Incompatible fish of other species:

.Very small fish (smaller than one inch) may be eaten.
.Fish with long, flowing fins may trigger aggression. This includes fancy guppies, white cloud mountain minnows (which are suited to cooler water than bettas), and some long-finned tetra species.
.Slow-swimming fish will be unable to escape bullying.
.Mollies may bite the betta's fin or, if large enough, eat the betta.
.Fish belonging to the same biological family as the betta, such as Paradise Fish and gouramis, may attack or be attacked due to their relatively similar appearance and cross species aggression.
.Goldfish are unsuitable tank-mates because of their great appetites, preference for cold water, and high excretion-rate.
.Cichlids are aggressive and certainly incompatible with bettas except for peaceful cichlids like German rams.

Like many tropical fish, Betta splendens might harass and kill small, slow fancy goldfish; in return, goldfish have been known to bite a betta's tail. Goldfish also are best suited to a cooler-water tank than the tropical Betta splendens. It's commonly thought that bettas are best housed in extremely small vessels; this is a misconception derived from the limited display space available in pet shops and the fact that males cannot be housed together. In fact, bettas need as much living volume as other tropical fish of comparable size, meaning that a tank of 1.5-2 gallons in capacity is the practical lower limit for an individual fish. Table-top tanks should be kept in warm locations, given optimal betta water temperature of 77 to 82 degrees Fahrenheit, and thus are unsuitable for places that are air-conditioned to cooler temperatures. If a larger tank is used and the filtration is strong enough to cause a current, it is important to make sure the betta has plenty of tank space without a strong current, as this can damage the betta's fins and make it difficult for the betta to reach the surface.

In popular culture
The Siamese fighting fish has been used as the default background in the first official beta version of the Windows 7 operating system, in an apparent reference to the name "betta".
In the movie From Russia with Love, the James Bond villain Blofeld compared the strategy of SPECTRE to three Siamese fighting fish fighting each other. There, two will fight each other to the death while the third will wait its turn, symbolizing the conflict between the USA and the Soviet Union as the two fighting fishes and SPECTRE as the third waiting fish.