You are talking about guppies, right? This kind of fish is easy to be divided into males and females. The males are generally small and thin, with large and colorful fins. The anal fin has evolved into a mating device, while the anal fin of the females is fan-shaped. The female fish is big and fat, and its body color is relatively simple. During pregnancy, the female fish will have dark spots near the anus.

When they reach maturity, the male fish will keep chasing the female fish to inseminate them.

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