Well, Keith doesn't know how it started.
The term big pig is usually put on a big round zoo creature of a fish that is revered, not despised.
I've heard it used on Bass too. Like big Striped Bass are referred to as 'Cows' in NE parts.
Personally, I think it does no harm, its just a pet name. I've used it. Don't see a problem.
Each to their own but a Big Wrasse in a small hole is like greased pig to land on light gear.
Me and Kev call small Bass sea rats and some people don't like that.
On the other hand, we treat our catch with 'respect'. Wrasse, Pout, Bass, all deserve to treated the same.
I even cut a dogfish free from a load of line the other day, and it must have been out the water for hours.
Now I know, people call those some horrible names, leave em to die needlessly etc.
So, sticks and stones and all that....
Each to their own.