养殖密度对克氏原螯虾幼虾生长、消化酶活力和生理生化指标的影响

以体质量(0.015±0.004)g克氏原螯虾幼虾为研究对象,研究了50、100、300、600、900尾/m25种养殖密度对克氏原螯虾幼虾生长、消化酶活力和生理生化指标的影响,实验周期为30 d。结果显示,克氏原螯虾幼虾的终末体质量随着养殖密度的增大而减小。胃蛋白酶、类胰蛋白酶和淀粉酶活力随着养殖密度的增大表现出减小趋势,纤维素酶和脂肪酶活力在5种养殖密度下变化规律不显著(P>0.05)。克氏原螯虾幼虾体内水分含量在5种养殖密度下差异较小(P>0.05);粗蛋白含量随养殖密度的升高呈增高趋势,由54.02%增高至60.75%(P<0.05);粗脂肪含量不断减少(P<0.05),由26.19%减少至19.19%(P<0.05)。随着养殖密度的增大,克氏原螯虾幼虾肌肉葡萄糖的含量呈下降趋势(P<0.05),甘油三酯、总蛋白、尿素氮和胆固醇含量呈不断增多趋势(P<0.05)。克氏原螯虾幼虾肝胰腺葡萄糖、甘油三酯、总蛋白和尿素氮含量随着养殖密度的增大呈不断增多趋势。结果表明,高密度养殖对克氏原螯虾幼虾生长和消化酶活力具有一定负面影响,体内蛋白、脂肪、葡萄糖和尿素氮等物质的含量也随着养殖密度的增大而发生变化。     

养殖密度对克氏原螯虾大规格苗种生长和存活的影响

以体重(2.03±O.19)g克氏原螫虾(Procambarus clarkii)大规格苗种为研究对象,研究了26℃下,27、36、45、55、64、73尾/m~2 6种养殖密度下,克氏原螯虾大规格苗种生长及存活情况。实验周期为32 d。结果显示:克氏原螯虾幼虾的体长增长、平均日增重、增重率和存活率都随养殖密度的增大而降低,其中日增重由0.110 6 g下降到0.067 8 g,存活率由100%下降到63%。结果表明,养殖密度的增大不利干克氏原螯虾苗种的生长和存活,养殖密度为45尾/m~2是克氏原螯虾大规格苗种生长的最佳密度。     

养殖密度对克氏原螯虾生长及消化酶、免疫酶活性的影响

水温(25±1) ℃时,将体质量(3.11±0.10) g的克氏原螯虾幼虾饲养在120 cm×60 cm×20 cm的水族箱中,密度分别为14尾/m^( 2) (低密度组)、28尾/m^( 2) (中密度组)和42尾/m^( 2) (高密度组),研究室内养殖不同密度对生长、摄食、消化酶活性及非特异性免疫的影响。8周的养殖结果显示,克氏原螯虾的存活率随养殖密度的增大而降低。在28尾/m^( 2) 组中,其特定生长率[(1.82±0.12)%/d]和质量增加率[(196.73±0.76)%]显著高于其他两组( P< 0.05)。摄食率与养殖密度成正相关,即42尾/m^( 2) 组的摄食率高于14尾/m^( 2) 组和28尾/m^( 2) 组。28尾/m^( 2) 组消化酶活性显著高于14尾/m^( 2) 组的消化酶活性( P< 0.05),但与42尾/m^( 2) 组差异不显著( P >0.05)。不同养殖密度对非特异性免疫有显著影响,28尾/m^( 2) 组显著优于其他两组( P< 0.05)。综合所有指标,在本试验条件下,28尾/m^( 2) 的养殖密度最适合克氏原螯虾幼虾的养殖。     

饲料脂肪水平对克氏原螯虾幼虾生长性能及肌肉品质的影响

本研究旨在探讨饲料脂肪水平对克氏原螯虾(Procambarus clarkii)幼虾生长性能和肌肉品质的影响。实验选取600尾初始体重为(4.00±1.00) g的克氏原螯虾幼虾，随机分为5组(L1、L2、L3、L4和L5组)，分别投喂脂肪水平为2.86%、5.11%、7.67%、10.19%和13.02%的等氮实验饲料，养殖周期为60 d。结果显示，随着脂肪水平的升高，特定生长率(SGR)呈先升高后降低的趋势(P<0.05)，饲料系数(FCR)呈先降低后升高的趋势(P<0.05)，L3组的FCR显著低于其余组(P<0.05)；对SGR进行折线回归分析，得出最适脂肪含量为6.82%。饲料脂肪水平对克氏原螯虾肌肉的水分、粗蛋白和粗灰分含量无显著影响(P>0.05)；随着饲料脂肪水平的增加，肌肉的蒸煮损失率、粗脂肪含量、总多不饱和脂肪酸(∑PUFA)和总氨基酸(∑TAA)含量呈上升趋势，L5组的二十碳五烯酸(EPA)显著高于其余组，L5组的二十二碳六烯酸(DHA)含量显著高于L1和L2组(P<0.05)；随着饲料脂肪水平的增加，肌肉硬度、弹性、凝聚性和黏性呈下降趋势，且L1~L3组间均无显著差异(P>0.05)，L5组的总鲜味氨基酸(∑FAA)、丙氨酸(Ala)及天门冬氨酸(Asp)的含量显著低于L1组(P<0.05)。综上所述，适宜的饲料脂肪含量可以提高克氏原螯虾幼虾的生长性能和肌肉的营养品质，在本实验条件下，克氏原螯虾幼虾饲料中脂肪的建议添加量为6.82%~10.19%。     

湖北地区温棚养殖与稻田养殖克氏原螯虾生长特性研究

2018年12月—2019年3月间,定期从温棚养殖和稻田养殖的克氏原螯虾中采集599尾样本,测量克氏原螯虾的体质量(y)、全长(x1)、头胸甲长(x2)、头胸甲宽(x3)、腹节总长(x4)、第一腹节长(x5)、第一腹节宽(x6)、尾节长(x7)、第六腹节长(x8)、第六腹节宽(x9)和螯长(x10),探明温棚养殖幼虾与稻田养殖幼虾以及温棚养殖雌雄幼虾的生长特性,以期为克氏原螯虾温棚养殖及单性养殖提供参考。试验结果表明,克氏原螯虾全长(L)和体质量(m)呈幂函数,回归方程为:m=0.0209L3.1132;温棚养殖和稻田养殖克氏原螯虾幼虾均在2—3月生长最快,1月生长最慢;克氏原螯虾幼虾各时期各生长指标温棚养殖幼虾均大于稻田养殖幼虾,至3月,温棚养殖的克氏原螯虾体质量接近稻田养殖的2倍;在温度较低的12月—翌年2月期间,温棚养殖的克氏原螯虾幼虾的平均体质量增加率比稻田养殖的克氏原螯虾幼虾的平均体质量增加率高14.00%,温棚养殖的克氏原螯虾幼虾全长平均增长率比稻田养殖的高3.96%。温棚养殖的各时期雄虾体质量均略高于雌虾,但差异不显著(P>0.05);在所有生长指标中,只有雄性克氏原螯虾螯长一直大于雌性,且自12月后,雌、雄虾螯长间一直存在极显著差异(P<0.01)。     

利用生物絮团技术对克氏原螯虾的养殖效果初探

为探究将生物絮团技术应用到克氏原螯虾养殖的可能性，本实验利用生物絮团技术和普通饲料投喂2种方式短期养殖体质量为(9.70±0.32) g的克氏原螯虾30 d。比较养殖期间2实验组的水化学指标以及实验结束时2实验组幼虾的生长情况，肌肉及肝胰腺营养成分组成，胃、肠和肝胰腺组织的消化酶活性，肝胰腺和肌肉组织的抗氧化能力。结果显示，①在养殖期间，絮团组水体总氮(TN)、亚硝态氮(NO₂^--N)、硝态氮(NO₃^--N)的质量浓度均维持在较低的水平。②本实验条件下2实验组虾的终末体质量、增重率(WG)、特定生长率(SGR)、存活率(SR)均无显著差异。③絮团的粗蛋白含量可以达到36.8%，能够满足克氏原螯虾对于蛋白的需求。但絮团的粗脂肪含量较低，这也影响了絮团组幼虾肌肉组织的粗脂肪沉积量。④絮团组幼虾肝胰腺中α-淀粉酶(α-AL)、脂肪酶(LPS)、纤维素酶(CL)活性均显著高于饲料组幼虾，而饲料组幼虾在胃、肠组织中的α-AL活性较高，2实验组幼虾的胃蛋白酶活性无明显差异。⑤絮团组幼虾的抗氧化能力与饲料组幼虾相比，肝胰腺中超氧化物歧化酶(SOD)活性较高，丙二醛(MDA)含量较低，但总抗氧化能力(T-AOC)、过氧化氢酶(CAT)、谷胱甘肽还原酶(GR)以及溶菌酶(LZM)无明显差异。研究表明，生物絮团技术在克氏原螯虾的养殖中具有积极作用，可以达到与饲料投喂相同甚至更好的养殖效果。     

克氏原螯虾幼虾培育技术研究

对克氏原螯虾幼虾进行培育,即克氏原螯虾从破膜再经3次蜕皮体长到0.9～1.0cm后(即仔虾离开母体后)进行培育,经22d培育试验,幼虾体长平均从1.0 cm增长到3.0 cm,体重平均从0.012 g增重到1.64g.采取两种培育方式(即繁殖池原池培育和幼虾池培育),其成活率平均分别为75.6%和71.2%.     

虾青素对微囊藻毒素MC-LR胁迫下克氏原螯虾的生长、繁殖及免疫力的影响

本文目的旨在研究虾青素对微囊藻毒素MC-LR胁迫下(25μg/L)克氏原螯虾的免疫力及生长繁殖的影响。实验设计四个梯度的饲料中虾青素添加比例分别为(0、5、10、20 mg/g)养殖周期持续8星期。结果表明虾青素显著提高了克氏原螯虾肝脏中超氧化物歧化酶(SOD)和碱性磷酸(AKP)的活力(P0.05)。5g/kg虾青素的添加量即可对SOD酶活具有明显提升(P0.05);10 g/kg的虾青素添加量对AKP的提升最为明显(P0.05);研究还发现虾青素可显著提高微囊藻毒素MC-LR胁迫下克氏原螯虾的存活率和特定生长率(SGR)(P0.05),提高克氏原螯虾雌虾的抱卵量。研究表明虾青素作为一种抗氧化剂适宜于在克氏原螯虾饲料中添加,并且具有提高虾体免疫活力,缓解微囊藻毒素MC-LR对虾体氧化胁迫的作用。     

发酵饲料对克氏原螯虾生长性能、肌肉品质、抗氧化能力和肠道微生物群落的影响

为探究克氏原螯虾配合饲料经发酵处理后的饲喂效果，分别用未发酵和发酵饲料在室内循环水系统中饲养体重为(4.91±0.18) g的克氏原螯虾幼虾8周，采样分析发酵饲料对克氏原螯虾生长、肌肉品质、消化力、抗氧化能力及肠道菌群结构的影响。结果显示，(1)发酵饲料水中溶失率显著低于未发酵饲料；(2)发酵饲料显著提高克氏原螯虾增重率和特定生长率，降低饲料系数，但对存活率、肝体比、含肉率和体成分无显著影响；(3)发酵饲料显著提高克氏原螯虾肌肉硬度、弹性、咀嚼性和胶黏性，降低了黏附性；(4)发酵饲料显著提高克氏原螯虾肝胰腺及肠道中胰蛋白酶和脂肪酶活性，血清和肝胰腺中超氧化物歧化酶、酸性磷酸酶和碱性磷酸酶活性，以及肝胰腺总抗氧化能力；(5)发酵饲料显著提高了肠道绒毛长度和宽度；(6)发酵饲料改善了克氏原螯虾肠道微生物结构，显著升高了厚壁菌门和放线菌门相对丰度，同时提高了肠道菌群多样性。研究表明，饲料经发酵处理后可以有效提高克氏原螯虾生长性能、肌肉品质、消化力和抗氧化能力，改善了肠道组织结构，改变了肠道微生物结构，为克氏原螯虾新型环保饲料的生产提供理论依据。     

克氏原螯虾对配合饲料感知能力的研究

在稻田养殖环境条件下，利用特定设计的试验设施，研究了克氏原螯虾对配合饲料感知能力，以期为合理确定养殖水体投饵点数量和空间布局、增加饲料利用率提供科学依据。克氏原螯虾对配合饲料感知的最大间隔距离估算为12 m；在食物间隔距离3 m和6 m捕获的雌虾与雄虾数量无显著性差异（χ2>1.19, df =1, P>0.270），表明雌性与雄性对配合饲料的感知能力可能没有显著差异。食物感知-搜索时间与食物间隔距离呈正相关，在食物间隔距离为3 m、6 m、9 m、12 m时，食物感知-搜索的最短时间分别为(1.8±0.5) min、(5.0±1.1) min、(11.4±1.7) min、(25.2±2.4) min，最长时间分别为(3.4±0.9) h、(7.3±0.6) h、(9.0±0.8) h、(10.0±1.3) h。当食物间隔距离为3 m和12 m时，接受配合饲料刺激后分别有(68.2±1.6)%和(36.3±1.9)%的克氏原螯虾能在3 h内到达食物源。研究结果表明，克氏原螯虾对配合饲料感知的能力在12 m以内，食物间隔距离越小，食物感知-搜索的时间越短。     

Effect of stocking density on growth performance of juvenile sea cucumber Holothuria tubulosa (Gmelin, 1788)

Stock density is one among the most important factors in aquaculture that directly influences the growth of organisms; however, there is limited information about the effects of stocking density on growth performance of sea cucumber Holothuria tubulosa (Gmelin, 1788) that has a commercial potential and represents a new species for aquaculture. In this study, we investigated the effect of stocking densities on the growth performance of juvenile H. tubulosa (40.3 ± 3.34 g) in laboratory conditions. Stocking densities were selected as 6, 15 and 30 ind m^?2 with total biomass 253.3 ± 0.18, 601.2 ± 0.11 and 1201.4 ± 0.15 g m^?2 respectively. We monitored the growth by wet weights and calculated the growth performance through weight gain, growth rate, specific growth rate, relative weight gain, coefficients of variation and survival rate during 8 weeks of research period. We found that individual mean weight gain in 6 ind m^?2 group was approximately 29.53 g while it was 3.03 g and ?4.36 g for 15 ind and 30 ind m^?2 groups respectively. Results have shown that the specific growth rate tends to decrease as the number of individuals in unit area increases. The final mean weight, growth rate, specific growth rate, relative weight gain and coefficients of variation were significantly different among treatment groups. In conclusion, a density of 6 ind m^?2 is recommended for stocking juvenile H. tubulosa under rearing conditions. Stocking density of 15 ind m^?2 is not favourable for long term as the growth rate is negligible where 30 ind m^?2 should be avoided in tank‐based rearing units.     

Growth and Feed Utilization of Captive Wild Subadult Black Sea Bass Centropristis striata Fed Practical Diets in a Recirculating System

The effects of four practical diets on growth, feed utilization, and body composition of wild‐caught juvenile and subadult black sea bass Centropristis striata (316 ± 113 g =±± SD) were compared for 221 d in a recirculating tank system consisting of 12 2,660‐L tanks. Salinity averaged 33.5 ppt and temperature averaged 20.9 C but vaned from 12 to 27.1 C. Diets differed in crude protein (CP) and crude lipid (CL) as follows: 1) low CP (44.0%), low CL (11.4%) trout diet; 2) low CP (44.8%), high CL (15.0%) trout diet; 3) midlevel CP (47.9%), midlevel CL (12.8%) Bounder diet; and 4) high CP (53.9%), high CL (15.1%) marine finfish diet. Energy: protein ratios (E: P) were 44.6, 45.3, 41.8, and 39.1 W/g. Survival to 221 d on all diets was 100%. Significant (P < 0.05) differences in growth rates were observed among diets. Final weights were higher for midlevel and high CP diets 3 and 4 (1,051 and 1,013 g) than for low CP diet 1 (873 g). Relative growth rate (RGR, % total increase in weight), specific growth rate (SGR, % increase in body weight/d), and daily weight gain (DWG, g/d) were higher for higher CP diets 3 and 4 (RGR = 223 and 221; SGR = 0.53; DWG = 3.28 and 3.16), than for low CP diet 1 (RGR = 181; SGR = 0.47; DWG = 2.54). There were no significant differences between initial and final whole body protein and fiber content among diets. Lipid and gross energy levels significantly increased (P < 0.0001) in all treatments while moisture levels significantly decreased (P < 0.001). Although these differences were not significant, feed conversion ratio (FCR = dry weight fed/wet weight gain) was lower for fish given midlevel CP diet 3 (1.49) and high CP diet 4 (1.52) than for those fed low CP diets 1 and 2 (1.60 and 1.62). Protein efficiency ratios (PER = weight gain/weight protein fed) (1.43 to 1.24), apparent net protein retention (ANPR = weight protein gain/weight protein fed) (20 to 25%), and apparent net energy retention (ANER = energy gain/energy fed) (53.3 to 56.8%) were not significantly different among treatments. The midlevel CP (50%), midlevel CL (12%) diet maximized growth rates and was also significantly less expensive per kg fish weight produced ($1.40) than the high CP diet ($1.94) which produced the second highest growth rates. These results demonstrated that wild‐caught black sea bass can be successfully reared in recirculating tanks from juvenile to marketable sizes with high survival and with good feed conversion and growth on commercially prepared diets with a wide range of protein and lipid levels.     

Effects of rearing density on growth, brain neurotransmitters and liver fatty acid composition of juvenile white sea bream Diplodus sargus L.

White sea bream Diplodus sargus L. is a fish species that develops dominance hierarchies and aggressive behaviour against its conspecifics. On the other hand, stocking density is known to affect social interactions, while an appropriate density for D. sargus efficient farming remains to be elucidated. For this purpose, juvenile D. sargus (14.3 g) were reared in 88.4 L tanks, for 10 weeks, under six rearing densities (10, 15, 20, 25, 30 and 35 fish tank^?1). Water quality was not affected by rearing density. Best growth, in terms of final weight, specific growth rate, weight variation and food utilization, was achieved at 10 fish tank^?1. At this treatment the lowest body water content, hepatosomatic and splenosomatic indices, higher body and liver lipid content were also observed. Brain neurotransmitter results indicated increased dopaminergic activity in populations held at higher rearing densities, while serotonergic activity was not affected. Moreover, no significant differences were detected for liver fatty acids. Results of the present study, compared with previously reported data, suggest that, within the range tested, the lowest realistic rearing density for juvenile white sea bream would be 10 fish tank^?1. Higher rearing densities led to decreased growth, which seemed to be related to changes in intraspecific competition and social behaviour.     

Effect of rearing density on the growth and welfare indices of juvenile spotted wolffish,Anarhichas minor (Olafsen)

The goal of this study was to determine the optimal stocking density for rearing juvenile spotted wolffish, Anarhichas minor (Olafsen), at two different sizes and assess the welfare status in relation to density. No major growth impairment was observed, although smaller fish (50–100 g) were significantly affected by density during the 120 days of the experiment, with final mean weights of 119.6 ± 11.6, 118.0 ± 5.8 and 88.7 ± 0.6 g for initial rearing densities of 10, 20 and 40 kg m^?2 respectively. No effect of rearing density was seen for larger fish (100–160 g) during the 90 days of the experiment, with final mean weights of 160.2 ± 5.9, 159.7 ± 3.7 and 163.7 ± 11.5 g at fixed rearing densities of 20, 30 and 40 kg m^?2 respectively. Our results suggest that the optimal rearing density of juvenile spotted wolffish is below 40 kg m^?2 for smaller size fish (～50–100 g) and probably ≥40 kg m^?2 for the larger fish (100–160 g). Furthermore, it appears that the range of rearing density used did not have a significant effect on a selection of stress indicators (Na⁺ and K⁺ concentration, haematocrit, hepatosomatic index, total amount of plasma proteins and liver and muscle water content) and immunity response (plasma lysozyme activity) of juvenile spotted wolffish, making it a very tolerant species to crowding.     

Culture of Juvenile Atlantic Surfclams, Spisula solidissima solidissima and Spisula solidissima similis, in Forced-Flow Upwellers in a Bivalve Hatchery in Coastal Georgia

Four experimental growth studies for juvenile Atlantic surfclams, Spisula solidissima solidissima and Spisula solidissima similis , under hatchery conditions were conducted in 10-cm diameter forced-flow upweller units. Experiments were designed to determine optimum food ration (2%, 5%, and 8% g dry weight of algae/g wet weight of clam), water culture temperature (20, 25, and 30°C), flow rate (2, 4, and 6 Lpm), and stocking density (7, 14, and 21 g wet weight of clams) for rearing juvenile clams in upweller units. Each experimental trial was performed for a 14-d period. Nested Analysis of Variance showed that juvenile surfclams Spisula solidissima similis grew significantly faster at a temperature of 20°C and food rations of 5 % and 8%. In all four experiments, clam mortalities were not observed except in the temperature experiment, where total mortality occurred for clams cultured at 30°C. Clam growth in biomass and size decreased significantly with increases in culture temperature. For Spisula solidissima solidissima , clam growth was significantly reduced in terms of size and biomass at a flow rate of 6 Lpm. No difference in size or biomass was determined between clams grown at a flow rate of 2 or 4 Lpm. Surfclams at the lowest stocking density of 7 g wet weight significantly increased more in net biomass compared to those at higher stocking densities. Clams were significantly larger in shell length when grown at the two lower stocking densities compared to those at the highest stocking density. Hatchery-rearing protocol for juvenile surfclams is discussed.     

Feeding Rates, Growth Performance and Gametogenesis of Wreckfish (Polyprion americanus) kept in Captivity

Wreckfish (Polyprion americanus) is a panoceanic, antitropical distributed species. Despite the high market price, high growth rate, good quality flesh and the potential for aquaculture, research data are scarce. In this study, the growth performance and food intake was investigated in juvenile fish, while gametogenesis was studied in adult fish. Three groups were created from 19 individuals, which were collected during neustonic sampling, using fish aggregating devices, in association with floating objects and during tuna fishing with drift nets from Greece (Crete), Italy (Ionian Sea) and the Atlantic coast of France from September 1999 to March 2001. All individuals (initial weight between 0.5 g and 4.5 kg) were reared in aquaculture facilities so as to monitor growth performance and food intake. Food (de-frozen fish – bogue, mackerel and squid – or moist pellets) was delivered ad libitum. Total length and wet weight were measured regularly. Daily food intake, the food conversion index and daily growth rate were calculated. Individuals, aging 0+, grew exceptionally fast, reaching 2.0 kg (total length 50 cm) in 12 months and 5.0 kg (total length 65 cm) in 24, while at later stages, the growth rate decreased and depended on the water temperature during rearing. Food consumption varied during the rearing period according to the developmental stage and the rearing conditions. The food conversion ratio ranged between 0.9 and 2.5 on dry weight basis during the period of the study. Gametogenesis was monitored in a separate stock of 15 individuals (11.7 ± 3.7 kg) by biopsis while blood samples were taken for steroid estimation. Increased oocyte diameter was observed in females from August to January, while plasma estradiol levels also increased from October to March. However, neither egg or sperm were collected from the stock. Young wreckfish presented a high growth rate in captivity, thus supporting the feasibility of the species for rearing. Further research, however, is required for the reproduction of the species.     

The effect of light intensity on growth of juvenile dusky kob Argyrosomus japonicus (Temminck & Schlegel 1843)

South African juvenile dusky kob Argyrosomus japonicus are more abundant in turbid estuaries than in clear marine‐dominated estuaries. Turbidity can reduce light penetration into the water and create an environment different from that experienced by fish under culture conditions in mechanically filtered clear water. In order to optimize rearing conditions of this species, the effects of light intensity (23–315 lx) and feeding method (restricted ration vs. feeding to apparent satiation) on growth and food conversion ratio (FCR) of juvenile A. japonicus were assessed in a 56‐day growth trial. Fish weight increased from 7.2±1.6 to 41.9±10.2 g fish^?1 at a growth rate of 3.25% body weight day^?1. Light intensity did not significantly affect growth or FCR. Feeding method did not significantly affect growth rate, but average FCR was significantly better in treatments fed a ration of 3.6% body weight day^?1 than in treatments fed to apparent satiation. Therefore, a light intensity range of 23–315 lx can be used to culture dusky kob juveniles. The better FCR in fish fed a restricted ration suggests that a ration of 3.6% body mass day^?1 allowed good growth of juvenile dusky kob.     

Effects of Bdellovibrio and Like Organisms on Survival and Growth Performance of Juvenile Turbot,Scophthalmus maximus

In this study, the impact of Bdellovibrio and like organisms (BALOs) on juvenile turbot rearing was investigated in a static water rearing system with weekly partial change of water. A 60‐d‐long rearing experiment showed that, compared with control, survival rate, percent weight gain, percent length gain, and average daily growth were 92 ± 2.8%, 387.1 ± 4.6%, 78.6 ± 1.5%, and 1.87 ± 0.79 g/d, respectively, significantly higher than those in the control, viz., 81 ± 3.2%, 248.2 ± 5.3%, 56.7 ± 2.1%, and 1.16 ± 0.68 g/d, respectively. Water quality results demonstrated that no significant difference (P > 0.05) was observed between test and control with the addition of BDW03. Compared with the control, total culturable bacteria and total vibrio numbers in rearing water and in intestines were significantly (P < 0.05) reduced by 0.8–1.4 log CFU/mL/ log CFU/g, with the addition of BDW03. Furthermore, denaturing gradient gel electrophoresis profiles in rearing waters collected at a 1.5‐d interval over a week revealed that BDW03 simplified bacterial community structures with time, and some vibrios disappeared with the addition of BDW03. To the best of our knowledge, this is the first report that BALOs can promote growth and survival of juvenile turbots and be beneficial to coldwater fish aquaculture at the production level.     

Effects of dissolved oxygen concentration and stocking density on the growth,energy budget and body composition of juvenile Japanese flounder,Paralichthys olivaceus (Temminck et Schlegel)

An energetic method was used to investigate the effects of stocking density and dissolved oxygen (DO) concentration on the growth of juvenile Paralichthys olivaceus. Fish, with initial weights of 14±2.1 g, were exposed to a normal and a high DO of 5.5±0.5 and 14±2 mg L^?1, as well as four stocking densities per DO concentration (100, 200, 300 and 400 ind m^?2 for the normal DO and 200, 400, 600 and 800 ind m^?2 for the high DO). The feed efficiency (FE_W) decreased significantly with increasing stocking density and increased significantly with increasing DO concentration. The maximum weight was achieved at 400 ind m^?2 under a high DO depending on our rearing conditions. The stocking density and DO concentration change energy ingestion and its allocation for respiration, growth and excretion lost in nitrogen excretion, but do not affect the energy loss through faeces. The results of the body composition of fish indicated that the stocking density and DO concentration had no significant effects on the moisture, lipid content and gross energy, but are affected by the same. Energetic analysis demonstrated that high DO concentrations could alleviate the growth depression caused by high stocking densities, decrease energy loss in respiration and nitrogen excretion and increase the energy proportion allocated to growth.     

Effect of feeding frequency on growth,feed efficiency and nutrient utilization of juvenile flounder (Platichthys flesus luscus)

An experiment was conducted to determine the effects of optimal feeding frequency on growth performance, feed efficiency, nutrient utilization and body composition in juvenile flounder. Four feeding frequencies of one (F1), two (F2), three (F3) and four (F4) times a day were evaluated as treatments in triplicate for a period of 60 days. Forty-seven hatchery produced juveniles (2.5 ± 0.7 g) were stocked into 160-L rectangular fiberglass tanks and fed with a commercial diet containing 54 % protein to satiation. At the end of the experiment, the final weight of F1, F2, F3 and F4 were 5.06 ± 0.29, 5.91 ± 0.42, 6.24 ± 0.42 and 6.16 ± 0.46 g, respectively. Growth rates and feed consumption were highest in F3 and lowest in F1. Feed conversion ratios ranged between 0.83 ± 0.04 and 0.90 ± 0.03. There were no significant differences in either moisture or ash content of the fish groups. Protein content decreased with increasing feeding frequency, while lipid content partly increased with increasing feeding frequency. Nitrogen intake and lipid intake were significantly higher in fish fed under F3 and F4 treatment, whereas the nitrogen gain decreased and lipid gain increased with increasing feeding frequency. It is concluded that the flounder juveniles can achieve maximum growth performance and better nutrient utilization when they are fed a given ration two times a day. The findings have practical significance toward establishing an appropriate flounder nursery rearing and will directly benefit the nursery operations.