The halfbeaks occur in southeast Asia and are found in both fresh and brackish environments. Most of those available in aquatic outlets have been acclimatized to freshwater conditions (with maybe a level teaspoonful of salt per 4.5 litres/1 gallon), so you should have no problems with them
These popular fish are characterized by their breeding habits. The eggs are fertilized internally; in most species, sperm are transferred to the female via the male’s gonopodium—a tubelike projection of the anal fin—and the eggs subsequently develop in the relative safety of the female’s body.
Some of you may be tempted to keep Cyprinus carpio (Koi Carp) in an aquarium and we would like to advise against this. Koi are potentially large fishes best housed in large purpose-built ponds with powerful filtration systems.
[Ebook] The New Guide to Aquarium Fish A comprehensive and authoritative guide to tropical freshwater, brackish, and marine fishes Mary Bailey – Gina Sandford
