Raising kids is hard work. Male blenny fish sometimes eat their babies if they think they鈥檙e not worth the effort and want a better batch.
The barred-chin blenny (Rhabdoblennius nitidus), a fish found in Asia, has an unusual parenting arrangement. After females lay eggs, they leave their male partners in sole charge of caring for them until they hatch.
This arrangement usually works well. But if the female leaves only a small number of eggs 鈥� less than one thousand or so 鈥� the male typically eats them instead of looking after them.
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Until recently, it was thought this was because the nutritional value of eating the small number of eggs outweighed the benefits of protecting only a few offspring. But at Nagasaki University in Japan and his colleagues found that the motivation was听actually to breed again as soon as possible to get a larger, healthier batch of children.
They showed that the breeding cycle of male R. nitidus fish is tightly controlled by the presence or absence of eggs. When eggs are laid in their nests, their testosterone levels drop and they cannot mate 鈥� perhaps to听make them听stick to the task of parenting. When the eggs hatch and their offspring leave the nest about a week later, their testosterone levels shoot back up and they can court females once again.
Empty nesters
When males are left with only a meagre number of eggs, they may choose to eat them straight away so that their empty nest signals for their testosterone levels to be restored, says Matsumoto. That way they can find a mate to give them more children with better survival prospects as soon as possible, he says.
The finding explains why males often spit eggs out of their nests in addition to eating them, says Matsumoto. 鈥淚t strongly implies that egg removal is urgent and that males eat the eggs primarily to remove them, not merely for nutrition,鈥� he says. It also explains why well-fed males are just as likely to eat their eggs as hungry ones, he says.
R. nitidus is the first known species in which males eat their babies to regulate their breeding cycle, but cannibalism听of offspring has been observed in a small number of other species.
For example, male and female burying beetles eat some of their offspring when they have , and some male fish eat their babies when they are .
Read more:听听Honey, I ate the kids: When caring fish turn cannibal
