Ligula intestinalis (Cestoda: Pseudophyllidea) infection of Engraulicypris sardella (Pisces: Cyprinidae) in Lake Malawi
Fish parasites have diverse ecological impacts on fish populations and are presently becoming useful as bio-indicators of fish migration and feeding. Studies of fish parasite in Lake Malawi severely lag behind the strides made in eco-evolutionary studies of its ichthyofauna. Over a period of eleven months from April 2003, we examined more than 1300 Engraulicypris sardella from Lake Malawi for cestode parasites. About 54 % of the fish had infections of between one and eight Ligula intestinalis plerocercoids. The infection occurred throughout the study period (mean prevalence 59 ±13%) but was most prevalent in December and June and was least prevalent in April. The majority of the hosts (78%) had a light parasite burden (one or two). Parasite prevalence increased with age of the fish. Prevalence and infection intensity oscillated closely with periods of peak abundance of zooplankton, the main food of E. sardella and intermediate hosts (copepods) of L. intestinalis. Increased exposure to the parasite with age aggravated by an ontogenetic diet shift from phytoplanktivory to zooplanktivory may be interacting with fluctuations in zooplankton production in driving the trophic transmission patterns of L. intestinalis in this ecosystem.
Keywords: Engraulicypris sardella; Ligula intestinalis; trophic transmission; Lake Malawi