Most fish that are sold as tropical fish are freshwater species. Most species available are generally bred from fish farms in the far east[2] and Florida[3] where tropical temperatures make the commercial production more viable. Mass production of tropical fish from farms has led to many inexpensive fish available to aquarists. Tropical freshwater fish are the most popular group of fish because of the low price and ease of keeping in aquaria. Some species are difficult to breed in captivity and so are still sourced from the wild. These species are generally more expensive. Among the bred-in-captivity species, the most expensive freshwater species include arowanas and flowerhorn cichlids. Some male flowerhorns are sterile due to many cross breedings.[4]. Read more here.