Bathypterois grallator

The tripod fish or tripod spiderfish, Bathypterois grallator, is a deep-sea benthic fish in the family Ipnopidae found at lower latitudes. It is now an iconic deep-sea fish, being observed and photographed by submersibles, using elongate fin rays of the tail and pelvic fins to stand on the ooze. B. grallator is hermaphroditic.

Tripodfish
Illustration
Bathypterois sp., which may be of this species, off Eleuthera
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Aulopiformes
Family:	Ipnopidae
Genus:	Bathypterois
Species:	B. grallator
Binomial name
Bathypterois grallator (Goode & T. H. Bean, 1886)

Characteristics

The tripodfish has long, bony rays that extend from the lower lobe of its tail fin and both pelvic fins. B. grallator is the largest member of its genus, commonly exceeding a standard length of 30 cm (12 in)^[1] and reaching total lengths of up to 43.4 cm (17.1 in) long.^[2] The tripodfish is often seen in its distinctive stance; standing on its three fin extensions (the namesake tripod) on the seabed, facing upstream with the antennae-like pectoral fin rays extended out, waiting for food.^[3] Even though the fins are presumably quite stiff to be able to support its weight, observations of swimming fish shows that their fins seem flexible; it is suggested that fluids are pumped into these fins when the fish is 'standing' to make them more rigid.^[4]

The tripodfish is closely related to the spider fish Bathypterois longifilis, which is similar in appearances and habits but is smaller and has much shorter fin extensions. They are often found standing very close to each other.^[5]

Habitat

Bathypterois grallator has been found relatively widely in the Atlantic, Pacific, and Indian oceans from 40°N to 40°S. It is a wide-ranging eurybathic fish found from 878 to 4,720 m (2,881 to 15,486 ft) deep.^[3]

Biology

Feeding

The tripodfish faces into the current, waiting for prey to drift by.^[6] The fish uses tactile and mechanosensory cues to identify food; it apparently does not have special visual adaptations to help it find food in the low-light environment. When the fish is perched with its long rays on the ocean floor, it can get food without even seeing it. The tripodfish's mouth ends up at just the right height to catch shrimp, tiny fish, and small crustaceans swimming by. They seem to prefer to perch on the mud using much elongated fin rays in their tails and two pelvic fins to stand, facing upstream into the current to ambush with the pectoral fins turned forward so the outthrust projecting fins resemble multiple antennae. The fish senses objects in the water with its front fins. These fins act like hands. Once they feel prey and realize it is edible, the fins knock the food into the fish's mouth.^[5][tone] Recorded prey includes copepods and other planktonic crustaceans, such as larvae.^[2]

Reproduction

Each individual has male and female reproductive organs. If two tripodfish happen to meet, they mate. However, if a tripodfish does not find a partner, it makes both sperm and eggs to produce offspring by itself; thus, it is a true hermaphrodite.^[7]