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.     

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.     

The effects of dietary lipid levels on performance and heat‐shock protein response of juvenile white seabass,Atractoscion nobilis

A feeding trial was conducted to study the effect of dietary lipid on growth performance and heat‐shock protein (HSP70 and HSP60) response of white seabass (WSB), Atractoscion nobilis. Five diets were formulated to contain 440 g kg^?1 protein from 300 g kg^?1 fish meal, 240 g kg^?1 soybean meal and 100 g kg^?1 soy protein concentrate with different levels of lipid: 100, 120, 140, 160 or 180 g kg^?1. At the end of the trial, heat shock response based on HSP70 and HSP60 was measured in liver and white muscle from fish at ambient temperature and temperature shock conditions. Final weight and percent gain were significantly higher for fish fed the 100 g kg^?1 lipid diet than for fish fed the rest of the diets (P ≤ 0.05). Feed conversion ratio was lowest for fish fed the 100 g kg^?1 lipid diet. The HSP70 and HSP60 responses were positively correlated to dietary lipid levels following temperature shock. At ambient temperature, HSP60 and HSP70 responses in muscle and HSP60 response in liver increased with dietary lipid level. Temperature shock significantly increased the HSP response of fish in all treatments. Results of this study demonstrated that a moderate (110–120 g kg^?1) level of dietary lipids would be recommended for production diets but a higher dietary lipid level may be required for optimal stress tolerance.     

Optimum dietary protein and lipid levels for juvenile rockfish (Sebastes schlegeli,Hilgendorf 1880)

Optimum dietary protein and lipid levels for juvenile rockfish were determined. Eight hundred and ten juvenile fish averaging 3.22 g were randomly chosen and distributed into 27 flow‐through tanks of 50 L (30 fish per tank). Nine experimental diets were prepared according to a 3 × 3 factorial experimental design: three crude protein levels (45%, 50% and 55%) × three crude lipid levels (11%, 15% and 19%). Crude protein and crude lipid levels increased at the expense of dextrin and cellulose in the experimental diets. Survival of fish was not affected by either dietary protein or lipid level. Weight gain of fish was affected by dietary protein level, but not by dietary lipid level. Weight gain of fish fed the 50P‐15L (50% protein and 15% lipid) diet was higher than that of fish fed the 45% protein diets regardless of lipid level, but not different from that of fish fed the 50P‐11L (50% protein and 11% lipid), 50P‐19L (50% protein and 19% lipid), 55P‐11L (55% protein and 11% lipid), 55P‐15L (55% protein and 15% lipid) and 55P‐19L (55% protein and 19% lipid) diets. Feed consumption of fish was affected by dietary protein level, but not by dietary lipid levels. Feed efficiency ratio (FER) of fish was affected by dietary protein level, but not by dietary lipid level. Protein efficiency ratio (PER) of fish was affected by dietary protein level, but not by dietary lipid level. Nitrogen retention efficiency (NRE) of fish fed the 45P‐19L diet was higher than that of fish fed the 45P‐11L, 50P‐11L, 50P‐15L, 50P‐19L, 55P‐11L, 55P‐15L and 55P‐19L diets, but not different from that of fish fed the 45P‐15L diet. Moisture, crude protein and crude lipid contents of fish was affected by dietary protein and/or lipid level. Plasma triglyceride of fish was affected by dietary lipid level, but not by dietary protein level. In conclusion, optimum protein and lipid levels for growth and feed utilization (PER and NRE) for juvenile rockfish were 50% and 15%, and 45% and 19%, respectively, and the optimum dietary protein‐to‐energy ratio of 27.4 and 23.9 mg protein kJ^?1.     

Effects of dietary protein and lipid levels on growth,feed utilization and body composition in Pseudobagrus ussuriensis fingerlings

An 8‐week feeding trial was conducted to investigate the optimum dietary protein and lipid levels for growth, feed utilization and body composition of Pseudobagrus ussuriensis fingerlings (initial weight: 3.40 ± 0.01 g). Twelve diets containing four protein levels (350, 400, 450 and 500 g kg^?1 crude protein) and three lipid levels (50, 100 and 150 g kg^?1 crude lipid) were formulated. Fish were randomly allotted to 36 aquaria (1.0 × 0.5 × 0.8 m) with 25 fish to each glass aquarium. Fish were fed twice daily (08:00 and 16:00) to apparent satiation. The results showed that weight gain and specific growth rate (SGR) decreased with increasing dietary lipid level from 50 to 150 g kg^?1 at the same dietary protein level. Fish fed the diets containing 150 g kg^?1 lipid exhibited higher feed conversion ratio (P < 0.05), lower protein efficiency ratio (PER) and nitrogen retention efficiency (NRE) relative to fish fed the diet containing 50 and 100 g kg^?1 lipid. Weight gain and SGR significantly increased with increasing dietary protein from 350 to 450 g kg^?1 at the same dietary lipid level, and even a little decline in growth with the further increase in dietary protein to 500 g kg^?1. Daily feed intake, NRE and PER were significantly affected by both dietary protein and lipid levels (P < 0.05) and tended to decrease with increasing dietary protein and lipid levels. Whole‐body protein content increased as protein levels increased and lipid levels decreased. Whole‐body lipid and muscle lipid content increased with increasing dietary lipid level, and decreased with increasing dietary protein at each lipid level. There was no significant difference in condition factor and viscerosomatic index among fish fed the diets. Hepatosomatic index was affected by dietary lipid level (P < 0.05), and increased with increasing dietary lipid level at the same protein level. These results suggest that the diet containing 450 g kg^?1 protein and 50 g kg^?1 lipid with a P/E ratio of 29.1 mg protein kJ^?1 is optimal for growth and feed utilization of P. ussuriensis fingerlings under the experimental conditions used in the study.     

Effect of dietary protein and lipid levels on gonadal development of female redclaw crayfish Cherax quadricarinatus

The effect of two crude dietary protein (26% and 32% P) and two lipid levels (4.7% and 12% L) on gonadal development of female redclaw crayfish Cherax quadricarinatus was determined. The gonadosomatic index (GSI), hepatosomatic index (HSI), biochemical composition of gonad and hepatopancreas, oocyte diameter and frequency of the developmental stage of oocytes were analysed. The GSI was significantly less using 26% P to 4.7% L. A significant interaction between P and L content was found for GSI. A significantly higher HSI value was obtained when L was 12%. P content in the hepatopancreas was significantly higher using 32% P and 4.7% L. The maximum L content in the hepatopancreas was obtained from the 32% P and 12% L diet. A significant interaction between P and L content was found for L content in the hepatopancreas. A higher frequency of post‐vitellogenic oocytes was obtained with diets containing 32% P. There was an interaction between dietary P and L level causing lipid accumulation in the hepatopancreas and changes in GSI. For an optimum 32% P, excess dietary lipid is bioaccumulated in the hepatopancreas, indicating that there is excess available energy. When the P and L levels are restricted, there is a limited gonad development, thus affecting overall reproduction in female C. quadricarinatus.     

花幼鱼饲料中脂肪水平适宜量的研究

以等量混合的鱼油、豆油作为添加的脂肪源,设计成脂肪水平为1.62%、3.71%、5.77%、7.96%、9.95%和12.01%的6种饲料进行60 d养殖对比试验研究了饲料中花(Hem ibarbus maculatus)幼鱼脂肪水平适宜量。结果显示:花幼鱼饲料中不同脂肪水平对花的相对增重率、饲料系数和蛋白质效率存在显著差异(P<0.05),其中以投喂脂肪水平为7.96%的饲料花的生长最快,相对增重率为(1066.35±13.15)%;以投喂脂肪水平为5.77%的饲料花对蛋白质利用最高,蛋白质效率为(1.84±0.10);以投喂脂肪水平为5.77%的饲料花对饲料的利用最好,饲料系数仅1.39。研究结果表明:花幼鱼饲料中脂肪含量以5.77%~7.96%为最佳,考虑到饲料成本,把花幼鱼饲料脂肪的最适含量定为6%~7%。     

Optimum dietary protein and lipid levels for growth of juvenile sea cucumber Apostichopus japonicus

A feeding trial of three protein (200, 300 and 400 g kg⁻¹) and two lipid levels (20 and 100 g kg⁻¹) was conducted to determine the proper dietary protein and lipid levels for growth of juvenile sea cucumber Apostichopus japonicus. Dietary protein and lipid levels were adjusted by adding with different levels of soybean meal, squid liver oil and soybean oil, respectively. Three replicate groups of sea cucumbers (average weight of 1.3 g) were fed the experimental diets for 12 weeks. At the end of the feeding trial, survival was not affected by dietary protein and lipid levels (P > 0.05). Weight gain (WG) and specific growth rate (SGR) of sea cucumbers were significantly affected by dietary protein (P < 0.006) and lipid levels (P < 0.001). The highest WG and SGR were observed in sea cucumbers fed the 200 and 400 g kg⁻¹ protein diet with 20 g kg⁻¹ lipid (P < 0.05). WG and SGR of sea cucumbers fed the diet containing 20 g kg⁻¹ lipid were higher than those of sea cucumbers fed the 100 g kg⁻¹ lipid diets (P < 0.05) at each dietary protein level. Apparent digestibility coefficients of dry matter, crude protein, carbohydrate and gross energy of sea cucumbers fed the 20 g kg⁻¹ lipid diets were significantly higher than those of the 100 g kg⁻¹ lipid diets at 200 and 400 g kg⁻¹ protein (P < 0.05). Moisture, crude protein, crude lipid and ash contents were not significantly different among the groups. The results of this study indicate that the diet containing 200 g kg⁻¹ protein (170 g kg⁻¹ digestible protein) with 20 g kg⁻¹ lipid (13 g kg⁻¹ digestible lipid) may be sufficient for optimum growth of juvenile sea cucumber.     

Effects of dietary lipid sources on growth performance,lipid metabolism and antioxidant status of juvenile Russian sturgeon Acipenser gueldenstaedtii

Six isonitrogenous and isoenergetic diets were used to test the influence of lipid source on growth performance, antioxidant status and lipid metabolism of juvenile Russian sturgeon, Acipenser gueldenstaedtii. Each diet was supplemented with 90 g kg^?1 of lipid from each of six sources including fish oil (FO), beef tallow (BT), sunflower oil (SO), linseed oil (LO) and equal combinations of FO + SO + BT (FSB) or LO + SO + BT (LSB). After 56 days, fish fed LSB demonstrated highest weight gain, specific growth rate and lowest hepatosomatic index among all groups. The n‐6 polyunsaturated fatty acids (PUFAs) in the whole fish were highest in the SO group, and n‐3 PUFAs were highest in fish fed LO. The fish fed FO contained highest n‐3 highly unsaturated fatty acids. Triglyceride in the serum of fish fed LSB was lowest, but was not significantly different from that in the SO group. Triglyceride in the serum of fish fed FO and BT was highest among all groups. Lipase, malate dehydrogenase and lipoprotein lipase activities were highest in fish fed LSB. Serum malondialdehyde in fish fed LSB was significantly lower than in fish fed FO or SO, but no significant differences were found among fish fed LSB, BT, LO or FSB. Fish fed LSB showed higher catalase activity and total antioxidant capacity than fish fed FO or FSB. This study indicates that linseed, sunflower oil and BT mixed oil are a suitable lipid source and can benefit growth performance and antioxidation in juvenile sturgeon.     

饲料蛋白质和能量水平对红姑鱼生长和鱼体组成的影响

采用 3× 3因子试验确定不同蛋白质和脂肪水平实用饲料对红姑鱼生长和鱼体组成的影响。初始平均体重为 2 .73g的试验鱼放养在 2 7个 2 .5m× 1.5m× 1.3m的网箱中 ,每箱放养 6 0尾。用饲料蛋白质水平为38% ,42 %和 46 % ,脂肪水平为 5 % ,8%和 12 %的试验饲料饲养鱼 8周。结果表明特定生长率和饲料系数以高蛋白质组 (HP ,46 % )显著高于中蛋白组 (MP ,42 % )和低蛋白组 (LP ,38% ) (P <0 .0 5 ) ;饲料脂肪水平对鱼的生长和饲料系数没有显著影响 (P >0 .0 5 ) ;随饲料DP/DE降低 ,脏体比和肝体比增加 ;随饲料可消化能增加 ,全鱼和肝脏的脂肪含量增加 ,但对机体的蛋白含量、氨基酸构成和灰分含量没有多大的影响。从本试验可初步认为红姑鱼幼鱼最适饲料蛋白质水平为 46 % ,可消化蛋能比 (DP/DE)为 119mg·kcal-1。     

Effect of dietary lipid level on growth,lipid metabolism and health status of the Pacific white shrimp Litopenaeus vannamei at two salinities

Three isonitrogenous diets containing 60 g kg^–1, 90 g kg^–1 or 120 g kg^–1 lipid were formulated and fed to the Litopenaeus vannamei (2.00 ± 0.08 g) under two salinities (25 or 3 psu) in triplicate for 8 weeks. Shrimp fed 90 g kg^–1 lipid had higher weight gain and specific growth rate than shrimp fed the other two diets regardless of salinity, and the hepatosomatic index increased with increasing dietary lipid at both salinities. The shrimp at 3 psu had significantly lower survival and ash content, higher condition factor, weight gain and specific growth rate than the shrimp at 25 psu. Increasing dietary lipid level induced the accumulation of serum MDA regardless of salinity, and at 3 psu, it reduced the serum GOT and GPT activities and the mRNA expression of TNF‐α in intestine and gill of L. vannamei. The hepatopancreatic triacylglycerol lipase (TGL) and CPT‐1 mRNA expression showed the highest value in shrimp fed 90 g kg^–1 lipid diet at 3 psu. This study indicates that 120 g kg^–1 dietary lipid may negatively affect the growth and induce oxidative damage in shrimp, but can improve immune defence at low salinity; 60 g kg^–1 dietary lipid cannot afford the growth and either has no positive impact on the immunology for L. vannamei at 3 psu.     

哲罗鱼稚鱼的蛋白质和脂肪需求量

采用4×3两因素完全随机设计,研究了哲罗鱼(Hucho taimen)稚鱼蛋白质和脂肪的需要量。初始体质量为7-8 g的哲罗鱼饲养于玻璃钢水簇箱中(直径90 cm,水深45 cm)。实验共设4个蛋白质水平(50%、46%、42%、38%),每个蛋白质水平设3个脂肪水平(10%、15%和20%),共12种饲料,每种饲料投喂组设3个重复,每个重复100尾鱼。实验期间水温11.5-17.5℃,溶解氧7.8-10 mg/L,每天饲喂3次,实验共进行8周。结果表明,不同处理对成活率未产生显著影响;脂肪水平对蛋白质需要量影响较大,在10%脂肪水平,与其他蛋白质水平相比,50%蛋白质水平显著提高了终末体质量、终末体长和平均日增重(P<0.01),特定生长率和饵料系数也得到改善(P<0.05);在15%脂肪水平下,与38%蛋白质水平相比,42%、46%和50%蛋白质水平各组终末体质量、平均日增重、特定生长率和饵料系数都显著改善(P<0.05);在20%脂肪水平下,38%与50%蛋白质水平相比,终末体质量、平均日增重和饵料系数差异显著(P<0.05),但其他各组差异不显著;与10%和15%脂肪水平相比,20%脂肪水平显著提高了蛋白质效率(P<0.05);鱼体脂肪含量随饲料中脂肪含量增加而显著提高(P<0.01);50%蛋白质水平显著降低了鱼体水分和脂肪含量,提高了体蛋白含量(P<0.05);鱼体总能随着蛋白质和脂肪水平的提高也极显著提高(P<0.01)。本实验结论为:在10%脂肪水平,哲罗鱼稚鱼最适蛋白质水平为50%,在15%和20%脂肪水平下,最适蛋白质水平为42%。     

Effects of dietary protein and lipid levels on growth performance,fatty acid composition and antioxidant‐related gene expressions in juvenile loach Misgurnus anguillicaudatus

Dojo loach (Misgurnus anguillicaudatus) is one of the most important cultured freshwater fish in several East Asian countries. However, a little information is available in its nutritional requirements. Thus, this study was conducted to evaluate the effects of feeding varying levels of dietary protein and lipid on growth, fatty acid composition and antioxidant‐related gene expressions in juvenile loach. Six practical diets at three levels of protein (30%, 40% and 50%) and two levels of lipid (6% and 12%) were fed to loach juveniles (initial weight 0.40 g) in triplicated groups (20 fish per replicated) for a period of 8 weeks. Results showed that regardless of lipid level, body weight gain of fish was significantly increased with incremental dietary protein level. Meanwhile, feed conversion ratio was significantly decreased by dietary protein levels, and the lowest value was observed in fish fed dietary protein levels of 50%, regardless of dietary lipid level. Moreover, the percentage of 22:6n‐3 in viscera was significantly increased by different protein levels. The expression level of catalase was significantly increased with incremental dietary protein level with both lipid levels. Meanwhile, the expression level of hepatic nuclear factor erythroid 2‐related factor 2 (Nrf2) was downregulated with incremental dietary protein level with 6% of lipid level, but the expression was upregulated with incremental dietary protein level with 12% of lipid level. In conclusion, these data suggested that 6% lipid and 50% protein in diet was optimal for loach during early development stage.     

饲料蛋白和脂肪水平对云纹石斑鱼幼鱼免疫和抗氧化性能的影响

采用蛋白和脂肪水平双因素实验,通过检测云纹石斑鱼血清、肝脏和肌肉中免疫与抗氧化指标,为饲料蛋白和脂肪的适宜配比提供依据。以鱼粉和豆粕作蛋白源,鱼油和大豆油混合油作脂肪源,3个蛋白水平分别为:35%、40%、45%,每个蛋白水平分别设3个脂肪水平:9%、12%、15%,每组3个重复。LZM活力和IgM含量在蛋白水平40%~45%时较高,也呈现随脂肪水平增加而上升的趋势,且蛋白水平比脂肪水平和交互作用对LZM和IgM有更显著的影响。肝脏SOD活力在40%蛋白水平时较高,在低蛋白水平(35%)时SOD活力随脂肪水平上升而增强,而高蛋白水平(45%)时则相反。蛋白、脂肪水平和交互作用对CAT活力均有显著影响,蛋白水平较高CAT活力较强。肌肉SOD和CAT活力变化趋势与肝脏大致相反。MDA含量随蛋白水平增加而减小,蛋白水平对肝脏和肌肉MDA都有显著作用,随着饲料脂肪水平增加肝脏MDA显著下降。实验表明,饲料中蛋白质含量维持在一定水平(40%左右)是必要的,当蛋白需求满足时,适当增加脂肪水平有利于鱼体健康。     

Effects of fish meal replacement by low‐gossypol cottonseed meal on growth performance,digestive enzyme activity,intestine histology and inflammatory gene expression of silver sillago (Sillago sihama Forsskál) (1775)

A 56‐day feeding trial was conducted to evaluate the effects on the growth performance, digestive enzyme activity, inflammatory genes expression and intestine histology of silver sillago, Sillago sihama (Forsskål 1775), by replacing fish meal (FM) with low‐gossypol cottonseed meal (LCSM). Five isonitrogenous and isolipidic diets were formulated, including R0 group (control, containing 550.0 g/kg FM), R16 group (88.5 g/kg LCSM and 461.5 g/kg FM), R32 group (177.0 g/kg LCSM and 373.0 g/kg FM), R48 group (265.5 g/kg LCSM and 284.5 g/kg FM) and R64 group (354.0 g/kg LCSM and 196.0 g/kg FM). Fish fed R0 and R16 groups had a significantly higher weight gain rate (WGR) and specific growth rate (SGR) than R48 and R64 groups (p < .05). In contrast to whole‐body crude protein, whole‐body moisture increased with the FM level of substitution (p < .05). With the increased amount of LCSM in the diet, the activity of intestinal amylase (AMS) increased significantly (p < .05), and intestinal trypsin (TRP) decreased (p < .05). Dietary LCSM substitution upregulated the expression of intestinal tumour necrosis factor‐α (TNF‐α), the nuclear factor kappa‐light‐chain‐enhancer of activated B cells (NF‐κB), and interleukin one beta (IL‐1β), but downregulated tight junction proteins ZO‐1(ZO‐1), transforming growth factor beta‐3 (TGF‐β3) and interleukin 10 (IL‐10) expression. Histological analysis revealed progressive morphological damage to the mid‐intestine with higher levels of FM replacement. These results showed that 88.5 g/kg (16%) of FM replaced by LCSM with amino acids (methionine and lysine) supplementation did not significantly reduce growth compared with FM‐based control.     

Optimal dietary protein levels in juvenile Senegalese sole (Solea senegalensis)

A study was undertaken to determine the dietary protein level for optimal growth performance and body composition of juvenile Senegalese sole. Five experimental extruded diets were formulated to contain increasing levels of protein [430, 480, 530, 570 and 600 g kg^?1 dry matter (DM)] and a constant lipid level, ranging from 100 to 130 g kg^?1 DM. Triplicate groups of 35 sole (initial body weight: 11.9 ± 0.5 g) were grown over 84 days in 60‐L tanks supplied with recirculated seawater. Fish were fed by means of automatic feeders in eight meals per day. At the start and end of the trial, whole‐body samples were withdrawn for proximate composition analysis. At the end of 84 days of experimental feeding, daily weight gain and specific growth rate in fish fed diets P43 and P48 were significantly lower than those found in fish fed higher protein level diets (P53, P57 and P59). Similarly, feed efficiency was also significantly lower in fish fed diet P43 than in fish fed all other dietary treatments. Sole juveniles fed lower protein level diets (P43 and P48) showed a significantly lower protein content than fish fed the higher dietary protein level treatments (P53, P57 and P60). Changes within the tested dietary protein levels did not affect significantly protein productive value or total nitrogen (N) losses in fish. However, daily N gain was significantly higher (P < 0.05) in fish fed diets P53 and P60 than in fish fed the lowest protein level diet (P43). Data from the present study indicate that diets for juvenile Senegalese sole should include at least 53% crude protein to maintain a good overall growth performance. Based on a second‐order polynomial regression model, the daily crude protein requirement for maximum whole‐body N gain as estimated here for Senegalese sole juveniles was 6.43 g kg^?1 body weight day^?1 which corresponds to a value of 1.03 g N intake kg^?1 body weight day^?1. If the present data are expressed on a dietary crude protein concentration basis, the allowance for maximum protein accretion (N gain) would be met by a diet containing a crude protein level of 600 g kg^?1.     

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.     

Effects of dietary tea polyphenols on growth,immunity and lipid metabolism of juvenile black carp Mylopharyngodon piceus

An 8‐week feeding experiment was aimed to investigate the effect of dietary tea polyphenols (TP) on growth, immunity and lipid metabolism in juvenile black carp Mylopharyngodon piceus (initial weight 5.90 ± 0.03 g). Tea polyphenols were added at different levels (0, 25, 50, 100 and 500 mg/kg; TP₀, TP₂₅, TP₅₀, TP₁₀₀ and TP₅₀₀). The results are as follows: the highest specific growth rate (SGR) and condition factor (CF) and activity of trypsin (TRS) of intestine in TP₅₀, but SGR and activities of lipase (LPS)and TRS of intestine and content of whole body crude protein in TP₅₀₀ were remarkably lower than TP₀. Compared with TP₀, content of serum superoxide dismutase (SOD) and glutamic oxalacetic transaminase (GOT) remarkably increased (p < .05), but contents of glutathione (GSH), glutathione peroxidase (GSH‐Pox), malondialdehyde (MDA), triglyceride (TG) and low‐density lipoprotein cholesterol (LDL‐C) were significantly decreased (p < .05), content of cortisol was remarkably lower in TP₅₀ and TP₁₀₀ (p < .05), expression of growth hormone (GH) and melanocortin 4 receptor (MC4R) in liver and GH in muscle were remarkably up‐regulated in TP₅₀, but expression of apolipoprotein A‐1 (ApoA1), GH and MC4R of intestine, ApoA1 of liver and MC4R of muscle in TP₅₀₀ were remarkably down‐regulated, contents of complement 3 (C3), complement 4 (C4), high‐density lipoprotein cholesterol (HDL‐C) and LDL‐C were significantly reduced in TP₅₀₀ (p < .05). In conclusion, TP could improve growth performance and oxidative capacity on juvenile black carp, and its optimal dosage was 50 mg/kg.     

饲料脂肪水平对江黄颡鱼幼鱼生长性能的影响

研究了饲料中脂肪水平对江黄颡鱼幼鱼(平均体重0.44g)生长性能的影响。实验共设5个水平组,饲料脂肪水平分别为3.77%,4.82%,7.29%,8.37%,9.87%。每组20尾,3个平行,饲养66d。结果显示:随着饲料脂肪水平的升高,江黄颡鱼幼鱼的饲料系数呈上升趋势,蛋白质效率则呈下降趋势,增重率和特定生长率呈抛物线变化,但饲料系数和蛋白质效率差异不显著(P0.05),增重率和特定生长率差异显著(P0.05)。江黄颡鱼幼鱼肝脏中脂肪的蓄积量随饲料中脂肪水平的增加而增加。综合各项指标并分析增重率、特定生长率与脂肪水平的回归性关系,可以推测江黄颡鱼幼鱼期的饲料脂肪水平应该维持在7.59%~7.65%。