New Research Illuminates Life History of Kala, or Bluespine Unicornfish

Studies are underway to learn more about the life history of the bluespine unicornfish ("kala", Naso unicornis), a shallow-water reef fish found in Hawaii and much of the tropical Indo-Pacific. The species is important in artisanal and commercial fisheries throughout the Pacific Islands.

Kala, or bluespine unicornfish (Naso unicornis). Photo courtesy of Richard Field, FishBase.
Kala, or bluespine unicornfish (Naso unicornis). Photo courtesy of Richard Field, FishBase.

Drs. Ed DeMartini and Allen Andrews of the Pacific Islands Fisheries Science Center have been conducting research on kala in collaboration with Dr. Jeff Eble, a post-doctoral fellow at the University of Arizona. While completing his doctoral research on surgeonfish genetics at the University of Hawaii's Hawaii Institute of Marine Biology, Eble started a side project on life history of kala in waters around Oahu in the main Hawaiian Islands, funded by the State of Hawaii. That project produced a report on kala body size-at-age and size-at-sexual maturity, based on 150 sample fish collected primarily during a 4-month period, March-June 2009. Based on visual counts of annuli in kala otolith ("ear stone") cross-sections, Eble's study suggested maximum ages of more than 50 yr for this species in Oahu waters. Andrews arranged for bomb-carbon dating of 4 of the putatively oldest fish in Eble's sample and corroborated ages exceeding 50 yr for the Oahu kala. In spring 2011, DeMartini and Andrews began a project to study the age-growth, maturation, and longevity of kala, building on Eble's specimens and analyses. Because of its comprehensive nature, the new study represents the first of its kind for shallow-water reef fishes in Hawaii.

DeMartini and Andrews have begun analyzing an additional 250 kala specimens collected from Hawaii fish markets during June 2011-March 2012. On Oahu, kala spawning occurs over several months in early-to-mid summer, so more specimens are still needed from the April-July 2012 period to increase the precision of size-at-maturity estimates for females and to cover the entire spawning season and the period just prior to commencement of spawning.

Besides expanding knowledge of the size-at-maturity of kala, the study has yielded a way to determine the gender of specimens without dissection of the fish. The new method, using external morphometric characteristics, will be useful in future research employing live kala, e.g., studies using tag-and-release methods to learn about kala movements and survival. Of the several external morphometric measures thought to indicate sexual identity and maturity in kala, the development of "knives" on the caudal keel of the fish appears to provide the best indicator of sexual identity.