Cytochrome oxidase variants of the bacterial fish pathogen, Aeromonas salmonicida , were characterized for genetic and molecular homology with cytochrome oxidase-positive isolates that typically induce furunculosis in salmonids. Protein and lipopolysaccharide moieties of the cytochrome oxidase-negative variants were similar to their typical counterparts, based on sodium-dodecyl-sulfate polyacrylamide gel electrophoresis. Pathogenicity of aberrant isolates to brook trout ( Salvelinus fontinalis ) was similar to typical cytochrome oxidase-positive isolates. Colorimetric deoxyribonucleic acid (DNA) hybridization in 96-well microplates yielded homology values greater than 82.5% for typical aberrant A. salmonicida isolates when photobiotinylated DNA for reference A. salmonicida 3.101 was used as a probe. The only variation of these isolates from typical A. salmonicida was a negative cytochrome oxidase reaction.

Journal of Wildlife Diseases↗

USGS1990

Immunological discrimination of Atlantic striped bass stocks

Stocks of Atlantic striped bass Morone saxatilis that were assumed to be geographically isolated during spawning showed strong antigenic differences in blood serum albumin. A discriminant function was estimated from the immunologic responses of northern (Canadian and Hudson River) and southern (Chesapeake Bay and Roanoke River) stocks to two reference antisera. The function correctly classified 92% of the northern and 95% of the southern fish in the training set. Cross-validation revealed similar percentages of correct classification for fish that were of known origin but not used to estimate the discriminant function. Monte Carlo experiments were used to evaluate the ability of the discriminant function to predict the relative contribution of northern fish in samples of various size and stock composition. Averages of predicted proportions of northern fish in the samples agreed well with actual proportions. Coefficients of variation (100 × SD/mean) in the predicted proportions ranged from 1.5 to 36% for samples of 50–400 fish that contained at least 10% northern stock. In samples that contained only 2% northern stock, however, at least 1,600 fish were required to achieve similar levels of precision.

Transactions of the American Fisheries Society↗

USGS1990

Establishment of a cell line with reticulo-endothelial characteristics from a rainbow trout spleen explant

A cell line from rainbow trout ( Oncorhynchus mykiss ) with phagocytic-like characteristics was established. First we found that it was necessary to inject the fish with antibiotics (penicillinstreptomycin) in order to clear tissue of bacterial contamination. Two days later, the spleen was excised and minced with scissors in MEM10. The large number of erythrocytes in the suspension were removed by low centrifugation, then the tissue fragments were incubated on tissue culture flasks at 18°C for 30 days with complete changes of media every other day. After 30 days in culture, primary explants from spleen were composed of three types of cells. The majority were large mononucleate, plecmorphic cells with thinly spread cytoplasm. These cells were trypsinized and subcultured. Another cell types was simple, round cells, somewhat similar to mature lymphocytes, while the third type appeared to be similar to fibroblastic cells. After 9 months with the culture in 17 to 20 passages, the predominate cell type was showing similarities to phagocytic cell. These cells had a marked reticular cytoplasm and grew individually without parallel orientations. By enzyme-specific stains, the cells were observed to have abundant acid phosphatase and β-glucuronidase activities of the cytoplasm. They were negative for peroxidase. The cells were also found to have highly adherent and phagocytic properties when incubated with latex particles. The morphological, enzymatic, and functional findings suggested the possibility that these cells in culture have some properties similar to the cells which are composed of reticulo-endothelial system.

Fish Pathology↗

USGS1989