Spinal compression of Atlantic cod Gadus morhua from the German Wadden Sea

Abstract

A definition of spinal compression of Atlantic cod Gadus morhua from the German Wadden Sea is presented, based on the relation of head length to total body length of the fish. Compressed individuals are defined as having values of x = H/T x 100 > 27.74 (where H = head length and T = total body length). Epizootiological results of an extensive field survey in 1989 revealed decreasing prevalence of compression with increasing fish length. In small cod of the Eider and Elbe estuaries, prevalence varied seasonally with a maximum in March-April, apparently due to abnormal migration behaviour of deformed fish. Prevalence was significantly higher in the northern part of the German Wadden Sea than in the estuaries of the Ems, Weser and Elbe.