It is Not Recommended to Keep Them in a Mixed Tank
It is not advisable to keep goldfish and betta fish together. The main reasons are as follows:
Betta Fish Are Highly Aggressive
Betta fish are well-known for their aggressiveness. Especially male betta fish have an extremely strong sense of territory and will launch attacks on other fish that invade their territory. Goldfish, on the other hand, have a gentle temperament and swim relatively slowly. They are unable to effectively avoid attacks from betta fish and are likely to get injured or even die.
Different Requirements for Water Quality and Water Temperature
Betta fish and goldfish may have different needs regarding water quality and water temperature. Keeping them together in a mixed tank will increase the difficulty and risk of fishkeeping.
Potential Risks of Mixed Cultivation
Even under certain special conditions (such as a large enough water body and a reasonable layout of aquatic plants), betta fish and goldfish may coexist peacefully for a while. However, there is still a high risk in long-term mixed cultivation. Once a conflict occurs, goldfish are often at a disadvantage.
Conclusion: To ensure the health and safety of the fish, it is recommended to keep goldfish and betta fish separately and avoid keeping them in a mixed tank. If you are interested in mixed cultivation, you can choose other fish species that are more suitable to coexist with betta fish, such as tiger barbs or molly fish. But you still need to closely observe the behavior of the fish.