The fetal spots of guppies are black and pink. Black is the scales on the mating male or female fish, and pink is that there is no black scales on the mating male or female fish.

Peacock fish, also known as anchovies, rainbow fish, rainbow fish, peacock fish and so on. It is a tropical fish, belonging to Anthuridae. There are great differences between male and female fish in size and color. Adult male fish is thin, 3-4 cm long, colorful and beautiful. The adult female fish is about 5 cm long, and the tail stalk and fins account for more than 1/3 of the whole body, and each fin is shorter than that of the male fish. It is much worse than the male fish.

Extended data

The gluteal fin of male guppy is specialized as reproductive foot for in vivo fertilization. The male will keep chasing and mating with the female. Female fish can store sperm for later fertilization, and may give birth every four weeks.

The pregnant female fish is characterized by a black triangular color block between the anal fin and the ventral fin. After four to six weeks of pregnancy, the female will give birth to 20-40 young fish. Neither parent will take care of the young fish, and even eat their own young fish (FishBase, 2006).

Peacock fish can easily distinguish between males and females. The female fish has a large abdomen and a transparent fetal spot in front of the anus, which turns black when it breeds rapidly. The male fish is characterized by a small abdomen and a slender abdomen. Most importantly, its gluteal fin evolved into a connector for transporting sperm during reproduction. Therefore, the fins in front of the male's anal fin are thicker. The female fish's anal fins are even.