THE EFFECT OF ANTIBIOTICS ON THE RESPIRATION OF BROWN SHRIMP LARVAE AND POSTLARVAE (Penaeus aztecus IVES) AND THE BACTERIAL POPULATIONS ASSOCIATED WITH THE SHRIMP1

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Abstract
The oxygen consumption rates of brown shrimp (Penaeus aztecus) larvae and postlarvae were measured by manometric techniques in the absence and presence of four concentrations of an oxytetracyclineoleandomycin antibiotic combination, and the ability of these antibiotics to control bacterial populations associated with the shrimp was determined.The data suggest that brown shrimp mysis and postlarvae can tolerate all four concentrations of antibiotics tested. However, definite tolerance levels were not determined for the nauplial and protozoeal stages.The average initial bacterial population associated with brown shrimp nauplii is lower than that found in older stages. The average bacterial populations associated with brown shrimp protozoea, mysis, and postlarvae after a 1 hour incubation in autoclaved sea‐water (ASW) was 2 times 106 cells/ml ambient solution.In the absence of antibiotic, the bacterial population associated with the brown shrimp larvae and postlarvae increased exponentially. In 24 hours the bacterial population had become as high as 1 times 108 cells/ml ambient solution.The concentration of 62.5 μg oxytetracycline (OTC) and 25 μg oleandomycin (OLE) per ml ASW has a bacteriostatic activity for 6 hours and a concentration double this amount has a bacteriostatic activity for 6–18 hours. A concentration of 250 μg OTC + 100 μg OLE/ml ASW has a greater than 99% bacteriostatic activity after four hours of exposure time and will maintain the bacterial population at 100 cells or less from 12 to 24 hours. A concentration of 500 μg OTC + 200 μg OLE/ml ASW has a greater than 99.4%. bactericidal activity after 1 hour of incubation and thereafter is better than 99.9% bactericidal. After 12 hours of exposure, the bacterial population is reduced to 10 cells or less per ml ambient solution and this level is maintained for another 12 hours until the termination of the experiment.