News / Species Spotlight / Tuamotu or Zebrastripe Hawkfish (Paracirrhites nisus) (10/03/18)

Tuamotu or Zebrastripe Hawkfish (Paracirrhites nisus)

Species Spotlight -Tuamotu or Zebrastripe Hawkfish (Paracirrhites nisus)
Lurking within the hawkfish genus Paracirrhites is one of the more intriguing mysteries among Indo-Pacific reef fishes. This group is small, with just six described species, but is well-represented in aquarium exports by the widespread Arceye Hawkfish (P. arcatus). Youll also find a couple larger examples, the Freckled Hawkfish (P. forsteri) and the Whitespot Hawkfish (P. hemistictus), neither of which is terribly popular among aquarists owing to their size and temperment.

But the rarest and most interesting of the lot are a trio of nearly indistinguishable species found only in the isolated Polynesian islands of the Central Pacific. But indistinguishable is a relative term here, as the three are easily told apart by their color patterns. Rather, its in their morphology that these poorly understood fishes are rendered identical.

Unquestionably the most beautiful and highly sought after of these is the Yellow Hawkfish (P. xanthus), which is, true to its name, bright yellow (and not to be confused with the distantly related Golden Hawkfish Cirrhitichthys aureus). Records for this one occur widely, from the Phoenix and Line Islands to the southernmost portions of French Polynesia.

Much rarer is the Bicolor Hawkfish (P. bicolor), known from just a handful of specimens in the Tuamotu Islands of French Polynesia. This fish is darkly colored, save for the yellowish rear third of the body and caudal fin. And then theres P. nisus, sometimes referred to as the Zebrastripe Hawkfish, which has records that indicate a similar distribution as P. xanthus, though it appears to be generally less common.

But, oddly enough, these three may actually just be one variable species. In captivity, it has been noted that the yellow P. xanthus can transition to a zebra-striped P. nisus, and this has also been noted in reverse, with nisus turning into xanthus. A recent specimen at Quality Marine appeared intermediate in coloration between the dark P. bicolor and the striped P. nisus, but, who knows, maybe itll turn yellow too.

The mystery here is why these three distinct colorations exist. Is it related to the sex of the individual? Cirrhitids are protogynous hermaphrodites, so perhaps one of these species is a male and another is a female. The change from one form to the other is reported to take place in a matter of days or weeks, which is what one might expect from a transitioning specimen. Or perhaps this has something to do with diet? This has been implicated as a possibility for some of the aberrantly colored angelfishes and surgeonfishes and triggerfishes that enter the aquarium trade, as these sometimes revert to a normal coloration quickly once taken from the wild.

Fully grown, P. xanthus/nisus/bicolor are on the smaller side for this genus, measuring in at around 7 inches. At this size, they are more than capable of consuming smaller crustaceans and fishes, so care should be taken when choosing tankmates. They are, however, completely coral safe, aside from their predilection for resting upon them. As hermaphrodites, it is possible to keep them in pairs in an aquarium, though this is best done by acquiring two small individuals and letting them work out their living arrangement. Larger specimens are apt to fight. They are also quite fine on their lonesome.

Theres still much we have to learn about this curious genus of hawkfish. Every species shows some amount of variability in its coloration, with dark morphs or striped morphs, but its only in the Polynesian P. xanthus that we find a yellow one. Aquarists have an opportunity to directly contribute to our understanding here by documenting their own specimens and any changes that take place.