Effects of dietary supplementation with coconut oil on the growth,fatty acid profiles and some lipid metabolism relative gene expressions of orange‐spotted grouper Epinephelus coioides

This study investigated the effects of coconut oil as a dietary supplement on the growth, lipid metabolism and related gene expressions of juvenile orange‐spotted grouper Epinephelus coioides. Coconut oil at concentrations of 0, 10, 30 and 50 g/kg was used to replace dietary lipids in a basal diet containing 150 g/kg lipids. The four experimental diets were, respectively, fed to triplicate groups of juvenile groupers (initial weight: 8.53 ± 0.13 g) in a recirculating system for 8 weeks. Fish fed the diet containing 50 g/kg coconut oil exhibited lower (p < .05) weight gain than did fish fed the diet containing 30 g/kg coconut oil; however, no significant differences in weight gain were observed between fish fed diets containing 0 and 10 g/kg coconut oil. Hepatic carnitine palmitoyltransferase‐1, fatty acid synthase, fatty acid elongase, fatty acid desaturase and peroxisome proliferator‐activated receptor gamma gene expressions were all the highest in fish fed the diet containing 10 g/kg coconut oil. Fish fed the coconut oil‐free basal diet demonstrated upregulated gene expression of neuropeptide Y. The results suggest that dietary supplementation with 10 g/kg coconut oil exerted beneficial effects on lipid metabolism by E. coioides.     

Growth response,body composition,plasma metabolites,digestive and antioxidant enzymes activities of Siberian sturgeon (Acipenser baerii,Brandt, 1869) fed different dietary protein and carbohydrate: lipid ratio

Knowing the effect of dietary nutrients on physiological parameters, especially oxidative stress, during fish rearing can be useful to improve fish health and optimize production in aquaculture. In this study, four iso‐energetic (2 × 2 factorial design) diets differing in nutrient composition were submitted to the Siberian sturgeon juveniles, to analyse biochemical and physiological responses. The juveniles were fed for as long as 10 weeks with the following diets: low protein–high carbohydrate (CHO): lipid ratio (LP‐St), high protein–high CHO: Lipid ratio (HP‐St), low protein‐low CHO: Lipid ratio (LP‐L) and high protein‐low CHO: Lipid ratio (HP‐L). It was shown that HP‐L diet significantly induced higher growth performance in the juveniles than LP‐L; however, there was not a significant difference between them with other treatments. HSI was increased by higher dietary CHO: L ratio. The result obviously showed the higher dietary fat led to an increase in sturgeon body fat content. In addition, dietary protein and CHO: lipid ratio significantly affected plasma metabolites (glucose, cortisol, cholesterol and triglyceride) but did not affect IGF‐1 and insulin levels. Based on enzyme activities results, incorporation of high protein (44%) in the diet induced lower amylase activity and carbohydrate digestion in the sturgeon juveniles. Moreover, antioxidant enzyme activities in this species were more influenced by lipid than other nutrients. In conclusion, using appropriate carbohydrates (~30%) in the sturgeon diet helps to spare protein. Furthermore, it is suggested to decrease the amount of lipid in high protein diet, to improve higher sturgeon fillet quality and less oxidative damage in liver.     

Protein‐sparing effects and LPL gene expressions of dietary lipids in the juvenile soft‐shelled turtle,Pelodiscussinensis

The aim of this study was to evaluate the effects of dietary lipids on protein‐sparing and lipoprotein lipase (LPL) mRNA expression in culture using 360 juvenile soft‐shelled turtles (Pelodiscussinensis) (initial weight 4.26 ± 0.14 g). The turtles were allotted to six diets with three duplicates for 60 days. A control diet with 46% protein and 55% fishmeal (CD) and five isonitrogenous diets with 41.3% protein and 45% fishmeal (F, S, L1, L2 and L3) were used, containing the following three lipid types: fish oil, soybean oil and mixed oils (soybean oil: fish oil = 1:1). The results showed that the survival rate was not affected by dietary lipids (P > 0.05). The highest weight gain and lowest feed coefficient ratio were seen in the L3 diets (P < 0.05). Turtles fed with L2 and L3 diets had lower superoxide dismutase activities, higher alanine aminotransferase activities and higher cholesterol concentrations than those exposed to other diets (P < 0.05). Hepatic LPL activity and LPL mRNA expression were higher in the L3 diets than in the other diets (P < 0.05). Overall, there were obvious protein‐sparing effects of dietary lipids and LPL mRNA expression was stimulated by high dietary lipids in soft‐shelled turtles in this study.     

Comparison of L‐lysine·HCl and L‐lysine sulphate in the feed of Penaeus monodon and re‐evaluation of dietary lysine requirement for P. monodon

Two trials were conducted to compare L‐lysine HCl and L‐lysine sulphate regarding its availability to Penaeus monodon, and further evaluate the optimum dietary lysine requirement. In experiment 1, five experimental diets were formulated (D1, D2, D3, D4 and D5), a basal diet (D1), aimed at a low‐lysine concentration (2.22% dry matter), with lysine concentration of the other four diets increasing in two 0.25% L‐lysine intervals from either L‐lysine HCl (D2 and D3) or L‐lysine sulphate (D4 and D5). Each diet was fed at a restricted rate to three groups of 40 shrimp for 74 days. The highest values of growth performance (weight gain, WG; specific growth rate, SGR) and survival were observed with shrimp fed the L‐lysine HCl diet. Feed efficiency (FE) of shrimp fed D2 was significantly higher than that of shrimp fed D1 and D5 (P < 0.05), but without significant difference with shrimp fed D3 and D4 (P > 0.05). In experiment 2, six diets (d1, d2, d3, d4, d5 and d6) were formulated with six graded levels of lysine (2.21%, 2.41%, 2.59%, 2.87%, 3.11% and 3.29% of diet). Each diet was randomly assigned to triplicate groups of 40 shrimp for 74 days. WG, SGR and survival increased increasing levels of lysine up to 2.41% of diet and reached an apparent plateau. Broken‐line model analysis on WG and SGR indicated that the optimum dietary lysine level for optimal growth of shrimp was 2.37% of diet, corresponding to 5.78% of dietary protein. In conclusion, results of this trial suggest that L‐lysine HCl is superior to L‐lysine sulphate when fed to Penaeus monodon and optimal growth can be obtained at lysine levels corresponding to 2.37% of diet, or 5.78% of dietary protein in this specie.     

Optimal dietary carbohydrate‐to‐lipid ratios for silvery‐black porgy (Sparidentex hasta) juveniles

Four isonitrogenous diets containing different carbohydrate:lipid (CHO:L) ratios (0.3, 0.6, 1.1 and 1.8) were tested in triplicate groups (16 fish per replicate) of silvery‐black porgy juveniles for 8 weeks. Growth performance was not affected by different dietary CHO:L ratios (P > 0.05); however, the viscerosomatic index, the intraperitoneal fat, whole‐body lipid, energy and n‐3 long chain polyunsaturated fatty acids levels increased with decreasing dietary CHO:L ratios (P < 0.05). Fish fed with 1.8 CHO:L diet had the lowest apparent digestibility coefficients of protein and lipid, as well as the lowest plasma haemolytic and lysozyme activities (P < 0.05). Red blood cell counts and plasma glucose levels were higher in fish fed with 1.1 and 1.8 CHO:L ratio diets than in the other groups (P < 0.05). Plasma alkaline phosphatase and alanine aminotransferase, as well as the level of lipid peroxidation and total antioxidant capacity in the liver and plasma increased as dietary CHO:L ratios decreased (P < 0.05). The results of the current study indicated that the diets with CHO:L ratios between 0.6 and 1.1 are optimal for silvery‐black porgy, whereas higher ratios may result in hyperglycaemia and immune suppression, and lower CHO:L ratios may lead to oxidative stress and liver dysfunction.     

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

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

Effects of dietary L‐lysine supplementation on growth,body composition and muscle‐growth‐related gene expression with an estimation of lysine requirement of GIFT tilapia

An 8‐week feeding trial was conducted with extruded practical diets containing 320 g/kg of crude protein from plant‐based sources to determine the effects of L‐lysine on growth performances, muscle‐growth‐related gene (myoD, myogenine and myostatin) expression and haemato‐biochemical responses in juvenile genetically improved farmed tilapia (GIFT). Five isonitrogenous and isoenergetic diets were formulated to contain graded levels of lysine (14.3, 16, 17.5, 19 and 20.5 g/kg of diet). Each diet was randomly assigned to triplicate groups of 30 juvenile fish (5.2 ± 0.1 g), which were fed thrice a day (9:00, 13:00 and 17:00 hr). Maximum growth performances were observed in fish fed with lysine at 19 g/kg of diet. There was no significant (p > .05) effect on whole‐body composition and amino acids profile by dietary lysine supplementation. Significant (p < .05) changes were observed in relative expression of muscle‐growth‐related genes namely myoD and myogenine and in plasma metabolites by dietary lysine supplementation. In contrast, the relative expression of myostatin was not affected by dietary lysine supplementation. Broken‐line regression analysis and second‐order polynomial regression analysis of weight gain and N gain against dietary lysine levels showed that the dietary lysine requirement for juvenile GIFT tilapia was 18–18.3 g/kg of diet and 19.3–19.5 g/kg of diet, respectively.     

Effects of Dietary Carbohydrate‐to‐lipid Ratio on Growth Performance,Body Composition,Digestive Enzyme Activities,and Hepatic Enzyme Activities in Juvenile Large Yellow Croaker,Larimichthys crocea

An 8‐wk feeding trial was conducted to investigate the effects of dietary carbohydrate‐to‐lipid ratios (CHO : L) on growth performance, body composition, digestive enzyme activities, and hepatic enzyme activities of juvenile large yellow croaker, Larimichthys crocea. Six isonitrogenous (45% crude protein) and isoenergetic (18 kJ/g gross energy) diets with varying CHO : L ratios (0.07, 0.48, 1.20, 2.19, 4.81, and 10.48) were fed to triplicate groups of large yellow croaker in floating sea cages. Results showed that the highest specific growth rate (SGR) was found in fish fed diets with CHO : L ratio of 2.19. Fish fed the lower (0.07 and 0.48) CHO : L ratios tended to produce lower growth (P < 0.05). The whole‐body lipid content significantly decreased, while hepatosomatic index, liver glycogen content, and plasma glucose concentration significantly increased as dietary CHO : L ratios increased (P < 0.05). Plasma total cholesterol, triglyceride, and low‐density lipoprotein cholesterol concentrations significantly decreased with elevated dietary CHO : L ratios (P < 0.05). The increasing dietary CHO : L ratios significantly stimulated the activities of intestinal amylase and hepatic pyruvate kinase and depressed the activity of hepatic phosphoenolpyruvate carboxykinase (P < 0.05). Based on a second‐order polynomial regression analysis of SGR, 2.38 was determined as the optimal dietary CHO : L ratio for juvenile large yellow croaker.     

The optimal dietary protein level of large‐size grouper Epinephelus coioides

An 8‐week feeding trial was conducted to determine the requirement of protein for large‐size grouper Epinephelus coioides (initial body weight: 275.07 ± 1.56 g). Six iso‐lipidic (124 g/kg) diets were formulated containing graded levels of protein (350, 400, 450, 500, 550 and 600 g/kg). Grouper was hand‐fed twice daily to apparent satiation with triplicate. The results showed that significantly high weight gain, specific growth rate and significantly low feed conversion ratio were observed in fish fed 450 g/kg protein group. High‐protein level diets significantly increased protein content and significantly decreased lipid content of fish body and muscle. Total protein and cholesterol content in serum of 600 g/kg group were significantly higher than those of 350 g/kg group. However, serum glucose and triglyceride contents of fish fed low‐protein diets were significantly higher than those of fish fed high‐protein diets. Meanwhile, liver glutamic‐pyruvic transaminase and glutamic‐oxaloacetic transaminase in high‐protein diet groups were significantly higher than those of low‐protein diet groups. The intestinal protease activity in high‐protein diet groups was significantly higher that of low‐protein diet groups, but lipase and amylase showed opposite trend. With the increasing of dietary protein level, the activities of alkaline phosphatase, superoxide dismutase and lysozyme in liver of grouper increased significantly compared with 350 g/kg group, while the activities of acid phosphatase decreased significantly. With specific growth rate as the evaluation index, the optimum dietary protein level of large‐size grouper Epinephelus coioides was 438.39 g/kg by fitting the broken‐line regression analysis.     

Fishmeal levels can be successfully reduced in white shrimp (Litopenaeus vannamei) if supplemented with DL‐Methionine (DL‐Met) or DL‐Methionyl‐DL‐Methionine (Met‐Met)

The main objective of this study was to evaluate the effect of methionine supplementation when reducing fishmeal levels in diets for white shrimp (Litopenaeus vannamei). Tested diets consisted of a positive control with 260 g/kg fishmeal (D1), two negative controls with 100 g/kg fishmeal and no amino acid (AA) supplementation (D2) or supplemented with lysine but not methionine (D3), and four additional diets with 100g/kg fishmeal supplemented with increasing levels of DL‐Met (1.0, 2.0 or 3.0 g/kg) (D4, D5, D6) or Met‐Met (1.0 g/kg) (D7). Each diet was fed to four groups of 30 shrimp for 8 weeks at a daily rate of 70 g/kg body weight. Reduction in fishmeal from 260 g/kg down to 100 g/kg did not significantly affect survival rate, feed conversion ratio (FCR), protein efficiency ratio (PER) or protein retention efficiency (PR%) of white shrimp. However, growth performance (final body weight, FBW; weight gain, WG; specific growth rate, SGR) was reduced when dietary fishmeal level was reduced from 260 g/kg (D1) to 100 g/kg without methionine supplementation (D2). The growth performance (FBW, WG and SGR) of shrimp was significantly increased by supplementation of the 100 g/kg fishmeal diet with increasing levels of DL‐Met (p < .05). Same performance as positive control (D1) was achieved with diets containing 100 g/kg fishmeal and supplemented with 3.0 g/kg DL‐Met or 1.0 g/kg Met‐Met. The highest values of growth performance (FBW, WG and SGR) were found in shrimp fed D6 and D7 diets, which were significantly higher than those of shrimp fed D2 and D3 diets (p < .05) but without statistical differences with shrimp fed D1, D4 and D5 diets (p > .05). The highest values of whole‐body and muscle protein contents were found in shrimp fed D1 diet, which were significantly higher than those of shrimp fed all other diets (p < .05). The highest value of intestinal tract proteolytic enzyme activity was found in shrimp fed Met‐Met‐supplemented diet (D7) and followed by the positive control diet (D1) and 3 g/kg DL‐Met‐supplemented diet (D6) (p < .05). The highest values of apparent digestibility coefficients (ADCs) of dry matter and crude protein were found in Met‐Met‐supplemented diet (D7) and followed by the positive control diet (D1) (p < .05). Shrimp fed the D1 diet showed the highest value of total essential amino acid (EAA) and was significantly higher than shrimp fed D2–D3 (p < .05) but without significant difference with shrimp fed D4–D7 (p > .05). In conclusion, results showed that same performance can be achieved with diets containing 260 or 100 g/kg fishmeal supplemented with 3.0 g/kg DL‐Met or 1.0 g/kg Met‐Met. Moreover, supplementation of limiting methionine in low‐fishmeal diets seems to improve the digestive proteolytic activity, improving digestibility of dry matter and protein, and eventually to promote growth of juvenile white shrimp in fishmeal reduction diets.     

Dietary manganese requirement of juvenile hybrid grouper,Epinephelus lanceolatus × E. fuscoguttatus

An 8‐week feeding trial was conducted to estimate the optimum dietary manganese (Mn) requirement for juvenile hybrid grouper, Epinephelus lanceolatus × E. fuscoguttatus. The basal diet was formulated to contain 520 g/kg crude protein from casein and fishmeal. Manganese methionine was added to the basal diet at 0 (control group), 2.5, 5, 10, 20 and 40 mg Mn/kg diet providing 7.48, 10.34, 13.76, 19.72, 31.00 and 53.91 mg Mn/kg diet, respectively. Each diet was randomly fed to triplicate groups of juveniles, and each tank was stocked with 20 fish (initial weight, 60.06 ± 0.68 g). The manganese content in rearing water was monitored and kept below 0.01 mg/L. Results showed that the weight gain ratio (WGR), protein efficiency ratio (PER), specific growth rate (SGR), Mn contents in whole body, liver and vertebra, and activities of hepatic Mn superoxide dismutase (Mn‐SOD), total SOD (T‐SOD) and glutathione peroxidase (GSH‐PX) were significantly improved by dietary Mn supplementation (p < .05). However, dietary Mn did not affect arginase (DArg) activity. The highest feed conversion ratio (FCR) was observed in fish fed the basal diet (p < .05). No significant differences were found on the Cu and Zn contents in whole body by supplementing dietary Mn. Supplemented Mn in diets had significantly effect on liver and vertebral trace element deposition (p < .05). Fish fed the basal diet had the highest Fe and Zn contents in vertebra (p < .05). There were no significant differences on hepatic pyruvate decarboxylase (PDC) activity with supplemented Mn levels below 13.76 mg/kg. As biomarker of oxidative stress, malondialdehyde (MDA) content in liver was significantly higher in fish fed the basal diet (p < .05). Using the broken‐line models based on SGR, dietary Mn requirement of the juvenile hybrid grouper was estimated to be 12.70 mg/kg diet.     

Effects of dietary n‐3HUFA on juvenile white shrimp,Litopenaeus vannamei: Growth,feed utilization,antioxidant enzymes activities and fatty acid compositions

Present study investigates the effects of n‐3 high‐unsaturated fatty acid (n‐3HUFA) levels on growth performance, antioxidant enzymes activities and fatty acid compositions of juvenile Litopenaeus vannamei. These represented seven iso‐nitrogenous and iso‐lipidic diets. Analysed n‐3HUFA concentrations were 0.16% (control), 0.48%, 0.74%, 1.39%, 2.39%, 2.92% and 3.44% respectively. A total of 840 juvenile L. vannamei were randomly stocked into 21 0.5 m³ tanks for 56 days. A significant increase (p < 0.05) was observed from 0.16% to 0.74% n‐3HUFA and a decrease when n‐3HUFA was above these levels in weight gain rate (WGR) and specific growth rate. Total cholesterol, triglyceride and low‐density lipoprotein in serum showed a significant decrease, high‐density lipoprotein showed a significant increase (p < 0.05). Phenoloxidase activity in serum and sodium‐potassium adenosine triphosphatase activity in gill were significantly affected by dietary n‐3HUFA (p < 0.05), both of them showing a downward trend after upward. Malic dehydrogenase and superoxide dismutase activities in serum were also significantly affected by dietary n‐3HUFA (p < 0.05), which rose first and then decreased in general, both of them have a maximum in 2.39% group. No significant differences of the activities of aspartate transaminase and alanine transaminase were observed among all groups (p > 0.05). With dietary n‐3HUFA increase, both ∑HUFA and n‐3HUFA contents gradually increased in hepatopancreas and tail muscles (p < 0.05). Based on broken‐line regression analysis of WGR, the optimal n‐3HUFA requirement is 0.89% for juvenile L. vannamei with initial weight of 0.50 ± 0.01 g.     

Effect of dietary carbohydrate levels on growth performance,non‐specific immune enzymes and acute response to low salinity and high temperature of juvenile sea cucumber Apostichopus japonicus

This study was performed to determine the optimum dietary carbohydrate (CHO) levels of sea cucumber, based on the parameters of growth, digestive enzymes, digestibility, non‐specific immune enzymes and acute low‐salinity (20 g/L) stress and high‐temperature (30°C) stress tolerance. Diets with eight different CHO (dextrin) levels (32.9, 107.6, 192.5, 257.2, 316.8, 428.0, 482.4 and 572.8 g/kg) were fed to sea cucumber juveniles (0.49 ± 0.01 g) for 60 days. Significant higher amylase activity was observed in sea cucumbers fed diet with CHO ranging between 32.9 and 192.5 g/kg than that of other treatments (p < .05). The sea cucumbers fed with 192.5 g/kg CHO showed significantly higher acid phosphatase activity than the treatments of 482.4 and 572.8 g/kg CHO (p < .05), and significantly higher alkaline phosphatase activity than other treatments (p < .05, except 257.2 g/kg). The treatments of 428.0–572.8 g/kg were found significantly lower values than other treatments in apparent digestibility coefficients for dry matter and crude protein (p < .05). The sea cucumbers fed with 192.5, 257.2 and 316.8 g/kg CHO showed better tolerance to high‐temperature (30°C) and low‐salinity (20 g/L) stress than other treatments. In brief, the optimal dietary CHO level for the growth of juvenile sea cucumber is 177.96 g/kg. However, excessive CHO will inhibit amylase enzyme activity and decrease digestibility, resulting in low growth of sea cucumber.     

Effects of dietary carbohydrate to lipid ratios on growth and body composition of juvenile and grower rockfish, Sebastes schlegeli

Two feeding trials were conducted to determine the optimal dietary carbohydrate to lipid (CHO:L) ratio for juvenile and grower rockfish. Triplicate groups of juvenile (initial mean weight 3.6 g) and duplicate groups of grower (initial mean weight 166 g) were fed the five isonitrogenous (51% CP) and isoenergetic (4.0 kcal g^?1) diets with the different CHO:L ratios (0.4–5.6 g:g) for 8 weeks respectively. The survival of juvenile and grower was above 93% and was not affected by the dietary CHO:L ratios. Weight gain of juvenile fed the diets with CHO:L ratios of 0.8 and 1.6 was significantly higher than that of the fish fed diets with CHO:L ratios of 2.8 and 5.6 (P<0.05). The feed efficiency and protein efficiency ratio of juvenile fed the diet with CHO:L ratio of 5.6 were the lowest among all groups (P<0.05). The daily feed intake of juvenile fed the diet with a CHO:L ratio of 5.6 was significantly higher than that of the other groups (P<0.05). The condition factors of juvenile fed the diets with CHO:L ratios of 0.8 and 1.6 were significantly higher than that of 5.6 (P<0.05). The crude lipid content of whole body, liver and viscera of juvenile decreased as the dietary CHO:L ratio increased, and the opposite was found for the moisture content. Weight gain, feed efficiency, daily feed intake, protein efficiency ratio and condition factor of grower were not affected by the dietary CHO:L ratio. Hepatosomatic and viscerasomatic indexes of grower were significantly influenced by dietary CHO:L ratio (P<0.05). Significant differences were observed in the lipid content of whole body and viscera of grower. Dietary CHO:L ratios significantly affected the major fatty acid composition of whole body in both juvenile and grower. The contents of 18:2n‐6 and 18:3n‐3 linearly decreased as the dietary CHO:L ratio increased, whereas the 20:4n‐6, 20:5n‐3 and 22:6n‐3 contents increased. Based on growth, feed efficiency and body composition, the optimal dietary CHO:L ratio was 1.6 for juvenile rockfish fed isonitrogenous (51% CP) and isoenergetic (4.0 kcal g^?1) diets, and starch could partially replace lipids in the diets with CHO:L ratios ranging from 0.4 to 5.6 for grower.     

Effect of dietary carbohydrate‐to‐lipid ratios on growth performance,body composition,nutrient utilization and hepatic enzymes activities of herbivorous grass carp (Ctenopharyngodon idella)

Six isonitrogenous (390 g kg^?1) and isoenergetic (16.2 kJ g^?1) diets with varying carbohydrate : lipid (CHO : L) ratios (202.5–1.74), were fed to triplicate groups of 25 fish in indoor recirculation system. Over 8‐week‐growth trial, best weight gain (WG), specific growth rate, feed conversion ratio, protein efficiency ratio and protein production value (P < 0.05) were observed in fish‐fed diets with CHO : L ratio of 7.5. Fish fed either the lowest (1.7) or highest (202.5) CHO : L ratio tended to produce lower (P < 0.05) growth and feed conversion efficiencies. The values of viscerosomatic index, hepatosomatic index and intraperitoneal fat ratio increased as dietary CHO : L ratios decreased. There were no significant differences in whole body and liver crude protein among dietary treatments. Whole body and liver lipid increased as CHO : L ratios decreased. Plasma cholesterol and triacylglyceride levels increased linearly as dietary CHO : L ratios decreased. Activities of glucokinase and pyruvate kinase were stimulated by elevated levels of dietary carbohydrate; however, activities of lipase (LPS) and alkaline phosphatase were stimulated by elevated levels of dietary lipid. Based on a second‐order polynomial regression analysis of WG against dietary carbohydrate and lipid levels, 275 g kg^?1 of carbohydrate and 59 g kg^?1 of lipid, corresponding to a CHO : L ratio of 4.7, in a diet holding 390 g kg^?1 of crude protein and 16.3 kJ g^?1 of gross energy, proved to be optimal for grass carp. These results indicated that utilization of dietary lipid and carbohydrate was moderate in grass carp, but the fish were a little more capable of utilizing lipid compared with carbohydrate.     

Effects of dietary inclusion of soybean meal and cholesterol on the growth,cholesterol status and metabolism of the giant grouper (Epinephelus lanceolatus)

The study evaluated effects of cholesterol supplementation in a diet with high soybean meal (SBM) on the growth and cholesterol metabolism of giant grouper (Epinephelus lanceolatus). All‐fish‐meal diet was used as control. The diet including SBM (replaced 50% of the fish meal protein, SBM diet) and the SBM diet supplemented with 10 g/kg cholesterol (SBM + cholesterol) were used as experimental diets. Three diets were each fed to triplicate groups of juvenile grouper (initial body weight: 12.39 ± 0.36 g) in a recirculating aquaculture system for 8 weeks. Grouper fed the control diet showed higher (p < .05) weight gain, feed intake, feed efficiency and protein efficiency ratio than the other two dietary treatments. Hepatic cholesterol concentrations and 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase gene expressions were higher in fish fed the control diet than fish fed the control diet and SBM + cholesterol diet. Hepatic cholesterol 7α‐hydroxylase gene expression was higher in fish fed the SBM + cholesterol diet than that in fish fed the control diet. Results indicate that giant grouper on a diet low in cholesterol can regulate cholesterol synthesis, suggesting that the reduced dietary cholesterol intake in the fish fed diet containing SBM is sufficiently compensated by increased cholesterol synthesis.     

The protein requirement of grouper Epinephelus coioides at grow‐out stage

The present study was conducted to investigate the protein requirement of grouper Epinephelus coioides at grow‐out stage (initial weight of 102.8 ± 1.02 g). Six iso‐lipidic diets were formulated using white fish meal and casein as protein sources with graded levels of protein (350, 400, 450, 500, 550 and 600 g/kg). Grouper was hand‐fed twice daily to apparent satiation in triplicates for 8 weeks. The results showed that lack of protein will lead to the declined of weight gain and specific growth rate and suitable protein not only improved growth, but also reduced feed coefficient rate. In addition, high‐protein level diet significantly decreased the morphological index of grouper. For the body proximate composition analysis, the high‐protein diets (500, 550, 600 g/kg) significantly increased the protein contents in the whole body and muscle which was contrary to as observed for the lipid content. High‐protein diets significantly improved the total protein levels of plasma which were contrast to as observed in triglyceride contents. Moreso, the cholesterol content was observed to be significantly decreased after high‐protein diet supplementation. The intestinal protease activity was observed to increase significantly with increasing protein supplementation whereas a decreasing trend was observed for the lipase and amylase activity with the highest going for the groups fed diets containing 350 g/kg protein as compared to the others. The liver alkaline phosphatase, superoxide dismutase and lysozyme activity increased with increasing protein level which later decreased. On the other hand, the acid phosphatase activity showed a significant downward trend. Based on SGR, the broken‐line regression analysis showed that the optimum dietary protein level and digestible protein level of the grouper Epinephelus coioides at grow‐out stage were 466.65 and 395.79 g/kg, respectively.     

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.     

Dietary potassium requirement of fingerling Indian major carp,Labeo rohita (Hamilton), based on growth parameters,gill Na+‐K+ ATPase activity,tissue mineralization and antioxidant activities

To quantify the dietary potassium requirement of fingerling Labeo rohita (6.2 ± 0.12 cm; 1.98 ± 0.06 g), seven purified experimental diets (350 g/kg crude protein and 16.72 kJ/g gross energy) with graded levels of potassium (0.32, 1.35, 2.41, 3.46, 6.48, 9.47 and 12.39 g/kg diet) were fed to triplicate groups of fishes at 08:00, 12:00 and 16:00 hr to apparent satiation for 8 weeks. Live weight gain (LWG; 671.46%), specific growth rate (3.65%/day), protein efficiency ratio (2.16), protein gain (PG; 2.41 g/fish) and feed conversion ratio (1.32) were found to be best in fish fed diet containing 3.46 g/kg potassium. Gill Na⁺‐K⁺ ATPase activity was also highest in fish fed diet with 3.46 g/kg potassium. Potassium content of whole‐body, vertebrae and scales increased significantly with the increase in dietary potassium level up to 6.48 g/kg. Significant changes were also noted in serum malondialdehyde content, superoxide dismutase, catalase, glutathione peroxidase and alkaline phosphatase activity. Based on the maximum live weight and protein gain observed in the present study, the inclusion of 3.55 g/kg potassium is recommended for developing potassium‐balanced commercial feeds for intensive culture of fingerling L. rohita.     

Nano zinc vis‐à‐vis inorganic Zinc as feed additives: Effects on growth,activity of hepatic enzymes and non‐specific immunity in rohu,Labeo rohita (Hamilton) fingerlings

The effects of dietary administration of inorganic zinc (zinc sulphate, ZnSO₄) and nano zinc (zinc oxide nanoparticles, ZnO‐NP) were evaluated in rohu, Labeo rohita fingerlings. Fish were fed with a basal diet (Control) supplemented with ZnSO₄ (T1, T2 and T3) and ZnO‐NP (T4, T5 and T6) at 10, 20 and 30 mg/kg, respectively, for a duration of 45 days. The results revealed that fish fed diet containing 20 mg ZnO‐NP per kg (T5) had the highest weight gain and specific growth rate (SGR, % per day), which was significantly different (p < .05) from the other experimental diets. Significantly (p < .05), higher activities of the digestive and metabolic enzymes were recorded in the fish fed ZnO‐NP containing diets as compared to the diets containing inorganic Zn or control diet. The maximum serum glucose and protein levels were noted in fish reared on diet T5. Both SGOT and SGPT activities were significantly increased in fish fed Zn‐supplemented diets (T1 to T6), as compared to the control group. Similarly, innate immune parameters were improved with feeding Zn incorporated diets. The highest phagocytic (40.74 ± 0.65%) and respiratory burst (0.33 ± 0.001, OD 630nm) activities were recorded in the fish fed diet containing ZnO‐NPs at 20 mg/kg (T5). The maximum superoxide production and serum peroxidase activity were detected in the fish fed T5 and T6 diets. Overall, results indicated that short‐duration feeding (≤45 days) of dietary ZnO‐NP (20 mg/kg) improved growth, enzyme activity, serum biochemical parameters and immune function in rohu fingerlings.