Age and Growth Estimations of Decapterus Kurroides Using Otolith in the Waters of Eastern Taiwan

Abstract

Aims: Redtail scad (Decapterus kurroides Bleeker, 1855) was once an economically important Carangidae species in Taiwan. This study determined age using otolith increments and re-evaluated the parameters of growth equations for this species. Place and Duration of Study: Fish samples were collected monthly off the coast of Taitung, eastern Taiwan. Methodology: A total of 367 specimens were observed in this study. To determine fish age, otolith age determination method was used. The largest and smallest otolith rings were seven and two, and their corresponding means of fork length (FL) were 29.2 and 12.2 cm, respectively. Results: Most samples had six otolith rings with a mean FL of 27.2 cm.  The von Bertalanffy growth equation is FLt = 30.44 (1 – e −0.52 (t - 1.50)) for females and FLt = 32.45 (1 – e −0.39 (t – 1.18)) for males. The otolith opaque zone annually formed from September to October. The relationship of body weight (BW) and Fork Length (FL) differed significantly between genders: BW = 0.334 × 10-2 FL3.463 for females and BW = 0.469 × 10-2 FL3.349 for males. The sex ratio was 0.56 over a whole year and varied among the age groups. Conclusion: This study using the otolith method revises the estimations of age and growth parameters for the D. kurroides, which would be beneficial to manage and recover this species stock in the waters of Taiwan.