Evrim Yazgin
Cosmos science journalist
Fish cognitive abilities have been underrated for years, even the butt of jokes. But slowly researchers are coming to understand how they think and feel.
A new observational study has revealed that Siamese fighting fish are often kept in containers which are a quarter the size they need to thrive.
Siamese fighting fish (Betta splendens) are one of the world’s most popular aquarium fish, known for their extravagant fins, and diverse and vibrant colours. They are a freshwater fish native to Southeast Asia. They were first domesticated about 1,000 years ago in Thailand.
Thailand alone exported 20 million Siamese fighting fish in 2018. These fish were most popular in the USA, China, Singapore, France and Iran.
Siamese fighters earn their name because of their highly territorial behaviour – males kept in the same tank are prone to attacking each other.
Despite being common pets, Siamese fighting fish are listed as “vulnerable” in the wild according to the IUCN’s Red List of Threatened Species, with numbers decreasing due to habitat loss and degradation.
In the new study, published in the journal Animal Welfare, researchers examined how tank size and furnishings impacted on the behaviour of 13 male Siamese fighting fish in Singapore. The fish’s behaviours were studied through videos and pictures.
The fish were recorded for 10-minute periods 4 times a day.
Their aquariums ranged from 1.5-litre jars to 19.3-litre aquaria, with and without environmental enrichment.
Fish in larger tanks were more active, swimming on average 92 seconds more per observation period compared to those in jars. They also displayed more natural behaviours, like foraging.
“Current guidelines for appropriate tank size for Betta fish are vague and more concerned with water quality than other fish welfare concerns,” says lead author Culum Brown from Australia’s Macquarie University.
The researchers also found that tank enrichment was equally important.
Fish spent nearly half their time resting in tanks with gravel, plants and hiding spots, rather than remaining suspended in open water.
“We recommend a minimum tank size of 5.6 L for the display and sale of Siamese fighting fish, and tanks larger than this for keeping Siamese fighting fish at home,” the authors write. “All tanks should contain gravel, live plants and refuges.”
They also add a sweet acknowledgement: “We would also like to acknowledge the Siamese fighting fish who participated in this research; animals unfortunately never have a choice for their participation in such studies, but we endeavoured to mitigate any animal welfare issues as much as possible.”
