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Diseases of Aquatic Organisms

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DAO 30:121-135 (1997)  -  doi:10.3354/dao030121

An enigmatic and possibly parasitic organism in the tissues of embryonated eggs of Baltic cod Gadus morhua

Bloch B, Pedersen BH, Jensen PV

Tissues and interstitial compartments of cod Gadus morhua embryos which were infected by an endoparasite in the yolk were investigated by transmission electron microscopy. Small enigmatic organisms, presumed to be of parasitic nature, were observed in the embryonic cells and tissues. The organisms lacked a cell wall. In addition to intermediate stages, at least 3 distinct stages of the organism were observed. The organisms were located both extra- and intracellularly, in the latter case often surrounded by vacuoles. The stages of the organism differed in their chromatin configurations. One stage contained groups of finely and coarsely flocculated chromatin without a nucleolemma. Juxtapositioned chromatin groups were separated by annulate lamellae. Another stage had one or more nucleus-like elements, each surrounded by a dilated cisterna with a few pores. The cisternae of such adjoining elements formed annulate lamellae, which could break to form a common vacuole. Vacuoles might then fuse with the outer membrane of the organism thereby freeing the nucleus-like elements as daughter elements. Such daughter elements were observed extra- and intracellularly in embryonic cod. The third stage contained several nucleated daughter cells, and lacked annulate lamellae. The identity of the organism is unknown.

Gadus morhua · Embryos · Presumed tissue endoparasites · Annulate lamellae

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