A well-matched cichlid couple can be a formidable team. When a predator approaches, both parents attack together, their combined ferocity often driving away much larger fish. Nesting cichlids will even attack the hands of researchers who try to clean the aquarium, said Dechaume-Moncharmont.
“They are not frightened by your size,” he said. “Sometimes their bite was strong enough to make my finger bleed.”
On the other hand, a poor match can spell disaster. The male and female may fight with each other, and males have even been known to cannibalize their own offspring and mates, said Dechaume-Moncharmont. Females tend to prefer males that are about 30 percent larger than themselves -- big enough to defend the nest, but not so big that they view their own partner as food.
In the new study, the researchers gave 35 females a choice of two males, separating the fish with mesh screens. Females quickly bonded to their favorite male, swimming close to him and engaging in courtship displays. Then, the researchers removed one of the males from the tank -- either the female’s chosen mate, or the one she had rejected.
The researchers tested the fishes' mood at each stage of the experiment. Under most circumstances, fish would quickly investigate the gray-lidded box, indicating that they hoped it might contain food. But when a female lost her chosen partner, she took significantly longer to approach the gray-lidded box than she had before. Fish separated from their mates continued to approach black- and white-lidded boxes at the same speed as before, indicating that they were not just lethargic or uninterested in food.
\"When we are removing the partner from the female, she is exhibiting pessimistic behavior,\" said Dechaume-Moncharmont. \"We have shown in this study that in the sexual context, the presence or absence of the partner may affect the emotion of the female.\"
A separate experiment showed that females had good reason to be disappointed at the loss of their mates. Compared to females that bred with their chosen partners, females paired with rejected males took longer to lay eggs and produced fewer young. The mismatched couples also showed more signs of aggression toward each other. The findings were published today in the journal Proceedings of the Royal Society B.
Emotions as motivators
While the study suggests that pair bonding is an emotional phenomenon, it says nothing about whether fish are aware of their emotions on a conscious level, noted Dechaume-Moncharmont.
\"I want to avoid as much as possible the debate about consciousness,\" he said. \"I don't know if they have any private mental space in the sense that we've got some private mental space.\"
Looking for biases in decision making is a well-established method for studying animal emotions, said Amber de Vere, an animal cognition researcher at Plumpton College in Brighton, U.K., who was not involved in the research. In this case, the new findings may help explain why animals would evolve the ability to form emotional bonds with their mates.
According to de Vere, animals avoid things that are unpleasant and seek out things that bring them pleasure. Thus, she said, if a fish feels happy when she is with a high-quality partner, \"she's more likely to seek him out, more likely to stay around him, more likely to bond with him, and therefore more likely to produce more successful offspring.\"
Inside Science is an editorially-independent nonprofit print, electronic and video journalism news service owned and operated by the American Institute of Physics.
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