Effect of antibiotics on survival of carangid fish larvae (Caranx mate), reared in the laboratory

Abstract

Techniques are described which have proved successful in rearing the larvae of nine species of marine fishes in Hawaii. The results of intensive experiments on larvae of the carangid fish, Caranx mate, are presented, with emphasis on the effects of various antibiotics on bacterial populations in rearing containers and on larval survival. Microcopepods, gastropod veligers, and rotifers were found to be suitable foods for C. mate larvae, and larval survival was enhanced when the phytoplankter Chlorella was added to cultures. Four bacterial genera were identified from natural water samples and from rearing containers in culture situations. Pseudomonas was the most abundant genus, Cytophaga next most abundant, followed by Vibrio; Flavobacterium was identified but uncommon. uncommon. In sea water containing low initial numbers of bacteria, bacteria increased more rapidly and stabilized at a higher density than in sea water containing higher initial densities. Of a number of antibiotics tested, the most effective in decreasing bacteria in sea water and enhancing hatching success and larval survival were the polymyxins, penicillins, and especially erythromycin. Repeated treatments with the same antibiotic on day 3 of the experiment did not reduce bacterial density or improve larval survival, when compared with a single treatment on day 1. These results are discussed in relation to the mode of action of the antibiotics, and suggestions are made concerning profitable lines of future research.