M.Sc. / Abalone are among the world’s leading shellfish consumed by human populations. Harvesting in California began in the late 1800s from intertidal zones and in the early 1900s wild abalone were collected by diving. Popular demand for abalone products in the Far East then led to extensive harvesting of wild abalone and a drastic decline in population numbers. This problem was overcome to a degree by the development of land-based abalone farms. At these farms it was possible to breed abalone on a large scale. Currently twelve abalone farms operate in South Africa and the estimated production for 2006 was 537 tons of meat, worth R 80 mil. Parasites and diseases pose threats to the production of abalone, especially under farmed conditions, and can cause considerable financial loss. Labyrinthuloides haliotidis, Haplosporidium nelsoni and Terebrasabelle heterouncinata are a few parasites that contribute to the above mentioned problems. Lately, a new protozoan parasite was discovered in the digestive glands of Haliotis midae farmed in the Western Cape Province, during routine health assessments. For the purposes of this dissertation it is designated an unidentified digestive gland parasite (UDP). The aims of this study are thus to undertake a comprehensive literature review of parasites infecting wild and farmed abalone, as well other shellfish species, describe and characterise the UDP infecting the digestive gland of Haliotis midae based on its structure and ultrastructure, evaluate the role of this parasite in disease by analysing data from histological studies, provide a preliminary indication of the life cycle of this parasite, attempt analysis of DNA from the UDP, and identify potential areas for further research into control of the parasite. A total of 180 abalone, (Haliotis midae) were collected from three abalone farms in the Western Cape during May 2005, October 2005, January 2006 and January 2007. To establish whether this parasite also occurs in wild abalone, a single sampling (six H. midae and 28 H. spadicea) took place during 2006 in Tsitsikamma National Park. Collected farmed and wild abalone were weighed and measured, removed from their shells and then killed according to accepted methods before their digestive glands were removed.

Thesis (MPhil (Animal Sciences. Aquaculture))--University of Stellenbosch, 2006. / T. heterouncinata is a sabellid polychaete endemic to South Africa and found primarily in the shells of the abalone Haliotis midae. With the intensification of abalone aquaculture around the world, T. heterouncinata has become a problematic pest by causing shell deformities, reducing abalone growth rates and, in some instances, high abalone mortalities. The problem of this sabellid was first noticed in Californian in the early 1980’s in Red abalone (Haliotis rufescens) production facilities. Many mitigation methods have been tested over the years and this paper investigates another two methods; a reduction in particulate load in the tank to reduce the food source of the sabellid which perhaps will reduce fecundity, and to use ultrasound as a possible mitigation method. This study found that filtration and reduction in suspended particles did not have a significant effect, but that ultrasound did have a significant effect in reducing T. heterouncinata populations.