A protistan endoparasite in embryos and yolk-sac larvae of cod Gadus morhua and turbot Scophthalmus maximus

Abstract

A protistan endoparasite has recently been discovered in the yolk of embryos and yolksac larvae of cod Gadus morhua and turbot Scophthalmusmaximus. Eight batches of cod embryos were studied, and all batches were infected with minimum prevalences ranging from 14 to 88 %. The endoparasite seemed to be transmitted to the cod embryos via the fish gametes, and the infection occurred in cod from all the major seas surrounding Denmark. Infected cod embryos and yolk-sac larvae have a higher mortality rate than uninfected ones. Several stages of the parasite were identified. The smaller stages of the cod endoparasite invaded the larval tissues and bloodstream. The large, multinucleated stages of the parasite can multiply by budding off small parasites. Other features are associated with endoparasitic infection, i.e. thin-walled and thick-walled spherical structures were observed in the yolk. The thin-walled structures ejected multiple parasite-like bodies of varying sizes into the yolk. The thick-walled, highly refractile hollow spheres in the yolk were of protistan origin. Light microscopy of the turbot endoparasite has previously indicated a strong resemblance with the cod endoparasite. Present transmission electron microscopy reveals that the turbot and cod endoparasites are identical or very closely related.

Endoparasitic Dinoflagellate of the Genus Ichthyodinium Infecting Fertilized Eggs and Hatched Larvae Observed in the Seed Production of Leopard Coral Grouper Plectropomus leopardus

“…No disease was noticed in fertilized eggs in the sterilized seawater, while disease outbreaks occurred in untreated seawater. This in vivo experiment reconfirmed the previous in vitro result that the parasite is transmitted horizontally, a clear contrast to the result of Atlantic cod (Pedersen and Køie, 1994). It is thus concluded that sterilization of rearing seawater is an effective method for the control of this endoparasitic infection of the leopard coral grouper.…”

“…A similar infection in Atlantic cod Gadus morhua and turbot Scophthalmus maximus was reported in Denmark (Pedersen and Køie, 1994). The infection occurred at 6-11∞C (Pedersen et al, 1993).…”

“…The infection occurred at 6-11∞C (Pedersen et al, 1993). In the experiment using sterilized seawater for fertilization of cod eggs and subsequent incubation of fertilized eggs, the embryos were infected, suggesting that the parasite transmitted vertically through the fish gametes (Pedersen and Køie, 1994).…”

Infection by a Protozoan Endoparasite of the genus Ichthyodinium in Embryos and Yolk-sac Larvae of Yellowfin Tuna Thunnus albacares

“…Regarding the transmission of the parasite to the embryo, Pedersen and Køie (1994) suggested the transmission via the fish gametes as fertilized eggs obtained from broodstock in sterilized seawater were infected by the parasite in their experiment, but they did not mention about the infection route of the parasite to the fish gametes. In this study, however, the prevention of the infection by transferring fertilized eggs to sterilized seawater, the existence of detectable parasites by PCR in the rearing water and no detection of the parasite from broodstock gonads suggest that the parasite infects the egg through the rearing water after spawning.…”

Scientific knowledge of biological processes potentially useful in fish stock predictions

“…Cameron et al, 1989), iii) toxic algal blooms affecting egg mortality (Aneer, 1985) and iv) endogene parasites affecting egg survival (e.g. Pedersen and Køie, 1994). However, in all cases we know, the variable impact on egg or larval survival in the field has not been quantified and causing endogenous factors are seldom identified.…”