Strains of Vibrio parahaemolyticus, the etiologic agent of "Shirasu" food poisoning in Japan, were isolated from moribund blue crabs Callinectes sapidus and identified by biochemical and serological techniques.

ABSTRACT. We studied the influence of the protozoan parasite P e r h s u s marinus (Mackin. Owen & Collier) on reproduction in the eastern oyster Crassostrea virginica (Gmelin) from 2 sub-estuaries of central Chesapeake Bay, Maryland, in 1990 and 1991 One hypothesis was that increased levels of infection by P marinus cvould result in smaller egg size and diminished lipid reserves within individual eggs. Our results did not reveal any consistent deleterious effects of l? marinus on these gametogenic characteristics, although some of our sample sizes were small and the average disease intensities were low. Our second hypothesis, that there would be a decllne in reproductive output as a result of high levels of P marinus infection, was supported for one estuary when those oysters were near their peak of reproductive condition (July). We found no evidence to support our third hypothesis that there would be a negative influence of infections during the 1990 reproductive season on subsequent reproductive output (summer 1991). Based on published evidence that P marinus can inhibit oyster growth, we speculate that oysters infected at low intensities by P marinus can divert energy from growth to reproduction. This differential energy partitioning allows infected oysters to produce fewer eggs than uninfected oysters but with no change in the amount of lipid reserves stored in each egg.

Striped bass Morone saxatilis from the Upper Chesapeake Bay were studied to determine if discrete populations exist. Spawning fish and juveniles in five rivers, the Patuxent, Potomac, Choptank, Elk, and Nanticoke were sampled. Discontinuous polyacrylamide gel electrophoresis separated the serum proteins for population analysis. Five proteins, which were not related to the age, sex, or time of collection of striped bass, were used to discern populations. The Elk River striped bass are very distinct. Both the Choptank and Nanticoke are also distinct but show some connection with the Patuxent and Potomac striped bass. The Patuxent and the Potomac striped bass could not be distinguished from each other on the basis of the five proteins studied. The geologic evidence supports the theory of population formation for striped bass in the Chesapeake Bay. Management implications of the striped bass populations are also discussed. INTRODUCTIONPopulations of the striped bass Morone saxatilis along the Atlantic Coast have been defined by many investigators by a variety of methods. To date, all studies of striped bass populations have been based on meristic characters, morphology, or tagging (Vladykov and Wallace

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The effects of exploitation on growth, condition, and surplus production were measured over an 8—year period for a population of seven species of warm—water fishes in a 4.05—ha lake. The lake was shallow, fertile, and moderately productive. Population estimates of individual species were made each spring concurrently with the annual removal of 34% to 71% of the existing population. The initial stock density of all species was 48.66 g/m2 in the spring of 1962. The optimum yield for this mixed population was calculated to be 14.56 g/m2 per year at a stock density of 18.67 g/m2, with the bluegill producing most of this surplus weight. When species were considered separately, there was poor correlation between exploitation rate and either growth or condition. The response of the entire population to thinning was more predictable, with both growth and condition related to stock density. Best growth occurred at densities near 20 g/m2 or approximately at the level for optimum yield.

A survey for naturally acquired antibodies against Aeromonas salmonicida in brook and brown trout in central Pennsylvania hatcheries showed great variation in the percentage of reactive individuals (0.8–87%) within 24 populations. Antibodies were not detected in fish less than 12 months old, and the percentage of serologically reactive individuals increased with the age of the population. Prevalence of antibodies in yearling trout populations in which furunculosis was epizootic was about twice as great as in fish experiencing enzootic furunculosis.

Summary The development of agglutinating antibody to Aeronomas salmonicida in brook and brown trout was demonstrated by a tube agglutination and a rapid slide agglutination test. Comparison of agglutinin titer development in rabbits and trout demonstrated that trout have a slow antibody response reaching maximum titer about 3 months after injection. Rabbits developed peak titers within a month after receiving the same dose of antigen. Trout immunized with a single injection of formalin-killed bacteria in a mineral oil adjuvant were protected against intraperitoneal injections of viable Aeromonas salmonicida.

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