The occurrence of gut associated parasites in the South African abalone, Haliotis midae, in Western Cape aquaculture facilities

Abstract

Abalone have been cultured in South Africa for seventeen years. The growing industry has led to increased intensification. Farms are concentrated in certain areas, notably Hermanus on the South coast, and may be close to wild abalone populations and processing facilities. These factors contribute to increased risk of disease emergence. Data on parasite prevalence generated from the abalone health management program between 2000 and 2004 was analysed for trends. Abalone were sampled systematically from participating farms and subjected to gross and histological examination. Data on age, size, gonad development, diet and type of system were recorded. This paper presents the most significant results for gut protozoa, digestive gland protozoa and rickettsia like prokaryotes, which are all gut associated. Prevalence was found to increase with increasing age and size. Higher parasite prevalences were found on the West coast than on the South coast, and outside Hermanus compared to within Hermanus, suggesting that concentration of farms is not leading to increased prevalence. Gut associated parasites were significantly more prevalent in animals fed on kelp than artificial feed. It was found that animals younger than 24 months are more at risk of infection when fed kelp than older animals. The results indicate that separation of age groups, removal of poor performers and use of artificial feed, especially in younger animals, are likely to reduce risk of infection with gut associated parasites.