Cannibals with fins: why certain fish eat their own children

Some fish seem to be particularly devoted parents: they protect their offspring by holding them in their mouths. These so-called mouthbrooders also include the cichlids (cichlids), a family of bony fishes. The mother fish of the Cichlid species Astatotilapia burtoni incubate the fertilized eggs in their mouths until they are large enough to hatch. Eggs and young that have already hatched remain in the mouth for a total of fourteen days.

During the time they hold their offspring in their mouths, the bass do not hunt or eat. This leads to weight loss, reduced immunity, faster aging and reduced chances of reproduction. To at least partially compensate for these disadvantages, the fish display unusual behaviour: they eat up to half of their offspring.

Presumably, the mother fish use not only the nutrients but also the antioxidants of their own offspring to reduce DNA damage. During incubation, chemicals are produced that damage the mother fish’s body cells. Cannibalism helps cichlids relieve the physiological stress of parenthood, according to a Central Michigan University study published in the Royal Society’s Biology Letters.

Of course, cichlids aren’t the only parents who feast on their own offspring. There are birds that do this as well, as well as insects, reptiles, amphibians and even some mammals. Why this behavior evolved isn’t clear – after all, it doesn’t seem very conducive to reproduction. Of course, not all offspring are eaten.

By eating part of the offspring, the parents also increase their own chances of survival. This also increases the chance that they will be able to hatch eggs again in the future. In addition, when food is scarce, the remaining young have a better chance of survival if a portion is eaten.

Maulbrood is the most stressful time in a cat’s life Astatotilapia burtoni-woman, who can then cope much less well with changes in the environment. For example, loud noises can already cause the female to give birth to her offspring prematurely or to eat it completely. However, the stress is not primarily caused by the fact that the cichlid cannot eat during this time: “Animals can go very well without food for a long time. This is quite normal for mouthbrooding females,” explains study author Peter Dijkstra.

Previous research showed that changes in the brains of these females – when they reproduce – reduced the feeling of hunger, Dijkstra notes. In addition, there are probably a number of changes in the energy metabolism of females. “But the fact remains that it is an incredible achievement to keep your mouth shut and not eat for two weeks.”

Dijkstra and his team divided the females into three groups (breeding animals, non-breeding animals and a control group) to study the effects of mouthbrooding in more detail. They paid particular attention to the degree of stress to which the females were exposed. To determine the level of oxidative stress before, in the middle and at the end of the mouthbrooding phase, the researchers took blood and liver samples from each mother fish two days, six days and two weeks after spawning.

It turned out that mouthbrooding significantly increased reactive oxygen levels (ROS) during the breeding season, pushing the fish to their limits. Reactive oxygen can damage DNA and is broken down by antioxidants. In the first period of mouth incubation, DNA damage was almost 24 percent higher than in the control group of female cichlids. However, they declined again after that, which is probably due to the fact that the beginning of the incubation period was the most difficult for the fish, when the physical changes are particularly dramatic.

Eating their own offspring was good for the motherfish: the more eggs they ate, the more antioxidants they produced and the healthier they were – especially at the end of the two-week incubation period in the mouth. So the mother fish sacrificed their offspring to promote their own health and reduce the stress caused by the mouthbrooding. The cannibalism appears to protect the fish from an increase in reactive oxygen (ROS).

Further research should now show whether the level of reactive oxygen influences the likelihood that the mother fish will eat their young and whether cannibalism is a symptom of stress or whether the fish know that they can reduce stress in this way. (i.e)