The authors have made a coast-wise investigation of the fishing ground of Kiangsu from1960 to 1963, and have found out that there is a relation between the variation of fish sch-ool and ammonia content in water. It is shown that the greater the density of fish schoolis, the larger the excretion becomes, and the more the ammonia content in water increases.Results of the investigation on Pseudosciaena polyaotis (Bleeker) , Pseudosciaena orocea(Richardson), Trichiurus haumela (Forskal), Setipinna taty (Cuvier Valenciennea) and Ilisha elongata (Bennett) show that, in the water level or vertical column of water, the am-monia contents are all very high, where the fish schools are crowdy.