Grey knifefish

Taxobox
name = Grey knifefish


image_caption = Drawing by Dr Tony Ayling
regnum = Animalia
phylum = Chordata
classis = Actinopterygii
ordo = Perciformes
familia = Kyphosidae
genus = "Bathystethus"
species = "B. cultratus"
binomial = "Bathystethus cultratus"
binomial_authority = (Forster, 1801)

The grey knifefish, "Bathystethus cultratus", is a sea chub of the genus "Bathystethus", found around the offshore islands of the east coast of Northland on the North Island of New Zealand, in surface waters. Its length is between 15 and 30 cm.

The grey knifefish is a moderate sized pelagic fish with a small head and distinctive knife-shaped body. The back profile is relatively straight but the belly is deeply rounded and sharply tapered in section. Minute pelvic fins fit into a groove on the belly. Both dorsal and anal fins are low and able to fold out of sight in grooves, leaving the body profile smooth and lowering water resistance.

Blue-grey on the back and silver on the flanks and belly, this fish is conspicuously countershaded. There are faint lines of blue-grey spots along each scale row on the flanks.

A plankton picking species completely lacking teeth, the grey knifefish lives in the surface layers swimming rapidly and continuously.

References

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* Tony Ayling & Geoffrey Cox, "Collins Guide to the Sea Fishes of New Zealand", (William Collins Publishers Ltd, Auckland, New Zealand 1982) ISBN 0-00-216987-8