Reproductive biology and breeding of Barbus paludinosus and B. trimaculatus (Teleostei: Cyprinidae) in Lake Chilwa, Malawi: implications for fisheries management
Barbus paludinosus and Barbus trimaculatus were sampled in Lake Chilwa and the Mnembo River mouth between February 2004 and January 2005, using nets equivalent to those used commercially, to analyse their reproductive biology and distribution as a basis for recommending sustainable fisheries management and conservation practices. Total length and fish and gonad weight were measured monthly for both species. Length maxima for female and male B. paludinosus were 130 mm and 113 mm respectively, and for female and male B. trimaculatus 120 mm and 85 mm respectively. Lengths-at-first-maturity for female and male B. paludinosus were 69 mm and 64 mm respectively, and for B. trimaculatus 61 mm and 59 mm respectively. Lengths-at-first-capture were 62.4 mm for B. paludinosus and 71.8 mm for B. trimaculatus. Females predominated 3:1 over males in both species. For the Barbus fishery in Lake Chilwa the optimal stretched mesh size for matemba seine-nets, in terms of rendering the fishery sustainable, was 10.53 mm. Barbus breed throughout the year, with a minor peak in April–March and a major breeding peak in October–January. Before the rainy season, Barbus migrate to the marshes, marginal swamps and the Mnembo River mouth to breed. Fishery management recommendations to ensure successful breeding and recruitment of Barbus into the fishery include: (1) a closed season for active fishing gears targeting Barbus spp. and juvenile tilapias from October to February for the lake and riverine fishing, (2) the increase of the permitted stretch mesh size for matemba seine-nets to 10.53 mm and (3) protection of the marshes, swamps and river habitats which act as breeding grounds for the Barbus spp.