Spiderfishes, Bathypterois spp

Introduction

Very little is known about the spiderfishes. They are some of the world's deepest living fishes. Some species use their very long pelvic and caudal fin rays to prop themselves up off the bottom, hence the common name, Tripod Fish.

Identification

Adult spiderfishes are slender fishes with large mouths and extremely small eyes. They have minute, needle-shaped teeth. Their fins lack spines and the dorsal fin is located foward of the anal fin. Usually, there is an adapose fin. Colouration is variable from brown or blackish to white. Fishes in the genus Bathypterois have elongated pectoral, pelvic and/or caudal rays.

The spiderfish genera Bathymicrops, Bathypterois, Bathytyphlops, Discoverichthys and Ipnops are currently recognised. Seven species of the spiderfish family Ipnopidae are recorded from Australian waters.

Habitat

Spiderfishes occur in continental slope and abyssal waters of all oceans. They are some of the world's deepest living fishes, living at depths ranging from around 1000 m to over 6000 m. They occur in areas where the seabed is made up of ooze or very fine sand. Larvae are sometimes encountered in shallow water.

It is a common strategy for the larvae of deepsea fishes to live in surface waters and descend to the depths as they mature. This is known as an ontogenetic vertical migration. This allows them to feed in comparatively prey-rich waters.The images show just such a larva, of the genus Bathypterois photographed at a depth of 5 m by Dan Dickinson on a night dive.

Distribution

Atlantic, Pacific and Indian Oceans

The map below shows the Australian distribution of the species based on public sightings and specimens in Australian Museums. Source: Atlas of Living Australia.

Other behaviours and adaptations

Much like cavefishes, it is thought that the eyes of spiderfishes are reduced because of the general lack of light at the great depths where these fishes live. Some species of spiderfishes are capable of splaying the elongate pelvic and anal fins allowing them to rest, tripod-like on the bottom, with the body raised above the soft mud. The elongate pectoral fins have an 'elaborate nerve supply'. These fins are held up and out to the side of the body and are used to detect water movement and to trap and direct towards the mouth the small crustaceans on which it feeds.

References

1. Banister, K. & A. Campbell. 1985. The Encyclopaedia of Underwater Life. George Allen and Unvin. Pp. 287.
2. Batson, P. 2003. Deep New Zealand. Blue water, black abyss. Canterbury University Press. Pp. 240.
3. Hoese, D.F., Bray, D.J., Paxton, J.R. & G.R. Allen. 2006. Fishes. In Beesley, P.L. & A. Wells. (eds) Zoological Catalogue of Australia. Volume 35. ABRS & CSIRO Publishing: Australia. parts 1-3, pages 1-2178.
4. Nelson, J.S. 2006. Fishes of the World. 4th Edition. John Wiley and Sons, Inc. Pp. 601
5. Paxton, J.R & V.H. Niem. 1999. Carpenter, K.E. & V.H. Niem (ed) pp 19239-1924 in The Living Marine Resources of the Western Central Pacific. Vol. 3. FAO species identification guide for Fishery purposes. FAO.