A collaborative team of oceanographers and marine biologists has unearthed evidence suggesting that certain deep-sea species of anglerfish spend their entire lives swimming upside down. The findings, detailed in a paper published in the Journal of Fish Biology, emerged from a meticulous study of video footage captured by remotely operated undersea vehicles.
While previous research had established that some anglerfish species possess natural lures dangling from their faces—a feature employed to attract bacteria, subsequently luring prey—this recent study delves into the unexpected behaviour of these deep-sea dwellers. Contrary to prior assumptions, the research unveils that these fish, characterized by their large size (up to 45 centimetres) and remarkably long lures (up to four times their body length), consistently navigate their surroundings while inverted.
The research team stumbled upon this revelation while analysing video footage obtained by a remotely operated vehicle (ROV) conducting research in the Izu-Ogasawara Trench off Japan. A large anglerfish was observed swimming upside down, challenging the conventional understanding of how these creatures utilize their lengthy lures. Further investigation, involving video data from multiple ROVs, confirmed that anglerfish swimming in an inverted position was a pervasive and constant behaviour rather than an occasional anomaly.
The scientists propose that this peculiar behaviour likely evolved as a practical adaptation, enabling the fish to more effectively manipulate their extended lures in the inverted position. The lure, hanging from the top lip, is closest to the seabed when the fish is upside down, providing a strategic advantage. This discovery underscores the significance of ROV research in unravelling the mysteries of deep-sea life and highlights the continuous evolution of our understanding of these enigmatic creatures.
