Distinguishing Sexes

 

Unless your fish are sexually mature it will be essentially impossible to distinguish the sexes. Determining the sex of even mature fish is not always easy, particularly if the fish are old or overfed and fat. If your tank contains 10 or more fish you can usually assume both sexes will be present, but if after all of your efforts, they fail to breed it is just possible that you have all males or females. Mature females are plumper, with rounded bellies (because of the eggs they contain), and have a silver-blue cast. Males are slimmer and and more yellowish in color, and generally more active in the tank (and more difficult to net). During spawning activities males generally chase females fish, not the reverse. The best ratio of sexes for your tank is 1-2 males per female.