Generally speaking, the larger the fish, the longer they’ll live (interestingly, the reverse is true for pet dogs). Most fishes in retail outlets are sold either as juveniles or young adults. Fighting fish for example are already >5 months old when sold at aquarium stores at >5cm in size. They have a lifespan of up to 5 years, but more commonly, 3 years. Goldfish can live for 20-25 years, but 10 years is more common. Similarly, oscars live for about 10 years. Kois (Japanese carp) can live in excess of 50 years and even up to 100 years! It’s a fish that you’ll have to pass on to your children. On the other hand, some killifishes are annuals and can live for 1-2 years in captivity.
Sadly, the average lifespan of a fish kept without adequate filtration and filter cycling may be as short as 4 weeks. The reason for this can be found in an article from my website – http://thefishvet.com.au/pdf/Ncycle_byRL.pdf
