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 eel Aethiomastacembelus platysoma were studied in Lake Tanganyika. Both males and females maintained individual territories though the frequency of aggressive interaction was low. The male guarded offspring in a rock hole within its 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 independent just after they began to feed. Guarding males seldom attacked fishes that approached the nest, and often went out of the nest to forage though the stomach contents of guarding males were less than those of non-guarding males. Compared with Tanganyikan cichlid fishes that show prolonged parental care at open sites, the post-hatching guarding 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.