Parasites of Kunene horse mackerel Trachurus trecae (Smith-Vaniz, 1986) with a comparison of parasites of Cape horse mackerel T. capensis (Castelnau, 1861) in the northern Benguela

Bachelor Thesis


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University of Cape Town

Two species of horse mackerel (Trachurus trecae and Trachurus capensis) reside in the northern Benguela ecosystem. Both are important economic commodities for the Angolan and Namibian fisheries and therefore need to be managed appropriately. Although the two species of horse mackerel share similar morphological characteristics and co-occur in Namibian waters in the northern Benguela, few studies have compared their parasite assemblages. To date there are no studies regarding the parasite profile of T. trecae. This study is the first to identify and document the parasite assemblage of T. trecae from the northern Benguela and forms the only parasite profile for this horse mackerel species. This study also assesses the effects of fish size and fish sex on the parasite assemblage of T. trecae, and compares the parasite assemblage of this species with that of T. capensis from the northern Benguela. Results indicate that the largest significant difference in parasite assemblage is between the two horse mackerel species (by convention p<0.01), but that significant differences are also found between small and large T. trecae and between immature, male and female T. trecae. The coccidian Goussia cruciata was found to have the strongest discriminatory power in all comparisons, and therefore serves as a potential indicator parasite or biotag for discriminating between different stocks of T. trecae and between T. trecae and T. capensis in the northern Benguela. Due to the lack of literature regarding the life history of T. trecae it is difficult to assess why there are sex effects on parasites infecting this species, as well as whether the interspecific difference in parasite assemblage is due to environmental conditions or species-specific relationships. Further investigations regarding the life history of T. trecae would assist interpretation of the results obtained here. This study provides a comprehensive knowledge of the parasite assemblages infecting T. trecae and thus lends to possible future studies regarding T. trecae stock structure. It also provides a starting point for conducting studies of the parasite assemblages of other fish in the northern Benguela.