As the sun sets and most of the reef’s inhabitants make their way home for the night, groups of reef-dwelling fish are just beginning their day. Nocturnal fish make scuba diving at night a fascinating experience, as these fish species are mostly hidden during the day. These fish tend to have more enormous eyes, are more solitary, slow-moving, and are often red or brown, making them indistinguishable as the light levels drop. Most nocturnal fish are carnivorous and predatory, preying on other reef fish or invertebrates. Here are some of the more commonly sighted creatures of the night you may spot in the glare of your dive light while reef diving.
Cardinalfish
With its brilliant red to light pink colors, the Cardinal fish can be easily found in shallow reefs of the Indo-Pacific at night. This fish has a large head and eyes, a comparatively more petite body, and an angled mouth with a protruding lower jaw. The Cardinalfish ranges in size from between 2- 8 inches (5-20 cm) in length, and there are known to be around 200 species of this fish.
Big Eyes
Bigeyes are carnivorous nocturnal fish that hide by daylight and come out at night. Most big eyes are bright red but can also be found in paler shades and can grow to a length of about 41 cm (16 inches). Bigeyes are found in almost all of the world’s oceans in over 18 different species and are often found in large numbers hidden in shipwrecks or caverns during the day. Bigeyes have a peculiar way of swimming; they hang motionless in the water to observe the slightest movement around themselves. Then, they suddenly dart forward to intercept their prey.
Squirrelfish & Soldierfish
Squirrelfish & Soldierfish are perhaps one of the most easily recognized nocturnal reef fish. Known to have a pinkish-red color and huge eyes, these fish are almost entirely nocturnal and remain hidden throughout the day. The squirrelfish and Soldierfish are members of the Holocentridae family of fish. Around 80 species inhabit most of the world’s oceans. Squirrelfish have a poisonous barb near their gills that can give painful stings if touched. Squirrelfish & Soldierfish are known to range in length from 5-50 cm or (6-20 in).
Porcupine Fish
One of the more common night diving sights is Porcupinefish. Like all boxfish, they are endearing and have large eyes and rounded balloon-like bodies. These slow-moving fish swim awkwardly in the water using their two fins near their tails. While Porcupinefish are closely related to pufferfish, porcupinefish have more prominent spines covering their body, almost resembling a porcupine. Like pufferfish, they, too, inflate to nearly twice their standard size when threatened and possess a neurotoxin a thousand times more potent than cyanide if eaten. These nocturnal fish choose to feed at night when their favorite food, mollusks, is most active.
Scorpionfish
Scorpionfish are nocturnal hunters that are often difficult to spot owing to their excellent camouflage. This fish hunts by sitting still and waiting until a victim comes close to its mouth. Then it lunges forward while opening its enormous mouth, sucking the victim inside. Coarse scales cover the body of the Scorpionfish and may contain spines that contain a potent neurotoxin lethal to humans.
Snappers
Snappers can be either nocturnal or diurnal (daytime) fish, depending on their species. With over 100 species of snapper, spotting a group of them on a night dive is relatively easy. Several species of snapper feed on crustaceans and fish and hunt voraciously.
Moray Eels
Moray eels which tend to remain in the nooks and crevices during the day, with only their vicious heads poking out, are more at ease at night and tend to leave their hiding places to swim about scavenging on tiny fish and crustaceans. One of the best opportunities for a scuba diver to see an eel’s length is often on a night dive.
Octopus
While you can spot octopuses on the reef during the daytime, several species become more active at night. These swim about the reef, hunting their favorite invertebrates, favoring the darkness.
Invertebrates
Many invertebrates, including lobsters, shrimp, crabs, and other crustaceans, mollusks, polychaete worms, and starfish, scavenge the sea beds at night. Starfish, especially those that remain tucked away during the day, appear everywhere at night. Many shrimp migrate to the surface to feed on plankton, and the sea beds often crawl with lobsters and crabs that brave the open areas under the cover of darkness.
