Assessment of the effects of plerocercoid larvae of Ligula intestinalis (Cestoda) on Engraulicypris sardella (Cyprinidae) from northern Lake Nyasa/Malawi/Niasa

Abstract

Engraulicypris sardella (Günter, 1868) is a cyprinid fish exploited in the waters of Lake Nyasa that has been found to be infested by Ligula intestinalis (Linnaeus, 1758). Although L. intestinalis has been the subject of a number of studies, there is no information on the effects of this parasite on E. sardella. This study was therefore aimed at assessing the prevalence and intensity of the parasite L. intestinalis, condition of the fish and impact on fecundity of E. sardella. Data recorded for each individual fish included: total length, weight, sex and maturity stage, number of parasites, gonad assessment and egg count. Number, length and total weight of L. intestinalis found per fish host were recorded. The average infestation rate from the two landing sites (Matema and Kafyofyo) was 32.5%. Kafyofyo had the highest infestation rate (50%) and Matema (15%); on average, each infested fish had 1.7 parasites. The majority of infested fish carried one parasite (57%) with 23.1% having two parasites, 13.8% three parasites, 1.5% four parasites and 4.6% five parasites. There was significant difference between the weight of fish with parasites and those without parasites (P < 0.05). Mean length and weight of parasites was 73.6 mm and 0.25 g, respectively. There was also a significant difference between the weight of gonads of infested and non-infested fish (P < 0.05). The average weight of gonads from infested fish was 0.28 g, while that of non-infected fish was 0.32 g. Gonads of all infected fish were atrophied. Number of eggs (fecundity) decreased significantly with parasite infestation. Condition factors of both infected and uninfected fish did not show any significant difference (Mann-Whitney U-test P > 0.01). Therefore, it was concluded that L. intestinalis parasites affect fecundity and consequently inhibit the reproductive capacity of this cyprinid fish population.