Admired for their splendid colors and fins, male Siamese fighting fishes — also known as bettas — are one of the most popular fishes to keep as companion animals. Often sold in tiny containers like jars or cups with no furnishings, many live out the rest of their lives in similarly neglectful conditions. While policies protecting animals often overlook fishes, people are paying more attention to the welfare of these sentient and intelligent animals.

Behavior often reflects an animal’s feelings and welfare. Although studies on how living conditions influence fish behavior exist, the authors of this study wanted to see how tank size and furnishings affect Siamese fighting fishes in particular. Species-specific research provides more accurate insights into these fishes’ distinct needs, which offers buyers, sellers, and policymakers clearer guidance on improving living conditions for these common companion animals.

The researchers rotated 15 male Siamese fighting fishes, purchased from an ornamental fish farm in Singapore, between five tanks with varying conditions:

• Jar: 1.5 liters (0.4 gallons) with three small surface plants and pebbles
• Small: 3.3 liters (0.9 gallons) with one medium plant and pebbles
• Medium: 5.6 liters (1.5 gallons) with one medium plant and pebbles
• Large: 19.3 liters (5.1 gallons) with one large plant, pebbles, and one barrel for refuge
• Large-barren: 19.3 liters (5.1 gallons) with no plants or furnishings

All fishes began their time in one of the four furnished tanks for seven days. Using an approach to minimize stress for the fishes, the researchers rotated each fish until they had spent seven days in each of the other three furnished tanks. If a fish displayed signs of suffering, the researchers moved him to a holding tank before re-entering him into the rotation, skipping the one that caused distress.

After the fishes had experienced all other tanks, they spent time in the large-barren tank for three days. The researchers shortened the observation time in this tank out of concern for the fishes’ welfare.

To prevent the activity of other fishes and people from influencing the results as much as possible, the researchers covered the tanks, and fishes only interacted with humans during feeding and cleaning.

On each of the last days in each tank, a camera recorded the fishes for 10 minutes at four points during the day. Using these recordings, the researchers categorized 10 types of behavior. Of the 15 fishes who began the experiment, 13 completed it and contributed to the data analyzed. Two fishes had been unwell from the start of the study and passed away.

Bigger Is Better

The researchers found that tank setup has a significant impact on how Siamese fighting fishes behave. While some individuals engaged in certain behaviors more than others, how their behavior changed between tanks generally supported overall trends. Fishes exhibited more active, natural behavior, including swimming and searching for food, in larger tanks. In contrast, fishes in smaller tanks displayed abnormal behaviors that suggested boredom or discomfort, including interacting with walls, stereotypic swimming (e.g., pacing or circling), and staying motionless.

Barren Is Bad

The analysis also showed that assorted furnishings in a tank can have a positive impact on the welfare of Siamese fighting fishes. When resting, fishes rested on or against the tank furnishings about half (47%) of the time and moved between different available spaces. Plants, barrels, gravel, and other objects seemed to provide the fishes with places to hide, emotional comfort, and physical support. Fishes in the large but unfurnished tank exhibited most of the same abnormal behaviors as those in the smaller tanks.

Unfortunately, fishes still swam anxiously or aimlessly even in the largest furnished tank. While people can improve welfare by offering a bigger tank with plenty of furnishings, the authors suggest it could be difficult to provide truly ideal living conditions for Siamese fighting fishes.

Study Limitations

Covering the tanks may have created an unrealistic environment. Captive Siamese fighting fishes usually have unobstructed views, and seeing or interacting with people can cause added stress. Even though the authors were trying to isolate the effect of tank size and furnishings, simulating natural levels of expected human interaction could have produced more realistic results.

The authors acknowledge that they could have designed their research to be even more confident in their findings, such as by studying more fishes. However, their decision to prioritize the fishes’ welfare still accomplished their goal of better understanding how tank size and furnishings impact the behavior of Siamese fighting fishes.

No More Jars

This study supports previous findings that more space and enriching environments lead to healthier, happier fishes. The authors ultimately recommend that shops selling Siamese fighting fishes should house fishes in well-furnished tanks of at least 5.6 liters. Once purchased, those who plan to keep them should upgrade to an even larger tank. Furnishings like gravel and pebbles, plants, and barrels or other hideouts function as more than just decor: they provide spaces for fishes to rest and retreat from outside disturbances.

As long as people continue to keep fishes as companion animals, advocates can help spread the word about the responsibility of both sellers and buyers to prioritize fishes’ well-being — starting with their homes.