Deutscher Beitrag zum internationalen Makrelen(Scomber scombrus) und Stöcker- (Trachurus trachurus) Eier-Survey

Based on the results from egg and larvae surveys, mackerel and horse mackerel are thought to form three more or less distinct stocks each in the North Sea and in the waters west of the British Isles. These are firstly the southern stocks in the southern part of the English Channel, Celtic Sea and Bay of Biscay, secondly the North Sea and finally the western stocks of both species, loeated between the Shetlands and southern Norway. It is argued here that in view of the high mobility and the extended seasonal migrations of both species a c1ear separation of the stocks can hardly be maintained. In this context the results of the 1995 mackerel and horse mackerel egg survey to the southern spawning location is presented.

Myxobolus aeglefini in Wittlingen (Merlangius merlangus)der Nordsee und der lrischen See

In June 1994 and 1995 stations in the North, Irish, Celtic Seas and the Channel were studied for the occurrence of Myxobolus aeglefini in whiting (Merlangius merlangus). The disease was visible externally as either white nodules of a few millimeters diameter in the upper mouth cavity, gill arches and the basis of pelvic fins and in severe cases also on the lower jaws or in the cornea and sclera of the eye. It was verified morphometrically in histological sections of infected eyes by size and shape of spores. Myxobolus aeglefini was present in low prevalences at two North Sea stations and high prevalences of up to 49 % in the Irish Sea (Solway Firth) during both cruises. Whiting between 23 and 55 cm were found to be infected. Neither length-age prevalences nor condition factors and gonado, spleen, liver somatic indices differed in diseased and healthy fishes.