Fish live in water, water pressure higher than at sea level is decuple, under such circumstances, the fish fat (help) to keep buoyant fish to work effectively. In order to keep buoyant, water density than water body by fish slightly smaller gelatinous material composition, slightly lighter than the water density, which makes it doesn't take much to easily from the bottom to the top. Lack of muscle to drop the fish is not really a problem, because it relies on the edible material before eating.
