Malformation rates in embryos of North Sea fishes in 1991 and 1992

Malformation rates in naturally-occurring fish embryos were examined in 4 surveys of the North Sea in the principal spawning seasons of 1991 and 1992. Pelagic fish eggs were collected and analysed according to species, developmental stage and morphological aberrations. Overall malformation rates declined with ongoing development. The highest malformation rates were found off the estuaries of the Elbe, Weser, Ems, Rhine, and Thames rivers. Whiting and sprat exhibited above-average prevalences of malformations. Long rough dab and sole showed low levels of malformations. In winter 1992, overall malformation rates in the North Sea were approximately 10 per cent. This value was similar to that found in 1984. Between these years, the malformation rates were much higher. Malformation was thought to be caused by anthropogenic contaminants in the marine environment.