Simple method to identify two species of hairtails, Trichiurus japonicus and T. sp.2, in Shikoku Island

Abstract

  A morphological method was developed to distinguish the two species of hairtails Trichiurus spp. (Trichiuridae) distributed in Shikoku Island. A total of 2,179 specimens of Trichiurus japonicus and T. sp.2. were collected from coastal waters off Ehime prefecture and Kochi prefecture from January 2004 to February 2006. The relationship between preanal length (PL) and total length (TL) was expressed as the linear discriminant function z=0.133 PL+59.6 TL/PL-207. The rate of misidentification of fish was 2.0% compared to the identification based on the previous criterion proposed by Nakabo (yellow dorsal fin and light-colored bottom of oral cavity for fresh specimens). Condition factor of T. sp.2 was higher than that of T. japonicus, and the range of condition factors was 13.81-22.66 and 9.88-18.02, respectively. Furthermore, comparing the condition factors, the misidentification rate was only 0.4%. This identification method may be applicable for past studies which measured only fish body without precise species identification.