Megrim (Lepidorhombus whiff-iagonis) populations in the English Channel and Approaches - lactate dehydrogenase and glycerol-3-phosphate dehydrogenase polymorphisms.

Polymorphism of lactate dehydrogenase (EC 1.1.1.27) and glycerol-3-phosphate dehydrogenase (EC 1.1.1.8) in megrim white skeletal muscle is described. Five phenotypes of both dehydrogenase isoenzymes were found after starch gel electrophoresis of muscle extracts. No association was obvious between phenotype and body length or sex. The five lactate dehydrogenase (LDH) phenotypes may be explained on the assumption that three co-dominant alleles are responsible and the five glycerol-3-phosphate dehydrogenase (GPDH) phenotypes can be explained assuming four co-dominant alleles. A significant difference in phenotype distribution was found between megrim samples caught in different areas of the English Channel in May. No significant difference was noted between similar samples caught during November to December. The results are discussed in relation to the migration of megrim stocks in the Channel and suggest the existence of more than one genetically distinct stock of megrim. It is suggested that LDH and GPDH isoenzymes should be useful in studies on the isolation and distribution of megrim populations. Analysis of the size and sex distribution of the samples suggests that, in general, the young female megrim and a few male megrim remain at the mouth of the English Channel and that only the older female fish enter the Channel proper