Fish that carry fry in their mouths eat some of them due to stress.

Female cichlid fish carry their young in their mouths, first as eggs and then as fry.

Researchers from Central Michigan University found that when stressed or lacking calories, mothers can eat up to 40% of their offspring. 

While observing the behavior of thesefish, the researchers noticed that part of the eggs were missing from the mouth of one of the female cichlids. Traditionally, a fish can hold up to 100 eggs in its mouth, but this individual had four times fewer. As a result of observing this and other individuals, scientists found that fish eat part of the brooding offspring.

A lobed cyphotilapia zebra carrying fish in its mouth. Image: MidgleyDJ at English Wikipedia., CC BY-SA 2.5, via Wikimedia Commons

Scientists examined 80 females in the laboratory,which laid eggs. After fertilization, the researchers observed how gestation occurred. As expected, mothers held their offspring in their mouths for up to two weeks. However, the researchers noted that the mothers did not eat regular food. They also found that mothers exhibited stress behavior. 

Researchers believe that cannibalism is associated withthe fact that the fish cannot eat normally during the gestation of the young, since the mouth is occupied with caviar and fry. At the same time, gestation in the mouth is a time of great stress for female cichlids. The researchers found that some mothers showed signs of liver damage, and the level of DNA damage was 24% higher than that of childless females.

We think that the females eat the young in order toget useful substances, such as calories. We also believe this is a way to get antioxidants, which is why mothers donate some of their babies to improve health. This preserves the ability to reproduce in the future.

Peter Dijkstra, study co-author

Scientists note that, no matter how terrible it may beIt sounded like filial cannibalism was actually a profitable reproductive strategy. The ability to sacrifice one child in order to preserve the ability to reproduce in the future and keep fit to care for children is reminiscent of long-term family planning, the researchers conclude.

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