At the beginning of the breeding season, the male selects a site for a nest, in a crevice between stones or rocks, and guards it against all intruders. Males can be distinguished from females by a prominent bulging forehead and by the dark colour which they assume at this season. The spawning behaviour is described. Each individual spawns several times during the season, the females producing over a thousand eggs in each spawning. The males not only guard and aerate the eggs but also keep them clean and free from fungal infection.
The incubation period lasts from forty days to sixty days, depending on the temperature. The embryonic stages are described and figured. Analyses of the contents of nests, collected from the field late in the season, showed that several batches of eggs were present in each, contributed in all probability by more than one female.
Hatching shows day and night periodicity. Fully developed embryos are stimulated to activity by light. Hatching follows after some delay. Mechanical shock also stimulates hatching.