Scientists have used an underwater robot to study a species of fish which lives at depths of 350m in the cold waters off Scotland.
Although scientists knew that the Monkfish, Lophius piscatorius, used its modified dorsal fin as a lure to catch other fishes, they'd not had an opportunity to study the feeding behaviour of the species in the oceans in detail, because it lives in such deep, dark waters.
A team of scientists from Southampton University, the University of Aberdeen and the North Atlantic Fisheries College used a remotely operated vehicle (ROV) equipped with a camera and special lighting to monitor the behaviour of the species and managed to capture footage of the fish feeding and "walking" along the sea bed. Their findings have recently been published in the Journal of Fish Biology.
The footage showed the Monkfish using its pectoral and pelvic fins to create a depression in the bottom substrate which allowed the fish to partially bury itself, effectively making it invisible to other fishes.
Once the fish was settled into its hidey hole, it simply sat and waited for prey fish to swim past, decreasing its movements by relaxing the dorsal fin and breathing more shallowly at about one gulp every 34 seconds.
The dorsal ray of the Monkfish is equipped with a fleshy lure (called an illicia) that the fish wiggles about to attract the attention of smaller prey fish, which it then engulfs in its capacious mouth.
The Monkfish was able to detect the presence of prey fish swimming as much as 5m away and reduced its breathing rate to just once every 65 seconds and raised its dorsal fin ray to attract the passing fish.
The ROV, which was lowered 350m to the sea floor in the waters off the Schielhallion oil fields, west of Scotland's Shetland Islands, also managed to capture rare footage of the "walking" behaviour of this species, whereby the fish uses its stumpy pectoral fins to pull itself along the sea bed.
For more details see: C. H. Laurenson, I. R. Hudson, D. O. B. Jones and I. G. Priede (2004) - Deep water observations of Lophius piscatorius in the north-eastern Atlantic Ocean by means of a remotely operated vehicle. Journal of Fish Biology, Volume 65: Issue 4.