TOXIC EFFECTS OF ZINC ON FOUR SPECIES OF FRESHWATER FISH

The toxic effects of Zn2+ on Silver Carp (Hypophthalmichthyps molitrix C. et V.), Big Head Carp (Aristrichthys nobilis Richardson). Grass Carp (Ctenopharyngodon ilellus C. et V.), and Blunt Snout Bream (Megalobrama aimbly-cephala Yih) are studied. The test results are: (1) There are linear correlations between 24h LC50 and 48h LC50 of Zn + for Silver Carp fingerling and tempera -ture . 24h LC50, 48h LC50 and 96h LC50 of Zn2+ for fry of the four species are also determined; (2) There are logarithmic correlations between the growth rates of the fry and the concentrations of Zn2+ and between expansion of fish egg membranes after absorbing water and concentrations of Zn2 + ; (3) The tolerance of fry of the four species to Zn + is in the following order: Grass Carp>Silver Carp > Blunt Snout Bream>Big Head Carp; (4) The safe concentrations of Zn2+ are: Big Head Carp : 0.008 mg/ L, Grass Carp : 0.046 mg/ L , Blunt Snout Bream: 0,010 mg/ L , Silver Carp : 0.012 mg/ L , Silver Carp fingerling: 0.09 mg/ L .     

长江口区水化学基本特征

本文根据近二年来对长江口区洪、枯季落潮五次水质调查所收集的部分资料,讨论本区水化学基本特征,并探讨水体中Fe、A1、Mn、SiO_2分布及其与沉积的关系。长江口区,自徐六泾至口门,以氯离子含量与ea/mg比值将本区水体划分为三段,吴淞口以西为河水为主段、吴淞口以东至122°25′一线为河、海水混合段、122°25′一线以东为海水为主段。