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141.
142.
南沙群岛重要珊瑚礁水域鱼类资源数量分布 总被引:6,自引:3,他引:6
1998年3—5月和1999年5—6月.采用手钓、延绳钓和流刺网3种作业方式在南沙群岛的渚碧、南薰、东门、美济、赤瓜、永署和华阳等7座珊瑚礁水域进行了2个航次的鱼类资源调查。结果表明,7座珊瑚礁水域不同作业方式的鱼类资源相对丰盛度差别较大,其中刺网以永暑礁最高,手钓以华阳礁最高,延绳钓以南薰礁最高;同时.刺网和手钓不同水深区域鱼类资源的相对丰盛度也不相同.其中刺网以11~30m区域最高.手钓以10m以浅和51~80m区域较高;分析认为,造成礁区之间鱼类相对丰盛度差异的主要原因不是初级生产力.而是生态环境因素,主要是礁盘形态和大型海藻的数量。另外.各礁区水域的优势类群有明显不同.这主要与洞穴的大小和数量、大型海藻及珊瑚的种类和数量等生物和非生物环境有关。 相似文献
143.
Myosin was isolated from two types of muscle, ordinary and dark muscles, of three species of fish living in sea water. The
compositions of light chains were visualized by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and the
mechanochemical activity was examined by in vitro motility and ATPase assays. Ordinary muscle myosin of either species had three species of light chain, whereas dark muscle
myosin had another two species of light chain judged by SDS-PAGE. Sliding velocity of ordinary muscle myosin was in the range
of 4.92–6.89 μm/S, whereas that of dark muscle myosin was in the range of 3.07–4.25 μm/s. Therefore, ordinary muscle myosin
showed 1.26–1.95 times higher sliding velocity than dark muscle myosin in either species. The ratios of Vmax of actin-activated Mg2+-ATPase activity of ordinary to dark muscle myosins were correlated quite well to the ratios of sliding velocity. Activity
of ordinary muscle myosin was comparable to that of mammalian fast muscle myosin, but that of dark muscle myosin was twice
of that of mammalian slow muscle myosin. These results may reflect the essential role of fish dark muscle myosin always used
in slow cruising. 相似文献
144.
Elizabeth Wood 《Aquarium Sciences and Conservation》2001,3(1-3):65-77
Currently, as many as 30 million coral reef fish belonging to 1,000 species are collected annually to supply private and public aquaria around the world. In addition, over 100 species of invertebrate are used, involving hundreds of thousands or even millions of individuals. The majority of these specimens come from coral reefs and associated habitats, with about 45 countries supplying the ornamental market. Considering the many pressures currently faced by reefs it is vital that ornamental fisheries are investigated and monitored, and management strategies formulated to ensure they are sustainable. This requires research, monitoring, training, use of non-damaging collecting methods and adoption of conservation strategies for controlling catch, such as reserves, quotas and closed seasons. There are also a number of possibilities for enhancing the fishery, such as mariculture and construction of artificial reefs. This paper concentrates on some of the conservation measures that can be taken and discusses their application and effectiveness. Such measures include limiting collecting effort, establishment of species-based or overall quotas, restrictions on rare and/or endemic species, temporary closures and establishment of fisherybreak reserves. 相似文献
145.
A group of Atlantic salmon (Salmo salar) was followed through their first year of maturation and spawning. At monthly intervals, starting with juvenile fish in December, 5–7 fish of each sex were killed, and liver and plasma were sampled. The last sampling point was of spawning fish in November a year later. Variables in the cytochrome P450 (P450) system were studied in hepatic microsomes, and estradiol 17 was measured in the plasma of females to assess the maturational status. The P450 1A1-mediated 7-ethoxyresorufin O-deethylase (EROD) started at high levels in winter, but decreased to non-detectable activities in pre-spawning females. Decreases, but not to the same extent, were also observed during this period in total cytochrome P450, cytochrome b5, NADPH-cytochrome P450 reductase, and in the content of two immunochemically determined P450 isozymes. At the same time, LSI levels increased in maturing females (starting in July), and GSI levels increased in both sexes (starting in May). Sex specific differences were observed in pre-spawning fish in September and October, with levels of total P450, b5, NADPH-cytochrome P450 reductase, EROD and P450 isozymes significantly lower in females. At the same time, plasma estradiol-17 levels reached peak values in females. The results point to the important role of sex steroids such as estradiol-17 as major factors in the regulation of final sexual maturation. However, this study also indicates that there may be estradiol-17 independent events of equal importance in the early stages of gonadal maturation that may involve the P450 system. The changes observed in the P450 system (as a major drug and steroid metabolizing system) of Atlantic salmon during sexual maturation may be of importance both in the endogenous transduction of hormonal signals, and as a pharmacological basis for designing therapeutic treatment of diseases in the aquaculture industry.Parts of this work were presented at the 5th International Symposium on Responses of Marine Organisms to Pollutants, April 1989 in Plymouth, United Kingdom (Larsen and Goks\/oyr 1989). 相似文献
146.
The relationships between surface area, stocking density and fish yield in 40 small reservoirs in India between 1994 and 1999 were examined. A significant positive correlation (r = 0.6) was found between stocking density and fish yield. Area was negatively correlated with stocking density (r = ?0.57) and fish yield (r = ?0.62), but its correlation with efficiency of stocking was not significant for all the size groups of small reservoirs. 相似文献
147.
148.
149.
中小型饲料企业是饲料产品经济发展中的重要组成部分,也是我国农牧行业经济发展的重要组成部分.随着计算机物联网技术的不断发展,当前线上销售模式应成为中小型饲料企业创新经济增长点的重点发展领域,而要想更好的发展线上运营模式必须考虑当前中小型饲料企业自身供应链管理物流配送的发展状况.本文研究分析当前中小型饲料企业供应链管理及物... 相似文献
150.
我国饲料行业已从发展的快速增长期步入成熟期.当前,饲料企业数量众多,分布广泛,但不少饲料企业规模较小,市场竞争力弱,急需进行转型升级.由于中小饲料企业信用评级低,经营风险大,且资产抵押物少,导致企业融资渠道较为狭窄,融资成本高.融资难的问题已经成为了制约饲料企业发展、扩大企业规模、提升企业技术水平的瓶颈.金融管理作为提... 相似文献