Carp, silver carp, carp, grass carp and chub head fish are all carp. The left and right branchial operculum membranes are connected with each other but not with the isthmus, and the difference between silver carp and bighead carp (silver carp) mainly depends on the completeness of the abdominal margin, which is silver carp (clever plan: silver carp is complete) and bighead carp (silver carp). Then, whether there are serrated spines on the trailing edge of dorsal fin is cypriniformes, and whether carp and crucian carp have whiskers can be distinguished. Carp has whiskers, but crucian carp does not (note: the distinguishing feature of carp and crucian carp is swallowing teeth).

Mackerel, also known as mackerel, has a ridge on its tail handle. You can feel it when you touch it.

I don't know the last one.