Parasitism of Northern pink shrimp (Pandalus borealis) eggs by an unclassified parasite :a report on the degree of infection during the winter of 1995/96 in the Gulf of Maine

Caldwell, Dylan H.
Daniel F. Schick
Department of Environmental Studies
The Northern pink shrimp Pandalus borealis can be found in boreal oceans worldwide and supports a large commercial fishery in the United States. The shrimp are hermaphrodites, thus each shrimp reaches sexual maturity as a male and then metamorphoses in its third fall and winter into a sexually mature female which will spawn in the following fourth fall and winter. The females extrude eggs which are fertilized by the younger males. Eggs are carried on the pleopods of females until hatching at which point larval shrimp emerge. Stickney (1978) has shown that the eggs of Pandalus borealis may become infected by an unclassified intracellular parasite. The infected eggs are identified by a whitish discoloration. The life cycle of this parasite before and after it infects the shrimp eggs is not known. Further, the mode of transmission into the shrimp egg is unknown. Past research suggests that the parasite is most likely a member of the dynoflagellate family possibly of the genus Syndinium described in 1920 by Chatton. Little work has been done to determine the impact this parasite has on shrimp stocks and data on the degree of infection from one year to the next are incomplete. A.P. Stickney found rates in the gulf of main to be 2-5%. Other studies done in the years 1964, 1974, 1975, 1979, and 1980 documented rates ranging from less than 1% to a high of 10% in 1975. The purpose of this study was to determine the amount of infestation of P. borealis eggs by the presumed Syndinium during the 1995/96 commercial shrimp fishing season off the coast of Cape Anne, Massachusetts. Another objective was to develop a methodology for determining the numbers of infected and uninfected eggs on a given shrimp. I describe quantitative grid point counting methods which give reproducible results.

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