Effect of dietary iron (Fe) levels on growth performance,hepatic lipid metabolism and antioxidant responses in juvenile yellow catfish Pelteobagrus fulvidraco

This study was conducted to determine effects of dietary Fe levels on growth performance, hepatic lipid metabolism and antioxidant response for juvenile yellow catfish Pelteobagrus fulvidraco. Yellow catfish were fed six isonitrogenous and isolipidic diets containing Fe levels of 16.20, 34.80, 54.50, 76.44, 100.42 and 118.25 mg/kg for 8 weeks. Weight gain (WG) and specific growth rate (SGR) increased with dietary Fe levels from 16.20 to 54.50 mg/kg diet and then plateaued over the level. Feed conversion rate (FCR) was highest and protein efficiency rate (PER) was lowest for fish fed the lowest Fe levels of diet. Fe contents in whole body and liver increased with increasing dietary Fe levels. Hepatic lipid content was lowest, but mRNA levels of carnitine palmitoyltransferase (CPT‐1) and peroxisome proliferator‐activated receptor α (PPARα) were highest for fish fed 54.50 mg Fe/kg diet. Fish fed adequate dietary Fe levels reduced hepatic malondialdehyde (MDA) level and increased activities of antioxidant enzymes Superoxide dismutase (SOD), Catalase (CAT) and GS. Based on the broken‐line regression analysis of WG against dietary Fe levels, optimal dietary Fe requirement for yellow catfish was 55.73 mg Fe/kg diets. Fe‐induced changes in MDA levels and antioxidant enzymatic activities paralleled with the change in hepatic lipid content, suggesting the potential relationship between oxidative stress and hepatic lipid accumulation in yellow catfish.     

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.     

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.     

The dietary zinc requirement of a benthic fish Paramisgurnus dabryanus

This study was conducted to assess the dietary zinc (Zn) on growth and antioxidant capacity of adult Paramisgurnus dabryanus. Zinc methionine (ZnM) of grade levels (0, 20, 40, 80, 120 and 160 mg/kg diet respectively) was supplemented, providing actual dietary Zn concentrations of 24.38, 28.03, 31.68, 38.98, 46.28 and 53.58 mg/kg diet respectively. P. dabryanus with an initial body weight of 5.21 ± 0.15 g were fed these Zn supplemented diets for 8 weeks. Results showed that the weight gain (WG) and specific growth rate (SGR) increased with increasing dietary Zn levels from 24.38 to 31.68 mg/kg, and then decreased above these levels. The hepatopancreas index (HIS) was the highest at 31.68 mg/kg, followed by 38.98 mg/kg. The enzymatic antioxidants in plasma and hepatopancreas firstly increased, and reached the peak at 31.68 or 38.98 mg/kg, then kept stable with the increase of dietary Zn levels. On the contrary, the content of MDA firstly decreased, and then increased. According to WG and T‐AOC in plasma, the Zn requirement was determined to be 32.02 and 32.24 mg/kg, respectively, based on regression analysis. The relatively low dietary Zn requirement of P. dabryanus may involve in the evolutional adaption of metal absorption and utilization to their habitat.     

Effects of dietary linolenic acid on growth,fatty acid composition,immune function and antioxidant status of juvenile blunt snout bream,Megalobrama amblycephala

A nine‐week feeding trial was performed to determine the dietary linolenic acid (LNA; 18:3n–3) requirements of juvenile blunt snout bream. Six iso‐nitrogenous, semi‐purified diets were prepared with different concentrations of LNA (0–25 g/kg). Dietary LNA had no significant effects on survival rate. However, final fish weight, weight gain (WG), specific growth rate (SGR) and feed efficiency ratio (FER) increased with increasing dietary LNA concentrations up to 20 g/kg. Dietary LNA increased muscle LNA and total n‐3 polyunsaturated fatty acid (PUFA) contents, but decreased total saturated fatty acid content. Fish fed 20 g/kg LNA had the highest plasma alkaline phosphatase activity, total protein, albumin and white blood cell count levels. Additionally, fish fed 20 g/kg LNA had higher triglyceride levels than control fish. Plasma glucose increased with increasing dietary LNA concentrations. Superoxide dismutase and glutathione peroxidase activities significantly increased with increasing dietary LNA concentrations up to 15 g/kg. Based on SGR and FER, the optimal dietary LNA requirements of juvenile blunt snout bream were 17.5 and 15.6 g/kg respectively.     

Effects of dietary protein levels on the growth,body composition,serum biochemistry and digestive enzyme activity in Chinese rice field eel (Monopterus albus) fingerlings

A 12‐week feeding trial was conducted to determine the influence of dietary protein levels on growth performance, body composition, haematological parameters and digestive enzyme activity of Chinese rice field eel (Monopterus albus) fingerlings. Six isolipidic experimental diets (27.89%, 32.23%, 35.95%, 40.06%, 43.31% and 46.53%) were formulated to randomly assign to triplicate groups of 50 rice field eel fingerlings (5.0 ± 0.5 g) cultured in plastic cages. Results indicated that the best growth performance of fish with the highest WG (158.68 ± 31.59%) and SGR (2.28 ± 0.21%) was obtained at 40.06% group. Significant alterations were demonstrated on whole‐body crude protein, crude lipid and amino acid profile by different dietary protein levels. Besides, haematological parameters including triacylglycerol, aspartate aminotransferase and alkaline phosphatase decreased with various levels by the increasing of dietary protein levels. The lowest pepsin activity was observed in 27.89% protein group, which suggested lower availability of protein as substrate for protease activity. Meanwhile, the highest amylase activity in fish of 27.89% group indicated higher carbohydrate level in this group. Based on the polynomial regression analysis of WG and SGR, the dietary protein requirement for fingerlings of Monopterus albus was estimated to be 386.4–390.8 g/kg, respectively, with the lipid level of 10.08%.     

Effects of dietary vitamin B1 on growth performance,blood metabolites,body composition,intestinal enzyme activities and morphometric parameters of juvenile yellow catfish (Pelteobagrus fulvidraco)

The effects of vitamin B₁ on growth, blood metabolites, body composition, intestinal enzyme activities and morphometric parameters were evaluated by a 63‐day feeding trial in Pelteobagrus fulvidraco fed diets containing vitamin B₁ with 4.29, 6.02, 7.86, 11.94 and 19.05 mg/kg, respectively. Results showed that 7.86 mg/kg vitamin B₁ resulted in significantly higher weight gain (WG), specific growth rate (SGR) and protein efficiency ratio (PER) (p < .05). Serum triglyceride, cholesterol and whole‐body lipid were observed in 11.94 mg/kg vitamin B₁ group significantly higher than those in 4.29 mg/kg group, accompanied by the lower serum glucose content in the same group (p < .05). Significantly higher values of whole‐body protein, serum total protein, relative intestinal length, fold height, intestinal trypsin, amylase, alkaline phosphatase, Na+/K+‐ATPase, γ‐glutamyl transpeptidase, creatine kinase, muscular layer thickness and intestosomatic index were observed in 7.86 mg/kg vitamin B₁ group compared with those in 4.29 mg/kg group (p < .05). These results suggested that diets supplemented with vitamin B₁ improved growth performance, feed utilization, intestinal digestive and absorption capacity of juvenile yellow catfish. The optimal dietary vitamin B₁ requirements estimated using a two‐slope broken‐line model based on WG and PER of yellow catfish were 7.42 and 6.01 mg/kg, respectively.     

Effect of dietary lipid source and vitamin E on growth,non‐specific immune response and resistance to Aeromonas hydrophila challenge of Chinese mitten crab Eriocheir sinensis

Six purified diets were formulated to contain three lipid sources, fish oil (FO), linseed oil (LO) and soybean oil (SO), at 6% diet lipid crossing two levels of vitamin E (100 and 300 mg α‐tocopheryl acetate/kg diet) for each lipid source (FO100, FO300, LO100, LO300, SO100, SO300). The juvenile Chinese mitten crab, Eriocheir sinensis, respectively, fed on these diets with four replicates for 6 weeks. The crab weight gain (WG) and specific growth rate (SGR) were significantly affected by dietary lipid sources. No difference was found between the crabs fed two levels of vitamin E, but the WG and SGR were numerically higher in crab fed 300 mg/kg vitamin E than those fed the other level of vitamin E. The lipid source and vitamin E level could affect fatty acid composition in the hepatopancreas. The contents of saturated fatty acids (SAFA) and n‐3HUFA were significantly higher in the crab‐fed fish oil. The highest contents of n‐6PUFA and n‐3PUFA were found in the crab‐fed soybean oil and linseed oil respectively. The contents of SAFA, n‐3HUFA and n‐3PUFA were higher in the 300 mg/kg vitamin E treatment. A lower malondialdehyde (MDA) content and higher phenoloxidase (PO) activity were observed in the crab fed 300 mg/kg vitamin E. The results of this study indicate that the Chinese mitten crab fed the diet with 6% fish oil and 300 mg/kg vitamin E showed better growth, antioxidant capacity and resistance to Aeromonas hydrophila.     

Effects of γ‐aminobutyric acid supplementation on the growth performance,serum biochemical indices and antioxidant status of pharaoh cuttlefish,Sepia pharaonis

This study evaluated the effects of dietary γ‐aminobutyric acid (GABA) on the growth performance, serum biochemical indices and antioxidant status of pharaoh cuttlefish, Sepia pharaonis. Cuttlefish were cultured in open‐culturing cement pool systems for 8 weeks. Six practical diets supplemented with graded levels of GABA (0, 20, 40, 60, 80 and 100 mg/kg) were formulated. Each diet was randomly assigned to triplicate groups of 60 cuttlefish (mean weight: 10.33 g), the cuttlefish were fed two times per day to apparent satiation. The results showed that the specific growth rate (SGR), weight gain (WG) and feed efficiency (FE) significantly increased with dietary GABA supplementation (p < .05). The survival rate (SR) and protein content in muscle significantly increased when 58.9 mg/kg GABA supplied. Moreover, the nitric oxide (NO) content and acid phosphatase (ACP) activity in serum were significantly increased with dietary GABA supplementation (p < .05), while the activity of aspartate aminotransferase (AST) in serum decreased significantly when supplied with GABA at 58.9 mg/kg (p < .05). In addition, dietary GABA improved antioxidation activity by significantly increasing the activities of superoxide dismutase (SOD) and catalase (CAT) but decreasing malondialdehyde (MDA) levels in the liver and gill (p < .05). On the basis of the quadratic regression analysis of FE, the optimum content of dietary GABA in S. pharaonis was estimated to be 55.3 mg/kg. The findings of this study demonstrated that dietary GABA had a positive effect on the growth performance, serum biochemical indices and antioxidant status of S. pharaonis.     

Effect of dietary sodium butyrate on growth performance,enzyme activities and intestinal proliferation‐related gene expression of juvenile golden pompano Trachinotus ovatus

The present study was conducted to investigate the effects of dietary sodium butyrate on growth performance, intestine enzyme activities and intestinal proliferation‐related gene expression of juvenile golden pompano Trachinotus ovatus. A basal diet was supplemented with sodium butyrate at 0.0 (control), 0.25, 0.5, 1, 2 and 4 g/kg feed for 8 weeks. The final body weight, weight gain (WG), specific growth rate (SGR) and condition factor (CF) increased with increasing dietary sodium butyrate up to 2.0 g/kg, and thereafter declined, while feed conversion ratio exhibited an opposite trend. Compared with the control, the 2.0 g/kg sodium butyrate group had higher condition factor (CF) significantly (p < 0.05). Whole body ash decreased with increasing dietary sodium butyrate level, with the lowest whole body ash content in 4.0 g/kg sodium butyrate (p < 0.05). Compared with the control, the 2.0 g/kg sodium butyrate group had significantly increased plasma glucose, cholesterol, albumin level, A/G ratio, ALT and AST contents (p < 0.05), while significantly decreased plasma ALT/AST ratio (p < 0.05). As for the intestinal digestive and brush border enzymes activities, compared with the control, the 2.0 and 4.0 g/kg sodium butyrate groups had significantly increased intestinal protease, amylase, AKP and Na⁺‐K⁺‐ATPase activities (p < 0.05), respectively. The relative level of intestinal CDX2 mRNA of fish significantly increased with dietary sodium butyrate level. Compared with the control, the 2.0 g/kg sodium butyrate groups had significantly increased the expression of intestinal CDX2 and CREB mRNA (p < 0.05), respectively. In conclusion, these results suggested that the optimum sodium butyrate level for juvenile golden pompano could be 2.0 g/kg of the diet.     

Dietary available phosphorus requirement of crucian carp,Carassius auratus

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

Growth performance,digestive enzyme activity and immune response of Japanese sea bass,Lateolabrax japonicus fed with fructooligosaccharide

In this experiment, a feeding trial was performed to determine the effects of fructooligosaccharide (FOS) on growth performance, digestive enzyme activity and immune response of Japanese sea bass, Lateolabrax japonicus juveniles (initial weight 38.3 ± 0.5 g), and the fish were examined following feeding with six levels of FOS (0, 0.5, 1, 2, 4 and 6 g/kg) for 28 days. Significant enhancement of weight gain (WG) and specific growth rate (SGR) was found in fish fed 1 g/kg FOS incorporated diets (p < .05), while the feed conversion ratio (FCR) in the 1, 2 g/kg FOS groups reduced significantly compared with the control (p < .05). Besides, the crude lipid in the 4, 6 g/kg FOS groups increased significantly compared with the control (p < .05). On the other hand, the erepsin and lipase activities significantly elevated in intestine of fish fed 2 g/kg FOS (p < .05) and the lysozyme activity in serum of fish fed 2 g/kg FOS were significantly higher than that in the control (p < .05). Moreover, the alkaline phosphatase activities in serum of fish fed 0.5, 1, 2 g/kg FOS were significantly higher than in control (p < .05). Regression analysis showed that the relationships between dietary FOS levels and either SGR, FCR, erepsin or lysozyme activities were best expressed by regression equations, and the optimal inclusion levels are 1.37, 1.80, 3.06, 3.11, 1.93 and 1.80 g/kg for SGR, FCR, erepsin, lipase, lysozyme and total superoxide dismutase activities, respectively. Overall, this study revealed that FOS incorporated diets could beneficial for L. japonicus culture in terms of increasing the growth, digestion and immune activities. Under the present experimental condition, the optimal supplementary level of FOS in the diet of L. japonicus is 1–3 g/kg.     

Modulation of growth,immunity and antioxidant‐related gene expressions in the liver and intestine of juvenile Sillago sihama by dietary vitamin C

An 8‐week feeding experiment was implemented to study the effect of dietary vitamin C (VC) on growth, immunity, oxidation resistance and relevant gene expressions in juvenile S. sihama (2.33 ± 0.02 g). Fish were fed six diets containing VC level of 5, 16, 27, 65, 122 and 233 mg/kg, respectively. VC‐deficient signs including ascites syndrome, skin decay and haemorrhage were found in the fish fed basal diets. Appropriate VC supplement in diets (a) increased weight gain (WG), specific growth rate (SGR), feed intake (FI) and protein efficiency ratio (PER); (b) increased contents of hepatic total immunoglobulin (IgM), complement 3 (C3) and complement 4 (C4) and activity of alkaline phosphatase (AKP); (c) increased hepatic and intestinal copper–zinc superoxide dismutase (CuZnSOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione S‐transferase (GST) activities, but decreased hepatic MDA content; and (d) up‐regulated gene expressions of NF‐E2‐related factor 2 (Nrf2), Kelch‐like ECH‐associated protein 1 (Keap1), CAT, GST, GPx, glutathione reductase (GR), CuZnSOD and manganese superoxide dismutase (MnSOD) in liver and intestine. These results indicated that dietary VC significantly influenced the growth, immunity and oxidation resistance at enzymatic and genic levels. Based on regression analysis for PER, IgM, intestinal CuZnSOD and hepatic VC concentration, the optimal requirement of dietary VC in juvenile S. sihama was estimated to be 98.33, 139.03, 104.23 and 143.69 mg/kg.     

Requirement of vitamin E of growing sea cucumber Apostichopus japonicus Selenka

This feeding trial was conducted to determine the vitamin E requirement of growing sea cucumber Apostichopus japonicus Selenka. Six isonitrogenous and isoenergetic experimental diets were formulated to contain graded levels of vitamin E (6.7, 81.2, 159.3, 237.8, 314.6, 395.9 mg/kg diet). Each diet was assigned randomly to 30 growing sea cucumber with initial body weight 15.43 g in triplicates for 8 weeks. Survival rate was not affected by dietary vitamin E; meanwhile, both the weight gain (WG) and specific growth rate were presented the trend of increasing first and then kept stable. With the increasing of dietary vitamin E, crude lipid content of body wall was evaluated firstly and dropped afterwards. When dietary vitamin E contents were lower than 159.3 mg/kg, vitamin E contents of body wall were increased by dietary vitamin E levels, but there were no more differences when dietary vitamin E higher than 159.3 mg/kg. There were minor effects on digestive enzymes of intestine by dietary vitamin E. Contents of malondialdehyde were decreased, while the total superoxide dismutase activity was increased first and then decreased with the increasing of dietary vitamin E. Activities of intestinal alkaline phosphatase were increased, and glutamic oxaloacetic transaminase were decreased first and then increased with the increasing of dietary vitamin E. In conclusion, analysis by a linear regression equation of WG or vitamin E contents in body wall indicated that the optimum requirement of vitamin E for growing sea cucumber (initial body weight 15.43 g) was 165.2–187.2 mg/kg diet.     

Dietary lysine requirement of juvenile Protonibea diacanthus

An 8‐week experiment was conducted to determine the optimal dietary lysine requirement for juvenile Protonibea diacanthus. Six isonitrogenous and isolipidic diets were formulated to contain levels of 10.8 (L10.8), 18.2 (L18.2), 26.1 (L26.1), 33.9 (L33.9), 40.7 (L40.7) and 48.6 g/kg (L48.6) of diets and were fed to the juvenile Protonibea diacanthus, respectively. The results indicated that weight gain (WG), specific growth rate (SGR), protein efficiency ratio (PER) and final weight (FW) increased as the dietary lysine level increased from 10.8 to 26.1 g/kg and then decreased as the dietary lysine levels further increased (p < .05). The lowest feed conversion ratio (FCR) was found when dietary lysine level was 26.1 g/kg. Analysis of specific growth rate by two slope broken‐line model indicated that the estimated optimal dietary levels of lysine for juvenile Protonibea diacanthus was 23.06 g/kg (51.24 g/kg dietary protein).     

Effects of dietary Leucas aspera levels on growth performance,nutrient utilization,digestive enzymes and physio-metabolic and health status of bagrid catfish,Rita rita (Hamilton, 1822)

The study was to examine the effects of dietary L. aspera on growth performance, physio-metabolic response and health status of Rita rita fish reared in tanks for 60 days. Six experimental diets were formulated containing 0 g/kg, 3 g/kg, 6 g/kg, 9 g/kg and 12 g/kg L. aspera and designated as D0, D3, D6, D9 and D12 respectively. The inclusion of L. aspera at graded levels resulted in significantly varying effects on growth performance where the weight gain (%), specific growth rate (SGR) and feed conversion efficiency (FCE) were significantly higher (p<0.05) in D6 and D9 groups than others. The protease and amylase activities were elevated in L. aspera supplemented groups than the control group (p<0.05), whereas lactate dehydrogenase, malate dehydrogenase and serum transaminase enzyme activities were significantly reduced with the increasing level of L. aspera and comparatively higher activities of the respective enzymes were found in the control group. The activities of oxidative stress enzymes were significantly higher (p<0.05) in the D9 group and lower in control. The blood glucose level significantly decreased with the increasing level of L. aspera in the experimental diets. The L. aspera supplemented fish had significantly higher liver glycogen, serum protein, albumin and globulin than control group. Red blood cell count was significantly higher (p<0.05) in D6-D12, whereas white blood cell count and haemoglobin content were significantly higher (p<0.05) in D6 and D9 groups. Regression analysis showed that L. aspera at the level of 7.3–7.9 g/kg is optimum for better growth and feed efficiency.     

Dietary riboflavin requirement of fingerling Channa punctatus (Bloch) based on growth,conversion efficiencies,protein retention,liver riboflavin storage,RNA/DNA ratio and carcass composition

A 16‐week experiment was conducted to determine the dietary riboflavin requirement of the fingerling Channa punctatus (6.7 ± 0.85 cm; 4.75 ± 0.72 g) by a feeding casein–gelatin‐based (450 g/kg crude protein; 18.39 kJ/g gross energy) purified diet containing graded levels of riboflavin (0, 2, 4, 6, 8, 10 and 12 mg/kg diet) to triplicate groups of fish near to satiation at 09:30 and 16:30 hr. Absolute weight gain (AWG), protein efficiency ratio (PER), specific growth rate (SGR, % per day), protein retention efficiency (PRE%) and RNA/DNA ratio were positively affected by increasing concentrations of dietary riboflavin to 6 mg riboflavin per kg diet. Feed conversion ratio (FCR) decreased up to 6 mg riboflavin per kg diet but did not decrease further with higher riboflavin supplementation. Hepatic thiobarbituric acid‐reactive substance (TBARS) concentration also supported the pattern of FCR, whereas superoxide dismutase and catalase activities increased with increasing concentrations of dietary riboflavin from 0 to 6 mg/kg. Liver riboflavin concentrations increased with increasing levels of riboflavin up to 8 mg/kg diet. Broken‐line regression analysis of AWG, PRE and liver riboflavin concentrations of fingerling C. punctatus with dietary riboflavin level indicated optimum growth and liver riboflavin saturation at 5.7, 6.1 and 7.7 mg riboflavin per kg diet, respectively.     

Effects of dietary protein levels on the growth,survival, amylase and trypsin activities in large yellow croaker,Pseudosciaena Crocea R., larvae

A feeding trial was conducted to investigate the effects of dietary graded protein levels on the growth, survival, amylase and trypsin activities of large yellow croaker (Pseudosciaena crocea R.) larvae from 12 to 42 days after hatching (DAH). Five approximately isoenergetic microbound diets (16.65 MJ/kg diet) were formulated to contain different protein (47.1%, 52.0%, 57.1%, 62.2% and 67.5%) levels. Frozen copepods, containing 54.5% crude protein (CP), 6.0% crude lipid, 27.2% ash and 6.7% glycogen, were used as a control. Each diet was randomly fed to triplicate groups of larvae with an initial mean body weight of 1.76 ± 0.09 mg (mean ± SD) in 180 L white plastic tanks, and each tank was stocked initially with 3500 larvae. Both the survival and the specific growth rate (SGR) of large yellow croaker larvae significantly increased with increasing dietary protein level up to 57.1%, and decreased thereafter. Frozen copepods resulted in intermediate survival and low SGR compared with the other diets. Whole‐body moisture and protein of larvae were not significantly affected by the dietary protein level. In contrast, whole‐body lipid of larvae fed diet with 47.1% CP was significantly higher (P<0.05) than those from fish fed the diets containing more than 57.1% CP. Additionally, fish fed the frozen copepods had the lowest whole‐body protein and lipid. The amylase‐specific activity increased with increasing dietary carbohydrate level during the period of this experiment. However, trypsin activity was not significantly affected by the dietary protein content before 42 DAH, indicating a later onset of trypsin than amylase in the regulation of enzymatic synthesis induced by a dietary substrate.     

Investigations on zinc bioavailability of different sources and dietary zinc requirement in juvenile grouper Epinephelus coioides

An experiment was implemented to study the effect of dietary zinc levels from three zinc sources on growth performance, immunity, and tissue mineral elements deposition on juvenile grouper. Based on the zinc free feeds, dietary zinc levels of 0, 10, 20, 40, 80, and 160 mg/kg were added from zinc sulphate (ZnSO₄), tetrabasic zinc chloride (TBZC), and 2‐hydroxy‐4‐(methylthio) butyrate zinc (Zn‐HMB). The results of the 8‐week study indicated that the weight gain rate (WGR) and specific growth rate (SGR) at level 10 mg/kg were significantly higher than the control fed and the reached a plateau until level 80 mg/kg, when the sources were ZnSO₄ and Zn‐HMB. WGR and SGR decreased significantly at level 160 mg/kg compared to 80 mg/kg in group TBZC. Feed coefficient (FCR) of all zinc source groups showed trend of decrease before rising. The alkaline phosphatase (AKP) in serum, catalase (CAT), total superoxide dismutase (SOD), copper‐zinc superoxide dismutase (Cu‐Zn SOD) in liver and zinc concentrations in whole body and vertebrae increased significantly than those in control group and then kept steadily in all treatments. Regardless of the sources, the manganic content of whole body or vertebra showed a downtrend. Based on the WGR, the dietary zinc requirements in juvenile grouper were 52.94 mg/kg from ZnSO₄. The average relative bioavailability (RBV) of TBZC and Zn‐HMB was 169.33% and 200.33%, respectively, compared to ZnSO₄.     

Effect of Dietary Astaxanthin on Growth,Survival, and Stress Tolerance of Postlarval Shrimp,Litopenaeus vannamei

The effect of dietary astaxanthin on growth, survival, and stress tolerance was determined in postlarval Litopenaeus vannamei. An experiment was performed with postlarval shrimp (mean initial wet weight 1.2 mg) fed four isoenergic and isonitrogenous diets containing four supplemented levels of astaxanthin (0, 100, 200, and 400 mg/kg diet, respectively). Shrimp fed diets containing 100, 200, and 400 mg astaxanthin/kg diet for 30 d showed higher weight gain (WG, %) and survival compared to the control (without supplementation of astaxanthin). Specific growth rate (SGR, %/day) and final body wet weight (FBW, mg) showed the same pattern as WG. There were no significant differences in growth performance (FBW, WG, and SGR) among the groups fed the diets with astaxanthin supplementation at the termination of feeding trial. Survival of shrimp in the control and 100 mg/kg diet treatments was significantly lower than that of shrimp in the treatments with 200 and 400 mg/kg diet. After 9 d of a stress tolerance test, survival of shrimp in the 200 and 400 mg astaxanthin/kg treatments was significantly higher than that of shrimp in the 0 and 100 mg astaxanthin/kg treatments (P < 0.05). We concluded from this experiment that astaxanthin was a necessary ingredient for the development of larval L. vannamei. Considering the effect of astaxanthin on both, growth performance and survival of postlarval L. vannamei, the level of astaxanthin supplemented in the diet should be between 100 mg and 200 mg/kg of diet.