罗非鱼养殖池塘水和表层沉积物中蓝藻的群落结构及影响因素研究

为了研究罗非鱼养殖池塘水和表层沉积物中蓝藻(蓝细菌)的群落结构、多样性状况和影响因素,采用高通量测序技术平台对细菌16S rRNA基因进行测序,对其中的蓝藻组成进行分析。结果表明:水和表层沉积物中的蓝藻群落结构存在显著差异,但其中的优势目是相同的,为聚球藻目、Cyanobacteria_norank和色球藻目;水中的蓝藻群落结构受到月份变化的影响比较大,并且与系统中氮净输入量有关。表层沉积物中的蓝藻群落受到池塘差异的影响更大,且与系统中磷净输入量有关。试验条件下,罗非鱼对系统中蓝藻群落多样性的影响主要来自于直接或间接的营养物质输入。     

Salmon testes meal as a functional feed additive in fish meal and plant protein‐based diets for rainbow trout (Oncorhynchus mykiss Walbaum) and Nile tilapia (Oreochromis niloticus L.) fry

Fishery processing by‐products are a large resource from which to produce fishmeal and other products for a variety of uses. In this study, testes meal (TM) produced from pink salmon processing by‐product was evaluated as a functional ingredient in aquafeeds. Nile tilapia and rainbow trout fry were fed five isonitrogenous and isoenergetic experimental diets for 4 and 9 weeks respectively. Two diets were fishmeal‐based (FM) and three were plant protein‐based (PP). Salmon TM was added to the FM and PP diets at 7% to replace 20% of fishmeal protein (FMTM and PPTM respectively). An additional control diet was prepared in which fishmeal was added to the PP diet to supply an equivalent amount of protein as supplied by TM (PPFM). Inclusion of TM in both the FM‐ and PP‐based diets resulted in higher final body weights, although differences were only significant between rainbow trout fed FM or FMTM diets. Similar differences were calculated for other indices of fish performance, e.g. specific growth rate, feed conversion ratio, protein efficiency ratio and protein retention efficiency. Feed intake was significantly higher for fish fed FMTM compared with FM in rainbow trout. For tilapia, final weights were numerically higher, but not significantly different for fish fed diets containing TM compared with non‐TM diets (FM vs. FMTM; PP vs. PPTM). Performance of trout or tilapia fed the PPFM diet did not increase compared with the PP diet. The results indicate that TM addition to both FM and PP diets increased feed intake and also increased metabolic efficiency, demonstrating that TM can be a functional ingredient in aquafeeds.     

Effects of C/N ratio and periphyton substrates on pond ecology and production performance in giant freshwater prawn Macrobrachium rosenbergii (De Man, 1879) and tilapia Oreochromis niloticus (Linnaeus, 1758) polyculture system

The production performances of giant freshwater prawn Macrobrachium rosenbergii and Nile tilapia Oreochromis niloticus in C/N‐controlled periphyton‐based polyculture systems were evaluated in triplicate. Three different management practices were compared: the traditional practice without addition of periphyton substrates and carbohydrate (Control), addition of maize flour to maintain a carbon: nitrogen rate of 20:1 (treatment CN) and addition of both maize flour and periphyton substrates (treatment CN+P). This experiment used a pre‐optimized stocking density of tilapia and freshwater prawn by Asaduzzaman et al. Aquaculture [286 (2009) 72]. All ponds were stocked with prawn (3 m²) and monosex Nile tilapia (1 m^?2). Bamboo side shoots were posted vertically into the pond bottoms as periphyton substrate covering an additional area of 171 m² for periphyton development. A locally formulated and prepared feed containing 17% crude protein with C/N ratio close to 15:1 was applied twice daily in all ponds considering the body weight of freshwater prawn only. Water quality parameters, except total alkalinity did not vary significantly (P > 0.05) among treatments. Both, organic matter and total heterotrophic bacterial loads (THB) in the sediment were significantly (P < 0.05) higher in treatment CN+P followed by treatment CN and control. Periphyton biomass in terms of dry matter and chlorophyll a values constantly decreased during the culture period. Substrates contributed 66% and 102% higher net yield of freshwater prawn than CN and control treatment respectively.     

Efficacy of florfenicol for control of mortality associated with Francisella noatunensis subsp. orientalis in Nile tilapia,Oreochromis niloticus (L.)

Francisella noatunensis subsp. orientalis (Fno) (syn. F. asiatica) is an emergent Gram‐negative facultative intracellular bacterium. Although it is considered one of the most pathogenic bacteria in fish, there are no commercially available treatments or vaccines. The objective of this project was to determine the most efficacious concentration of florfenicol (FFC) [10, 15 or 20 mg FFC kg^?1 body weight (bw) per days for 10 days] administered in feed to control experimentally induced infections of Fno in Nile tilapia, Oreochromis niloticus (L.), reared in a recirculating aquaculture system. The cumulative mortality of fish that received 0, 10, 15 or 20 mg FFC kg^?1 bw per day was 60, 37, 14 and 16%, respectively. Francisella noatunensis subsp. orientalis genome equivalents were detected in water from all challenged groups with slight reduction in the concentration in the florfenicol‐treated groups 4 days after treatment. The mean LOG of CFU Fno mg^?1 spleen was 3–5 and was present in all challenged groups at necropsy 11 days after treatment (21 days after challenge). Results show that florfenicol administered at doses of 15 and 20 mg FFC kg^?1 bw per days for 10 days significantly reduced mortality associated with francisellosis in Nile tilapia.     

低温对罗非鱼基因组DNA甲基化的影响

以经过连续多代抗寒选育获得的尼罗罗非鱼耐寒品系为实验材料,采用DNA甲基化敏感扩增多态性(methylation sensitive amplified polymorphism,MSAP)分析方法从全基因组水平上探讨了低温适应对罗非鱼DNA序列中CCGG位点的甲基化水平的影响。结果显示,选用的18对选择性扩增引物共检测到849个位点。耐寒品系检测到的位点数为411个,对照组为438个,其中发生甲基化的位点数分别为72和104个,总甲基化率分别为17.52%和23.74%;全甲基化位点分别为37个和65个,全甲基化率分别为9.00%和14.84%;半甲基化位点分别为35个和39个,半甲基化率分别为8.52%和8.90%。结果分析表明,尼罗罗非鱼耐寒品系的总甲基化水平、全甲基化水平和半甲基化水平较对照组均有一定程度的下降。与对照组相比,尼罗罗非鱼耐寒品系基因组DNA甲基化总体水平下降了6.22%,其中以全甲基化位点变异为主,其下降幅度比例明显,为5.84%。由此可见,经过连续多代的低温胁迫可导致尼罗罗非鱼DNA甲基化水平发生改变,发生了去甲基化反应,表现为基因组甲基化程度降低的特征,说明了DNA甲基化与罗非鱼抗寒性反应密切相关。     

水温、饲料蛋白及其互作效应对吉富罗非鱼生长与血清能源物质的影响

采用中心复合实验设计和响应曲面分析方法,在实验室条件下,探讨了温度(20~34℃)、饲料蛋白水平(25%~50%)及其互作效应对吉富罗非鱼(Oreochromis niloticus)幼鱼生长、饲料效率与血清能源物质(葡萄糖、甘油三酯和总蛋白)的影响。整个实验持续8周。结果表明,温度与饲料蛋白水平的一次效应对特定生长率和饲料效率有显著影响(P<0.05)。高温与饲料高蛋白水平会降低生长与饲料效率。温度的一次效应对血清葡萄糖、甘油三酯和总蛋白水平有显著影响(P<0.05)。饲料蛋白水平为37.5%时,随温度的升高,血清葡萄糖水平逐渐增加;甘油三酯和总蛋白水平呈先下降后上升的变化。饲料蛋白水平对血清葡萄糖有显著影响(P<0.05),但对甘油三酯和总蛋白水平无显著影响(P>0.05)。温度与饲料蛋白水平的互作效应对饲料效率、血清葡萄糖、甘油三酯和总蛋白有显著影响(P<0.05)。温度对生长、饲料效率和血清甘油三脂与总蛋白水平的影响较饲料蛋白明显,而对血清葡萄糖的效应则与之相反。因子与特定生长率、饲料效率、血清葡萄糖、甘油三酯及总蛋白水平这5项响应值间二次多项回归方程的决定系数分别达到0.958、0.955、0.971、0.977和0.870(P<0.01),可用于预测。综合以上实验结果,温度/饲料蛋白水平最优组合为29.9℃/40.3%,此时,特定生长率和饲料效率均较高,分别为2.748%/d和0.775,其可靠性达0.888。不同饲料蛋白水平下,水温对吉富罗非鱼血清代谢物质的影响也不同,增加水温有助于更好地利用饲料蛋白,提高血清中蛋白的分解与转化。     

Geosmin and Off-Flavor in Nile Tilapia (Oreochromis niloticus)

Abstract

The concentration of geosmin (1,10-trans-dimethyl-trans-9-decaol) in fresh tilapia were analyzed by applying high-vacuum distillation, extraction and gas chromatography techniques. The distribution of geosmin in the fish was determined by examining tissues from various parts of tilapia, along with the rates of geosmin absorption and purging. Analysis showed that when geosmin was added to fish flesh at concentrations ranging from 2.8 to 390 μg per kg of flesh, the rate of recovery was 51 to 89%. Sensory evaluation detected muddy flavor in freshwater tilapia with geosmin content ranging from 7.55 to 9.85 μg/kg of fish flesh. However, panelists failed to detect muddy flavor in brackish water tilapia that contained geosmin only in the range of 1.5 to 2.6 μg/kg. Among various tissues of the fish, the intestines contained the highest geosmin concentration, and appeared in descending order in the abdominal, skin and muscle tissues. After holding for 2 h in water with 5 and 50 μg/l geosmin, tilapia absorbed 17.6 and 42.2 μg/kg geosmin in the flesh, respectively. Holding the fish over longer periods in water with higher geosmin content resulted in a greater amount of absorption. In contrast, transferring muddy-flavored fish to static clean water purged geosmin from the fish but it required at least 16 days to eliminate the muddy flavor.     

吉富罗非鱼生长过程中氮收支变化的研究

为充实有关鱼类研究数据,提供实际生产理论依据,研究了吉富品系尼罗罗非鱼（Oreochromis niloticus）从鱼种（18 g）生长至成鱼（180 g）过程中氮收支变化。试验为期73 d,每日饱食投喂并收集鱼粪,溶解氧质量浓度为8.0-6.0 mg·L-1,pH为 7.5-6.5,水温为24-30 ℃。在鱼均质量达到50 g、100 g和180 g时测定并计算当前生长阶段氮收支。结果表明,生长氮比例在养殖初期最高（64%）,养殖中期最低（47%）;粪氮比例在养殖中期最高（9%）,养殖初期和末期分别为5%和4%;排泄氮比例随鱼的生长而逐渐增加。此外,试验期间水中总氮增加速度在养殖中期减慢,养殖末期再次加快。     

Relationship Between Dietary Protein Source and Feeding Frequency During Feeding Nile Tilapia,Oreochromis niloticus (L.) Cultured in Concrete Tanks

ABSTRACT

A 24-week feeding trial was conducted in concrete tanks with Nile tilapia, Oreochromis niloticus (L.) with an average initial weight and length of 50.87 ± 6.03 g and 14.4 ± 0.45 cm, respectively, to examine the effect of two protein sources and two feeding frequencies on growth performance, production traits, and body composition. Twelve 4 m³ concrete tanks (2 × 2 × 1.25 m, long, width, and height) were each stocked with 100 fish and fed diets containing either fish meal protein or soybean meal protein at two feeding frequency of two times daily or four times daily (2 × 2 × 3 factorial experiment). The results revealed that there was no significant effect of dietary protein sources on growth rate, whereas there was a significant increase in growth rate with increasing feeding frequency (P < 0.05). The same trend was also observed for mean body weight (g), production rate (kg/m3), specific growth rate (SGR % day^?1). The best final mean body weight (g), specific growth rate (SGR % day^?1), and production rate (kg/m3) were recorded in groups of fish fed with feeding frequency four times daily. Whole fish moisture, protein, fat, and ash contents were significantly influenced (P ≤ 0.05) by protein sources and feeding frequency, except protein not influenced with feeding frequency. Energy was significantly (P < 0.05) influenced by feeding frequency, but not by dietary protein sources. Economic evaluation indicated that soybean meal (Diet B) at four times feeding daily was the most cost-effective and affordable feed strategy for farmers. We conclude that a soybean diet fed four times daily is recommended for adult Nile tilapia reared in concrete tanks.