Cook Islands’ Needlefishes

Gerald McCormack, CINHT

Illustration showing identifying features of the four needlefish species found in Cook Islands

The Cook Islands’ biodiversity database lists 650 species of marine bony-fishes. In looking at the distribution of fishes across the Pacific it is obvious that there must be at least another hundred to be recorded locally. The Trust is always interested in information on new and unusual records.

For the needlefish family the database lists four species: Keeled Needlefish (Miro Va‘a-roroa, Platybelone platyura), Houndfish or Crocodile Needlefish (‘Aku, Tylosurus crocodilus), Reef Needlefish (‘Aku, Strongylura incisa ) and the Flat Needlefish (Pāpā, Ablennes hians).

The Keel-jawed Needlefish has been recorded across the South Pacific, but not specifically in the Cook Islands. However, it is an off-shore species and therefore very unlikely to have been caught in Ngatangi‘ia harbour.

Many species of fish have distinctive features and are reasonably easily identified from photographs, but some require a more detailed analysis of specimens. In the illustration we show some of the more conspicuous features of the four species of needlefish positively identified in the Cook Islands.

Keeled Needlefish

Keeled Needlefish is the one commonly seen in the lagoon swimming with the half-beaks. They grow to about 40cm Total Length (TL). Their most distinctive feature is the long keels on each side of the tail-base. Local names include Miro Va‘a-roroa and Miromiro on Rarotonga, Akuaku and Kakukaku on the Makatea islands, and Miromiro on Aitutaki.

Crocodile Needlefish and Reef Needlefish

These two needlefish are very similar and share the name ‘Aku. The Crocodile Needlefish grows to about 130cm TL while the Reef Needlefish grows to about 100cm. Both have cylindrical bodies, lack distinctive colour markings, and have similar teeth as adults.

The most obvious separating feature is on the base of the tail – the Crocodile Needlefish has a conspicuous black keel on the sides while the Reef Needlefish has no keels. Another identifying feature is the Crocodile Needlefish’s tail which has a deep fork and a conspicuously long ventral lobe, while the Reef Needlefish has a blunt tail with the ventral lobe only slightly longer.

Both species are common near reefs and enter lagoons. The Crocodile Needlefish is known as Houndfish in America and Crocodile Longtom in Australia.

Flat Needlefish

The Flat Needlefish is easily recognised and is known as Pāpā on most islands, including Rarotonga. It has a deeper, flat-sided body with conspicuous black blotches on the sides of its body especially below the dorsal fin. It grows to about 130cm TL. It is an off-shore species and is not known to enter lagoons.

Injuries

The larger needlefishes can be attracted to the lights of night-fisherman and have been known to leave the water like a living javelin. There are a couple of known fatalities. In 1977 a boy was killed on Kaua‘i (Hawai‘i) and in 2007 a boy was killed in Vietnam.

What was the mystery fish (CINews 18/08) caught at Avana Wharf?  Without seeing the tail it could be either a Crocodile Needlefish or a Reef Needlefish. Local fishermen, who distinguish between these two species, might notice features of the fish or its behaviour that makes it more likely to have been one species rather than the other.