Abstract
Seasonal surveys were conducted at the Vaal Dam between April 2000 and January 2001. Twenty smallmouth yellowfish (Labeobarbus aeneus) and 20 largemouth yellowfish (Labeobarbus kimberleyensis) were collected with the aid of gill nets. Surface water quality variables were included. The cestodes were identified as either Bothriocephalus acheilognathi Yamaguti, 1934 or "other cestode spp.". The majority (99.8%) of the cestodes found in both yellowfish species were identified as B. acheilognathi (Asian tapeworm). The prevalence, mean intensity and abundance of B. acheilognathi in both yellowfish species were calculated. Ecological parameters including species specificity, seasonality, gender specificity and relationships between fish size and the Asian tapeworm prevalence were also included. In this study, B. acheilognathi preferred L. kimberleyensis over L. aeneus although a low intensity was observed in smallmouth yellowfish. Furthermore, the infection (in terms of prevalence, abundance and mean intensity) in largemouth yellowfish was markedly higher. Seasonal patterns observed in the Asian tapeworm's infection of smallmouth yellowfish are attributed to breeding and subsequent feeding patterns of this fish species with relatively high infections recorded in winter and spring. For L. kimberleyensis no explanation can be given regarding the seasonal patterns observed for the mean intensity and abundance of B. acheilognathi. The maximum and minimum mean intensity and abundance values in largemouth yellowfish were recorded in autumn and spring, respectively. In addition, the prevalence of B. acheilognathi was consistently high in all four seasons.
Highlights
Surveys conducted by the fish parasitology group have shown unexpectedly high numbers of helminth parasites in yellowfish species in the Vaal Dam
The high number of helminth parasites can be attributed to Bothriocephalus acheilognathi which has been introduced with cyprinid fish into South Africa from Asia
Similar prevalence and mean intensity values to those obtained in this study were recorded for L. aeneus and L. kimberleyensis in a separate preliminary study conducted by Nickanor, Reynecke, Avenant-Oldewage & Mashego (2002) in the Vaal Dam during 2001
Summary
Surveys conducted by the fish parasitology group have shown unexpectedly high numbers of helminth parasites in yellowfish species in the Vaal Dam. The high number of helminth parasites can be attributed to Bothriocephalus acheilognathi which has been introduced with cyprinid fish into South Africa from Asia Localities in South Africa where B. acheilognathi has been found include the Komatipoort area (Mpumalanga Province) (Boomker et al 1980), Marble Hall (Mpumalanga Province) (Brandt et al 1981), Boskop Dam (KwaZulu-Natal Province) (Van As, Schoonbee & Brandt 1981), Hartbeespoort Dam (North West Province), Piet Gouws Dam (Limpopo Province) (Mashego 1982), Olifants River (Limpopo Province) (Mashego 1982), Glen Alpine Dam (Limpopo Province) (Mashego 1982) and the Vaal Dam (Gauteng Province) (Mashego 1982). Cyprinus carpio has been found in the Vaal Dam but its introduction date is uncertain
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