Nest building and brooding behavior of the bagrid catfish, Auchenoglanis occidentalis (Valenciennes, 1840), in Lake Tanganyika

Brooding and nest-maintenance behaviors of the bagrid catfish Auchenoglanis occidentalis (Valenciennes, 1840) were studied in the southern end of Lake Tanganyika, We observed huge saucerlike nests, 1.2-3.8 m across, on the fi ne sand bottom of the littoral zone. The lowest parts of the nests were cov ered with an accumulation of coarse particles consisting mainly of gastropo d and bivalve shells and shell-fragments, which the catfish sifted out from the sediment, Broods were buried within the shell accumulation and tended solely by males for up to two weeks until the juveniles were motile, Broodi ng males spent most of their time fanning the pectoral fins and undulating the posterior body. These movements resulted in water flow over the broods, which might serve to prevent oxygen deficiency. They did not act aggressiv ely against intruding potential brood-predators. Nest distribution and rela tionships between nest size and shell content in the sediment suggest that nest site selection and nest size are determined by the shell availability in the sediment.