Sea-water chlorination and the survival and growth of the early developmental stages of plaice, Pleuronectes platessa L., and Dover sole, Solea solea (L.)

Abstract

The response of the developmental stages tested was examined under constant flow conditions using direct electrolysis of sea water as a source of chlorine. From LC 50 determinations, the eggs of plaice were found to be more tolerant than the newly-hatched larvae, and for both plaice and Dover sole the tolerance of the larvae increased as their development proceeded up to metamophosis. Less change in tolerance was evident with increasing size of fish after metamorphosis. Determinations of time to kill 50% of a test population showed that at chlorine concentrations only slightly higher than the LC 50 level the time for survival was considerably reduced. Growth of the metamorphosed fish of both species at sub-lethal levels only showed a very marked depression at concentrations very close to the LC 50 level. There was some evidence of acclimation to chlorine during long exposure. The growth of fish in power station effluents should not be affected by the use of low level chlorination as an anti-fouling measure, since the chlorine is normally rapidly absorbed by reactions taking place in the sea water. Large fluctuations in the chlorine dose could however present a hazard.