The black spot at the base of the tail is worth understanding, because half the cardinalfish on this reef have one and it is doing real work.
A spot at the wrong end of a fish is a deflection mark. A predator striking at what it takes to be the head commits to the tail instead, and the fish accelerates away from the strike rather than into it. It is the same trick as the false eyespots on butterflyfish, and it works because an attack has to be aimed somewhere and the aiming is done fast on a small number of cues.
For a diver it is also the identification. Cardinalfish are a genus of near-identical silvery fish with big eyes, and the differences that matter are exactly this granular: whether the tail spot is centered or high, whether the stripe runs through the eye or stops at it, whether it reaches the tail. This one has a fine stripe from snout to tail and the spot placed on the upper half of the tail base.
It is a common fish of ledges and cave mouths, out at night over the reef for plankton.
The genus. Pristiapogon Klunzinger 1870 - pristis (sawyer). ETYFish
- silvery body with a fine dark stripe running from the snout through the eye to the tail
- distinct black spot on the tail base, on the upper half rather than centered
- large eye and a blunt snout
- up to 11 cm
Why it's threatened
This species is a component of the marine ornamental trade, but the potential impact is unknown.
Threat classification from the IUCN Red List.
