Description

Also known as Coppery Siphonfish, Crown-of-Thorns Cardinalfish, Nurseryfish, Sea Urchin Cardinalfish, Tube Siphonfish, Tubifer Cardinalfish, Two-spot Cardinalfish, Two-spot Urchin Cardinalfish, Urchin Cardinal, Urchin Cardinalfish.

Found in small schools usually amongst the spines of either sea urchins or the crown-of-thorns sea star, over outer lagoons and sheltered coastal reefs.
They feed on small invertebrates and zooplankton.
These cardinalfish can rapidly change colour from stripes to dark brown with a couple of white spots.
Length - 7cm
Depth - 0-100m
Widespread Indo-West Pacific

Usually among the spines of Spiny Sea Urchin - Diadema setosum http://www.whatsthatfish.com/fish/spiny-sea-urchin/332
Also amongst the spines of the Crown-of-Thorns Sea Star - Acanthaster planci
http://www.whatsthatfish.com/fish/crownofthorns-sea-star/323

Males incubate their eggs inside their mouths, as the egg masses increase in size they can be found with wide open mouths where they shift the eggs around to aerate the egg masses. Ref: https://www.fishbase.se/summary/Siphamia-tubifer.html