Effects of flow rate on growth performance and welfare of juvenile turbot (Scophthalmus maximus L.) in recirculating aquaculture systems

The effects of flow rate on growth and welfare of juvenile turbot (Scophthalmus maximus L.) were investigated in the present study. Fish with same initial weight (102.5 ± 10.6 g) were subjected to four flow rates, equalling to 0.5, 1, 1.5 and 2 tank volumes per hour in twelve 392 L tanks during 80 days. Results showed that specific growth rate of turbots increased (0.40–0.58% day^?1) significantly with promoted flow rate (P < 0.05). Total ammonia nitrogen, nitrite nitrogen, unionized ammonia nitrogen, chemical oxygen demand, total bacteria and total vibrio in tanks were affected significantly by flow rate and accumulations were found in low rate (200 L h^?1) (P < 0.05). Free carbon dioxide increased significantly with the increased flow rate and ranged between 4.5 and 13.5 mg L^?1 (P < 0.05). Both superoxide dismutase activity and lysozyme activity increased significantly with flow rate (P < 0.05), with ranges of 108.51–131.57 U mL^?1 and 551.81–869.28 U mL^?1. Serum cortisol showed reversed tendency and ranged between 7.39–19.26 ng mL^?1. The principal components analysis suggested that increased flow rate promoted fish welfare. It was concluded that increased flow rate promoted the growth of juvenile turbot, possibly explained by fish welfare differences in combination of health, water quality and serum parameters.     

The effect of ozone on water quality and survival of turbot (Psetta maxima) maintained in a recirculating aquaculture system

Turbot, Psetta maxima, represent a valuable and growing subsector of global finfish aquaculture, although bacterial infections such as edwardsiellosis have adversely affected the industry in recent years. During an experiment designed to investigate the effect of direct ozonation on fish performance in RAS, a bacterial disease outbreak (Edwardsiella tarda) occurred, presenting an opportunity to record additional effects of experimental ozonation regimes on performance of turbot grown in RAS. This short note thus collates phenomenological information on survival, growth and water quality parameters recorded during a 91 day experiment with juvenile fish. Alongside antibiotic therapy, a high ozone treatment (360 mV) improved survival of stock compared to those in a non-ozonated control (200 mV) and significantly so compared to low ozone treatment (320 mV). Both experimental treatments reduced total heterotrophic and Vibrio sp. bacterial loading and nitrite concentration in culture water compared to the control. Experimental ozone treatment also suggested a trend for improved growth and feed intake. Although no confirmed link or mechanism between ozonation and reduced impacts of bacterial infection are proven in this study, the observations add further evidence to the body of work demonstrating beneficial effects of ozonation on water quality, survival and growth of farmed fish.     

The effect of high ortho-phosphate water levels on growth,feed intake,nutrient utilization and health status of juvenile turbot (Psetta maxima) reared in intensive recirculating aquaculture systems (RAS)

In intensive recirculating aquaculture systems (RAS) ortho-phosphate (ortho-P) is one of the main accumulating substances, but effects of chronically elevated concentrations on fish health and production performance are still unknown. Therefore 120 juvenile turbot (Psetta maxima) were exposed to ortho-P concentrations of 3 mg/L (control – C), 26 mg/L (low – LP), 52 mg/L (medium – MP) and 82 mg/L (high – HP) for 56 days and fed until satiation with a commercial diet. Health status and feed conversion ratio (FCR) were not significantly affected by treatment (p > 0.05). Specific growth rates (SGR) and daily feed intake (DFI) of C were not considered significantly different from LP, MP and HP treatments, however LP showed significant higher DFI and SGR than HP (p < 0.05). Using non-linear regression between SGR and ortho-P concentrations, 27 mg/L ortho-P was found as the optimum for turbot growth. Although not reflected in blood plasma P levels (p > 0.05) a potential aqueous P uptake might result in metabolic benefits leading to the observed growth enhancement in the LP treatment.In a second experiment 114 juvenile turbot were exposed to ortho-P concentrations of 2 mg/L (C2) and 25 mg/L (LP2) for 63 days and fed until satiation with a low P diet (4.6 g digestible-P/kg diet). Overall production performance was low due to low voluntary feed intake. Whereas the FCR was unaffected by treatment (p > 0.05), significantly higher feed intake and biomass gain were observed for LP2 compared to C2 (p < 0.05). LP2 treatment showed a trend for higher protein retention efficiency and lower whole body lipid content (p < 0.1). The dry matter, ash, Phosphorus, Calcium and protein content in whole body did not significantly vary between treatments (p > 0.05).In conclusion the accumulation of ortho-P in RAS does not negatively affect health of turbot. Elevated ortho-P seems to have slight positive effects on production performance of juvenile turbot. Further research to quantify dietary P requirements for turbot in general, as well as for turbot raised under elevated ortho-P conditions in RAS is strongly required.     

在循环水养殖系统中养殖密度对红鳍东方鲀应激反应和抗氧化状态的影响

养殖密度是影响养殖水体水质和鱼类生长性能的重要因素。通过红鳍东方鲀(Takifugu rubripes)循环水养殖试验和硝酸盐氮急性处理试验,分别研究不同养殖密度(12.5~20.0 kg/m^3)和不同硝酸盐氮质量浓度(1.0、25.0、100.0和150.0 mg/L)对养殖水体水质、红鳍东方鲀生长性能、应激反应和抗氧化状态的影响。结果显示:不同养殖密度对红鳍东方鲀养殖水体的pH、氨氮和亚硝酸盐氮质量浓度无显著性影响,但较高密度会导致硝酸盐氮质量浓度显著升高,最高升至24.5 mg/L。在较高养殖密度条件下,红鳍东方鲀的生长性能(终体质量、特定增长率和饲料转化率)和抗氧化能力(总抗氧化能力、超氧化物歧化酶、谷胱甘肽过氧化物酶)较弱,但其脂质过氧化(丙二醛)和应激反应(葡萄糖、乳酸和皮质醇)较强。此外,在硝酸盐氮急性处理试验中,红鳍东方鲀未出现死亡。当硝酸盐氮质量浓度为100.0和150.0 mg/L时,红鳍东方鲀抗氧化能力较弱,而应激反应较强。综上,当养殖密度为16.5 kg/m^3时,红鳍东方鲀的生长和抗氧化状态较好,且应激压力较小,这表明在较高密度条件下,养殖水体硝酸盐氮质量浓度的升高不是引起鱼类生长抑制的主要原因。     

Effect of turbidity on the ultraviolet disinfection performance in recirculating aquaculture systems with low water exchange

This research was carried out to study the effect of turbidity on the effectiveness of ultraviolet light (UVC) for removing heterotrophic bacteria (HB) from two commercial recirculating aquaculture systems (RAS). We developed a simple and straightforward UV disinfection model based on water turbidity to predict the cost‐effectiveness of disinfection. The UVC from RAS1 (12.8 m³, 80 L min^?1, indoor system) was tested at 9.2, 9.9, 16.3, 17.2, 23.1 and 28.2 nephelometric turbidity units (NTU) after 24 h of exposure. The RAS2 (140 m³, 1140 L min^?1, outdoor system) was tested at 8.0, 9.2, 11.0, 12.1, 16.0, 24.2, 27.0, 31.3 and 31.7 NTU after 72 h. An increase in turbidity in the water was achieved by rearing Oreochromis niloticus fish. The RAS1 achieved a maximum UV efficiency (89.8%≈1 Log) at 9.2 NTU after 24 h and RAS2 at 8.0 NTU (86.4%≈0.9 Log) after 72 h of exposure. For RAS1, the UVC removed 90% of HB in 24 h when the turbidity was <9.9 NTU. For RAS2, without restrictions on particle size and relatively high phytoplankton abundance, the UV was unlikely to be a cost‐effective way of removing HB at turbidity above 11.0 NTU.     

池塘养殖水体不同水层水质变化研究

为探讨池塘养殖水体时间和空间上的变化特征,在上海市标准化养殖池塘里进行了水质参数监测和分析,研究了池塘上层、中层、下层不同水层的水质变化情况。结果表明:一年中池塘水质呈季节性变化,氨氮均值在9—11月最高,在5月份最低;溶氧均值在9—11月最低,在12月至次年3月最高;pH无明显季节性变化。不同水质参数日变化研究发现,一天中氨氮值在6:00左右最高,在17:00左右最低;溶氧最高值出现在15:00—17:00,最低值在5:00左右;pH在1:00最低,14:00左右最高。养鱼池塘水体有较明显的分层现象,上层、中层、下层不同水层的氨氮、溶氧、pH均有差异。一天中氨氮与溶氧总体呈负相关性(t<0.05),溶氧值升高时氨氮值下降。     

Vaccination of turbot, Psetta maxima (L.), against the protozoan parasite Philasterides dicentrarchi: effects on antibody production and protection

The efficacy of a vaccine against the fish pathogen Philasterides dicentrarchi was evaluated in turbot by measuring the production of specific antibodies and duration of protection. Four groups of turbot were vaccinated twice, on days 0 and 30, with phosphate-buffered saline, mineral oil adjuvant, antigen or antigen plus adjuvant. Specific serum antibodies were determined on day 0 and 1 month after the first and the second vaccinations. Protection was evaluated 1 month after the first vaccination and 1 and 5 months after the second vaccination. Serum antibody titres, measured by enzyme-linked immunosorbent assay, and protection, assessed by challenges, increased significantly 1 month after the second vaccination in the group injected with antigen plus adjuvant and the protection lasted for at least a further 5 months in this group. The relative protection was 77% and 66% 1 and 5 months after the second vaccination, respectively. Administration of antigen or adjuvant separately had no effect on antibody response or protection. The results indicate that emulsion containing antigen plus adjuvant induced durable protection against P. dicentrarchi after the administration of the two vaccinations, and that this preparation can be used as a vaccine against the pathogen.     

Water flow and diurnal variation in metabolite production rates of Atlantic salmon (Salmo salar L.) post‐smolt

Diurnal variation of carbon dioxide (CO₂) and total ammonia production in Atlantic salmon post‐smolt were studied at different water flow rates. The experiment comprised four groups each with two replicates representing specific flow levels of 0.5, 0.4, 0.3 and 0.2 L kg^?1 min^?1. During the first diurnal cycle, the seawater samples were collected eight times during 21 hr. In the second diurnal cycle, six samplings were performed during a prolonged sampling period of 35 hr. The highest CO₂ concentrations were observed in the lowest water flow group (0.2 L kg^?1 min^?1) between 4 and 10 p.m. for the first sampling period and at about 2 p.m. for the second sampling period. The overall real CO₂ production rates were in the range 1.7–5.5 mg kg^?1 min^?1 including diurnal variation in all groups for both sampling periods. In general, a second‐order polynomial model describes the relationship between specific water flow and real mean CO₂ production rate (p < 0.001). Maximum concentrations of total ammonia nitrogen (TAN) occurred around 7 and 8 p.m. in all groups and was highest for the 0.2 L kg^?1 min^?1 group for both sampling periods. Note that maximum concentration of TAN and CO₂ both occurred in the afternoon. The TAN production rates were in the range 0.06–0.44 mg kg^?1 min^?1 including both sampling cycles.     

陆基圆池循环水条件下养殖密度对大口黑鲈生长及养殖效能的影响

为研究陆基圆池循环水养殖条件下大口黑鲈(Micropterus salmoides)适宜的养殖密度,设置55、65、75、85、95尾/m²等5种养殖密度(分别标记为A1、A2、A3、A4、A5组),进行了63 d的大口黑鲈养殖试验,通过测定和分析试验鱼的体质量日增长率、体长日增长率、饲料系数、体质量均匀度和单位面积产量等指标,评价不同养殖密度对大口黑鲈生长和主要养殖效能的影响。结果显示:(1)从次低密度的A2组(65尾/m²)至密度最高的A5组(95尾/m²),试验鱼的体长日增长率基本上随着养殖密度的提高而下降,最高的A2组比A3、A4和A5组分别高了31.6%、82.9%和92.3%,并且差异显著(P<0.05);(2)从A2组至A5组,试验鱼的体质量日增长率和特定生长率均随着养殖密度的提高而下降;(3)A2组的饲料系数比A1、A3、A4和A5组分别降低了16.7%、28.6%、55.4%和56.9%;(4)单位面积产量和产品均匀度均在A2组达到最高。基于生长性能及养殖效能的综合评价,陆基圆池循环水养殖条件下大口黑鲈成鱼养殖阶段较适宜的养殖密度为65尾/m²。     

The future of genetic engineering to provide essential dietary nutrients and improve growth performance in aquaculture: Advantages and challenges

Advancements in gene technology in recent years have been driving the aquaculture industry forward. Improvements in growth performance, feed efficiency, and omega‐3 content are goals of the industry that could capitalize on applications of genetic engineering. One of the major challenges in the industry is to reduce the use of fish meal and oil, to improve the environmental and economic sustainability of aquaculture. The recent development of genetically engineered feed ingredients is one potential solution to the looming problem of fish meal and oil dependency. Furthermore, the development of transgenic fish has potential to improve production efficiency and other future desirable characteristics that relate to feed utilization and product quality. New gene technologies are beginning to revolutionize how we produce our food, and in aquaculture, will ultimately reduce pressure on wild fish stocks, help to preserve natural aquatic ecosystems, and improve nutritional profiles of farmed fish for human consumption. The purpose of this review is to provide an update on the current applications of genetic engineering technology to improve aquaculture through nutrition, including the development and use of transgenic feed ingredients, transgenic fish, and ultimately their impacts on nutrition, product quality, and consumers.     

The effect of ultrafiltered fish protein hydrolysate level on growth performance,protein digestibility and mRNA expression of PepT1 in juvenile turbot (Scophthalmus maximus L.)

The intention of the study was to investigate the effect of ultrafiltered fish protein hydrolysate (UF) level on growth, feed utilization, apparent digestibility coefficients and proximal intestine peptide transporter 1 (PepT1) mRNA level for juvenile turbot (Scophthalmus maximus L.). Experimental diets (UF‐0, UF‐5, UF‐10, UF‐15 and UF‐20) were prepared containing about 68% plant protein, and fish meal protein was, respectively, replaced by 0%, 5%, 10%, 15% and 20% UF of dietary protein. Diet PP contained about 78% plant protein, and diet CAA contained about 10% crystalline amino acid mixture. All diets were fed to seven triplicate groups of turbot (initial weight 16.05 ± 0.03 g) for 68 days. Fish fed diet UF‐10 had an increasing tendency in growth compared with diets contained UF, while dietary UF level was not significantly correlated with specific growth rate and feed intake. Feed efficiency, protein efficiency ratio and protein productive value significantly correlated with dietary UF level, and fish fed diets contained low‐level UF had higher digestibility than that diets UF‐0, PP and CAA. There was a decreasing tendency in PepT1 expression level with dietary UF level. The results indicated that low‐level UF showed a positive effect on growth and feed utilization in juvenile turbot.     

Taurine alone or in combination with fish protein hydrolysate affects growth performance,taurine transport and metabolism in juvenile turbot (Scophthalmus maximus L.)

The study was conducted to investigate the effects of taurine (Tau) alone or in combination with fish protein hydrolysate (FPH) on growth performance, the expression of Tau transporter (TauT) and metabolic profile in juvenile turbot. FM, FPH0, FPH0+T, FPH10 and FPH10+T diets, respectively, contained 300, 150, 150, 80, and 80 g/kg fishmeal. FPH10 and FPH10+T diets contained 62 g/kg FPH. FPH0+T and FPH10+T diets were, respectively, prepared by supplementing the FPH0 and FPH10 diet formulations with 8 g/kg Tau. Specific growth rate was the highest in FM group and the lowest in FPH10 group. TauT mRNA levels in fish fed Tau supplemented diets were significantly lower than that in Tau unsupplemented diets. NMR‐based metabolomics analysis showed that Tau contents in liver of FPH0+T and FPH10+T were significantly higher than that of FM, FPH0 and FPH10. In muscle, Tau contents were significantly decreased in the FPH10+T versus FPH0 and the FPH10+T versus FPH10 comparisons. In conclusion, 62 g/kg FPH to replace fishmeal may not affect Tau synthesis, transport and metabolism. However, Tau supplemented alone or in combination with a certain level of FPH could reduce the requirement for Tau synthesis and transport and increased Tau levels in muscle and liver.     

Effects of feeding rate and frequency on growth performance,digestion and nutrients balances of Atlantic salmon (Salmo salar) in recirculating aquaculture systems (RAS)

A 10‐week study was conducted to investigate the effects of feeding rate and frequency on growth performance, digestion and nutrients balances of Atlantic salmon (Salmo salar) in replicated recirculating aquaculture systems (RAS). Replicated groups of juvenile salmon weighing 90 ± 2.5 g (mean ± SD) were fed a commercial feed (21.63 MJ kg^?1 gross energy) to designed feeding rate (1.4%, 1.6% and 1.8% body weight day^?1, BW day^?1) and feeding frequency (2 and 4 meals day^?1) combinations. Specific growth ratio varied between 1.15 ± 0.02 and 1.37 ± 0.16% day^?1, and feed conversion ratio ranged from 0.96 ± 0.03 to 1.16 ± 0.02. The nitrogen and phosphorus retention rates were from 36.50 ± 1.94 to 47.08 ± 5.23% and from 20.42 ± 1.05 to 38.59 ± 2.80%. Apparent digestibility coefficients (ADC) in dry matter, protein, lipid and energy showed no significant differences for all groups. However, fish fed at 1.6% BW day^?1 and 4 meal day^?1 groups had relatively better growth and nutrient retention efficiency compared to other groups. In addition, concentrations of nitrogenous and phosphorous compounds were also detected in this study. These results suggested that salmon of 100–200 g in RAS could in practice be fed at 1.6% BW day^?1 and 4 meals day^?1, taking environmental impacts into account.     

Chronic exposure to nitrate significantly reduces growth and affects the health status of juvenile Nile tilapia (Oreochromis niloticus L.) in recirculating aquaculture systems

Studies on chronic or acute toxicity of nitrogen species on fish in recirculating aquaculture systems (RAS) usually focused on adverse effects of total ammonia nitrogen (TAN: sum of NH₃ + NH₄⁺) and nitrite (), while underestimating the potential effects of high nitrate accumulation on growth and health status of fish. In our study, Nile tilapia (Oreochromis niloticus) were exposed to five different nitrate concentrations (0, 10, 100, 500 and 1000 mg L^?1 ‐N) over 30 days. Growth parameters (feed conversion ratio (FCR), specific growth rate (SGR), hepatosomatic index (HSI)), blood samples (concentrations of haemoglobin, methaemoglobin, plasma /) and the histology of the gills were studied to evaluate growth and health status of the fish. At the highest nitrate concentration, the fish showed significantly reduced growth and impaired health status (SGR, FCR, plasma /, haemoglobin and methaemoglobin concentration), demonstrating that too high nitrate concentrations can negatively influence tilapia production in RAS. Here, we recommend not exceeding concentrations of 500 mg L^?1 ‐N in juvenile tilapia culture to ensure an optimal health and growth status of the fish, as below that concentration no effects on the tilapia have been observed.     

The use of tuna industry waste in the practical diets of juvenile Nile tilapia (Oreochromis niloticus,L.): effect on growth performance,nutrient digestibility and oxidative status

A 45‐day feeding trial was conducted to study the effect of replacing dietary fish meal (FM) with a tuna by‐product meal (TBM) on the growth, feed efficiency, carcass composition and stress oxidative status of juvenile Nile tilapia, Oreochromis niloticus L.). Triplicate groups of fish (2.21 ± 0.01 g) were fed on four iso‐nitrogenous and iso‐energetic diets. The control diet (A₀) used FM as the sole source of animal protein. In the other three diets (A₁₀–A₃₀), 33%–100% of FM was substituted by TBM at 10% increments. There were no significant differences (P>0.05) in growth performance among fish fed on diets A₀, A₁₀ and A₂₀. Fish fed these experimental diets (i.e., A₀, A₁₀ and A₂₀) showed significantly (P<0.05) better daily mass gain, specific growth rate and protein efficiency ratio than those fed on diet A₃₀. Feed conversion ratio increased with increasing TBM content, but only the value found in fish fed on diet A₃₀ differed significantly (P<0.05) from the other treatments. The fish accumulated increasing quantities of lipids and decreasing levels of ash in their carcasses with increasing levels of dietary TBM. At the end of the experimental period, a significant increase (P<0.001) in catalase and glutathione S‐transferase activities was seen only in groups fed on diet A₃₀. Similarly, a significant enhancement in glutathione peroxidase and superoxide dismutase activities was observed in groups fed on diets A₂₀ and A₃₀ compared with the other groups. The results show that this product can be included up to 20% in practical Nile tilapia diets without any detrimental effects.     

循环水养殖条件下水温对大菱鲆氨氮排泄、转氨酶及免疫因子的影响

在高密度工业化封闭循环海水养殖条件下（养殖密度为14?2±0?48 kg／m2）,选取大菱鲆（371?68±43?15 g）360尾,随机均分4组,设置4个水温梯度14℃、16℃、18℃和21℃,旨在探寻水温对大菱鲆氨氮排泄、转氨酶及血清免疫因子的影响,试验期为56 d。结果表明：（1）养殖水体总氨氮浓度随水温升高呈先升后降,18℃时总氨氮浓度极显著高于14℃、21℃时;大菱鲆氨氮排泄率随水温升高而升高,且二者呈指数关系。（2）大菱鲆肝脏GPT、GOT活力随水温升高呈先升后降,均在18℃达最大值;而血清两种指标变化趋势与之相反,均在21℃达最大值。（3）血清LZM、SOD活力及皮质醇含量均随水温升高呈先升后降,均在18℃达最大值;血氨含量则逐渐下降,14℃时极显著高于18℃、21℃时;鳃丝Na＋?K＋?ATPase活力随水温升高而升高,但组间差异不显著。综上,封闭循环水养殖大菱鲆的适宜水温为16～18℃。     

养殖密度对温室湿地循环水系统中鲫生长、生理及免疫指标的影响

研究了基于两级人工湿地的温室循环水系统中,养殖密度对鲫（Carassius cuvieri）生长、脏器系数、血清生理免疫指标及对嗜水气单胞菌（Aeromonas hydrophila）抵抗力的影响。试验设2 kg·m^-3、4 kg·m^-3、8 kg·m^-3和16kg·m^-3共4种密度组,每组2个平行,养殖68 d。结果显示：1）各养殖密度下鲫生长及脏器系数不存在显著差异;2）与2 kg·m^-3组鲫相比,16 kg·m^-3组鲫血清丙二醛（MDA）质量摩尔浓度显著升高,溶菌酶（LSZ）、酸性磷酸酶（ACP）和碱性磷酸酶（AKP）活性显著降低,超氧化物歧化酶（SOD）活性和总蛋白质量浓度虽有不同程度升高,但差异不显著;3）高密度组鲫对嗜水气单胞菌的抵抗力较低密度组弱。以上结果表明,如果以生长为考量指标,温室湿地循环水系统中鲫养殖密度可达16 kg·m^-3,但如此高的密度会对鲫免疫力造成负面影响。     

投喂频率对工厂化循环水养殖星康吉鳗生长、生理指标及其水质的影响

本研究采用生理学和实验生态学方法探究了工厂化循环水养殖模式下,不同投喂频率对星康吉鳗(Conger myriaster)生长、生理指标以及水质因子的影响。选用初始体重为(150.64±5.43) g的星康吉鳗为研究对象,实验共设2组,分别为1次/天(T1组)、2次/天(T2组),每组3个重复,实验周期为70d。实验每14d检测各养殖池实验鱼平均体重和循环水系统水质指标;实验结束时,采集星康吉鳗血液、组织相关样品,用于生长、生理指标的测定与分析。结果显示,T2组终末体重(FBW)、终末体长(FBL)、增重率(WGR)、特定生长率(SGR)显著高于T1组(P<0.05),T1组饲料系数(FCR)显著高于T2组(P<0.05)。T1组血清丙二醛(MDA)显著高于T2组(P<0.05),T2组肝脏谷草转氨酶(AST)、肝脏谷丙转氨酶(ALT)、肠道胰蛋白酶(TPS)显著高于T1组(P<0.05)。T1组、T2组出口水NH₄⁺-N、NO₂^--N 24 h变化中分别有1处(24:00)和...     

Growth performance and use of natural food by Oreochromis niloticus (L.) in polyculture systems with Barbodes gonionotus (Bleeker) and Cyprinus carpio (L.) in intensively cultivated rice fields

In the freshwater area of Vietnam's Mekong Delta, Oreochromis niloticus (L.), Barbodes gonionotus (Bleeker) and Cyprinus carpio (L.) are often reared together in rice fields. In this study, we report the results of eight such polyculture experiments, examining variables affecting the specific growth rate and the average daily food energy consumption of individual O. niloticus. The standing biomass of O. niloticus and the wild fish biomass had a negative impact on the specific growth rate, whereas added pig manure, extra feed and inorganic fertilizer had a positive effect. The standing biomass of O. niloticus and C. carpio, and the wild fish biomass had a negative impact on the consumption of natural feed. We inferred that O. niloticus mainly lacks food in rice fields. This results in intraspecific competition. As in rice fields, C. carpio has basically the same feeding niche as O. niloticus; we found interspecific competition between the two species. O. niloticus consumed relatively more food in the vegetative phase of the rice crop, probably because of a higher abundance of phytoplankton. To get higher growth of O. niloticus, we recommend that farmers increase nutrient inputs and stock O. niloticus according to the size of the trench adjoining the rice field and not according to the size of trench plus field as is generally done.     

Effects of silymarin on growth performance,antioxidant capacity and immune response in turbot (Scophthalmus maximus L.)

A 9‐week feeding trial was conducted using triplicate groups of turbot (6.50 ± 0.01 g) to explore the potential effects of silymarin. Three concentrations of silymarin (100, 200, and 400 mg/kg) were added to the plant protein‐based diet. Fish were randomly distributed into fiberglass tanks (30 fish per tank). The results showed that adding 100 mg/kg silymarin significantly improved the growth performance, with no effects on feed utilization. The antioxidant capacity in the liver was significantly improved in the 100 mg/kg and 200 mg/kg silymarin groups by not only inducing the activities of superoxide dismutase (SOD) and catalase but also increasing the messager RNA (mRNA) expression levels of SOD, glutathione peroxidase, and peroxiredoxin 6. Meanwhile, supplying 100 and 200 mg/kg of silymarin enhanced the heights of villi and enterocytes. Silymarin supplementation reduced the mRNA expression of interleukin‐8 and tumor necrosis factor‐α but induced the expression of transforming growth factor‐β (TGF‐β) in the intestine. These results indicated that silymarin was a potential nutraceutical that could enhance the growth performance and health status of turbot fed in a high plant protein diet. Adding 100 mg/kg silymarin to the plant protein diet achieved optimal performance in turbot.