1, because after fishing in the sea, this kind of fish is used for frozen sale, and the internal organs need to be removed. Fishermen are very experienced. They just pull out the fish head and internal organs together, which is fast and clean, because the fish head can't sell well.

2. Fish heads are inedible, and selling them head by head will increase the transportation cost. It has the characteristics of "stinging", difficult preservation of internal organs, poor edibility of fish heads, and increased transportation costs. The price in the market is not good. If fish heads are sold together, fewer people will buy them. In order to attract customers, fishermen will remove fish heads and sell clean meat.

Piranha is oblate, similar to the face of a horse. Generally, it is 10 ~ 20cm long and weighs about 40g. Short head, small mouth and teeth. Small eyes, high position, near the back edge. The branchial foramen is small, located below the eyes, and the scales are small and fluffy; The body is blue-gray with no lateral lines.