For deep-sea creatures where food is scarce and precious, wasting even a small amount can be disastrous. The black swallower has evolved an extreme solution to this scarcity: a massive appetite relative to its size. Although rarely observed in nature, a specimen was recently filmed by the Schmidt Ocean Institute during dives in the waters of Trinidad and Tobago, providing a unique glimpse into its feeding habits.
These small fish, which rarely exceed 20 centimeters in length, possess an incredibly extensible stomach capable of swallowing prey up to twice their own length and ten times their bulk. When fully distended, the skin stretches so significantly that it becomes nearly transparent, allowing observers to see the animal's internal organs.
However, this voracious nature can lead to overindulgence. There are documented cases where a black swallower consumes prey so large that it cannot digest it before decomposition begins. The resulting gas formation causes the fish to rise to the surface, which is how many specimens have been encountered. Capturing them in their natural deep-sea environment is far more difficult, making the recent video an exceptional record.
Despite the clear footage, the specific contents of the meal consumed by this particular fish remain a mystery. Diva Amon, the expedition leader, noted that without an underwater CT scanner, it is impossible to know exactly what was eaten. Generally, these fish feed on other bony fish and are believed to swallow prey tail-first using hooked teeth that point backward. While this hunting strategy is a plausible hypothesis, no black swallower has yet been observed actively hunting, leaving the behavior unconfirmed.
Sources: Focus.it.