Myxosporean gall bladder parasites of gadid fishes in the North Atlantic: Their geographical distributions and an assessment of their economic importance in fisheries and mariculture

Abstract

Between 1992 and 2003, samples of four species of gadid fish from the northern North Sea, the Faroe Islands and northern Norway were examined for myxosporean gall bladder parasites. Total numbers of each host species examined were: 665 cod Gadus morhua L., 621 haddock Melanogrammus aeglefinus (L.), 389 saithe Pollachius virens (L.) and 445 whiting Merlangius merlangus (L.). Nine species of myxosporeans were found: Ceratomyxa arcuata Thélohan, 1892, Leptotheca informis Auerbach, 1910, Leptotheca longipes Auerbach, 1910, Myxidium bergense Auerbach, 1909, Myxidium gadi Georgévitch, 1916, Myxidium oviforme Parisi, 1912, Myxidium sphaericum Thélohan, 1895, Sphaeromyxa hellandi Auerbach, 1909, and a hitherto undescribed species of Myxidium. The taxonomy and likely geographical distributions of these and other gall bladder myxosporeans of gadid fish reported from both sides of the North Atlantic are discussed. These myxosporeans fulfil most criteria for use as biological tags in host population studies and some have been used successfully already. They also have potential use as indicators of environmental change and marine pollution. Some species are likely to become serious pathogens in mariculture, particularly of cod and haddock. It is clear from our assessment that a great deal has still to be learned about their taxonomy, host specificities, life cycles and general ecology. For their more efficient use as tags and indicators, and for successful control of infections and the application of preventative measures in mariculture, more information on the their biology and ecology is essential.