Abstract
BackgroundTeleost fish are known to respond to environmental manipulation, which makes them an ideal model animal for testing relationships between the environment and behavior. The Siamese fighting fish, Betta splendens, is a solitary, highly territorial fish that displays fierce stereotyped aggressive behavior toward conspecifics or members of other species. Adult fish, especially males, are generally housed in isolation in captivity. Here we report evidence that an enriched rearing environment can decrease the level of aggression in bettas and enable adults to be housed in groups.ResultsB. splendens individuals were hatched in our laboratory and raised in groups in an enriched environment. At the juvenile or subadult stage, some individuals were relocated to a poor environment and kept in isolation. To evaluate aggression, a mirror-image test was conducted at the juvenile, subadult, and adult stages for each fish, and body parameters as well as plasma concentrations of 11-ketotestosterone, estradiol, and cortisol were evaluated. Male and female adult bettas raised in a group showed lower levels of aggression than other adult fish. The magnitude of threatening behavior was greater in adult bettas isolated as subadults, whereas the magnitude of fighting behavior was grater in adult bettas isolated as juveniles. The influence of rearing conditions on behavior was greater in females than in males. Plasma cortisol concentrations of adult bettas isolated as subadults after the mirror-image test were higher than those in other experimental groups. Adult males isolated as subadults had significantly higher plasma concentrations of 11-ketotestosterone than males raised in a group and isolated as juveniles. Females isolated as subadults had a higher gonadosomatic index than females raised in a group and females isolated as juveniles.ConclusionsThese results indicate that bettas can be kept in a group under enriched environments and that the timing of isolation influences the aggression and sexual maturity of bettas. Female and male bettas responded differently to environmental manipulation. Judging from their level of sexual maturity, bettas isolated as subadults show proper development.
Highlights
Teleost fish are known to respond to environmental manipulation, which makes them an ideal model animal for testing relationships between the environment and behavior
Our study revealed that bettas, regardless of sex, can be housed in groups and display lower levels of aggression if they are housed in groups since hatching under enriched environmental conditions
In this study, the timing of isolation altered the level of aggressive behavior; earlier isolation into poor environment increased finghting behavior and later increased threatening behavior
Summary
Teleost fish are known to respond to environmental manipulation, which makes them an ideal model animal for testing relationships between the environment and behavior. The Siamese fighting fish, Betta splendens, is a solitary, highly territorial fish that displays fierce stereotyped aggressive behavior toward conspecifics or members of other species. We report evidence that an enriched rearing environment can decrease the level of aggression in bettas and enable adults to be housed in groups. The fish, which is highly territorial in nature, was initially domesticated for fighting in Thailand [1], and the natural history of bettas is not well known. Their natural habitat is characterized by heavy emergent vegetation and shallow water, such as muddy bottoms or flooded rice paddy fields [2]. A study found that domesticated bettas are more aggressive than wild bettas and are well adapted to confinement [5]
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