Coccidians in the liver and testis of the herring Clupea harengus L.

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Abstract
The coccidians Goussia clupearum from liver and Eimeria sardinae from testis of herring caught in waters near Nova Scotia were studied by light and electron microscopy. Unsporulated and sporulatcd oocysts were the most frequently encountered stages. Oocyst walls of both species were thin and closely apposed to the host cell. At least a part of the oocyst wall appeared to serve also as the boundary of the parasitophorous vacuole. In G. clupearum, membranes lining parasitophorous vacuoles of various stages seemed to be involved in host–parasite nutrient transfer. Wall-forming bodies were found in the sporont of E. sardinae, and presumptive wall-forming bodies were found in the sporont of G. clupearum. The sporocyst wall of G. clupearum appeared to consist of two valves. The wall had a thick transversely striated inner layer and a thin outer layer consisting of several closely apposed membranes. The lamellated membranes extended from the outer layer. The sporocyst wall of E. sardinae was thin and consisted of three loosely organized membranes. The sporocysts of neither species had a Stieda body. Goussia clupearum, which often elicited an intense host reaction, infected 85% of mature fish whereas E. sardinae infected 90–100%. Replacement of hepatic tissue by G. clupearum could stress fish and replacement of testicular tissue by E. sardinae could reduce sperm production, thus detrimentally affecting herring stocks.