Parasites of Healthy and Diseased Juvenile Grouper (Epinephelus malabaricus (Bloch and Schneider)) and Seabass (Lates calcarifer (Bloch)) in Floating Cages in Penang, Malaysia

Abstract

One hundred eighty healthy juvenile grouper, Epinephelus malabaricus (Bloch and Schneider), and 642 healthy juvenile seabass, Lates calcarifer (Bloch), purchased by fish farmers, either locally or imported for stocking in floating cages in Penang, were examined for parasites. Diseased grouper (n = 211) and seabass (n = 102) showing symptoms of hemoIThage on the body, fin rot and scale loss, were also examined for parasites. Grouper and seabass from Malaysia, Thailand and the Philippines each had the same parasite species which were numerically abundant, regardless of source of origin of the fish host. Both species of marine fmfishes imported into Malaysia carried with them a large variety of parasites, some of which, such as Cryptocaryon irritans Brown, 1951 and Trichodina sp., are known pathogens. The most common parasite recovered from healthy and diseased grouper was Pseudorhabdosynochus epinepheli (Yamaguti, 1938). The prevalence and mean intensity of infection of P. epinepheli in healthy grouper originating from Malaysia were 86.0% and 39.6 helmi,nths per infected fish, respectively; from the Philippines: 92.0% and 51.1 helminths per infected fish, respectively; and from Thailand: 92.9% and 29.5 helminths per infected fish, respectively. The diseased grouper originating from Malaysia had a prevalence of 88.5% for this monogenean with a mean intensity of 17.4, whereas those originating from Thailand were not infected. A large proportion of healthy (97.0%) and diseased (90.0%) grouper from Thailand were infected with Trichodina sp. A major factor that may cause the disease outbreaks in grouper originating from Malaysia was the high intensity of P. epinepheli together with the infection of the protozoans Cryptocaryon irritans and Trichodina sp., whereas Trichodina sp. was likely the primary cause of disease outbreaks in grouper originating from Thailand. Both healthy and diseased juvenile seabass from Thailand were heavily infected by C. irritans, Trichodina sp., Pseudorhabdosynochus latesi (Tripathi, 1957) and Diplectanum sp. The prevalence of C. irritans in healthy and diseased seabass from Thailand was 20.4% and 22.5%, respectively, whereas it was 62.8% and 37.3% for Trichodina sp. The prevalence and mean intensity of P. latesi for healthy seabass were 14.8% and 9.5, respectively, and for diseased seabass, 78.4% and 10.8, respectively. A large proportion (20.5%) of diseased seabass was also infected by Diplectanum sp., with a mean intensity of 15.1. Heavy infections of protozoans and monogeneans in seabass from Thailand were the primary cause of disease outbreaks in these fish. In contrast, juvenile seabass originating from Malaysia had very few parasites and no disease outbreaks were observed after their introduction into the floating cages.