This is one alluring fish.

The anglerfish is one of the most famous deep-sea animals. This bulbous beast has a “fishing pole” projecting from its head. The first ray of its dorsal fin is modified into a filament (called an illicium) with a sac of glowing bacteria at the tip (called an esca). Each species has its own unique rod and lure—some have simple lures, some have elaborate ones, and some even have multiple lures. In the vast and expansive waters of the midnight zone, meals are few and far between. Instead of expending energy to chase food, a hungry anglerfish merely sets out its bioluminescent bait and waits. The glowing tip entices small fishes and crustaceans to come closer, then the anglerfish’s massive mouth and sharp teeth snap shut for a meal.

Food isn’t the only thing that’s scarce in the midnight zone. Mates can be hard to find too, so some anglerfishes have a unique strategy for reproduction. The blobby, softball-sized anglerfishes spotted by MBARI’s remotely operated vehicles (ROVs) are females. The males are dwarfs, growing just a few centimeters long. The tiny males have a strong sense of smell and follow pheromones to find females. In some (but not all) species, the males are parasitic, so when they encounter a mate, they permanently attach themselves to her body.

Deep-sea anglers may be most recognizable, but there are more than 200 anglerfish species in the order Lophiiformes. They come in all sorts of shapes and sizes, and occupy a variety of habitats. Sea toads (family Chaunacidae) and batfishes (family Ogcocephalidae) live on the deep seafloor, but some anglerfishes live in shallow water. Frogfishes (family Antennariidae) have vibrant colors to camouflage among the corals on tropical reefs, while speckled coloration helps goosefishes (family Lophiidae) blend into the sandy seafloor on the continental shelf. Just like their deep-sea kin, these anglers are ambush predators. But seafloor anglers don’t use luminescence to fish for food. Instead, they flick a frilly, decorative lure to draw in potential prey.

We still have a lot to learn about deep-sea anglerfishes. MBARI’s ROVs only rarely encounter these curious creatures. Each observation sheds new light on these mysterious residents of the midnight zone, but inevitably raises new questions too.