The complex age and growth of Chloroscombrus chrysurus: Formation of two increments per year in the otolith and biphasic growth

Abstract

Fish age and growth are essential information for fisheries management and ecological assessment. Chloroscombrus chrysurus is a small pelagic fish distributed along both margins of the Atlantic Ocean, with a key ecological role and fishery relevance. In the Southeastern Brazilian Bight (21°S-28°40'S), it is one of the three main target species of the industrial purse seine fishery, and there is no detailed study of its sagitta otolith focusing on age structure and growth pattern in this area. To this end, a dataset of 1009 otoliths from individuals ranging from 155 to 400 mm TL was analyzed. Techniques to assess the relative growth and absolute growth were used. Both techniques revealed a biphasic growth pattern. The stanza changing point in the otoliths corresponds to a total length of 245.43 mm. Two increments (translucent zones) are formed in the otolith per year. Up to eight increments were observed, corresponding to ages ranging from 0.8 to 4.5 years. The biphasic von Bertalanffy growth model best described the growth of the species: $\mathrm{TL}=356.10A_t[1-e^{-0.758\left(t+0.0027\right)}]$, t_h = 2.32 years, h = 0.180. The total length and age of the transitional growth phase correspond to the total length at which all individuals are adults (TL₁₀₀), indicating a rapid growth pattern during first maturity, followed by relatively stable length in older individuals. These results represent a novel approach to age and growth of C. chrysurus and provide a standard for accurate age estimation based on otolith analysis for small and medium-sized pelagic species.