(Goode & T. H. Bean, 1886)
Tripod fish, Bathypterois grallator, are a deep-sea benthic fish in the Ipnopidae family found at lower latitudes. They are now relatively well known from photographs and submersible observations. They seem to prefer to perch on the ooze using much elongated fin rays in their tails and two pelvic fins in order to stand, facing upstream with the pectoral fins turned forward so that the outthrust projecting fin rays resemble multiple antennae, and are indeed used as tactile organs. Bathypterois grallator are hermaphroditic. There are at least eighteen species in the genus Bathypterois, several of which have similar appearance and behavior to Bathypterois grallator. Like a lot of deep sea creatures, they tend to grow larger than most shallow-water fish. This benthic fish grows to be 3 ft (0.91 m) long and 4 ft (1.2 m) tall (counting their tripod-like fins).
The tripod fish has long, bony rays that stick out below its tail fin and both pectoral (chest) fins. Even though the fish’s body is 36 cm (14 in), its fins can be more than 1 m (3 ft 3 in). Most of the time, the tripod fish stands on its three fins on the bottom of the ocean. Even though the fins are presumably quite stiff, researchers have been successful in surprising the fish into swimming, and then the fins seem flexible. It spends much of its adult life standing on the sea floor hunting its food.
Bathypterois grallator has been found relatively widely in the Atlantic, Pacific and Indian oceans from a northern latitude of the 40th parallel north to a southern latitude of the 40th parallel south. It is a wide ranging eurybathic fish and it is found from 878 to 4,720 m (2,881 to 15,490 ft) deep. Along with the giant squid, deep-sea anglerfish and black swallower, it is one of the permanent residents found in the Abyssal zone and was directly observed on the historic voyage of the bathyscaphe Trieste to the Mariana Trench.
The tripod fish uses tactile and mechanosensory cues to identify food; the tripod fish apparently does not have special visual adaptations to help them find food in their low-light environment. When the fish is perched with its long rays on the ocean floor, it can get dinner without even seeing its meal. The tripod fish’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 in order to stand, facing upstream into the current to ambush with the pectoral fins turned forward so that 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. The fish faces into the current, waiting for prey to drift by.
Each individual has male and female reproductive organs. If two tripod fish happen to meet, they mate. However, if a tripod fish does not find a partner, it makes both sperm and eggs to produce offspring by itself.
Related and similar species
There are at least eighteen species included in the genus Bathypterois. Similar species are often observed in the same areas. A 2001 report included observations of Bathypterois dubius as far as 50 degrees north latitude in the Bay of Biscay.
There is a striking parallel between some icefishes and the tripod fishes. Marshall drew attention to the similarities between tripod fish and one of the icefish, Pagetopsis, which was described by Robilliard and Dayton as perching on a sponge. The stance of Chionodraco is an even more striking parallel. Both icefishes and the tripod fish use a similar strategy of sitting motionless above the substrate with the attendant benefits that motionlessness brings to a nonvisual, particularly mechanosensory, function.
The tripod fish 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. The family to which both fish belong, Inopidae, is called the family of tripod fishes or spiderfishes interchangeably.
- Jones, AT; KJ Sulak (1990). "First Central Pacific Plate and Hawaiian Record of the Deep-sea Tripod Fish Bathypterois grallator (Pisces: Chlorophthalmidae)" (PDF). Pacific Science 44 (3): 254–7.
- Hoar, W.S.; Randall, D.J., Conte, F.P. (1997). Deep-Sea Fishes. Fish Physiology 16. Academic Press. p. 344. ISBN 0-12-350440-6.
- Hyde, N. Deep Sea Extremes. Crabtree Publishing Company, 2009. ISBN 0-7787-4501-5, p. 16; Winner, C. Life on the Edge. Lerner Publications, 2006. ISBN 0-8225-2499-6, p. 18; Gage, J.D., Tyler, P. A. Deep-sea biology: a natural history of organisms at the deep-sea floor. Cambridge University Press. 1992. ISBN 0-521-33665-1, p. 86
- Winner, C. Life on the Edge. Lerner Publications, 2006. ISBN 0-8225-2499-6, p. 18
- Trenkel VM, et al. First results of a quantitative study of deep-sea fish on the continental slope of the Bay of Biscay: visual observations and trawling. ICES CM 2001/L:18