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Can a Male Betta Go Into a Tank With a Large Goldfish?

If two pet fish species were ever polar opposites of each other, it's the goldfish and the betta, also known as the Siamese fighting fish. A goldfish, usually bright orange with a rounded body, is unable to respect the space of other fish and has the undesirable habit of gulping down anything it can fit in its mouth. The betta has a long, elongated body with impressive fins and a desire to be left alone, particularly once it has established its territory. But those differences are just the beginning of a long list.

Fin warfare
- Designed to fight males of its own species, the male Siamese fighting fish is ferociously aggressive when it comes anywhere near another betta male. This wouldn't usually be a problem with the males of other fish species because the betta can differentiate between them. But it's different with a goldfish, particularly a fancy one. The betta's attack response could be triggered by the goldfish's long, showy fins, resulting in a state of permanent warfare -- hardly the tranquil environment you had in mind when you placed them together.
Hot and cold water
- Descended from the carp, the goldfish is a coldwater fish best suited to temperatures of between 15 and 20 degrees Celsius (about 60 to 68 degrees Fahrenheit). The betta, on the other hand is tropical and prefers between 23 and 25 degrees Celsius (about 73 to 77 degrees Fahrenheit). Satisfying the requirements of both fish is a delicate balancing act that could easily go wrong with a prolonged blast of cold air over the water or a broken heater during a cold spell.
Territorial issues
- Male Siamese fighting fish are fiercely territorial and usually stake out a corner of an aquarium. They like almost motionless surface water so they can build a nest by blowing bubbles on the surface. If a fish comes near their territory, they push out their gills in an intimidating show of fury from which the trespasser usually flees. Unfortunately, goldfish don't respect another fish's space -- they'll swim where they please. This is a recipe for disaster, particularly if the goldfish is bigger than the betta.
Water quality
- The betta may have started out as a swamp dweller in Southeast Asia, but its water quality requirements are very stringent. The goldfish, on the other hand, is renowned as a messy fish that produces a lot of waste. This creates obvious hygiene hazards and means if you aren't prepared to clean your tank and change the water far more regularly than usual, you could endanger your fish. For this reason alone, two species are not compatible to live together.

Animals & Science