There are about 2400 species of catfish, belonging to about 34 families. Most of them are tropical freshwater species, but some of them are distributed in temperate regions (Siluridae and Siluridae), and two families (Siluridae and Marine Siluridae) are marine species.
Catfish are sticky and have no scales. The dorsal fin is very small, without spines, with 4 ~ 6 fins. Fat-free fin The anal fin is very long, and the rear end is connected with the caudal fin. Catfish are usually dark brown or gray-black, with slight dark cloud spots. Freshwater catfish are distributed in various freshwater areas around the world, while seawater catfish live near tropical coasts.
Extended data
Catfish is a fierce bottom fish. Afraid of light, I like to live in crevices, deep pits, earth caves or caves at the bottom of tree roots, and slow flowing water near rivers. In the still water of reservoirs, ponds, lakes and weirs, most of them lie at the dark bottom or under pieces of water hyacinths, peanuts and water hyacinths. In spring, activities and foraging begin.
After winter, it doesn't eat, but lurks in deep water or caves for the winter. If nothing bothers it, it usually can't swim. Catfish have small eyes and weak eyesight. They lie down during the day and go out at night. They hunt by smell and two pairs of tentacles. They are very greedy. The hotter the weather, the greater their appetite, and they are active on cloudy days and at night.
Catfish can reach maturity at the earliest age of 1 day, but only some of them grow faster (the smallest mature catfish is: female fish is 22.4cm long and weighs 51g; ; The male fish is 17.8cm long and weighs 34g), accounting for about 50% of the population, and the 2 nd instar individuals are all sexually mature. In natural environment, the breeding season is from April to July, and the suitable water temperature for spawning is 9~30℃.