(Host) Some male bluegill fish will risk their lives rather than undertake the work of protecting their young for ten days while they’re too young to survive independently. Ruth Page describes their tricky tactics.
(Page) Females of the species are usually the homemakers, those most responsible for child-care, right? But some male animals help with their young: male birds help with feeding and nest-protection, seahorse males carry the eggs, wolf-pack siblings assist in various jobs.
There’s one male fish that’s supposed to nurture its young but sometimes avoids it with the slickness of a teenager when asked to clean up his room.
Each fatherly male of the bluegill sunfish usually makes a nest by sweeping his tailfins back and forth on the lake or river-bottom to make a bowl-shaped dip. Then he gets a female, sometimes two, to release eggs in his nest, and he quickly releases sperm over them. The process can repeat until he has a cache of thousands of eggs.
Dad then has to provide ample oxygen for the eggs, so he spends a couple of days fanning his tail back and forth in the water over them. The fry appear on the fourth day, and he must protect all those kids from numerous predatory other fish. He has no time to seek food, so he gets pretty skinny until the tenth day, when his babies swim away on their own.
But one in five bluegill males cheats. This group, dubbed cuckolders, matures early and gets right to work. Each cheater will lurk behind a rock or a growth near someone else’s nest until a female appears and deposits eggs. Then he sweeps in, fertilizes the eggs and flashes away before the nest-building male can catch him. He must be quick, because the parental male is bigger and will kill him if they meet.
As one of these “sneakers” gets older, he turns into the outward image of a female, though he’s still a sperm-producer. Sometimes a fatherly male will actually court a false “female” so he can enter the nest and freely fertilize eggs laid by a true female bluegill.
The parental male doesn’t have a clue, so he cares for all the eggs. Research shows that sometimes as many as 80 percent of them aren’t his own. Luckily the sneaky males are in a minority, or they could seriously alter the gene-bank. Some are spotted before they can get to the nest, and some are caught and killed. Overall, the great majority of baby bluegills are the offspring of a female and a very hard-working father.
Research shows that bluegill fathers are far from stupid. They can identify their own fry by the smell of their urine; and if they notice many cuckolders trying to hide, they may abandon that nest and start elsewhere.
This is Ruth Page, shocked to find the lengths to which some fish will go to escape child-care chores.