Effect of Different Dietary Protein and Lipid Levels on the Growth,Body Composition,and Intestinal Digestive Enzyme Activities of Juvenile Yellow Drum Nibea albiflora(Richardson)

An 8-week feeding trial was conducted to determine the optimal dietary protein-to-lipid ratio for juvenile Nibea albiflora with an initial weight of(11.76 ± 0.20) g.Nine experimental diets containing different concentrations of protein(40%,47%,or 54%) and lipids(5%,9%,or 13%) in a 3 × 3 factorial experimental design were tested in triplicate groups of fish,while the protein-to-energy(P/E) ratios of the diets varied in the range of 19.74–28.32 mg k J~(-1).Results showed that fish fed diets containing 9% or 13% lipids with 54% protein exhibited significantly higher weight gains and specific growth rates than those fed other diets.The feed conversion rate of fish fed the diet with 40% protein and 5% lipids was significantly poorer than that of fish fed other diets.The protein efficiency rate of fish fed diets with 5% lipids was significantly lower than that of fish fed 9% or 13% lipid diets.Carcass lipid and energy contents were positively correlated with dietary lipid level regardless of protein level.Fish fed a 54% protein diet showed the highest trypsin activity.The intestinal lipase activity of fish fed the diet containing 13% lipids was significantly higher than that of fish fed 5% or 9% lipid diets.These results demonstrate the high protein dietary requirements of N.albiflora.A diet containing 54% protein and 9%–13% lipids with a P/E ratio of 26.2–27.81 mg protein k J~(-1) can be considered optimal for juvenile N.albiflora.     

Dietary Protein Requirement of Juvenile Turbot(Scophthalmus maximus Linnaeus)

The dietary protein requirement of juvenile turbot(initial average weight, 38.2 g ± 0.1 g) reared indoor in aerated aquaria was determined in this study. Five energy equal experimental diets were formulated with fish meal as protein source, which contained different concentrations of protein(47.2%, 51.0%, 54.6%, 59.3% and 63.6% of dry diet). Three groups of fish with 18 individuals in each, were cultured in 300-L tanks and fed twice a day for 8 weeks. During culture, temperature was controlled between 15.0 and 18.0℃, salinity was controlled between 28.5 and 32.0, acidity was controlled between p H7.8 and p H8.5, and ammonia nitrogen was maintained below 0.03 mg L-1 and dissolved oxygen was maintained about 7 mg L-1. Results showed that the growth of fish was significantly affected by dietary protein content(P 0.05). Specific growth rate(SGR) of turbot increased when dietary protein content varied between 47.2% and 51.0%(P 0.05), and then kept stable when dietary protein content was higher than 51.0%. Fish which were fed the diet containing 63.6% protein showed the highest SGR while those fed the diet containing 59.3% protein showed the highest feed efficiency rate. No significant difference of feed intake and protein efficiency ratio was found among experimental diets(P 0.05). Broken-line regression analysis of SGR showed that the optimal dietary protein requirement of turbot was about 57.0%.     

Effects of Dietary Carbohydrate-to-Lipid Ratio on the Growth Performance and Feed Utilization of Juvenile Turbot(Scophthalmus maximus)

A 9-week feeding trial was conducted to investigate the effects of dietary carbohydrate to lipid ratio(CHO:LIP) on the growth performance and feed utilization of juvenile turbot Scophthalmus maximus(initial body weight 8.75 g ± 0.04 g). Four isonitrogenous and isoenergetic low protein level(39%) diets were formulated with increasing ratios of dietary carbohydrate to lipid(2:18, 6:18, 18:12 and 28:6). A high protein level(50%) diet with the 2:12 ratio of carbohydrate to lipid was used as the control. Results showed that the survival rate, contents of moisture, crude protein and ash in muscle were not significantly affected by dietary treatments. With the dietary CHO:LIP ratio increased from 2:18 to 18:12, weight gain rate significantly increased(P 0.05). Higher dietary CHO:LIP ratio(28:6) resulted in the significantly decreased weight gain rate(P 0.05). Meanwhile, this treatment also resulted in the highest daily feed intake and liver glycogen content, as well as the lowest feed efficiency(P 0.05). Muscle glycogen content in fish fed the diet with 2:12 or 2:18 CHO:LIP ratio was significantly lower than those fed with the other three diets(P 0.05). The present results confirmed that the juvenile turbot can utilize carbohydrate. Furthermore, the appropriate ratio of dietary carbohydrate to lipid was important to the growth and feed utilization of turbot. The proper CHO:LIP ratio based on the growth performance in the present study was determined to be 18:12 when the dietary protein level was 39%.     

Effects of dietary corn gluten meal on growth performance and protein metabolism in relation to IGF-I and TOR gene expression of juvenile cobia (Rachycentron canadum)

A growth experiment was conducted on cobia(Rachycentron canadum,initial weight 108.2 g ± 3.0 g) to investigate the effects of dietary corn gluten meal(CGM) levels on the fish growth,whole body composition and protein metabolism in relation to specific gene expression.Five isonitrogenous(crude protein 45%) and isoenergetic(gross energy 20 kJ g 1) practical diets were formulated by replacing 0%(the control),17.5%,35.0%,52.5%,and 70.0% of fish meal(FM) protein with CGM protein.No significant differences were observed in the survival,feed intake(FI),specific growth rate(SGR),feed efficiency(FE) and protein productive value(PPV) among fish fed diets with 0%,17.5%,35.0%,and 52.5% of CGM protein.However,these indices were significantly lower in fish fed the diet with 70.0% of CGM protein than those in fish fed the control diet(P < 0.05).The whole-body crude protein and lipid contents were significantly lower while the whole-body moisture content was significantly higher in fish fed the diet with 70.0% of CGM protein compared with the control group(P < 0.05).When 70.0% of FM protein was replaced by CGM,plasma total protein and cholesterol contents were significantly lower than those in the control group(P < 0.05).Fish fed the diet with 70.0% of CGM protein had significantly lower hepatic insulin-like growth factor I(IGF-I) expression levels than those in the control group(P < 0.05).However,no significant differences were observed in hepatic target of rapamycin(TOR),dorsal muscle IGF-I and TOR expression levels among dietary treatments.Results of the present study indicated that 52.5% of FM protein could be replaced by CGM in the diets without significant influences on the growth,feed utilization and protein metabolism of juvenile cobia.The present results might be useful for developing cost effective and sustainable cobia dietary formulations.     

Effects of Dietary Protein and Lipid Levels on Growth Performance,Muscle Composition,Immunity Index and Biochemical Index of the Greenfin Horse-Faced Filefish(Thamnaconus septentrionalis) Juvenile

The effects of different dietary protein and lipid levels on juvenile greenfin horse-faced filefish(Thamnaconus septentrionalis) was experimentally evaluated in a 56-day study. Fish(initial weight 6.47 ± 0.56 g) were fed with nine different diet combinations containing three varying levels of protein(37%, 43%, 49%) and lipids(4%, 7%, 10%) in triplicates, where the protein-to-energy(P/E) ratios of the diets varied in the range of 19.17–26.99 mg kJ-1. Results showed that fish fed diets containing 49%protein and 10% lipid exhibited significantly lower feed intake than those fed other diets. The weight gain of fish fed diets with 43%protein was significantly higher than that of fish fed 37% or 49% protein diets. While no significant change in weight gain was observed when lipid content was increased from 4% to 7%, weight gain decreased significantly when lipid increased from 7% to 10%.The protein efficiency ratio and feed efficiency were highest when the fish were fed the diet with 49% protein and 7% lipids. Muscle crude lipid content was positively correlated with dietary protein level regardless of lipid level. The diet of 43% protein or 7% lipids significantly reduced the activity of alanine aminotransferase and aspartate aminotransferase in liver. The contents of aspartate aminotransferase, superoxide dismutase and malondialdehyde were significantly increased from 4% to 10% lipids in plasma. The plasma total cholesterol and triglyceride contents were positively correlated with dietary lipid level at the same protein level. Our comprehensive analysis concluded that a diet with 43% protein and 7% lipid, with a P/E ratio of 23.07 mg kJ-1, significantly promote the growth performance, feed utilization and health of juvenile greenfin horse-faced filefish.     

Effects of dietary carbohydrate-to-lipid ratio on the growth performance and feed utilization of juvenile turbot (<Emphasis Type="Italic">Scophthalmus maximus</Emphasis>)

A 9-week feeding trial was conducted to investigate the effects of dietary carbohydrate to lipid ratio(CHO:LIP) on the growth performance and feed utilization of juvenile turbot Scophthalmus maximus(initial body weight 8.75 g ± 0.04 g). Four isonitrogenous and isoenergetic low protein level(39%) diets were formulated with increasing ratios of dietary carbohydrate to lipid(2:18, 6:18, 18:12 and 28:6). A high protein level(50%) diet with the 2:12 ratio of carbohydrate to lipid was used as the control. Results showed that the survival rate, contents of moisture, crude protein and ash in muscle were not significantly affected by dietary treatments. With the dietary CHO:LIP ratio increased from 2:18 to 18:12, weight gain rate significantly increased(P < 0.05). Higher dietary CHO:LIP ratio(28:6) resulted in the significantly decreased weight gain rate(P < 0.05). Meanwhile, this treatment also resulted in the highest daily feed intake and liver glycogen content, as well as the lowest feed efficiency(P < 0.05). Muscle glycogen content in fish fed the diet with 2:12 or 2:18 CHO:LIP ratio was significantly lower than those fed with the other three diets(P < 0.05). The present results confirmed that the juvenile turbot can utilize carbohydrate. Furthermore, the appropriate ratio of dietary carbohydrate to lipid was important to the growth and feed utilization of turbot. The proper CHO:LIP ratio based on the growth performance in the present study was determined to be 18:12 when the dietary protein level was 39%.     

Verification of protein sparing by feeding carbohydrate to common carp Cyprinus carpio

A 9-week feeding trial in floating freshwater cages(1.0 m×1.0 m×2.0 m) was conducted to study the effects of different dietary levels of protein and starch on growth,body composition,and gene expression of enzymes in common carp,Cyprinus carpio(mean body weight,36.12±1.18 g) to evaluate the protein-sparing effect of dietary carbohydrate.Four diets were formulated with corn starch as the carbohydrate source to obtain corn starch levels of 6.5%,13%,19.5%,or 26%and protein levels of 30.5%,28.2%,26.4%,and 24.2%.The results showed no differences in growth performance of fish fed the diets with different protein and corn starch levels,but body composition and glucose metabolic enzyme activity of carp were significantly affected by the different diets(P0.05).Weight gain,specific growth rate,and the feed conversion ratio were not different in fish fed the different dietary treatments.Protein efficiency ratio increased significantly as corn starch level increased(P0.05).Whole-body crude lipid composition increased with increasing dietary corn starch level(P0.05).Glucokinase(GK),hexokinase,and pyruvate kinase(PK) activities increased significantly with increasing dietary corn starch level(P0.05),whereas glucose-6-phosphate(G6Pase) activity decreased with increasing dietary corn starch level(P0.05).GK gene expression was significantly higher in fish fed the high-corn starch diet than those fed the low-corn starch diet(P0.05).G6 pase gene expression tended to decrease with increasing starch level(P0.05).In summary,the results indicate a protein-sparing effect by substituting carbohydrate in the diet of common carp.     

Effect of Replacing Fish Meal with Extruded Soybean Meal on Growth,Feed Utilization and Apparent Nutrient Digestibility of Juvenile White Shrimp (Litopenaeus vannamei)

Extruded soybean meal(ESBM) was evaluated as a protein source for partial replacement of fish meal(FM) in diets of juvenile Litopenaeus vannamei. In the control diet(Diet 1), FM protein was replaced with increasing dietary levels of ESBM(4.28%, 8.40%, 12.62%, 16.82%, and 25.26%) at 10%, 20%, 30%, 40%, and 60% levels(Diets 2 to 6, respectively). An eight-week feeding trial was conducted on 720 juvenile shrimp(0.67 g ± 0.01 g mean initial weight), and nutrient digestibility of the six diets was determined. ESBM could replace 20% of FM without causing a significant reduction in growth of shrimp, but other dietary treatments strongly affected whole body composition. Crude protein content of the whole body fed Diet 6 was significantly lower than that fed Diet 2(P 0.05), while crude lipid content of the whole body fed Diet 5 or 6 was significantly higher than that fed Diet 2(P 0.05). Protein digestibilities of Diets 5 and 6 were significantly lower than that of Diet 1(P 0.05). Digestibility of lipids ranged from 96.97% in Diet 6 to 98.34% in Diet 3, whereas dry matter digestibility decreased with increasing replacement level. This study indicates that 20% FM replacement with ESBM in the basic diet containing 40% protein and 30% FM is optimal for juvenile L. vannamei.     

Effects of supplemental coated or crystalline methionine in low-fishmeal diet on the growth performance and body composition of juvenile cobia Rachycentron canadum （Linnaeus）

We evaluated the effects of supplemental coated and crystalline methionine （Met） on the growth performance and feed utilization of juvenile cobia （Rachycentron canadum Linnaeus） in a 60-d feeding trial. Fish groups were fed one of six isonitrogenous and isolipidic diets： 1） fishmeal control; 2） un- supplemented experimental （low-fish-meal diet deficient in Met）; or 3） one of four Met diets supplemented with crystalline L-Met, cellulose-acetate-phthalate coated L-Met, acrylic-resin coated L-Met, or tripalmitin- polyvinyl alcohol coated L-Met. The test diets were fed to triplicate groups of cobia （initial body weight 5.40-4-0.07 g） twice a day. The weight gain and specific growth rate of the fish fed the RES diet were highest among the Met-supplemented groups and were 23.64% and 7.99%, respectively, higher than those of the fish fed with the un-supplemented experimental diet （P〈0.05）. The protein efficiency ratio of the fish fed the MET diet was significantly higher than that of the fish fed the un-supplemented experimental diet and the fish in the other methionine supplementation groups （P〈0.05）. Our results suggest that supplementation of crystalline Met in low-fish-meal diets promotes the growth performance of juvenile cobia.     

Growth and antioxidant status of oriental river prawn Macrobrachium nipponense fed with diets containing vitamin E

A feeding trial was carried out to investigate the dietary vitamin E requirement of the oriental river prawn Macrobrachium nipponense(weight of 0.3–0.4 g) and its effect role on antioxidant activity.Prawns were fed with seven levels of vitamin E(0,25,50,75,100,200,and 400 mg/kg diet) for 60 days.The results show that dietary vitamin E supplementation could significantly increased the prawn weight( P 0.05).The activity of superoxide dismutase(SOD) in the hepatopancreas was significantly higher in prawns fed with diets supplemented with ≤75 mg/kg vitamin E than in those fed with diets supplemented with 100–400 mg/kg vitamin E( P 0.05).The activity of catalase(CAT) in the hepatopancreas decreased significantly as dietary vitamin E supplementation increased( P 0.05),and no significant difference was detected in glutathione peroxidase(GSH-Px) activity between different dietary groups( P 0.05).The contents of vitamin E in the hepatopancreas and in the muscle increased with increasing dietary vitamin E.There was a linear correlation between the vitamin E level in diet and that in muscle,and between the vitamin E level in diet and that in the hepatopancreas.All the above results indicated that dietary vitamin E can be stored in the hepatopancreas and muscle and lower both the activities of SOD and CAT in the hepatopancreas,suggesting that it is a potential antioxidant in M.nipponense.Broken line analysis conducted on the weight gains of prawns in each diet group showed that the dietary vitamin E requirement for maximum growth is 94.10 mg/kg.     

The eco-nutrition requirements for dietary protein and its rhomb characteristics in juvenile turbot (Scophthalmus maximus L.)

We evaluated the dietary protein requirements of juvenile turbot (Scophthalmus maximus L.) and their effects on aquatic quality. Five experimental diets were formulated containing 450, 480, 500, 520, and 540 g/kg. Each diet was randomly assigned to triplicate groups of juvenile turbot (mean initial body weight 34.5 ± 5.5 g) for 88 d. Both the weight gain ratio and feed efficiency increased with increasing dietary protein up to 500 g/kg, but no further improvement was detected when dietary protein levels were >500 g/kg. Protein intake and digestion increased with protein levels, while fecal nitrogen and nitrogen content in seawater increased only when dietary protein exceeded 500 g/kg. Protein digestibility was highest at intermediate dietary protein levels. Chemical oxygen demand, nitrite-nitrogen (NO2--N) and phosphatic-phosphor (PO43--P) levels increased in the rearing water as dietary protein levels increased. The optimum eco-nutrition level of dietary protein for juvenile turbot was 500 g/kg under the current experimental conditions. The diets containing 540 and 500 g/kg protein had similar growth rates and feed conversion ratios, but levels of ammonia (NH4+) and nitrogen were considerably higher in the water and feces, respectively, at the higher level of dietary protein. The difference in the pattern of change between body weight gain and ammonia concentration in water with increasing dietary protein is described by rhomb characteristics.     

Effect of dietary cottonseed meal on growth performance,physiological response,and gossypol accumulation in preadult grass carp,Ctenopharyngodon idellus

Cottonseed meal(CM) was used at up to 36.95% content in the diet(replacing 60% of dietary fish meal protein) without any negative effects on growth performance of pre-adult grass carp(initial body weight,761 g) under outdoor conditions.A culture trial was conducted in net cages installed in a large concrete pond.Seven isonitrogenous and isoenergetic diets containing a gradient of CM concentrations(0,12.2%,24.4%,36.6%,48.8%,54.8%,and 61.0%) as replacement for dietary fish meal protein(0,20%,40%,60%,80%,90%,and 100%) were formulated.Dietary non-resistant starch(from maize) was inverse to dietary CM.Growth performance and feed utilization of fish fed the diets containing CM replacing 0-40% fishmeal protein were not affected after the 6-week feeding trial.Accumulation of hepatopancreatic total gossypol in the hepatopancreas was significantly correlated with free gossypol content in the diets(HTG=88.6+1.5×DFG,R~2=0.89,P0.05).Intestinal a-amylase and γ-glutamyl transpeptidase activities rose along with increasing dietary CM level.The structure of the mid-intestinal tissues and the ultrastructure of the enterocyte microvilli were normal when dietary CM was 36.6%(60% protein replacement).Increasing dietary CM content increased serum alanine aminotransferase levels but decreased serum alkaline phosphatase,cholesterol,high-density lipoprotein cholesterol,low-density lipoprotein cholesterol,triglycerides,and albumin(P0.05).     

Effect of dietary olaquindox on the growth of large yellow croaker (Pseudosciaena crocea R.) and the distribution of its residues in fish tissues

Olaquindox(OLA), one of quinoxaline-N, N-dioxides, has been put under ban. However it was used as a medicinal feed additive early; it promotes the growth of livestock and prevents them from dysentery and bacterial enteritis. In this study, we evaluated the effect of dietary OLA on the growth of large yellow croaker(Pseudosciaena crocea R.) and the histological distribution of OLA and its metabolite 3-methyl-quinoxaline-2-carboxylic acid(MQCA) in fish tissues. Four diets containing 0(control), 42.5, 89.5 and 277.2 mg kg-1 OLA, respectively, were formulated and tested, 3 cages(1.0 m × 1.0 m × 1.5 m) each diet and 100 juveniles(9.75 ± 0.35 g) each cage. The fish were fed to satiation twice a day at 05:00 am and 17:00 pm for 8 weeks. The survival rate of fish fed the diet containing 42.5 and 89.5 mg kg-1 OLA was significantly higher than that of fish fed the diet containing 0 and 277.2 mg kg-1 OLA(P 0.05), while the weight gain rate of fish fed the diet containing 42.5 and 89.5 mg kg-1 OLA was significantly higher than that of fish fed the diet without OLA(control)(P0.05), but similar to that of fish fed the diet with 277.2 mg kg-1 OLA. Fish fed the diet with 277.2 mg kg-1 OLA had the highest content of OLA and MQCA in liver(3.44 and 0.39 mg kg-1, respectively), skin(0.46 and 0.09 mg kg-1, respectively) and muscle(0.24 and 0.06 mg kg-1, respectively). In average, fish fed the diet containing OLA had the highest content of OLA and MQCA in liver which was followed by skin and muscle(P 0.05), whereas OLA and MQCA were not detectable in control. Our findings demonstrated that OLA and MQCA accumulated in large yellow croaker when it was fed with the diet containing OLA, thus imposing a potential safety risk to human health.     

Dietary Leucine Requirement for Juvenile Large Yellow Croaker Pseudosciaena crocea (Richardson,1846)

Dietary leucine requirement for juvenile large yellow croaker, Pseudosciaena crocea Richardson 1846 (initial body weight 6.0 g±0.1 g) was determined using dose-response method.Six isonitogenous (crude protein 43%) and isoenergetic (19 kJ g-1) practical diets containing six levels of leucine (Diets 1-6) ranging from 1.23% to 4.80% (dry matter) were made at about 0.7% increment of leucine.Equal amino acid nitrogen was maintained by replacing leucine with glutamic acid.Triplicate groups of 60 individuals were fed to apparent satiation by hand twice daily (05:00 and 17:30).The water temperature was 26-32℃, salinity 26-30 and dissolved oxygen approximately 7 mg L-1 during the experimental period.Final weight (FW) of large yellow croaker initially increased with increasing level of dietary leucine but then decreased at further higher level of leucine.The highest FW was obtained in fish fed diet with 3.30% Leucine (Diet 4).FW of fish fed the diet with 4.80% Leucine (Diet 6) was significantly lower than those fed Diet 4.However, no significant differences were observed between the other dietary treatments.Feed efficiency (FE) and whole body composition were independent of dietary leucine contents (P0.05).The results indicated that leucine was essential for growth of juvenile large yellow croaker.On the basis of FW, the optimum dietary leucine requirement for juvenile large yellow croaker was estimated to be 2.92% of dry matter (6.79% of dietary protein).     

Effects of brown fish meal replacement with fermented soybean meal on growth performance, feed efficiency and enzyme activities of Chinese soft-shelled turtle, Pelodiscus sinensis

A 120-day feeding experiment was conducted to investigate the effects of partial replacement of brown fish meal (BFM) by fermented soybean meal (FSBM) in diets of Chinese soft-shelled turtle (Pelodiscus sinensis). The turtles (initial mean body weight, (115.52 ± 1.05) g) were fed with three experimental diets, in which 0%, 4.72% and 9.44% BFM protein was replaced by 0%, 3% and 6% FSBM, respectively. Results showed that the feeding rate (FR), specific growth rate (SGR) and feed efficiency ratio (FER) of turtles fed with the diet containing 3% FSBM were not significantly different from the control group (0% FSBM) (P > 0.05). However, FR, SGR and FER of turtles fed with the diet containing 6% FSBM were significantly lower than those of the control group (P < 0.05). No significant differences were observed in the activities of serum glutamic-oxalacetic transaminase and glutamicpyruvic transaminase among dietary treatments (P > 0.05). However, the uric acid concentration in turtles fed with the diet containing 3% or 6% FSBM was significantly lower than that in the control group (P < 0.05). There were no significant differences in the activities of lysozyme, alkaline phosphatase and total superoxide dismutase among dietary treatments (P > 0.05). The results suggested that FSBM could replace 4.72% BFM protein in turtle diets without exerting adverse effects on turtle growth, feed utilization and measured immune parameters.     

Replacement of Dietary Fish Oil with Vegetable Oils Improves the Growth and Flesh Quality of Large Yellow Croaker （Larmichthys crocea）

We investigated the effect of the replacement of dietary fish oil with vegetable oils on the growth and flesh quality of large yellow croaker(Larmichthys crocea). The basal diet(FO) was formulated to contain 66.5% fish meal and 6.4% menhaden fish oil; whereas the other 3 experimental diets were formulated by replacing the fish oil with 50% soybean oil(SO50), 100% soybean oil(SO100) and 100% palm oil(PO100), respectively. The 4 diets were randomly assigned to 4 floating sea cages(3.0 m × 3.0 m × 3.0 m), and each was stocked with 250 fish individuals with an initial average weight of 245.29 g ± 7.45 g. The fish were fed to apparent satiation twice a day at 5:00 and 17:00, respectively, for 12 weeks. Experimental analysis showed that the specific growth rate of fish fed SO50 or PO100 were significantly higher than that of fish fed FO or SO100(P0.05), and crude lipid contents of ventral muscle and viscera were significantly lower in fish fed FO than in those fed the other 3 diets(P0.05). No significant differences in condition factor, viscerosomatic index, hepatosomatic index, gutted yield and colorimetric values of fish among the dietary treatments were observed(P0.05). Compared to FO diet, SO50, SO100 and PO100 diets led to substantial decreases in the liquid loss and water loss from fresh fillets(1 d, 4℃)(P0.05). Similarly, thiobarbituric acid reactive substance(TBARS) values of fillets under different storage conditions(1 d, 4℃; 7 d, 4℃; 4 weeks,-20℃; 8 weeks,-20℃) decreased significantly after partial or complete replacement of fish oil with vegetable oils. These findings indicated that the growth performance and selected flesh quality properties(liquid holding capacity and TBARS value) of large yellow croaker were substantially improved by replacing dietary fish oil with vegetable oils.     

Effects of dietary soy isoflavones on feed intake, growth performance and digestibility in juvenile Japanese flounder (Paralichthys olivaceus)

An 8-week feeding trial was conducted to investigate the effects of dietary soy isoflavones on feeding intake,growth performance,and digestion of juvenile Japanese flounder(Paralichthys olivaceus).Four isonitrogenous(49% crude protein) and isoenergetic(20.1 MJ kg-1) diets were formulated to contain four graded levels of soy isoflavones,namely,0,1,4 and 8 g soy isoflavones in 1 kg of diet.Each diet was randomly fed to triplicate tanks of fish(Initial average weight:2.58 g ± 0.01 g),and each tank was stocked with 35 fish.No significant difference was observed among diets with levels of 0,1 and 4 g kg-1 soy isoflavones in feed intake,weight gain,feed efficiency ratio(FER),proximate composition of fish whole body and apparent digestibility coefficients(ADC) of nutrients and energy(P>0.05).However,high dietary soy isoflavones level(8 g kg-1) significantly depressed weight gain,FER,whole-body crude lipid content of fish and ADC of nutrients(P<0.05).These results indicate that high level of dietary soy isoflavones(above 4 g kg-1) significantly depresses growth responses and FER of Japanese flounder.However,as the content of soy isoflavones in soybean meal is around 1 to 3 g kg-1,the adverse effects might be neglected when soybean products are used as a fish feed ingredient.     

Dietary Leucine Requirement of Juvenile Japanese Seabass (Lateolabrax Japonicus)

A 56-day feeding trial was conducted to examine the dietary leucine requirement of juvenile Japanese seabass in seawater floating net cages(1.5 m × 1.5 m × 2.0 m). Six isonitrogenous(crude protein 40%) and isoenergetic(gross energy 20 k J g-1) diets were formulated to contain different concentrations of leucine(0.9%, 1.49%, 2.07%, 2.70%, 3.30% and 3.88% of dry matter). Crystalline L-amino acids were supplemented to simulate the whole body amino acid pattern of Japanese seabass except for leucine. Three groups(30 fish individuals each, 8.0 g ± 0.20 g in initial weight) were fed to apparent satiation at 5:00 and 17:30 every day. During the experimental period, the water temperature ranged from 26 to 32℃ and salinity from 26 to 30, and the dissolved oxygen was maintained at 7 mg L-1. The results showed that weight gain(WG), nitrogen retention(NR), feed efficiency(FE) and protein efficiency ratio(PER) were significantly increased when dietary leucine was increased from 0.90% to 2.70% of dry matter, and then declined. WG was the highest when fish were fed D4 containing 2.70% of leucine. No significant differences were observed in body composition among dietary treatments(P 0.05). Considering the change of WG, the optimum dietary leucine requirement of juvenile Japanese seabass was either 2.39% of dry matter or 5.68% of dietary protein.     

Effect of Dietary Olaquindox on the Growth of Large Yellow Croaker（Pseudosciaena crocea R.） and the Distribution of Its Residues in Fish Tissues

Olaquindox（OLA）, one of quinoxaline-N, N-dioxides, has been put under ban. However it was used as a medicinal feed additive early; it promotes the growth of livestock and prevents them from dysentery and bacterial enteritis. In this study, we evaluated the effect of dietary OLA on the growth of large yellow croaker（Pseudosciaena crocea R.） and the histological distribution of OLA and its metabolite 3-methyl-quinoxaline-2-carboxylic acid（MQCA） in fish tissues. Four diets containing 0（control）, 42.5, 89.5 and 277.2 mg kg^-1 OLA, respectively, were formulated and tested, 3 cages（1.0 m × 1.0 m × 1.5 m） each diet and 100 juveniles（9.75 ± 0.35 g） each cage. The fish were fed to satiation twice a day at 05：00 am and 17：00 pm for 8 weeks. The survival rate of fish fed the diet containing 42.5 and 89.5 mg kg^-1 OLA was significantly higher than that of fish fed the diet containing 0 and 277.2 mg kg^-1 OLA（P 0.05）, while the weight gain rate of fish fed the diet containing 42.5 and 89.5 mg kg^-1 OLA was significantly higher than that of fish fed the diet without OLA（control）（P0.05）, but similar to that of fish fed the diet with 277.2 mg kg^-1 OLA. Fish fed the diet with 277.2 mg kg^-1 OLA had the highest content of OLA and MQCA in liver（3.44 and 0.39 mg kg^-1, respectively）, skin（0.46 and 0.09 mg kg^-1, respectively） and muscle（0.24 and 0.06 mg kg^-1, respectively）. In average, fish fed the diet containing OLA had the highest content of OLA and MQCA in liver which was followed by skin and muscle（P〈 0.05）, whereas OLA and MQCA were not detectable in control. Our findings demonstrated that OLA and MQCA accumulated in large yellow croaker when it was fed with the diet containing OLA, thus imposing a potential safety risk to human health.     

Effects of different dietary lipid sources on growth performance and tissue fatty acid composition of juvenile swimming crab Portunus trituberculatus

This study was conducted to evaluate the effects of dietary lipid sources on the growth performance and fatty acid composition of the swimming crab, P ortunus trituberculatus. Four isonitrogenous and isoenergetic experimental diets were formulated to contain four separate lipid sources, including fish, soybean, rapeseed, and linseed oils(FO, SO, RO, and LO, respectively). With three replicates of 18 crabs each for each diet, crabs(initial body weight, 17.00 ±0.09 g) were fed twice daily for 8 weeks. There were no significant differences among these groups in terms of weight gain, specific growth rate, and hepatosomatic index. However, the RO groups' survival rate was significantly lower than FO groups. The feed conversion and protein efficiency ratios of RO groups were poorer than other groups. The proximate compositions of whole body and hepatopancreas were significantly affected by these dietary treatments. Tissue fatty acid composition mainly reflected dietary fatty acid compositions. Crabs fed FO diets exhibited significantly higher arachidonic, eicosapentaenoic, and docosahexaenoic acid contents in muscle and hepatopancreas compared with VO crabs. Linoleic, oleic, and linolenic acids in muscle and hepatopancreas were the highest in the SO, RO, and LO groups, respectively. The present study suggested that SO and LO could substitute for FO in fishmeal-based diets for swimming crabs, without affecting growth performance and survival.