Effect of ration on the growth and energy budget of Chinese longsnout catfish, Leiocassis longirostris Günther

The effect of ration on growth and energy budget of Chinese longsnout catfish was investigated in a growth trial. Fish of initial body weight of 6.5 g were fed at six ration levels (RLs): starvation, 0.8%, 1.6%, 2.4%, 3.2% of body weight per day, and apparent satiation for 8 weeks. Fish were weighed biweekly to adjust feed amount. The results showed that specific growth rate in wet weight, protein and energy increased logarithmically with increased RLs. The relationship of specific growth rate in wet weight (SGRw, % day^?1) and RL (%) was a decelerating curve: SGRw=?0.62+3.10 Ln(RL+1). The energy budget equation at satiation was: 100 IE=12.94 FE+5.50(ZE+UE)+40.07 HE+41.49 RE, where IE, FE, (ZE+UE), HE, RE are food energy, faecal energy, excretory energy, heat production and recovered energy respectively. Body composition was slightly but significantly affected by ration size except for protein content. The most efficient ration based on the relationship between RL and feed efficiency ratio in energy (FERe) was 1.8% of body weight per day.     

Effect of water temperature on the growth performance and digestive enzyme activities of Chinese longsnout catfish (Leiocassis longirostris Günther)

The present study was carried out to investigate the influence of water temperature on the growth performance and digestive enzyme (pepsin, trypsin and lipase) activities of Chinese longsnout catfish. Triplicate groups of Chinese longsnout catfish (35.6±0.48 g, mean±SE) were reared at different water temperatures (20, 24, 28 and 32 °C). The feeding rate (FR), specific growth rate (SGR) and feed efficiency ratio (FER) were significantly affected by water temperatures and regression relationships between water temperature and FI, SGR as well as FER were expressed as FR=−0.016 T ²+0.91 T −10.88 ( n =12, R ²=0.8752), SGR=−0.026 T ²+1.39 T −17.29 ( n =12, R ²=0.7599) and FER=−0.013 T ²+0.70 T −8.43 ( n =12, R ²=0.7272). Based on these, the optimum temperatures for FR, SGR and FER were 27.66, 26.69 and 26.44 °C respectively. The specific activities of digestive enzymes at 24 or 28 °C were significantly higher than that at 20 or 32 °C. In addition, there was a significant linear regression between FR or SGR and specific activities of pepsin and lipase, which indicated that pepsin and lipase played important roles in regulating growth through nutrient digestion in Chinese longsnout catfish.     

Effects on growth and feed utilization of Chinese longsnout catfish Leiocassis longirostris Günther of replacement of dietary fishmeal by soybean cake

Four practical diets containing different levels of soybean cake (0, 155, 320, 490 g kg⁻¹) were prepared to investigate the effect of replacement of fishmeal by soybean cake on the Chinese longsnout catfish ( Leiocassis longirostris Günther) during a 62-day growth trial. The diets were isonitrogenous, isoenergetic and contained about 430 g kg⁻¹ crude protein and 20 MJ kg⁻¹ gross energy. With increasing levels of dietary soybean cake, growth rate and feed utilization decreased; feeding rate and the contents of dry matter, fat and energy of fish body were not significantly affected while body protein showed lowest value in the fish fed the diet containing 320 g kg⁻¹ soybean cake.     

Effect of dietary carbohydrate sources on growth performance and utilization for gibel carp (Carassius auratus gibelio) and Chinese longsnout catfish (Leiocassis longirostris Günther)

The nutritional function of monosaccharides, disaccharides and polysaccharides for omnivorous gibel carp and carnivorous Chinese longsnout catfish were investigated and the ability of these two species to utilize carbohydrates was compared. For each species, triplicate groups of fish were assigned to each of five groups of isoenergetic and isonitrogenous experimental diets with different carbohydrate sources: glucose, sucrose, dextrin, soluble starch (acid‐modified starch) and α‐cellulose. The carbohydrates were included at 60 g kg^?1 in Chinese longsnout catfish diets and at 200 g kg^?1 in gibel carp diets. A growth trial was carried out in a recirculation system at 27.8 ± 1.9 °C for 8 weeks. The results showed that fish with different food habits showed difference in the utilization of carbohydrate sources. For gibel carp, better specific growth rate (SGR) and feed efficiency (FE) were observed in fish fed diets containing soluble starch and cellulose, but for Chinese longsnout catfish, better SGR and FE were observed in fish fed diets containing dextrin and sucrose. Apparent digestibility coefficient of dry matter (ADC_d) and apparent digestibility coefficient of energy (ADC_e) were significantly affected by dietary carbohydrate sources in gibel carp. ADC_d and ADC_e significantly decreased as dietary carbohydrate complexity increased in Chinese longsnout catfish except that glucose diet had medium ADC_d and ADC_e. In both species, no significant difference of apparent digestibility coefficient of protein was observed between different carbohydrate sources. Dietary carbohydrate sources significantly affected body composition, and liver phosphoenolpyruvate carboxykinase (PEPCK), pyruvate kinase (PK), glucose 6‐phosphate dehydrogenase (G6PD) and malic enzyme (ME) activities also varied according to dietary carbohydrate complexity. Fish with different food habits showed different abilities to synthesize liver glycogen, and the liver glycogen content in gibel carp was significantly higher than in Chinese longsnout catfish. The influence of carbohydrate source on gluconeogenesis and lipogenesis was also different in the two fish species.     

Effect of replacement of dietary fish meal by meat and bone meal and poultry by-product meal on growth and feed utilization of gibel carp, Carassius auratus gibelio

Triplicate groups of gibel carp Carassius auratus gibelio (initial body weight: 5.25 ± 0.02 g) were fed for 8 weeks at 20–25 °C on five isonitrogenous (crude protein: 400 g kg^?1) and isoenergetic diets (gross energy: 17 kJ g^?1). Meat and bone meal (MBM) or poultry by‐product meal (PBM) were used to replace fish meal at different levels of protein. The control diet contained fish meal as the sole protein source. In the other four diets, 150 or 500 g kg^?1 of fish meal protein was substituted by MBM (MBM₁₅, MBM₅₀) or PBM (PBM₁₅, PBM₅₀). The results showed that feeding rate for the MBM₅₀ group was significantly higher than for other groups except the PBM₅₀ group (P < 0.05). Growth rate in the MBM₁₅ group was significantly higher than that in the control (P < 0.05), while there was no significant difference in growth between the control and other groups (P > 0.05). Feed efficiency and protein efficiency ratio in MBM₅₀ was significantly lower while that in MBM₁₅ was significantly higher (P < 0.05). Replacement of fish meal by MBM at 500 g kg^?1 protein significantly decreased apparent dry matter digestibility (ADC_D) and gross energy (ADC_E) while apparent protein digestibility (ADC_P) was significantly decreased by the replacement of MBM or PBM (P < 0.05). The results suggest that MBM and PBM could replace up to 500 g kg^?1 of fish meal protein in diets for gibel carp without negative effects on growth while 150 g kg^?1 replacement by MBM protein improved feed utilization.     

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

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

饥饿后再投喂对异育银鲫生长和体成分的影响

在(25±2)℃条件下,对体重(15.6±0.84)g的异育银鲫(Carassius auratus gibelio)进行了不同时间的饥饿处理和再投喂的恢复生长实验。实验把异育银鲫分为4组,为Ⅰ组(持续投喂48 d)、Ⅱ组(饥饿8 d后再投喂40 d)、Ⅲ组(饥饿16 d后再投喂32 d)和Ⅳ组(饥饿24 d后再投喂24 d),每组20尾鱼,研究再投喂后体重和体成分(粗蛋白、粗脂肪、水分和灰分)的变化。结果显示:与持续投喂组相比,饥饿8 d后异育银鲫体重下降了13.28%,饥饿16 d和24 d后体重分别下降了22.36%和33.03%。短期饥饿(Ⅱ)组,再恢复投喂8 d后能实现完全补偿生长,而中长期饥饿组(Ⅲ和Ⅳ)分别在投喂16 d和24 d后表现为部分补偿生长。在饥饿和恢复投喂过程中其体成分呈现规律性变化:各试验组饥饿后,粗蛋白和粗脂肪显著下降,而水分和灰分含量上升,而再投喂后,各营养成分逐渐恢复。Ⅱ组再投喂8 d后,粗脂肪和粗灰份恢复到对照组水平,蛋白质显著低于对照组水平,水分显著高于对照组;再投喂40 d后,粗蛋白和水分亦恢复到对照水平,Ⅲ组恢复投喂16 d后,粗蛋白、粗脂肪和灰分不能恢复到对照水平,恢复投喂32 d后,除灰分外,其余成分皆不能恢复到对照水平。Ⅳ组再投喂24 d后,除水分外,其余各营养成分皆不能恢复到对照水平。结果表明,实现异育银鲫完全补偿生长,其饥饿时间以短时间饥饿8 d为宜。     

分级对银鲫生长和个体大小差异的影响

在室内水槽进行12周的饲养实验以检验分级对银鲫生长和鱼群内个体大小差异的影响。用隔网将实验水槽分为两部分,每个水槽内放养10尾大鱼（体重8.0~9.0 g）和10尾小鱼（体重6.5~7.5 g）,分级时将个体大小相近的10尾鱼分布在隔网同一侧。实验中,3组鱼分别隔1周、2周或4周分级1次,1组鱼不进行分级作为对照。鱼摄食率和生长率随分级间隔时间缩短而降低。实验结束时,隔1周分级1次的鱼体重低于对照组,隔4周分级1次的鱼体重与对照组无显著差异。实验结束时被分级的鱼群中大鱼体重的变异系数高于小鱼,表明大鱼对分级操作更敏感。本实验结果表明,分级未能明显提高银鲫生长速度和降低鱼群内个体大小的差异程度。     

基于转录组测序技术挖掘长吻鮠生长关键基因

为挖掘我国名优鱼类长吻鮠 (Leiocassis longirostris)生长相关基因,本研究运用Illumina高通量测序技术比较分析了快速生长组[平均体质量为(534.02±53.68) g]和缓慢生长组[平均体质量为(108.41±4.96) g]各9尾长吻鮠的脑组织基因表达谱。测序共获得267 404 674个高质量测序片段(clean reads),通过2种不同生长速率长吻鮠脑组织转录组比较筛选出518个差异表达基因,其中,412 个基因表达量上调,106个基因表达量下调。对12个差异表达基因进行实时荧光定量PCR验证的结果与转录组测序结果一致。GO功能分类显示,大量差异表达基因富集到生长(growth)、生长因子活性(growth factor activity)和激素介导的信号通路(hormone-mediated signaling pathway) GO条目中。KEGG富集分析显示,一些差异表达基因在MAPK信号通路(MAPK signaling pathway)、转化生长因子β信号通路(TGF-beta signaling pathway)、钙离子信号通路(calcium signaling pathway)和神经活性配体–受体相互作用(neuroactive ligand-receptor interaction)等途径中富集。根据GO功能注释和KEGG富集分析,筛选出gnrh、thr、egr1、fgf18、sst、gipr、cart和crf等基因是调控长吻鮠生长发育的关键候选基因。本研究结果为后续深入研究长吻鮠生长调控机制提供了重要的参考资料。     

The effects of dietary selenium on growth performances,oxidative stress and tissue selenium concentration of gibel carp (Carassius auratus gibelio)

A 100‐day growth trial was executed to determine the dietary selenium (Se) requirement of juvenile gibel carp (Carassius auratus gibelio). Selenomethionine was supplemented to casein‐gelatin diets at 0, 0.1, 0.25, 0.5, 1.0, 2.5 and 5 mg Se kg^?1, respectively. Each of these seven semi‐purified diets containing 0.34, 0.47, 0.66, 0.82, 1.23, 2.77 and 5.13 mg Se kg^?1 was fed to triplicate groups of gibel carp (2.74 ± 0.02 g) in a flow‐through system. No behaviour abnormalities and no mortality were found in fish exposed to dietary Se concentrations. With the increasing dietary Se supplemented concentrations, weight gain of fish remarkably increased at the levels of ≤1 mg Se kg^?1 diet and then showed no significant difference above 1 mg Se kg^?1 levels. Although growth performances (weight gain, hepatosomatic index, condition factor and survival) were not impaired in gibel carp fed at above the levels of 2.5 mg Se kg^?1, indicators of oxidative stress were changed significantly. Serum superoxide dismutase (SOD) activities significantly declined, hepatic glutathione peroxidase (GPx) activities significantly increased and the tissue Se concentrations significantly raised at the highest supplemented level of 5 mg Se kg^?1. A clear linear relationship between Se‐depended GPx activities and hepatic Se concentrations was observed. The present results indicated that the dietary Se requirement for gibel carp is 1.18 mg Se kg^?1 diet based on weight gain, GPx activities and tissue accumulation.     

Effects of dietary betaine in allogynogenetic gibel carp (Carassius auratus gibelio): Enhanced growth,reduced lipid deposition and depressed lipogenic gene expression

A 10‐week feeding experiment was conducted to evaluate the effects of supplemental betaine on growth performance, body composition and lipid deposition in allogynogenetic gibel carp. Four isoproteic (37% crude protein) and isolipidic (5% crude lipid) artificial diets with 0%, 0.08%, 0.4% and 2% betaine supplementation were formulated, and named VB₀, VB_0.08, VB_0.4 and VB₂, respectively. Each diet was fed in triplicate to fish about 10 g in weight. The results showed that 0.4% betaine supplementation significantly improved growth performance and reduced lipid content in the hepatopancreas, muscle and the whole body compared with the control group. Moreover, both fatty acid synthase and acetyl‐CoA carboxylase, two important lipogenic genes, showed significantly lower expression in the VB_0.4 group than in the control group, and a strong correlation was detected between lipid content and mRNA expression levels for FAS and ACC in the hepatopancreas. Taken together, appropriate (0.4%) betaine supplementation in the diet not only improved growth, but also reduced lipid deposition in allogynogenetic gibel carp, probably by diminishing lipogenic gene expression.     

Effect of partial replacement of dietary monocalcium phosphate with neutral phytase on growth performance and phosphorus digestibility in gibel carp,Carassius auratus gibelio (Bloch)

A feeding trial was conducted to study the effect of partial replacement of dietary monocalcium phosphate (MCP) with neutral phytase on growth performance and phosphorus digestibility in gibel carp, Carassius auratus gibelio (Bloch). Control diet was prepared with 2% MCP but without phytase (P0). Other three experimental diets were prepared by replacement of MCP by 25%, 50% and 75% respectively in comparison with control with supplementation of neutral phytase at 500 U kg^?1 diet in each and designated as P25, P50 and P75 respectively. Gibel carp (initial body weight of 30.22 ± 1.98 g) were reared in twelve 300‐L cylindrical fibreglass tanks provided with filtered flow‐through tap water at 26–28°C. After 8‐week experiment, gibel carp fed with P50 had no obvious differences from the control group on weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency rate (PER) and survival rate. Phytase supplementation did not affect body compositions or muscle compositions. Crude protein and phosphorus (P) contents in the faeces of fish fed with the phytase‐supplemented diets were significantly lower than those of the control group. The apparent digestibility coefficients (ADCs) of crude protein and P in gibel carp were increased when fish fed with the diets in which MCP was replaced by neutral phytase. This study suggested that partial replacement of dietary MCP at 50% with neutral phytase was considered as a recommended dietary supplemental level and increased dietary P and protein availability.     

Effect of biofloc technology on water quality and feed utilization in the cultivation of gibel carp (Carassius auratus gibelio var. CAS III)

This study was designed to use sucrose as carbon source to investigate the effect of biofloc technology on water quality and feed utilization in the cultivation of gibel carp (Carassius auratus gibelio var. CAS III). Three isolipidic and isoenergetic diets were formulated containing graded levels of dietary protein (257.4, 300.7 and 353.4 g/kg). The control group (P34) was fed with 353.4 g/kg protein diet without biofloc. Three biofloc treatments (P24 + B, P29 + B and P34 + B) were fed with the three diets with daily sucrose supplementation and continuous air inflation. The results found that the sucrose supplementation could generate biofloc and increased biofloc volume (BFV, p < 0.05). The concentration of total ammonia nitrogen (TAN), nitrate nitrogen (NO₃‐N) and the total phosphorus (TP) of all tanks decreased in biofloc groups, and the total nitrogen (TN) of P24 + B treatment tanks was significantly lower than that of the control group (p < 0.05). The growth of P24 + B and P29 + B group was similar with that of control group (p > 0.05). Feed conversion ratio (FCR) of P29 + B was lower than P24 + B and P34 + B (p < 0.05). Protein retention efficiency (PRE) of P24 + B group was significantly higher than other treatments (p < 0.05). Phosphorus retention efficiency (PhRE) of P24 + B group was the highest among all treatments. Compared with the control group, P29 + B group had an improved total antioxidant capacity (T‐AOC), superoxide dismutase (SOD) activity and contained the lowest malondialdehyde level (MDA). The present results indicated that low‐protein diet is more suitable for gibel carp in zero‐water exchange biofloc system compared with high‐protein diet.     

Response of gibel carp (Carassius auratus gibelio) to increasing levels of dietary lysine in zero fish meal diets

To investigate the response of gibel carp to dietary lysine levels in zero fish meal (FM) diets, 8 experimental diets were designed. Among them, diet 1 and diet 2 with 150 g/kg FM, methionine, lysine and threonine were supplemented in diet 2. Diet 3 was without FM but matched the amino acid profile of diet 2 except for lysine. Diets 4–8 were based on diet 3, with graded levels of lysine. After 8‐week feeding trail, final body weight, weight gain (WG), specific growth rate, feed conversion ratio (FCR) and feed intake were significantly improved by diets 1–2 and 6–8 compared with diet 3. Plasma glucose, triglyceride, immunoglobulin G and aspartate aminotransferase levels in diets 4–8 were higher than those in diet 1. Apparent digestibility coefficients (ADCs) of protein, energy, methionine, lysine, valine, histidine and phenylalanine in diet 1 were significantly lower than those in diet 6. The highest ADC of isoleucine was found in diet 3. TOR, IGF‐1, JAK3, STAT4, STAT6 and PepT2 mRNA levels were significantly increased with increasing dietary lysine up to a certain level in zero FM diet and lower than diets 1–2. Based on WG and FCR, the optimal lysine requirement of juvenile gibel carp was determined to be 24.4 g/kg and 24.2 g/kg (65.9 g/kg and 65.4 g/kg of dietary protein) in zero FM diet, respectively, using quadratic regression analysis.     

生物絮团技术对异育银鲫生长性能和抗性的影响

为研究生物絮团技术(Biofloc Technology,BFT)在沿海滩涂鱼类养殖中的应用效果,本实验以滩涂主要养殖种类——异育银鲫(Carassius auratus gibelio)为研究对象,按照BFT养殖模式(BFT组,不换水,只补存蒸发掉或取样部分的水分)和一般养殖模式(对照组,每日换水1次,每次换水1/4~1/3)分别饲养,测定各处理组异育银鲫的生长指标、消化酶活性和免疫相关酶活性,应用实时荧光定量PCR法定量分析热休克蛋白HSP70的相对表达,人工感染试验对比分析BFT养殖模式组和一般养殖模式组异育银鲫生长性能和抗性的变化。结果显示:(1)BFT组异育银鲫增重率、特定生长率和存活率均高于对照组(P0.01),肥满度、脏体比和肝体比与对照组间无显著差异(P0.05);(2)BFT组异育银鲫肠道中淀粉酶、脂肪酶和胃蛋白酶活性显著高于对照组(P0.05),分别提高了53.10%、28.10%和17.99%;(3)BFT组异育银鲫体表黏液中超氧化物歧化酶活性、血清中总抗氧化能力和溶菌酶活性高于对照组(P0.01);(4)BFT组脾、肾、肝和鳃中热休克蛋白HSP70的表达量分别上调了1.29倍、1.34倍、1.87倍和1.68倍;(5)嗜水气单胞菌(Aeromonas hydrophilia)人工感染试验证实,BFT组异育银鲫抗细菌感染能力显著增强。研究表明,BFT养殖模式适于异育银鲫养殖,可促进鱼体生长,增强其应激能力和抗病力。     

循环饥饿后异育银鲫幼鱼的补偿生长及部分生理生化指标的变化

在(28±1)℃水温条件下,以4种循环饥饿的投喂方式饲养初始体重为1.58 g的异育银鲫(Carassius auratus gibelio)幼鱼,研究其补偿生长和部分生理生化指标的变化。实验分为四组,第一组每天投喂,为对照组,第二组投喂4 d后饥饿1 d,第三组投喂2 d后饥饿1 d,第四组投喂1 d后饥饿1 d,4种方式分别以C、R1/4、R1/2和R1/1表示,试验持续60 d。结果显示,3个试验组的实际摄食率均显著高于对照组(P<0.05),但饲料转化效率均显著低于对照组,导致3个试验组的特定生长率显著下降,体重未赶上对照组,而且饥饿时间越长,体重增长率越低。鱼体的蛋白质、灰分含量未受到投喂方式的显著影响,干物质、脂肪和能量含量随饥饿时间增加显著下降;肥满度、肝体比、ATP酶、SOD酶活性以及谷丙转氨酶和谷草转氨酶活性也随饥饿时间的增加显著下降。     

Effect of dietary magnesium supplementation on the growth performance of juvenile gibel carp,Carassius auratus gibelio

Gibel carp (Carassius auratus gibelio) of mean initial weight 3.1 g were fed one of seven casein‐dextrin‐based diets containing graded levels of magnesium (Mg) (39, 120, 220, 380, 700, 1600 and 2900 mg kg^?1) for 3 months with the waterborne Mg concentration of 10.6–12.7 mg L^?1. Magnesium sulphate was used as the supplementation Mg source in the diets. The experiment was carried out in a flow‐through system. Growth, survival rate, Na⁺/K⁺‐ATPase, Mg²⁺‐ATPase and tissue mineral contents were measured to investigate the effect of dietary magnesium in gibel carp. At the end of the experiment, the hepatopancreas of fish were collected for enzyme determination. The hepatopancreas, vertebrae and whole body were collected for tissue magnesium content analysis. After 3 months, dietary magnesium supplementation did not improve the growth performance, including feed intake, weight gain and feed conversion efficiency of juvenile gibel carp. On the contrary, negative impacts on survival, reduced growth performance and dramatically decreased Na⁺/K⁺‐ATPase, Mg²⁺‐ATPase and superoxide dismutase activities were observed in gibel carp fed a high Mg diet of 2900 mg kg^?1. Although serum and hepatopancreas Mg and Ca contents were not affected by dietary Mg supplementation, vertebrae and whole‐body Mg contents increased significantly with the increasing dietary Mg concentrations. Based on the relationship between whole‐body Mg retention and dietary Mg concentration, a suitable dietary Mg level of 745 mg kg^?1 could be estimated for gibel carp. It could be concluded that dietary Mg supplementation did not improve the growth performance, but could increase vertebrae Mg contents of gibel carp. Considering the adverse effects, a dietary Mg concentration of above 2900 mg kg^?1 is not recommended and it should be careful to supplement magnesium in practical diets for gibel carp as most feed ingredients contain high magnesium concentrations.     

Effects of dietary coated protease on growth performance,feed utilization,nutrient apparent digestibility,intestinal and hepatopancreas structure in juvenile Gibel carp (Carassius auratus gibelio)

This study was conducted to investigate the effects of dietary protease on growth performance, feed utilization, whole‐body proximate composition, nutrient digestibility, intestinal and hepatopancreas structure of juvenile Gibel carp, Carassius auratus gibelio (mean weight 8.08 ± 0.18 g). Six diets were prepared, including a positive control diet (dietary protein 350 g/kg, PC), one negative control diet (dietary protein 33 g/kg, NC) and four protease supplementations diets, which were 75, 150, 300 and 600 mg/kg protease NC diet. After 12 weeks of diet feeding in indoor recycle aquarium tanks, no significant difference (p > .05) was found on growth performance between fish fed diet with 75–600 mg/kg protease and the PC group. Compared with the fish fed the NC diet, the specific growth rate of fish fed 300 mg/kg protease increased significantly (p < .05), as well as protein efficiency ratios (p < .05), while feed conversion was the opposite (p < .05). The nutrient digestibility of crude protein and lipid was higher (p < .05) in fish fed 150 mg/kg protease diet than the PC diet. Whole‐body proximate composition of fish was not affected (p > .05) by the dietary treatment. Serum alkaline phosphatase and albumin were significantly affected by dietary protease (p < .05), while the content of total protein, glucose, triglyceride, total cholesterol, aspartate aminotransferase and alanine aminotransferase activities in serum was not affected (p > .05). Foregut muscular thickness was thinner (p < .05), when the fish fed diets supplementation of protease in 150 or 600 mg/kg diet than the NC diet. Protease activities in hepatopancreas and foregut were higher (p < .05), in the fish fed 150 or 300 mg/kg protease diet than the fish fed the PC diet, but those in the mid‐ and hindgut were not significantly affected (p > .05) by the dietary treatments. Based on the regression analysis of weight gain rate, the optimal dietary inclusion level of protease was 400 mg/kg in the diet for juvenile Carassius auratus gibelio.     

Effects of dietary vitamin C on growth,gonad development and antioxidant ability of on‐growing gibel carp (Carassius auratus gibelio var. CAS III)

An 88‐day experiment was conducted in a flowing system to evaluate the effects of dietary vitamin C on growth, body composition, antioxidant and gonad development of on‐growing gibel carp. Triplicate tanks of gibel carp (77.2 ± 0.1 g) were randomly fed with one of seven experimental diets containing l ‐ascorbic acid of 0, 101.1, 188.5, 313.1, 444.1, 582.1 and 747.0 mg/kg, respectively. The results showed that specific growth rate (SGR) and feed efficiency (FE) of fish were not affected by dietary l ‐ascorbic acid. Dietary l ‐ascorbic acid of 444.1 mg/kg diet led to low levels (p < .05) of gonadosomatic index (GSI) and hypothalamic gonadotropin‐releasing hormone (GnRH) in on‐growing fish, as well as the early ovarian stages (Developing stages) compared with fish (Maturing stages) from the other groups. Dietary l ‐ascorbic acid supplementation increased (p < .05) the dorsal muscle collagen content, but did not affect the protein or lipid content of dorsal muscle in gibel carp. Plasma total antioxidant capacity (T‐AOC) and superoxide dismutase (SOD) activity increased (p < .05) and then remained unchanged with the increase in dietary l ‐ascorbic acid levels. Dietary l ‐ascorbic acid of 101.1 mg/kg diet improved (p < .05) plasma lysozyme activity of the fish. Broken‐line regression indicated that dietary l ‐ascorbic acid requirement of 77 g gibel carp was 223.3 or 225.0 mg/kg diet based on plasma T‐AOC or SOD activity, which was a little higher than that based on plasma l ‐ascorbic acid concentration (193.2 mg/kg).     

Effect of dietary lysozyme on growth,immune response,intestine microbiota,intestine morphology and resistance to Aeromonas hydrophilia in gibel carp (Carassius auratus gibelio)

A 75 days experiment was conducted in a flow‐through system on juvenile gibel carp (Carassius auratus gibelio) (3.43 ± 0.01 g) to evaluate the effects of dietary lysozyme on growth performance, intestine morphology, microbiota and immune response. Four isonitrogenous (crude protein: 367 g kg^?1) isolipid (62 g kg^?1) and isocaloric (gross energy: 17.92 kJ g^?1) diets were formulated to contain 0, 100, 500 and 1000 mg kg^?1 lysozyme, respectively. The results showed that specific growth rate (SGR) and feed efficiency (FE) increased at 1000 mg kg^?1 lysozyme. Blood leucocyte phagocytic activity (PA) and serum lysozyme (LZM) decreased with dietary lysozyme on day 25, 50 and 75. There were no significant differences in alternative complement pathway (ACP), respiratory burst (ROS), serum superoxide dismutase (SOD), glutathione peroxidase (GSHpx) or malonaldehyde (MDA). After Aeromonas hydrophilia challenge, higher survival was obtained at 500 mg kg^?1 group. PA, ROS, SOD, LZM and ACP increased with increasing dietary lysozyme, while MDA reversed. Goblet cells in mid‐intestine and microvilli height in distal intestine increased with dietary lysozyme on day 75. Dietary lysozyme reduced the diversity of intestine microbiota. In conclusion, oral administration of 500 mg kg^?1 dietary lysozyme for 75 days is recommended for the survival of gibel carp and 1000 mg kg^?1 dietary lysozyme for fast growth.