2.2 The host
Engraulicypris sardella (Günther, 1868), locally known as Usipa or Lake Malawi sardine, is a small, slender, silvery, zooplanktivourous, pelagic social fish endemic to Lake Nyasa (Lowe‐McConnell, 1993; Rufli and Van Lissa, 1982). The fish occurs in shoals, which are widely distributed within the lake and found in both near-shore areas and offshore pelagic water, down to a depth of approximately 200 m (Maguza-Tembo et al., 2009). E. sardella is an annual species, where hatchlings grow and age to reproduce and die in a yearly cycle (Iles, 1960), although some studies have reported that they can live longer (Rusuwa et al., 2014; Thompson and Bulirani, 1993).
During early developmental stages E. sardella feeds exclusively on phytoplankton, then switches to feeding on zooplankton once reaching adulthood (Allison et al., 1996; Degnbol, 1982). E. sardellademonstrates a rapid growth rate and can attain a maximum total length of about 130 mm in a year (Thompson, 1996; Tweddle and Lewis, 1990). Males and females mature at a size of about 70 and 75 mm respectively (Thompson and Allison, 1997; Thompson et al., 1996). They have been reported to breed throughout the year but with bi-annual recruitment peaks occurring during both the wet season and dry season (Morioka and Kaunda, 2005; Rusuwa et al., 2014). We continuously observe small individuals of E. sardella in the lake suggesting a continuous spawning behaviour in this species (pers. obs.).
E. sardella forms an important part of the food web of Lake Nyasa. The species is primary consumer of zooplankton (Degnbol, 1982; Konings, 1990), but they are also an important native prey of pelagic piscivorous fishes, particularly Diplotaxodon spp. andRhamphochromis spp. (Allison et al., 1996), as well as piscivorous birds (Linn and Campbell, 1992). E. sardella is also of high commercial value, and for many decades it has been the main animal protein source for most of the local human population (Manyungwa-Pasani et al., 2017).