Reproductive biology of Eretmodus cyanostictus, a cichlid fish from Lake Tanganyika

One of the most widely accepted explanations for monogamy is the need for biparental care. However, the occurrence of monogamy combined with biparental care is extremely rare in oral incubating (mouthbrooding) cichlid fishes. Few studies have been performed on cichlid species that exhibit this behaviour, and therefore the ecological factors that favour monogamy in these cases remain obscure. Here we present new information on the natural history and reproductive biology of Eretmodus cyanostictus (Boulenger 1898), a monogamous biparental mouthbrooder from Lake Tanganyika. The populations studied consisted of territorial pairs and a male-biased non-territorial population of smaller 'floater' individuals. We present the first detailed description of spawning in this species, show that breeding does not appear to be synchronised within the population, and provide evidence that parental care is costly. We discuss the implications of this information for our understanding of monogamy.