Effects of dietary starch and energy levels on maximum feed intake, growth and metabolism of Nile tilapia, Oreochromis niloticus

The aim of this study was to gain insight into how Nile tilapia (Oreochromis niloticus) regulate feed and energy intake in response to diets low and high in starch and cellulose. It was hypothesized that high-starch diets would reduce feed intake due to the effect of high blood glucose level, and that stomach volume may limit feed intake of fish fed diets low in energy. Four experimental diets, low starch–no cellulose inclusion, high starch–no cellulose inclusion, low starch–with cellulose inclusion, and high starch–with cellulose inclusion, were formulated. The high-starch diets and diets with cellulose inclusion were 17.5% more energy-diluted than the low-starch diets and diets without cellulose inclusion, respectively. Male tilapia were fed to apparent satiation for six weeks. Feed and digestible energy intake of fish fed diets with cellulose inclusion increased and decreased by 8.3% and 5.5%, respectively, compared to fish fed diets without cellulose inclusion. This suggests the role of stomach volume in restricting feed consumption. Fish fed high-starch diets achieved only 0.5% more feed intake and 13.9% less digestible energy intake than fish fed low-starch diets. The lower increase in feed intake and higher decrease in digestible energy intake of fish fed high-starch diets than of fish fed diets with cellulose inclusion suggests that high blood glucose suppresses feed intake in Nile tilapia. An alternative explanation for the differences in feed and digestible energy intake of fish fed different diets was based on the fact that heat production was not influenced by starch nor cellulose-inclusion levels. Thus, under satiation feeding, oxygen uptake capacity may determine feed and digestible energy intake in fish rather than blood glucose or stomach volume.     

一种新型生物柴油原料的脂肪酸成分分析

[目的]分析罗非鱼下脚料油化学成分。[方法]用气相色谱法（GC）对成分进行分析,用面积归一化法计算各组分的相对质量分数。[结果]鉴定出22中脂肪酸成分,主要成分为油酸（22.1%）、二十四碳一烯酸（20.8%）、棕榈酸（14.2%）和二十二碳一烯酸（10.1%）。[结论]单不饱和脂肪酸是罗非鱼下脚料油的主要成分,该研究为进一步开发罗非鱼可再生资源提供了科学依据。     

Biochemical and histological hepatic changes of Nile tilapia Oreochromis niloticus exposed to carbaryl

The purpose of this study was to evaluate biochemical and morphological responses induced by carbaryl in the liver of Nile tilapia (Oreochromis niloticus) exposed during 21 days to sublethal concentrations (0.25 and 0.5 mg L⁻¹), testing also recover for 14 days in clean water, after 14 days exposure. The activities of the following enzymes were measured: superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), glutathione reductase (GR), and reduced (GSH) and oxidized glutathione (GSSG). Globally, our data showed that exposure to carbaryl decreased the SOD, CAT, GR, and GST activities, except for the SOD and GST activities after 14 days exposure to 0.25 mg L⁻¹. In contrast, after 14 days exposure the GR activity of the hepatic tissue from carbaryl-treated fish showed significant elevation in relation to the control. When fish were left to recover, a positive response was seen in the GSH and GSSG contents. The results of the recovery group suggest that the toxicity produced by carbaryl is reversible to some extent within 15 days. The liver histological analysis showed differences between fish concerning the cellular vacuolization degree (VD) of the hepatocytes. In fish exposed to carbaryl it was observed an increasing hepatocellular basophilia. No other histological alterations were observed when fish was exposed to carbaryl, except a few necrotic foci at day 7. The sections stained with PAS reaction showed that the vacuolization was always not due to glycogen deposits, thus suggesting lipid accumulation. The combined increased basophilia and glycogen depletion is a common, although non-specific, liver response to many toxicants. In short, this work shows a relation between histological and biochemical changes in liver and carbaryl exposure. The effects of carbaryl were observed at different concentrations.     

Comparative analysis of nitrogen and phosphorus budgets in a bioflocs aquaculture system and recirculation aquaculture system during over-wintering of tilapia (GIFT,Oreochromis niloticus)

Nitrogen (N) and phosphorus (P) budgets in a bioflocs technology (BFT) aquaculture system and a recirculation aquaculture system (RAS) during over-wintering of tilapia (GIFT Oreochromis niloticus)for 64 d were compared in the current study. Fish feed was the major input of N in both systems, specifically, 94±0 % and 82±4 % for the RAS and BFT aquaculture system, respectively. The rate of N recovery in the BFT aquaculture systems was estimated to be 48±5 % of input N, which was significantly different from that of the RAS (37±4 %). There was no significant difference between the RASs and BFT aquaculture systems in terms of P recovery rate. The regular backwashing of the drum filter and biological filter in RAS accounted for 41 ± 2 % of input N and 39 ± 2 % of input P. Approximately 54 % of unassimilated nitrogen N was removed by nitrification in the BFT aquaculture systems. The results from the present study suggest that nitrification may be the dominant pathway for ammonia removal in a BFT aquaculture system rather than by heterotrophic bacterial assimilation.     

罗非鱼海豚链球菌的分离鉴定及药敏试验

为明确广东佛山某罗非鱼鱼场暴发疑似链球菌病的病原情况,应用脑心浸液培养基、胰蛋白大豆琼脂 培养基对患病罗非鱼的肝、胆组织进行细菌分离,对获得的革兰氏阳性链球菌应用16S rDNA 引物进行基因序列鉴 定,并对被确定的链球菌进行基因进化分析,同时进行阿奇霉素、链霉素、阿米卡星等10 种抗生素的药敏试验。结果 表明,分离获得革兰氏阳性链球菌1 株,经16S rDNA 基因扩增鉴定为海豚链球菌;基因进化分析显示,该菌与海豚 链球菌和禽的副乳链球菌亲缘关系最近;药敏试验结果显示,该菌对阿奇霉素和头孢噻肟中度敏感,对其他抗生素 不敏感。     

奥尼鱼养殖池沉积形成的初步研究

在半封闭式奥尼鱼养殖池中输入饲料，探索养殖过程中鱼池沉积形成及其主要影响因子。试验结果表明：无论养鱼或不养鱼，投饲或不投饲，各池都发生不同程度的沉积；外源饲料输入量相同时，养鱼池新颗粒物生成量(干重)比不养鱼池大15．63％，而沉积量比不养鱼池小19．49％；无外源饲料输入时，养鱼池的沉积量比不养鱼池大75．76％；养殖系统内养殖对象与其所处环境的相互依存和相互制约对系统新颗粒物生成及沉积具有重要作用。     

尼罗罗非鱼胰岛的显微和亚显微结构

应用光镜、电镜及特殊染色等技术对尼罗罗非鱼(Tilapia nilotica)的胰岛及其细胞类型和形态进行了详细的研究。尼罗罗非鱼的胰脏与肝脏混合存在，属于肝胰脏。胰岛散布在胰腺内，无固定的形态，胰岛细胞的数量与类型因胰岛的大小而异。用Gomori醛复红特殊染色法，见尼罗罗非鱼胰岛有三种细胞：A细胞胞质中有黄色颗粒；B细胞胞质中有紫红色的颗粒；D细胞胞质内有浅绿色或淡灰色的颗粒。电镜下，B细胞的分泌颗粒较大,芯的形态多样，电子密度差异大,芯与界膜之间常有较大的间隙；A细胞分泌颗粒形态不规则，芯的大小不等，界膜与芯之间无间隙；D细胞分泌颗粒较多，芯的电子密度较低，界膜与芯之间无间隙。此外，胞质内可见较大的线粒体。     

Genetic variation inferred from RAPD fingerprinting in three species of tilapia

This study used random amplified polymorphic DNA (RAPD) fingerprinting for estimating genetic variation and species differentiation in three species of tilapia. A 16-mer random primer generated RAPD markers ranging from 250 to 2400 base pairs (bp). Genetic similarity estimates obtained by pairwise comparisons based on the method of Nei and Li (1979) indicated high genetic similarity (mean genetic similarity (± sd), 0.73 (± 0.15) for Nile tilapia; 0.78 (± 0.12) for Mozambique tilapia; and 0.87 (± 0.07) for Aureus tilapia) within each of the tilapia species. The average interspecies genetic similarities obtained among the three species were 0.59 (± 0.07) for Mozambique/Nile tilapia, 0.46 (± 0.09) for Aureus/Nile tilapia and 0.38 (± 0.07) for Aureus/Mozambique tilapia pair. DNA profiles generated in each species of tilapia were unique. A total of 13 RAPD markers differentiating the three species of tilapia were detected. Our study presented RAPD markers as a new class of useful genetic markers for assessment of genetic diversity and species differentiation in tilapia.     

Fish-management relationships in Israeli commercial fish farming

To analyse the relationships among fish species performance and management procedures, a database was built up with data from 31 fish farms during the period 1976–1987 (1673 observations) and analysed through multivariate statistics (factor analysis). The data include nurseries, grow-out and operational ponds with mono- and polycultures of common carp, Cyprinus carpio, tilapia hybrid, Oreochromis niloticus × O. aureus, silver carp, Hypophthalmichthys molitrix, and mullet, Mugil cephalus. The main conclusions include the following. (1) The highest total yields and best tilapia performances were obtained in polyculture ponds where tilapia was the main species. (2) The best carp performances occurred in grow-out polyculture ponds where carp was the main species. Carp performance was improved in polycultures with mullet and silver carp, irrespective of whether tilapia were present or not. (3) Carp and tilapia yields increased as the nutritional inputs (feed pellets, sorghum pellets, manure), pond size and culture duration increased. The effect of the nutritional input was not linear, but logarithmic. (4) Growth rate of common carp was more affected by total density and stocking size than that of tilapia. Better carp and tilapia growth occurred in grow-out ponds when stocked at large sizes and cultured during short periods, mainly when both species were present. (5) Carp growth varied with the geographical region and size of fish pond, being better in smaller than in larger ponds due to reduced access to natural benthic food in deep ponds.