I checked some Jewish site`s and mackerel is listed as permitted for human consumption.
So Traderdrew is right the mackerel has very small scales although very smooth, like tuna. But there has been alot of discussion if these fish should be considered as scaled or skinned fish.
Fact is that these fish, mackerel and tuna cause alot of health problems especially when they are canned or smoked. Just check the PH reading after eating this kind of fish.I agree with all the arguments given, cold versus warm water fish including the mackerel, fish breeding ponds, and pollution. Thanks for the links Johnny.