What do we know about tank size requirements for Betta splendens?
Recommendations from animal protection lobbyist group OATA in the U.K. is currently requiring member pet stores to maintain betta in containers of at least 3.4 liters (approximately one gallon)1.
Specifically, they say “The small size of Betta tanks is not in itself an issue for this small species, but small volumes of water are more likely to fluctuate in temperature and the water will more rapidly deteriorate in quality.” Stressing that water quality is the important factor for betta, not the smaller aquarium size.
However, for actual pet owners, OATA recommends a minimum aquarium size of 45 liters (approximately 12 gallons)2.
What does science say?
We really only have two peer-reviewed scientific articles to draw conclusions from.
In the first one, researchers found that betta grew healthier and had better feed utilization in containers of 150ml in size compared to 300ml, showing a preference for the smaller container size3. The fish color and water ammonia levels between the container sizes were not significantly different. Note that 150ml is approximately five fluid ounces, less than a cup of water.
In the second study, we find that confinement has a natural calming effect on domestic Betta splendens, but not on wild ones. The test measured cortisol level and physical activity when moving fish between 1.5 liter containers and 250ml containers. In confinement, the wild betta swam strenuously, increased breathing rates, and their cortisol levels (a typical measurement of stress) quadrupled. Whereas the domestic betta went instantly calm, slowing their breathing and movement. While the domestic betta’s cortisol level did go up in confinement, it was only a slight elevation4.
What is my conclusion?
- Keep wild betta species in at least 1.5-liter containers.
- Keep domestic betta in at least 150 ml containers.
- Domestic betta do not prefer larger aquariums.
First-time betta owners will probably want to shoot for 2.5 gallons, as smaller tanks are difficult to find and require more frequent partial water changes.
Due to research showing the value of environmental enrichment, even expert betta owners will want to aim for at least one gallon in order to provide at least one silicone or silk plant, a hide with a hole at least 1.5″ in size, and a heater.
Literature Cited
1 Jones, Deborah. Primary Authority Advice, OATA. March 26, 2022. https://ornamentalfish.org/wp-content/uploads/Assured-Advice-BETTA-13.03.15.pdf.
2 How to care for Bettas, Gouramis & Paradise fish, OATA. March 26, 2022. https://ornamentalfish.org/wp-content/uploads/2013/07/24-Bettas-Gouramis-Paradise-fish.pdf
3 Saekhow, S., Thongprajukaew, K., Phromkunthong, W. et al. Minimal water volume for intensively producing male Siamese fighting fish (Betta splendens Regan, 1910). Fish Physiol Biochem 44, 1075–1085 (2018). 10.1007/s10695-018-0495-z
4 Verbeek, Peter & Iwamoto, Toshitaka & Murakami, Noboru. (2008). Variable stress-responsiveness in wild type and domesticated fighting fish. Physiology & behavior. 93. 83-8. 10.1016/j.physbeh.2007.08.008.