Age and growth of Myctophum asperum in the South China Sea based on otolith microstructure analysis

Abstract

To estimate the age and growth of a dominant species of lanternfish, Myctophum asperum, in the South China Sea, 399 fish were collected by a midwater trawl in spring and autumn, 2014–2016. Age was estimated using counts of daily growth increments laid down across the sagittal section of otoliths (n = 52 fish). Three regions of deposition in the otolith microstructure were clearly evident: the larval, post-larval and post-metamorphic zones. Increments in the larval zone (average of 30) and the post-metamorphic zone appeared brighter under a light microscope than the increments in the post-larval zone. The age of the sampled fish ranged between 183 and 405 days. The von Bertalanffy growth model provided the best fit for the post-metamorphosis fish and was expressed as: SL = 85.3[1-exp{− 0.008(t − 28.1)}]. The maximum rate of growth occurred at 183 days after metamorphosis and 58 mm SL among the age determined samples, and the growth rate decreased with age. The length-weight relationship for the entire sample of fish was W = 0.000037234 SL2.7935, whereas for females and males it resulted Wf = 0.000050140 SL2.7255 and Wm = 0.000035459 SL2.8022, respectively. Fish reached the adult size by 74 mm SL and 5–8 g, and this size group was numerically the most and constituted the greatest portion of the biomass.