Taxon of the Week #1: Gonostomatidae

I had intended for this to appear earlier in the week, but it's been a fairly busy one for me. Here's how this is going to work, barring accidents - every week I'll do an introduction to a (somewhat) randomly-chosen taxon. As this is my first entry, you can be sure I've selected something exciting, cutting-edge, mind-blowing, insert your choice of superlative adjective here - the Gonostomatidae or bristlemouths.

If the names not ringing any immediate bells, then shame on you. Bristlemouths are possibly the most abundant vertebrates in the world (or so every source I've looked at [e.g. Bond (1996), Craddock & Hartel (2002)] says, though I've yet to find an actual figure). They are mesopelagic or bathypelagic fish (or 'feesh' as they say here in Western Australia), mostly quite small (according to Craddock & Hartel [2002], some species mature at less than 20 mm) and, like oh so many mesopelagic fish, not overly attractive (see images at wikipedia). Gonostomatidae have an elongate body form with relatively big mouths (according to the afore-linked wikipedia page, the name 'bristlemouth' refers to the evenly-sized bristle-like teeth, a description that appears more true for some genera [Cycothone] than others [Gonostoma]). There are one or more rows of photophores along the length of the body - some like Triplophos have multiple rows almost covering the animal, while others such as Bonapartia have only a single row on the lower edge of the body, plus a few scattered over the head (Harold, 1999). They are micropredators of small crustaceans and such (Craddock & Hartel, 2002).

The Gonostomatidae belong to the order Stomiiformes, sometimes known as dragonfishes (some of the other members of the order reach a reasonable size, and you may have seen illustrations of them before - they're the elongate deep-sea fish with the mouths full of enormous teeth). As an aside, the intro for Stomiiformes in Collette & Klein-MacPhee (2002) refers to it as a 'very large group'. Only vertebrate workers would consider a few hundred species a 'very large group'. The Gonostomatidae itself includes seven or eight genera in two subfamilies, the Gonostomatinae (Gonostoma, Sigmops, Margrethia, Bonapartia, Cyclothone) and Diplophinae (Diplophos, Manducus, Triplophos).

Unlike many mesopelagic fish, bristlemouths do not appear to engage in daily vertical migrations (McClain et al., 2001). Their small size and deep-water habitat mean that, despite their abundance, they are rarely seen except by researchers.

REFERENCES

Bond, C. E. 1996. Biology of Fishes, 2nd ed. Saunders College Publishing.

Collette, B. B., & G. Klein-MacPhee (eds.) 2002. Bigelow and Schroeder's Fishes of the Gulf of Maine, 3rd ed. Smithsonian Institution Press: Washington.

Craddock, J. E., & K. E. Hartel. 2002. Bristlemouths. Family Gonostomatidae. In Bigelow and Schroeder's Fishes of the Gulf of Maine, 3rd ed (B. B. Collette & G. Klein-MacPhee, eds.) pp. 181-184. Smithsonian Institution Press: Washington.

Harold, A. S. 1999. Gonostomatidae: Bristlemouths. In Western Central Pacific Identification Guide for Fishery Purposes (K. Carpenter & V. H. Niem, eds.) pp. 1896-1899. FAO Species Identification and Data Programme vol. 3.

McClain, C. R., M. F. Fougerolle, M. A. Rex & J. Welch. 2001. MOCNESS estimates of the size and abundance of a pelagic gonostomatid fish Cyclothone pallida off the Bahamas. Journal of the Marine Biology Association of the United Kingdom 81: 869-871.