Preliminary Observations of the Effect of Eimeria funduli (Protozoa: Eimeriidae) on the Gulf Killifish Fundulus grandis and Its Potential Impact on the Killifish Bait Industry

Abstract

Liver infections of Eimeria funduli, a pathogenic coccidium, greatly affected growth of Fundulus grandis (Gulf killifish) maintained in an aquaculture facility for 55 days. At termination of the experiment, average weight gained by uninfected killifish was 877.5% compared to 308.0% in diseased fish. There appeared t o be no correlation between mortality and disease in this study. INTRODUCTION Epizootics of Eimeria funduli Duszynski, Solangi, and Overstreet, 1979, a pathogenic hepatic coccidian of killifishes, have occurred in several coastal areas of the northern Gulf of Mexico and probably other areas (Solangi and Overstreet 1980, Fournie and Solangi 1980). Although 80 to 85% of both the liver and pancreatic tissues of heavily infected fish can be replaced by oocysts of E. funduli (Solangi and Overstreet 1980; Hawkins, Solangi, and Overstreet 1981), the disease does not appear to cause mortality in affected fish maintained in the laboratory. However, Solangi and Overstreet (1980) suspected that the parasite affected the growth of diseased fish. The Gulf killifish Fundulus grandis is an important member of the salt marsh ecosystem, supports a growing bait industry, and can be reared commercially (McIlwain 1977; Solangi and Overstreet 1980; Tatum et al. 1978). Consequently, the disease could have a considerable impact on the economic potential of Gulf killifish. This paper reports the effect of E. fundulz on growth of F. grandis, possible impact of the coccidian on the killifish bait industry, and means of preventing the disease in aquaculture facilities. MATERIALS AND METHODS Laboratory-reared Fundulus grandis were obtained by stripping gravid male and female killifish collected from Halstead Bayou, Ocean Springs, Mississippi. Parasite-free fish were 2 1/2 months old at the beginning of the experiment, and were maintained in the laboratory at a temperature of 25 f 2°C and salinity of 20 ?r 3 ppt. Infected individuals of the grass shimp Palaemonetes pugio Holthuis were collected from ponds adjacent to Halstead Bayou. A group of 50 fish, randomly picked, were fed a single dose of infected grass shrimp to initiate the coccidian infections, whereas, 48 fish constituting a second group were fed BamaO Minnow Chow and they served as controls. Fish 'This study was conducted in cooperation with U.S. Department of Commerce, NOAA, National Marine Fisheries Service, under PL 88309, Project 2-235-R. Manuscript received February 4, 1981; accepted March 9,1981. in both groups were fed BamaO Minnow Chow throughout the remaining days of the experiment. Diseased and control fish were maintained in separate 3500-liter recirculating tanks containing 15 ppt seawater seeded with unicellular algae to provide supplemental food. Prior to being introduced into culture tanks, all killifish were weighed in grams and their total length measured in millimeters. At the end of the study, all surviving fish from both groups were weighed and measured. Growth was calculated by differences in weight gained and statistical analyses on the growth data were conducted using procedures of Campbell (1967) and of Steel and Torrie (1960). RESULTS Infections of Eimeria funduli had a considerable impact on growth of Fundulus grandis (Table 1). Infected killifish weighed significantly less than their uninfected counterparts. Diseased fish weighed an average of 24.8% more than uninfected fish prior to the experiment; however, by termination of the study(% days) average weight of control fish exceeded that of parasitized fish by 9 1.6% (Table 1). Eimeria funduli infections did not appear to cause mortality in this study. Survival of killifish after the 55-day experiment was 64.0% and 87.5% in control and diseased fish, respectively. However, most deaths occurred during the last 7 days of the study when there was an overnight decrease in water temperature from 26°C to 13°C.