They tend to eat small creatures from the Benthic regions of the ocean such as crustaceans, shellfish, mollusks, and even algae and plankton. Some blennies can even venture out of the water thanks to their pectoral fins that act similarly to feet.
They swallow their prey whole, preferring bony fish. There have been instances where a washed up black swallower has been found to have fish almost four times bigger than it in its stomach.
They tend to grow to around 7 to 8 inches long, with the largest length known currently being 9.8 inches. This is impressive when considering they can swallow fish that are 34 inches! In terms of appearance, there is nothing particularly distinctive about it.
It is rather plain in color. What makes it so weird and wonderful is the amount that they can swallow. Their lower jaw is bigger than the upper part of the jaw to help them swallow these bigger animals.
They also have the added bonus of very sharp canine like teeth at the front. Their teeth fit together neatly, interlocking when the jaw is closed. This traps their prey, allowing them to swallow it.