投喂频率对凡纳滨对虾生长和水质的影响

研究了不同投喂频率(1,2,3,4和5次·d-1)对凡纳滨对虾生长、存活率和水质的影响。试验在室内2m3的圆形水泥池(d=1.6m)中进行,采用全封闭养殖模式,凡纳滨对虾(初始重量为0.24g)养殖密度为50尾·m-3,投喂人工配合饲料(粗蛋白含量为42.98%)。通过7周的试验,结果表明,投喂频率为1～4次·d-1时,随着投喂频率的增加,对虾增重率显著增加;投喂频率由4次·d-1增加到5次·d-1时,对虾增重率略有增加,但差异不显著。凡纳滨对虾的成活率在1次·d-1时最低,2次·d-1时最高,2～5次·d-1时随着投喂频率的增加而降低(投喂频率为1和2次·d-1之间、3和4次·d-1之间差异显著)。投喂频率为3次·d-1时饲料系数最低,蛋白质效率最高。随着投喂频率1～3次·d-1增加,饲料系数逐渐显著降低,蛋白质效率显著递增;而投喂频率从3～5次·d-1增加时,饲料系数增大,蛋白质效率逐渐下降(3和4次·d-1差异显著;4和5次·d-1之间差异不显著)。投喂频率对水环境中的pH值、H2S含量、COD、盐度等水质指标没有显著影响;在养殖后期水环境中投喂频率3～5次·d-1的NH 4和NO-2浓度较投喂频率1～2次·d-1时高。     

Regulation of growth, fatty acid composition and delta 6 desaturase expression by dietary lipids in gilthead seabream larvae (Sparus aurata)

The Δ6 and Δ5 desaturases and elongases show only very limited activity in marine fish, and little is known of the possibility of enhancing Δ6 desaturase gene expression in these fish. The use of plant oils in marine fish diets is limited by their lack of n−3 highly unsaturated fatty acids (HUFA) despite an abundant content of the 18C fatty acid precursor linoleic and α-linolenic acids. The objective of the present study was to determine the ability of larval gilthead seabream to utilize vegetable oils and assess the nutritional regulation of Δ6 desaturase gene expression. Seventeen-day-old gilthead seabream larvae were fed during a 17-day period with one of four different microdiets formulated with either sardine fish oil (FO), soybean, rapeseed or linseed oils, respectively, or a fifth diet containing defatted squid meal and linseed oil. Good larval survival and growth, both in terms of total length and body weight, were obtained by feeding the larvae either rapeseed, soybean or linseed oils. The presence of vegetable oils in the diet increased the levels of 20:2n−9 and 20:2n−6, 18:2n−9, 18:3n−6, 20:3n−6 and 20:4n−6, in larvae fed rapeseed and soybean oils in comparison to those fed FO. In addition, a sixfold increase in the relative expression of Δ6 desaturase-like gene was found in larvae fed rapeseed and soybean oils, denoting the nutritional regulation of desaturase activity through its gene expression in this fish species. However, feeding linseed oil did not increase the expression of the Δ6 desaturase gene to such a high extent.     

Role of free neuromasts in larval feeding of willow shiner Gnathopogon elongatus caerulescens Teleostei, Cyprinidae

ABSTRACT:   It has been reported that the larvae of willow shiner Gnathopogon elongatus caerulescens have many free neuromasts on their body surface. This study examined the ability of the willow shiner larvae to feed on zooplankton by mechanoreception by the free neuromasts. Feeding experiments using untreated larvae and larvae treated with streptomycin, which impairs free neuromast function, were conducted under light and completely dark conditions. The larvae were put into Petri dishes, then nauplii of Artemia salina were introduced. The average number of Artemia eaten by the larvae was expressed as the average ingestion rate of Artemia /10 min. The ingestion rate of Artemia for untreated larvae was 12.3 under light conditions and 10.6 Artemia /10 min. even in complete darkness. The ingestion rate in the larvae treated with streptomycin was 11 under light conditions and only 0.8 Artemia /10 min under dark conditions. The low rate in the treated larvae under dark conditions must be due to impairment by the streptomycin. Therefore, the high ingestion rate for the untreated larvae under dark conditions would be surely dependent on mechanoreception. The results indicate that larval willow shiner is able to feed on zooplankton under limited light conditions.     

鱼食性与肠道菌群关系的初步研究

对淡水养殖池中的乌鳢、鲢鱼、鳊鱼、鲫鱼不同食性鱼的后肠菌群进行了定性、定量分析,结果表明:四种鱼的后肠壁和后肠内容物都是厌氧菌总数远大于好氧菌总数;后肠内容物菌数远大于后肠壁菌数;不同的鱼,后肠壁的好氧菌总数差别很大,而厌氧菌总数差别不大;后肠内容物中的厌氧菌总数和好氧菌总数为:乌鳢>鲫鱼>鲢鱼>鳊鱼;而后肠壁细菌含量与食物没有明显的关系;后肠内容物和后肠壁中的双歧杆菌数为:乌鳢>鲫鱼>鲢鱼>鳊鱼。表明后肠内容物中的细菌总数、后肠内容物和后肠壁中的双歧杆菌数都与食性相关。大肠杆菌、肠球菌和乳酸菌在后肠的分布没有规律,说明它们与食物相关性不强。     

Accuracy of a machine-vision pellet detection system

Video cameras are employed on net pen fish farms for monitoring food pellet levels near the cage bottom. Herein, the accuracy of a new machine-vision system for the identification of a feed-wastage event and its response time are reported. Research involved novel tests and definitions, video footage recorded under different stocking and environmental conditions, and numerical filters to reduce the effects of misclassifications and patchiness of the pellet wastage record on overall system accuracy. Single-frame food pellet detection accuracy was based on the difference between computer-generated and actual frame counts of pellets greater than 30 pixels in size. A pellet wastage event was defined as a median of three or more visible pellets per frame. During tests on still video frames from different feeding events, the system missed 0.1±0.1 to 1.3±0.4 pellets frame⁻¹, and miss-classified as pellets 0±0.1 to 2.3±0.5 objects frame⁻¹ (n=264). Most missed pellet images were on top of fish images. Waste matter accounted for 65% of the misclassifications, while particles associated with poor camera maintenance accounted for approximately 24%. The average response time to a pellet wastage event was 5.1 and 11.4 s for sampling rates of 2 frames s⁻¹ and 0.5 frames s⁻¹, respectively (n=20 different pellet wastage events). The longest response time (26 s) occurred when fish were amassed against the camera and/or covering pellets. Using appropriate camera lens, camera positioning and/or ‘warning’ software can address fish-interference problems.     

Prey selectivity and diel feeding chronology of juvenile chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon in the Columbia River plume

We studied salmon feeding selectivity and diel feeding chronology in the Columbia River plume. Juvenile chinook and coho salmon were caught by trawling at 2–3 h intervals throughout a diel period on three consecutive days (21–23 June 2000) at stations located 14.8 and 37 km offshore from the mouth of the Columbia River. A total of 170 chinook salmon were caught at the inshore and 79 chinook and 98 coho salmon were caught at the offshore station. After each trawl, potential prey were sampled at different depths with 2–3 different types of nets (1‐m diameter ring net, bongo net, neuston net). Despite the variability in zooplankton abundance, feeding selectivity was surprisingly constant. Both salmon species fed selectively on larger and pigmented prey such as hyperiid amphipods, larval and juvenile fish, various crab megalopae, and euphausiids. Hyperiid amphipods were abundant in the salmon diets and we hypothesize that aggregations of gelatinous zooplankton may facilitate the capture of commensal hyperiid amphipods. Small copepods and calyptopis and furcilia stages of euphausiids dominated the prey field by numbers, but were virtually absent from salmon diet. Juvenile chinook salmon, with increasing body size, consumed a larger proportion of fish. Stomach fullness peaked during morning hours and reached a minimum at night, suggesting a predominantly diurnal feeding pattern. In general, both chinook and coho salmon appear to be selective, diurnal predators, preying mostly on large and heavily pigmented prey items, in a manner consistent with visually oriented, size‐selective predation.     

牙鲆仔鱼早期阶段的摄食能力

本文主要在实际观察值的基础上,利用发育反应方程Ｃ＝ＫＷ＾ｙ与功能反应Ｈｏｌｌｉｎｇ、Ｉｖｌｅｖ方程对２～１０日龄的牙鲆仔鱼的摄食能力进行了计算与预测。其结果表明：牙鲆仔鱼在２～６日龄、轮虫饵料密度不超过３０００ｉｎｄ．Ｌ＾－１的水体中,摄食强度不超过１．７μｇ．ｈ＾－１;随着日龄的增加,摄食强度迅速增强,在４、６、１０日龄、饵料密度为３０００ｉｎｄ．Ｌ＾－１的水体中,摄食强度分别是１．３５、１．６     

鱼类早期发育阶段摄食行为研究现状

对鱼类早期阶段的摄食行为研究进行了综述。重点阐述了胃含物分析法、饥饿对摄食的影响、摄食器官的形态发育特征与摄食行为的关系、食物选择及其生理生态因子对摄食的作用。初步探讨了仔稚鱼饥饿后的捕食量和捕食速度的变化,并结合食物保障,分析了食物选择性指数I在鱼类摄食行为研究中的应用。     

Transfer of toxaphene and chlordane into farmed rainbow trout, Oncorhynchus mykiss (Walbaum) via feed

The study was carried out to quantitate the transfer of toxaphene and chlordane compounds from commercial fish feed into the edible part of rainbow trout, Oncorhynchus mykiss (Walbaum) under normal rearing conditions. Trout were fed with unspiked high energy feed for salmon (fat content 26–30%) over a period of 19 months. The average weight of trout increased from 10 g to more than 2092 g, reaching sizes of 51 cm length. Considerable amounts of toxaphene and chlordane residues were transferred from fish feed into trout muscle. Toxaphene concentrations increased up to 8.6 µg (Σ toxaphene indicator compounds 1–3) kg^?1 wet weight (w.w.) and chlordane reached 5.3 µg Σoxy‐, trans‐, cis‐chlordane + t‐nonachlor kg^?1 w.w. Results are also discussed on the contaminant levels based on the fat content and the effect of sexual maturation is considered in this study. The data allow the establishment of transfer rates for toxaphene and chlordane congeners from high energy diet into the edible part of farmed rainbow trout.     

Dynamics of plasma free amino acids in rainbow trout (Oncorhynchus mykiss under variety of dietary conditions

Plasma amino acid profiles in the systemic circulation of rainbow trout acclimated to diets containing different protein sources, with and without supplementation with free amino acids, were monitored for up to 120 hours after consumption of the diets. Plasma concentrations of lysine, methionine, and isoleucine increased more rapidly after feeding a diet supplemented with these amino acids in free form and, depending upon the increase in plasma concentration, remained at concentrations above those in fish fed the basal diet for at least 24h after feeding. Dietary supplementation with isoleucine increased plasma concentrations of leucine and valine as well as of isoleucine. Maximum plasma concentrations for most amino acids were attained between 12 and 24h postprandial. Dietary inclusion of gelatin caused more rapid elevations in plasma glycine and serine than did free glycine. Feeding at three hour intervals resulted in stable plasma concentrations of individual amino acids in contrast to the fluctuations occurring when fish were fed once daily. Frequent feeding favoured a higher proportion of protein to lipid in body composition.