Gas Fish

The Gas Fish is a common enemy found in the Ancient Abyss.

Description
The Gas Fish is a weird, pink and yellow fish with an inflated, round body that is filled with pores, which it uses to filtrate the plankton from the water that enters its body, similarly to sea sponges. It's large belly is expanded and filled with toxic and volatile gases, which it presumably uses to increase its buoyancy, and that makes the Gas Fish explode upon its death.

Behavior
The Gas Fish is passive and will not attack the Submarine and will barely move. What makes this a dangerous enemy, however, is the fact that the gases inside its belly are incredibly volatile, and touching or shooting the Gas Fish will cause it to explode, dealing damage to anything nearby and sometimes releasing clouds of toxins where it once was.

Trivia

 * The Gas Fish was inspired by pufferfishes and sea sponges.