Why These Fish Sometimes Destroy Their Eggs

Male Rhabdoblennius nitidus, small fish that live on reefs in the western Pacific, care for eggs laid by females. But sometimes they deliberately destroy the eggs—especially when there are only a few.

Scientists first suspected that the males ate the eggs to get back energy. Experiments showed something more surprising: the fish destroyed eggs whether they were hungry or not, and sometimes even spat out chewed eggs.

Hormones are the key. Having eggs causes a sharp drop in a male’s androgen levels, which makes it harder for him to breed again. If there are too few eggs, it can be better for him to get rid of the whole clutch. His hormone levels rise again, and he can quickly court another female in hopes of having more offspring. In this case, destroying his own embryos is not about food—it is an unusual reproductive strategy that lets the male “reset” his breeding cycle.