The average Betta lives about three years. However, that doesn’t necessarily mean you'll have your Betta that long. Why? Because a Betta purchased at a pet shop is often one year old already. Males, in particular, are allowed to fully mature, so their fins and colors are well developed. Females may be sold at a bit younger age, but they will generally be at least six months old when offered for sale.
One of the keys to enjoying your Betta longer is to buy a healthy, young fish from a reputable pet shop. Avoid buying pale fish as that is a sign of disease. The fins shouldn't be torn or ragged. The eyes should be clear and not bulging out. Look for any signs of sores or injury on the body. A healthy Betta is active and will respond to you when you place your hand on the glass of the tank.
How to Give Your Bettas a Longer Life
Good care and a healthy diet can prolong the lifespan of your Betta. But don't overfeed it, as too much food can cause fatty liver disease (hepatic lipidosis), which can shorten your Betta's life span. Keeping the water clean by performing frequent water changes will help, especially if your Betta is kept in an non-aerated aquarium. Exercise has been shown to increase the life span of the Betta,so a gentle water flow through the tank to provide resistance when swimming will keep your Betta fit, but the flow should not be so excessive that it blows the Betta around the tank. Even so, it’s rare for a Betta to live more than five years. So if your fish only lives a year or two after you purchase it, don’t assume you’ve been a bad owner. That’s a perfectly normal lifespan.
Preventing Fights Between Male Bettas for a Full Lifespan
Another factor in longevity for Bettas is keeping the male Bettas apart, so they don't fight each other. Their common name is Siamese Fighting Fish, and the males are apt to engage in territorial battles. They can injure each other, and that may reduce their lifespan. Some aquarium owners who want to keep more than one male Betta use Betta condos to keep them separate. However, there is speculation that they still experience stress in seeing other males and that could have an effect on their health. Aquariums with multiple compartments for Bettas should have opaque material between the sections. In general, it's wise to follow the rule of one male Betta per tank. Males cannot be kept with female Bettas either, except during mating, and then the female needs to be removed. Female Bettas generally can be kept together, but even they may quarrel sometimes. One good note about Bettas is that one male can be kept in an aquarium with non-aggressive fish of other species that are similarly sized.
Keep Bettas in Appropriate Tanks - Not a Vase
There was a fad of keeping a Betta in a vase or another small container rather than in an aquarium. This was unhealthy for the fish in several ways. The water temperature isn't regulated and at common room temperature is probably lower than they are used to in the wild in Thailand. Their ideal water temperature is about 78 to 80 degrees F, as would be provided by an aquarium heater. Otherwise, the fish will be listless and may refuse to eat, which is not good for their health.
Bettas must have access to the surface air at the top of the water to breathe with their upturned mouths and labyrinth breathing organs. Cleanliness of the water is another important factor for good health. The water in a small container should be changed every other day if it isn't filtered, and filtered aquariums should still have 25% or more of the water changed at least once a month. Bettas are prone to fin rot if they aren't kept in good water conditions. Overall, it is best to keep a Betta in an aerated and filtered aquarium, either by itself or with other species of similar sized fish.
Are you wondering how long the oldest Betta lived? There are documented cases of Bettas living as long as nine or ten years in captivity.
Bettas Need More Than Bowls. University of Illinois at Urbana-Champaign College of Veterinary Medicine