Growth, sex ratio, and maturation rate with age in the blackspot tuskfish Choerodon schoenleinii in waters off Okinawa Island, southwestern Japan

Abstract

The growth, sex ratio with age, and age at sexual maturation were determined based on sectioned otoliths in 257 specimens of the blackspot tuskfish Choerodon schoenleinii collected in waters off Ryukyu Island. Opaque rings observed by reflected light in the sectioned otoliths were found to form once a year from January to July. The three growth parameters of the von Bertalanffy growth equation were L ? = 68.1 (cm), k = 0.263, and t 0 = -0.023 (year). The age at which the sex ratio reached 50% by sexual transition was about 6.15 years, and the age at which 50% of females were sexually mature was approximately 2 years. The oldest specimen among the samples was 17 years old.

Difference in age, growth, and sexual demography of black-spot tuskfish, Choerodon schoenleinii (Valenciennes, 1839), in two adjacent populations, Ryukyu Archipelago, southern Japan

“…In this study, estimated X 50 of the Opop was smaller than in the previous study (54.6 cm TL; Ebisawa et al., ). We used an enormous number of length composition data to estimate the X 50 .…”

“…Growth of the Ypop and Opop differed significantly, with the Ypop exhibiting faster growth than the Opop (Figure 3). The maximum length and age of the two populations, however, was only slightly different (Ypop: 75 cm TL [measured at fish market], 15 years old; 16 years old; Opop: 76.9 cm TL, 17 years old (Ebisawa et al, 2010) In the congeneric species C. venustus, sex ratio and length at sex change have been estimated from the body color (Platten et al, 2002).…”

“…Following Ebisawa et al. (), age of specimens with an opaque edge collected from November to December were calculated as the number of opaque zones −1 year, while age of specimens with a wide translucent edge collected from January to March were calculated as number of opaque zones +1 year. The fractions of age are the proportion of a year from the birth month to the month in which the specimen was collected.…”

“…where L t is TL at age t, and L ∞ , k, and t 0 are the asymptotic length, growth coefficient, and hypothetical age at TL = 0, respectively. The growth coefficient of this study was compared with those of previous studies (Ebisawa et al, 2010). Moreover, the VBGF parameters of Ypop and Opop were examined statistically by likelihood-ratio tests (Kimura, 1980), using the R language with the package "fishmethods" (http://cran.r-project.org).…”

“…and 50.0 ± 0.25 cm TL, respectively (Table 2). Fairclough (2005) and Ebisawa et al (2010) concluded that the opaque zone in the otolith of the blackspot tuskfish is formed annually. In this study, we observed a similar periodic change in the opaque zone.…”