These animals are foreign apex predators of lakes within forests, and unexpectedly, were capable of adapting to the habitat of the Abyss. However, they were unable to compete with other predators of the 2nd layer and were periodically driven to the innermost region of the Inverted Forest where the force field is thin.
While they were driven back, the evolutionary period they've spent after generations within the abyss made them much larger than they originally were, and they're capable of swallowing humans whole, so approaching one too closely is quite dangerous. They're omnivorous so they don't necessarily rely on hunting only.
They have a thick layer of fat and skin, so they're usually not fit for consumption. However, with proper care and preparation, one would be enough to feed about 200 people.