PARENTAL CARE AND SOCIAL-ORGANIZATION OF THE SPINY EEL, AETHIOMASTACEMBELUS-PLATYSOMA, IN LAKE-TANGANYIKA

This is the first report demonstrating the occurrence of parental care in mastacembelids. Social organization and parental care of a spiny e el Aethiomastacembelus platysoma were studied in Lake Tanganyika. Both males and females maintained individual territories though the freque ncy of aggressive interaction was low. The male guarded offspring in a rock hole within irs territory. The egg size was large (2.5-2.7 mm in diameter) and the brood size in a nest was 5.7 on average in spite of more oocytes in the ovary (65 large oocytes on average). The duration of guarding was around 30 days after hatching and the young became in dependent just after they began to feed. Guarding males seldom attacke d fishes that approached the nest, and often went out of the nest to f orage though the stomach contents of guarding males were less than tho se of non-guarding males. Compared with Tanganyikan cichlid fishes tha t show prolonged parental care at open sites, the posthatching guardin g interval is short and the egg size is large, which seem to be traits common to fishes that utilize closed spaces as guarding sites in the lake.