TEMPERATURE EFFECTS ON SPAWNING AND EGG DEVELOPMENT IN EURASIAN PERCH

Spawning, egg strand development and embryo survival was studied durin g 1995-1996 in perch Perca fluviatilis exposed to healed effluent from two coastal nuclear power plants on the Baltic. Spawning was earlier and more prolonged in the heated areas. Although the fertilization rat e was high, most egg strands sampled in the heated areas did not devel op to hatching. The egg strands disintegrated within a few days of spa wning, and egg mortality was very high. All samples collected from ref erence areas developed up to hatching. Exposure to high temperatures d uring the final maturation of the gonad influenced the follicular mech anism producing the jelly membrane which constitutes the matrix of the egg strand. Effects were observed in fish in open effluent areas as w ell as in an enclosed research basin. These results suggest that there is a conflict between optimal reproduction and temperature preference in temperate area fish. Fish are attracted to cooling water effluent, at the expense of reduced reproductive performance. (C) 1997 The Fish eries Society of the British Isles.