BLENNY · päo`o
Istiblennius zebra (Vaillant and Sauvage, 1875)
(JUMPING JACK, ROCKSKIPPER)
Anyone who pokes about the rocky seashore
is familiar with Zebra Blennies. They live in pools at or above the
high tide line, generally along turbulent shores where basalt rock
predominates. A small pool will sometimes support dozens of blennies,
especially if there is ample shelter in the form of large boulders
under which they can retreat. Their bodies vary from smart blue-black
to charcoal or brownish gray with indistinct bars (hence the name).
They become mottled when feeding in shallow water or when alarmed.
Adults have a row of tiny bright blue spots under the eye. A crest
and two tentacles (longer in males) adorn the head, but collapse entirely
when out of the water. Zebra Blennies feed almost entirely on organic
detritus that accumulates on the rocky sides and bottoms of their
pools. They adapt well to the aquarium and make fun, alert pets that
are unusually tolerant of temperature and salinity changes. If you
keep one or more of these fish, be sure their tank is well covered.
They grow to about 7 in. and are endemic to the Hawaiian Islands (but
apparently absent from the northwestern atolls, which lack basalt
shores). All photos were taken at Makapu`u Point, O`ahu.
Blennies fish swim with lateral undulations like little eels, their
pectoral fins folded back along their sides. With the same motion,
they can wriggle almost out of the water to bask in the sun, sometimes
sprawling all over each other. They can spot a potential predator
as much as 50 ft. away, and if alarmed can leap, slither and skip
a surprising distance over the rocks, somehow knowing in advance the
location of the next pool. They can even leap while swimming, sometimes
2 ft. above the surface! It is possible that they are evolving toward
an amphibious existence.
Spawning occurs throughout the year
but probably reaches a peak in spring and early summer. Large territorial
males develop yellowish tan cheek patches that brighten to yellowish
white when they chase intruders. The cheek patches fade when they
leave their territories. Smaller males and females are not territorial.
Typically, a male prepares a nest in a crevice then performs vertical
loops to attract a female. The female cements up to 10,000 eggs to
the crevice walls. The male fertilizes them then guards them until
hatching (about two weeks). The larvae go to sea for an unknown period
of time returning to pools when they are about 1/2 in. long.