It grazes a moving line. The most productive strip on a rocky shore is the band that has just been uncovered or just been covered by the tide: algae grows fastest there, and it is thin, soft, and not yet colonized by anything tough. A fish that can work that strip has the best food on the shore, and the strip moves twice a day.
So this blenny moves with it. As the water drops it follows the edge down, staying in a few centimeters of wash, and as the tide returns it works its way back up, grazing the film off rock that has been dry for hours. In the gap between it sits in a pool or a crevice and waits.
That means living in the worst physical conditions on the reef. The shallowest water is the hottest, the saltiest, the most oxygen-poor at midday, and it is where the surge does its work. Almost nothing else competes there, which is the entire point.
It is a barred brown fish with fine orange lines across the head, up to nine centimeters, and finding one usually means standing in ankle-deep water and watching a rock until it moves.
The genus. Istiblennius Whitley 1943 - istios (sail) + blennius (blenny). ETYFish
The species. Istiblennius rivulatus (Rüppell 1830) - rivulated. ETYFish
- barred brown body with fine orange lines on the head
- blunt head with tentacles over the eyes
- in the shallowest water, often in a few centimeters
- up to 9 cm
Why it's threatened
There are no major threats known for this species.
Threat classification from the IUCN Red List.
