Baltic larval cod Gadus morhua are infested with a protistan endoparasite in the yolk sac

A protistan endoparasite was d~scovered 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 transmiss~on electron microscopy. One stage was apparently mononucleated; the other stage was multinucleated and seemed to be b reak~ng-up into numerous, mononucleated organisms. The endoparas~te IS compared with the slngle example In the literature of infestat~ons in the yolk of marine fish larvae caused by the dlnoflagellate lchthyodini~~m chabelardiand the consequences for larval health are briefly discussed.