Mountain Fish

Warning spoilers through Blood in the Water.

Mountain Fish (also known as Island Fish and Leviathans) are colossal marine creature, dangerous for ocean-going ships.

Description:
Mountain Fish can grow over 300 meters long, and have a mass of the tens of thousands of tons (probably even hundreds of thousands-to-million), prey on Gri'kaka and are fully capable of devouring Grik Indiamen. Their taxonomy is completely unknown.

Biology:
The biology of Mountain Fish isare unknown, but presumably have almost nothing similar with any know species or even classes of animals. Their immensive size is thermodynamically impossible for any known Earth animals, which led to the suggestion that they originated from some parallel world where the fauna is radically different from ours.

It is known that they are generally plankton-filters (like baleen whales), but also capable of devouring larger prey, like gri-kakkas. This is the main reason why they are dangerous to ships, which they sometimes consider as their prey. Generally, the mountain fish aren't very agressive and can be driven off relatively easily, but an injured or enraged - or even just curious one - is a mortal threat to any vessel.

The mountain fish are capable of moving relatively quickly (at least 10-15 knots), and can dive at immensive depths. Strangely, they are quite susceptible to loud noises; Imperial experience shows that the underwater explosions or gunfire could disorient or even frighten away the mountain fish. It was later stated that they didn't like sonar pulses and tended to keep away from the sonar-equipped ships.

Natural habitat:
Known to live in Indian and Pacific Oceans. At this time it is unknown if they inhabit the Atlantic Ocean. Tend to stay along coasts and away from central ocean regions.