How do you tell the difference in male and female karp fish?

Beta (Fighting Fish) Gender DistinctionsAssuming that you mean Beta fish, it may help to tell them apart through these characteristics:

-Males have longer and more "flowing" tails and fins

-Females are less bright in color than males, as males use their vibrant color to attract mates; however, do not use this as the only indicator of gender... I've seen plenty of unimpressively colored males.

-Overall, females tend to look more "stubby" than males, meaning that they have short and stockier stature, and shorter fins.

HOWEVER, whether male or female, ALL BETAS SHOULD BE EXPECTED TO FIGHT. Betas are highly aggressive with one another, and are territorial. A period of mating is not an exception, and can still result in an injured fish.

As a general rule, one beta will be healthier NOT sharing its life with another beta.

If your main concern is about your beta's happiness or you wonder whether it is lonely, ask me for more information about things you can add to a beta's tank for recreation (such as an air pump, live plants, structures to hide in, etc.). There are quite a few things that can very much add to your beta's quality of life.