Within Ruiga's Water Release: Water Sky Convergence, Ruiga summons a shark inside the orb of water. The ninja fish can eat up to 1000 pounds of anything. However, it appears its only weakness is that it must be surrounded by water while it is summoned, which is why Ruiga encased it in a ball of water.
Ruiga used this against Naruto Uzumaki but only Chōji was caught in the bubble with the shark. Chōji managed to escape being eaten at first by holding the shark's mouth open. Chōji defeated the shark by sucking up all the water he surrounded by, causing the shark to be exposed to the air. Ruiga could not maintain the shark with a fresh supply of water from the ground, since he could not extract water out of the dry rock that surrounded him, thus resulting in the retreat of the shark.