Reproductive strategies of two sympatric "small barbs" (Barbus humilis and B. tanapelagius, Cyprinidae) in Lake Tana

Abstract

The reproductive strategies of two species of 'small barbs' (<100 mm forklength, LF) from Lake Tana (Ethiopia), the benthic-littoral Barbus humilis and the pelagic B. tanapelagius, were investigated. Monthly samples were collected from five different habitats over a 1 year period (>12,000 fish). Both species have a long breeding period (from March to September), and the distinct bimodal size-frequency distributions of eggs suggest multiple spawning for both species. Absolute fecundity increased exponentially with fish size, and was significantly higher for B. humilis than for B. tanapelagius. Egg size was similar. Relative fecundity was significantly higher in B. humilis. In most habitats B. tanapelagius reached first maturity at a smaller size (58.5 mm) than B. humilis (64.5 mm). However, in shallow habitats with clear water B. humilis females are much smaller at first maturity (48.3 mm), possibly due to high tapeworm infection rates. The range of fecundity in small barbs from Lake Tana (172-339 eggs per gram) was low compared with small lacustrine cyprinids and clupeids from other African lakes. The reproductive strategies of the two barbs were discussed in relation to their feeding potential, food availability, parasite infection rate and risk of predation