Succulence from Gelatin and Fat

Both gelatin and fat can contribute an impression of moistness to fish texture. Fish with little collagen—trout, bass—seem drier when cooked than those with more—halibut, shark. Because the motion for steady swimming comes mostly from the back end of the fish, the tail region contains more connective tissue than the head end, and seems more succulent. Red muscle fibers are thinner than white fibers and require more connective tissue to join them with each other, so dark meat has a noticeably finer, more gelatinous texture.