Was planning to grill whole but gutted mackeral. I'm not sure its totally gutted. Health,taste -wise how clean should the cavity be? I picture us eating the crispy skin and flesh and not getting close to inner cavity. Thanks
The cavity will be quite clean after you gut the fish properly and rinse it out. Remember that the Japanese eat mackerel raw (they call the fish "saba").
Gutting boned fish is mostly the same, regardless of the species.
I suggest you go to YouTube and just search for "gutting fish." My guess is that there are tens of thousands of videos about this and some of them are well done.
Here's one of a guy gutting a trout: https://www.youtube.com...
Despite the fact that it's a trout and not a mackerel isn't all that important since the technique is the same.
Agree with cv but I find that instead of a knife, you might try a pair of sharp kitchen shears. Makes my life easier!