Ecological aspects of the occurrence of asian tapeworm, Bothriocephalus acheilognathi Yamaguti, 1934 infection in the largemouth yellowfish, Labeobarbus kimberleyensis ( Gilchrist and Thompson, 1913) in the Vaal Dam, South Africa

Infection of fish by the Asian tapeworm can damage intestines and cause abnormal growth. Eighty largemouth yellowfish Labeobarbus kimberleyensis were collected in the Vaal Dam (26°52.249′S, 28°10.249′E) with the aid of gill nets during a study between April 2005 and February 2006. The fish were killed and the weight and length determined. Thereafter the intestines were removed, the length determined and the intestines opened to expose the tapeworms. The distance between the beginning of the intestine and the attachment position of the first tapeworm was measured, and thereafter all the worms were collected. The prevalence, abundance and mean intensity was calculated for all the surveys. Seasonality and intensity of tapeworms were compared to the intestine and total lengths of the fish. All the tapeworms were identified as the Asian Tapeworm Bothriocephalus acheilognathi Yamaguti, 1934. The position of the first tapeworm was located between 10% and 20% from the anterior end of the intestine in close proximity to the bile opening. A total of 100% prevalence was recorded for all the surveys and the highest mean intensity of 231.1 was recorded during the autumn survey. The lowest mean intensity of 73.7 was recorded during the summer survey. Although the infection rates were very high, the fish condition was good and apparently the fecundity of the fish was not negatively affected as young fish fry was collected during the summer survey. Parasite numbers are higher and differ from a study conducted in 2000 and this is attributed to water temperature and water quality. No correlation was observed between parasite intensity and total length of each fish. This indicates that intensity is not dependant on host size and that infection is not the result of a buildt of over years.