle and serum Cu concentrations remained significantly unchanged (p > .05). Superoxide dismutase and glutathione peroxidase had the highest activities in serum of fish fed with 15.9 and 28.3 mg Cu per kg diet, respectively. Analysis by the broken‐line regression of SGR, crude protein content and superoxide activity demonstrated that the optimum dietary Cu requirements in juvenile Siberian sturgeon were 9.51, 9.58 and 16.10 mg/kg diet, respectively.     

Dietary l‐lysine requirement of juvenile Chinese sucker,Myxocyprinus asiaticus

An 8‐week feeding trial was conducted to quantify the dietary l ‐lysine requirement of juvenile Chinese sucker with an initial weight of 1.81 ± 0.04 g reared in indoor flow‐through and aerated tanks. Six isonitrogenous and isoenergetic practical diets were formulated to contain graded levels of lysine (1.23%, 1.80%, 2.39%, 2.98%, 3.56% and 4.18% dry matter) at 0.6% increments from dietary ingredients and crystalline l ‐lysine. Each diet was randomly assigned to triplicate groups of 30 fish each and was fed to apparent satiation by hand three times a day (09:00, 13:00 and 17:00 hours) for 8 weeks. There were significant differences in growth performance and feed utilization among the treatments. Weight gain (WG), specific growth rate and protein efficiency ratio (PER) significantly increased with increasing lysine levels up to 2.39% of diet (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 when dietary lysine level increased from 2.39% to 4.18%. The N retention (% N intake) significantly increased with dietary lysine level but did not attain a plateau (P < 0.05). Survival could not be related to dietary treatments. Whole body protein increased (P < 0.05) and whole body lipid decreased (P < 0.05) with increasing dietary lysine level. The condition factor and hepatosomatic index were significantly affected by dietary lysine levels, however, viscersomatic index, whole body moisture and ash did not differ significantly among dietary treatments. Broken‐line analysis on the basis of WG and PER showed that dietary lysine requirements of juvenile Chinese sucker were 2.43% and 2.40% dry diet (5.52% and 5.45% dietary protein) respectively. Based on the ideal protein approach and the A/E ratios determined from muscle amino acid profile an estimation of the EAA requirements of Chinese sucker juveniles were calculated.     

Suitable dietary chitosan improves the growth performance,survival and immune function of tiger shrimp,Penaeus monodon

Different levels of dietary chitosan on growth performance, survival and stress tolerance to air exposure was studied in tiger shrimp, Penaeus monodon. Shrimp (mean initial wet weight about 1.16 g) were fed with six different diets (C0, C0.05, C0.1, C0.2, C0.3 and C0.4) containing six level of chitosan (0%, 0.05%, 0.1%, 0.2%, 0.3% and 0.4% respectively) in triplicate for 60 days. Growth performance [final body wet weight (FBW); weight gain (WG); biomass gain (BG)] of shrimp fed chitosan‐containing diets were higher (P < 0.05) than that of shrimp fed the basal diet, shrimp fed C0.1 diet showed the highest value of growth performance. Survival of shrimp in C0.1 and C0.2 diet groups were higher (P < 0.05) than that of shrimp in C0, C0.05 and C0.4 diet groups but without statistical difference (P > 0.05) in shrimp fed C0.3 diet group. Whole body and muscle lipid contents decreased with increasing dietary chitosan levels. Plasma total cholesterol and triglyceride contents of shrimp fed C0 diet was significantly higher (P < 0.05) than that of shrimp fed chitosan‐containing diets. Plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities of shrimp fed C0 diet were higher than those of shrimp fed chitosan‐containing diets. Digestive gland malondialdehyde (MDA) and carbonyl protein contents of shrimp fed chitosan‐containing diets were lower (P < 0.05) than that of shrimp fed C0 diet. Total haemocyte count of shrimp fed C0 diet was lower (P < 0.05) than that of shrimp fed chitosan‐containing diets. On the contrary, the haemolymph clotting time of shrimp fed C0 diet was higher (P < 0.05) than that of shrimp fed chitosan‐containing diets. In conclusion, all results suggested that dietary intake containing 0.1% and 0.2% chitosan enhanced the growth of shrimp, whereas a higher level than 0.3% and 0.4% decreased growth of shrimp. Second‐degree polynomial regression analysis of WG and BG indicated that the optimum supplement of dietary chitosan level should be 0.19–0.21%.     

Effects of dietary carbohydrate/lipid ratios on growth performance,body composition and glucose metabolism of fingerling blunt snout bream Megalobrama amblycephala

This study aimed to investigate the optimum dietary carbohydrate/lipid (CHO/L) ratio for fingerling blunt snout bream Megalobrama amblycephala (average initial weight: 6.61 ± 0.03 g). Six isonitrogenous and isoenergetic diets were formulated to contain various CHO/L ratios ranging from 1.62 to 24.20. Each diet was tested in four replicates for 10 weeks. Specific growth rate (SGR), feed conversion ratio and nitrogen and energy retention all improved significantly (P < 0.05) as dietary CHO/L ratios decreased from 24.20 to 5.64 but showed little difference (P > 0.05) as dietary CHO/L ratios ranged from 2.45 to 5.64. Hepatosomatic index increased significantly (P < 0.05) as dietary CHO/L ratios increased, whereas intraperitoneal fat ratio showed an opposite trend (P < 0.05). Opposite to moisture content, lipid content of whole body and carcass all increased significantly (P < 0.05) as dietary CHO/L ratios decreased. Liver lipid content showed little difference (P > 0.05) among all the treatments, while liver glycogen content increased significantly (P < 0.05) with increasing CHO/L ratios. High dietary carbohydrate enhanced the activities of liver hexokinase, pyruvate kinase and glucose‐6‐phosphate dehydrogenase but did not induce hyperglycaemia. Based on the second‐order polynomial regression analysis of SGR, the optimal dietary carbohydrate and lipid contents for fingerling blunt snout bream were 291.7 and 81.4 g kg⁻¹, respectively, with a corresponding dietary CHO/L ratio of 3.58.     

Effects of dietary lipid levels on growth performance,whole body composition and fatty acid composition of juvenile gibel carp (Carassius auratus gibelio)

We evaluated the effects of dietary lipid levels on the growth, whole body composition and fatty acid composition of juvenile gibel carp (Carassius auratus gibelio). Triplicate groups of 120 juvenile Carassius auratus gibelio (average weight: 2.05 g) were fed four isonitrogenic diets formulated with lipid levels of 1.4% (low), 6.1% (control), 11.6% (medium) and 21.1% (high) for 60 days. Weight gain in the 11.6% lipid group was significantly higher than that in the other groups (P < 0.05). The feed conversion ratio decreased and protein efficiency ratio increased (P > 0.05) as dietary lipid levels increased. N‐3 polyunsaturated fatty acids (PUFA) were not detected in faeces. The whole body lipid contents of 11.6% and 21.1% lipid level groups were significantly higher than that of the 1.4% and 6.1% lipid level groups (P < 0.05). The content of whole body n‐3 PUFA in the 21.1% lipid level group enhanced significantly (P < 0.05). The whole body contents of eicosapntemacnioc acid (EPA) and docosahexaenoic acid (DHA) in the 21.1% lipid level group were the highest (P < 0.05). These results indicated that high dietary lipid levels (21.1%) inhibit weight gain and promoted fat and n‐3 PUFA deposition in juvenile Carassius auratus gibelio, which led to liver damage. A dietary lipid level of 11.6% was determined to be optimal for growth performance of juvenile Carassius auratus gibelio.     

Growth,feed efficiency and body composition of juvenile cobia (Rachycentron canadum Linnaeus, 1766) fed increasing dietary levels of shrimp protein hydrolysate

A shrimp protein hydrolysate (SPH) containing 894.2 g kg⁻¹ crude protein (CP) and 54.3 g kg⁻¹ total lipids was tested as a partial replacement for fish meal (FM) in diets of juvenile cobia. The effects of increasing dietary levels of SPH on the survival, weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), nitrogen retention efficiency (NRE) and daily feed intake (DFI) of cobia with initial body weight of 11.9 g were evaluated. Four isoproteic (from 431.1 to 439.7 g kg⁻¹) and isoenergetic (20 825–21 347 MJ kg⁻¹) diets were formulated to contain 0 (Control), 120, 240 or 360 g kg⁻¹ of dietary CP derived from SPH. Survival, WG, SGR, FCR, NRE and DFI ranged from 90 to 100%, 40.2–56.5 g, 4.7–6.1% day⁻¹, 1.04–1.54, 26.3–44.0% and 4.7–6.0% fish⁻¹ day⁻¹ respectively. Survival and DFI were not affected by the dietary treatments. On the other hand, fish fed the control diet and the one containing 120 g kg⁻¹ SPH had higher WG, SGR and FCR. Nitrogen retention efficiency was significantly higher for fish fed diets 0 and 120. It is concluded that up to 120 g kg⁻¹ of SPH in cobia diets can be used with no significant effects on feed utilization and fish performance.     

Quantitative dietary methionine requirement of juvenile golden pompano Trachinotus ovatus at a constant dietary cystine level

A feeding trial was conducted to determine the dietary methionine requirement of juvenile golden pompano (initial body weight 12.40 ± 0.02 g). Six diets were formulated with six graded levels of methionine (8.6, 9.2, 10.4, 11.5, 13.2 and 14.5 g kg⁻¹). Each diet was randomly assigned to triplicate groups of 20 juvenile fish in seawater floating net cages (1.0 m × 1.0 m × 1.5 m). Fish were fed twice daily (08:30 and 16:30) to apparent satiation for 56 days. Weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), feed efficiency (FE), nitrogen retention efficiency (NRE), proximate body composition, morphometry and haematology were significantly (P < 0.05) affected by the dietary methionine levels. WG, SGR and FE increased with increasing levels of methionine up to 13.2 g kg⁻¹ diet (P < 0.05) and remained nearly the same thereafter. NRE also increased with increasing levels of methionine up to 13.2 g kg⁻¹ diet (P < 0.05) and remained nearly the same thereafter. Linear regression analysis on WG and NRE indicated that the recommended optimum dietary methionine levels for optimal growth of juvenile pompano were 10.6 and 12.7 g kg⁻¹ diet, respectively, corresponding to 24.6 and 29.5 g kg⁻¹ dietary protein, respectively, so the level of dietary methionine should be between 10.6 and 12.7 g kg⁻¹ diet, corresponding to 24.6–29.5 g kg⁻¹ dietary protein. Additionally, the estimated requirements for the other essential amino acids were calculated from A/E ratios of whole‐body amino acid profile based on the methionine requirement determined from the present experiment.     

Effects of different dietary lipid sources on tissue fatty acid composition,serum biochemical parameters and fatty acid synthase of juvenile mud crab Scylla paramamosain (Estampador 1949)

A 6‐week study was conducted to determine the effects of different lipid sources in pelleted diets on juvenile mud crab Scylla paramamosain. Five isonitrogenous and isolipidic diets containing 8% level of fish oil (FO), lard (LD), safflower oil (SO), perilla seed oil (PO) or mixture oil (MO; V_FO:V_SO:V_PO = 1:1:1), and a live food of marine bivalve Potamocorbula rubromuscula as the control diet (CF), were fed to groups of 25 juvenile crabs (average initial weight 7.4 g, carapace width 3.5 cm) in triplicate. The results showed that crabs fed MO had the highest survival (P < 0.05). The moisture content was significantly higher in crabs fed LD, SO and PO (P < 0.05). Crabs fed SO exhibited the lowest crude protein and lipid (P < 0.05). Ash contents were obviously lower in LD group (P < 0.05). Highest total lipid in the hepatopancreas and muscle was in LD and FO group respectively. Glucose, total cholesterol and low‐density lipoprotein were higher while high‐density lipoprotein was lower (P < 0.05) in LD group. Tissue fatty acid compositions were consistent with those in diets. FO and MO diets had the same depression effect like CF on fatty acid synthase activity and mRNA expression in the hepatopancreas. The results of this study indicated that FO and mixed oil are suitable for preparation of pelleted diets with better effects for juvenile S. paramamosain compared with live food, and the ratio of n‐6/n‐3 fatty acids in pelleted diets must be <1.