The Distribution of Perkinsus marinus, a protozoan parasite of the American oyster, Crassostrea virginica, along the Texas Gulf Coast

Abstract

The abundance and distribution of Perkinsus marinus in the oyster-producing bays of the Texas coast was determined from Nov. 1987 through Nov. 1988. Oysters were collected from five oyster-producing bays in Texas by Texas Parks and Wildlife Department personnel and tested for infection on a quarterly basis. Infection rates averaged over the five sampling periods for three of the bays tested; Galveston Bay (prevalence 52%), Matagorda Bay (prevalence = 78%), and Aransas Bay (prevalence 84%); showed increases with increasing temperature (21 'C, 21 'C, and 23'C respectively) and salinity (1 8 ppt, 28 ppt, and 22 ppt respectively). Explanations are offered for the deviations from this trend by the other two bays; Sabine Lake which had the highest infection levels (prevalence = 87%) with low temperature (21 C) and the lowest salinity (14 ppt), and South Bay which had the lowest infection rate (prevalence = 34%) with the highest temperature (25 C) and salinity (37 ppt). The relationships of infection rates with environmental conditions at the time of sampling are examined. Variations in the culture technique were also tried in order to compare the usefulness of two new antibiotics, Kanamycin and Gentocin, as replacements for the chloromycetin used in the current mycostatin/chloromycetin method. This work has provided information on alternative antibiotic combinations, some of which enhance the detection of Perkirisus infection more than the current mycostatin/chloromycetin method. In this study, Gentocin, at 800 ppm, was found to enhance detection 16% above the level of the current method. Thus, Gentocin appears to prevent tissue putrefaction in addition to enhancing enlargement of Perkinsus cells without the use of mycostatin. Kanamycin and Gentocin, at 800 ppm, each respectively, when used with mycostatin.