Occurrence and abundance of brachyuran larvae in the Manora Channel (Karachi, Pakistan) during 1993

The present paper investigates the occurrence and abundance of brachyuran larvae in the Manora Channel during August- December 1993. The fortnightly planktonic sampling was carried out in Manora Channel which is bordered by mangroves, during day time from surface and subsurface waters at shallow depth using Bongo net of 300 micron mesh size. Analysis of samples revealed presence of brachyuran larvae of 12 species belonging to 6 families. Of these 4 species are confirmed: Serenella indica, Dotilla blanfordi, Metopograpsus thukuhar and Clistocoeloma lanatum, 2 provisionally identified species are: Pilumnus ?karachiensis and Pinnotheres ?pisum, 2 species are identified upto generic level: Philyra sp. and Pinnotheres sp., and 1 Ocypodid species and 3 Xanthid species are identified upto family level. This study based on identification, occurrence and abundance of brachyuran larvae in the area, also gives percentage composition of brachyuran larvae collected during 1993, in the Manora Channel.

Physical and chemical characteristics of major aquatic ecosystems in the Victoria and Kyoga lake basins

The physical-chemical characteristics of any aquatic ecosystem include pH, conductivity, and temperature, water transparency, nutrient and the chlorophyll-a levels. Physical and chemical factors of any ecosystem determine the type and quality of flora present in it and these forms the basis on which the system operates. The elements required in largest amounts for plant productions are carbon, phosphorus, nitrogen, and silicon, which is important for diatoms as a major component of the cell wall. Nutrients may limit algal productivity in the tropics despite the high temperature there allowing rapid nutrient recycling. Nutrients most likely to be limiting African lakes are nitrogen (Talling & Talling 1965; Moss 1969; Lehman & Branstrator 1993, 1994) and phosphorus (Melack.et al l982; Kalff 1983) while silicon may limit diatom growth (Hecky & Kilham 1988). The objective of the study is to investigate the impact of physical-chemical characteristics on the distribution and abundance of organisms in the major aquatic ecosystems.

The diversity and abundance of zooplankton in the Lake Victoria and Kyoga basins and their relationship to fish production

Biological diversity of an ecosystem is considered a reliable measure of the state of health of the ecosystem. In Uganda's large lakes, the Victoria and Kyoga, the past three decades have been characterized by profound changes in fish species composition following the introduction of the piscivorous Nile perch (Oguto-Ohwayo 1990). Over 300 haplochromine cichlid species comprising a wide range of trophic groups were lost along with a host of non-cichlid fishes which occupied virtually all available ecological niches and in the lakes (Witte 1992). A second major ecological event has been the gradual nutrient enrichment of the water bodies (eutrophication) from diffuse and point sources, while at the same time pollutants have also gained entrance into the water systems in pace with indusfrial development and human population increases in the lake basins. Eutrophication and pollution have drastically altered the physical and-chemical character of the water medium in which different fauna and flora thrive. In Lake Victoria these alterations have resulted in changes of algal species composition from pristine community dominated by chlorophytes and diatoms (Melosira etc) to one composed largely of blue-green algae or Cyanobacteria (Microcystis, Anabaena, Planktolyngbya etc) (Mugidde 1993, Hecky 1993).

中国淡水鱼类单极虫病的研究Ⅰ.河南信阳鲤鱼单极虫病的研究

1993年作者对河南信阳市南湾水库网箱养殖鲤鱼肠道单极虫病进行了系统研究。该地区发病率高达 90 %以上 ,发病鲤鱼肠壁上寄生了大量单极虫孢囊 ,破坏肠道组织 ,吸收鱼体营养 ,病鱼失去光泽 ,体色呈暗黑色 ,肠管呈紫红色 ,充满脓血粘液 ,大型孢囊集中在中、后肠 ,孢囊形态大多为椭球形 ,最大个体为 4 .5× 2 .5cm ,肠管膨大一倍以上 ,肠壁变薄 ,肠道完全被堵塞 ,停止进食而死亡。经比较研究 ,该病原体被定为信阳单极虫新种 (Thelohanellusxinyangensissp .nov

围圈养鱼对浮游动物多样性的影响

1993—1994年在保安湖主体湖区开展围圈养殖草鱼对浮游生物多样性影响的研究，包括围圈内外浮游动物种类组成、密度、生物量和多样性指数的季节变化等。分析表明，围圈内共有常见浮游动物64种，围圈外共有常见浮游动物55种。围圈内外浮游动物的年平均密度分别为3738和3196ind/L，年平均生物量分别为0.8177和0.8135mg/L，年平均多样性指数分别为3.3808和2.9717。研究结果表明：围圈养殖草食性鱼类对浮游动物现存量以及多样性指数无显著影响.