by Jane Allyson

Created on: May 25, 2007

Telling what sex your fish can seem impossible and you need a keen eye. All fish are different and some are easier than others to sex, and some really are downright awkward! Sometimes you really need to know because you may be interested in breeding your fish. These are some of the common aquarium fish:

One of the more difficult to tell apart is the Angelfish. The only way you can tell the male from the female is that he will show a tiny bump on top of his head just above the eyes, but this is dependent on how mature he is.

A Betta is very easy to tell as the males are much more colorful than the females and their fins are long and flowing as opposed to the females which are short and stubby.

Catfish are impossible to sex and as the sexes can't be distinguished not many get bred in captivity.

Cichlids can be told apart fairly easily. Males are often slimmer, but larger than females, and are more intensely colored. The dorsal and anal fins of the male are more pointed, larger, and more flowing than the female. In many species the male will have egg shaped markings on the anal fin. Some males have a bump on the head.

Cyprinids can generally be sexed by the male who is more brightly colored and slimmer than the female. As you normally buy these fish in larger groups it isn't usually a problem as you will find them pairing off anyway.

With Gourami you have to have sharp eyes but you can tell the male from the female. The dorsal fin is long and and comes to a distinct point in males, while females have a shorter rounded dorsal fin. In certain species difference in coloration can also be seen.

Tetras have some differences, which vary from species to species.Generally the females are a bit bigger and fatter than the males. Males are often more brightly colored and may have longer fins than the females. Like the Cyprinids these are schooling fish and will pair easily then it is easier to tell.

Generally speaking any fish that gives birth to live young is usually easier to sex. These are known as sexually dimorphic. These include the family,Poeciliidae, which are mollies, guppies,swordtails,platies and wags. They are easily distinguishable by the gonopodium which is male modified anal fin used for copulation. The female has an anal fin shaped like a triangle. As is seen in some of the chidlids, the male has much more distinctive dorsal fins than the female. Even these fish can be difficult to tell until they are sexually mature. Up until then they pretty much look alike. Telling Koi Carp apart for example is pretty impossible until the female is ready to spawn.

Ultimately the best way to tell the gender of fish is to obtain some information on the species you are interested in. If you study their behavioral differences as well as physiological make up you may be able to make an informed decision. Another source of good information is your local pet store who can probably give many helpful tips.

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