Baltic larval cod Gaaus mornua are infested with a protistan endoparasite in the yolk sac

Abstract

A protistan endoparasite was discovered in the yolk of embryos and larvae of cod Gadus morhua L. from the Baltic. The prevalence of infestation ranged from 0 to 30 %. Two stages of the parasite were identified under transmission electron microscopy. One stage was apparently mononucleated; the other stage was multinucleated and seemed to be breaking-up into numerous, mononucleated organisms. The endoparasite is compared with the single example in the literature of infestations in the yolk of marine fish larvae - caused by the dinoflagellate Ichthyodinium chabelardi - and the consequences for larval health are briefly discussed.