Years ago I lived as a college-student houseguest in a house with a cat with gas problems. Well, HE didn't think it was a problem, but the humans residing there did. It could well be a dietary thing; this was long enough ago that the kitty kibble people thought one sort of cat food essentially suited all, so we just sort of lived through his windy-ness. He lived a long and dignified life, so this problem really didn't affect him much at all; just those who shared his place of home. It probably IS a food ingredient; not necessarily fish but that and dairy are things you should try eliminating first. Food made from lamb with modest grains like rice may possibly help.