Spawning behaviour of a pair kept in isolation. During mating, the sex partners agree on a place for the spawn. They always choose a firm, smooth bed, which can be either sloping or flat. The female spawns the eggs in lots of individual batches, each consisting of about 10 - 15 eggs. The eggs have adhesive filaments and stick firmly to their bed. The male fertilizes the eggs at irregular intervals, more often towards the end of spawning than at the beginning.