Some freshwater fish cannot resist hunger and occasionally eat eggs fertilized by them. That's what a group of researchers at Purdue University in the United States have seen. The researchers initially thought that ingested eggs could be fertilized by another fish. But analyzing the DNA of eggs extracted from the belly of male fish, they saw that fish eat their ‘descendants’.
Most freshwater fish reproduce by external fertilization. The male builds the nest, the female lays the eggs and the male pours sperm onto the eggs. Until the fry leaves the eggs, the male takes care and protects the nest and, if possible, does not separate much from the eggs. Therefore, sometimes he eats some egg, if the hunger will not die.