The Effect of Marine Bacteria on the Development and Hatching of Pelagic Fish Eggs, and the Control of Such Bacteria by Antibiotics

Abstract

THE occurrence of bacteria in the sea is widespread. ZoBell (1946) has reported an average of 1,000 bacteria per ml. in surface waters near shore. Such concentrations of bacteria may influence fishes by the liberation of proteolytic enzymes, by formation of toxins, or by the invasion of muscle, alimentary tract, and fins. Few investigators in marine microbiology have attempted to determine the significance of bacteria in the life cycle of marine fishes. Most of the fragmentary accounts refer merely to microorganisms that have caused the death or lesions on fishes (Plehn, 1924; Wells and ZoBell, 1934; Nigrelli, 1940; Rucker, 1949; Hodgkiss and Shewan, 1950). Studies involving the relationship between bacteria and the life cycles of fishes are usually difficult and have been heretofore relatively little attempted. The tendency of marine bacteria to stick to solid objects (ZoBell and Allen, 1933) complicates experimentation. In determining the effect of marine bacteria on living organisms, the primary difficulty is to minimize contaminations. This problem is acute in the study of marine fishes because most of the agents used to decrease the bacterial population are also harmful to the fishes (Wells and ZoBell, 1934). Of the several antibiotics that were employed in a recent study (Tarr, Southcott, and Bissett, 1950), aureomycin and terramycin were most effective in reducing the bacterial content of fishes during storage. At a concentration of 50 parts per million (ppm) these antibiotics did not inhibit all the bacteria but did decrease the total number which usually accumulated during fish storage. Spencer (1952) used antibiotics to decrease the bacterial population in studies with marine algae with reasonable success. These results suggested that antibiotics might 1 Contribution from the Scripps Institution of Oceanography, New Series, No. 732. 2 Research conducted in part as a Fulbright Fellow in marine microbiology in Norway, 1952-53. 43