Three and a bit centimeters, brown, and it lives in this sea and nowhere else.
What separates it from its close relatives is a single dark blotch on the side of the body and its position relative to the lateral line. That is the whole diagnosis. Change the light, photograph it at a slight angle, catch it as a juvenile, and the difference is gone.
This is the ordinary condition of small fish taxonomy and it is worth being honest about. A large part of the catalogue rests on characters at this scale, and where a group is small, brown, nocturnal and cryptic, the species boundaries are drawn by a handful of specialists working with preserved material, and they move. Fish that were one species become three; three become one.
So a record of this animal from a photograph should be read as probable rather than certain, and the same caution applies to a good many small cardinalfish, gobies and blennies on this site.
It is rare in the records, which for a three-centimeter nocturnal fish in rubble means very little indeed.
The species. Apogonichthyoides heptastygma (Cuvier 1828) - heptá (ἑπτά). ETYFish
- just over three centimeters, brown, deep-bodied
- single dark blotch on the side, below the middle of the body
- dark bar through the eye
- up to 3.3 cm
