Lake flies and the deep‐water demersal fish community of Lake Malawi

Abstract

Larvae and pupae of Chaoborus edulis may be the most important food resource of some deep-water demersal fish species in southern Lake Malawi. C. edulis feed on crustacean zooplankton, which in turn feed on phytoplankton. Hence, demersal fish production is supported directly by planktonic primary production, rather than through a detrital food chain. 1996 The Fisheries Society of the British Isles

Diets and food consumption rates of pelagic fish in Lake Malawi, Africa

“…Biomasses of larval C. edulis were very low in July 1992 (0.015gdry weight m-2 lake-wide average), had increased by an order of magnitude by October 1992 (0.174gm-2) and remained high in December 1992 and March 1993 (0.088 and 0.160 g md2, respectively) (Irvine, 1995a). Engraulicypris sardella larval biomass and production showed a similar pattern to that for the Crustacean zooplankton; they were high in August 1992, reached a maximum in December, and decreased rapidly through January and February 1993 (Thompson, 1996). The fractions of crustacean zooplankton, C. edulis larvae and E. sardella larvae in the stomachs of D. limnothrissa, the species with the most varied diet, partially reflected these fluctuations in zooplankton biomass and production.…”

“…12), as there was no QIB estimate applicable to larvae. High larval productivity (1.53 g dry weight m-2 yr-', Thompson, 1996) and generally high consumption rates of fish larvae Table 3 Fish biomass (g m-' wet weight) by species or group for each lake sector, defined by the six fishing locations . Area of each sector (m') is also given.…”

“…Biomass was estimated from acoustic and trawl surveys (Menz et a/., 1995) Fishing location and area (x10"m2) FL6 (Thompson & Harrop, 1991) indicate that E . sardella larvae are likely to be significant consumers of zooplankon, .despite their low standing biomass (0.025 g dry weight m-2; Thompson, 1996).…”

“…Prey consumption in dry weight m-2 yr-' is compared with mean production per unit area (P) for 1992-93, and the ratio of prey consumption to production ( Q l P ) is calculated. Production estimates (means for, 1992/93) are from: Patterson & Kachinjika (1995); (phytoplankton), Irvine (1995b); (crustacean zooplankton), Irvine (1995a); (Chaoborus edulis), Thompson (1996); (Engraulicypris sardella larvae) and Thompson & Allison (in press 'From a mortality rate (=PIE ratio) of 2.5 yr-' (Thompson & Allison, 1996) and biomass from Table 3. tFrom an assumed mortality rate of 0.5 and biomass from Table 3. were 3mm in length, but the numbers eaten were highest in the 4-10 mm length range.…”

“…and Opsaridium rnicrolepis. There were no estimates of production for zooplanktivores, but with an assumed P / B value of 0.5 (Thompson & Allison, 1996) predators probably consume 1948% of their production (Table 4).…”