Precision of age estimations from otolith, vertebra, and opercular bone of gymnocypris firmispinatus (Actinopterygii: Cypriniformes: Cyprinidae) in the anning river, China

Abstract

Background. Gymnocypris firmispinatus Wu et Wu, 1988 is a small fish with the maximum total length of 242 mm, which occurs only in the Jinsha River and its tributaries (China), at altitudes above 2000 m. Nowadays, G. firmispinatus had been placed in a dangerous situation, due to hydropower station and excessive fishing. However, attempts to develop an effective population management strategy have been obstructed by lack of basic biological information, especially for age estimation. As we known, sectioned otoliths provide the most precise age estimates of many Schizothoracinae fishes, vertebrae and opercular bones were also used for age determination of some fish species. This work aimed to assess the suitability of three calcified structures (otolith, vertebra, and opercular bone) for age estimation of G. firmispinatus. Materials and methods. The annulus characteristics of otolith, vertebra, and opercular bone were described. Annual periodicity was verified by marginal increment ratio (MIR) analysis in otoliths and edge analysis in vertebrae and opercular bones. Otoliths, vertebrae, and opercular bones were examined to determine which structure produced the most precise and accurate age estimates in G. firmispinatus, mainly by scoring for readability on a five-point scale and calculating the index of the mean percentage error (IMPE). Results. Microscopically, otoliths and vertebrae showed a typical pattern of opaque-and translucent-zones, attributed to slow and fast growth periods. Annuli formed between March and May once a year in otoliths and vertebrae. Forty-four percent of the opercular bones were scored as unreadable. The value of IMPE between the two counts was lowest for otoliths (4.25%), followed by vertebrae (6.21%) and opercular bones (11.58%). The IMPE value of vertebra vs. otolith was 11.05%, while that of opercular bone vs. otolith was 23.03%. Vertebrae and otoliths matched closely only for the first 4 years of life, while opercular bones appeared to underestimate the age of G. firmispinatus. Conclusion. Annuli in the otoliths and vertebrae both formed once a year up to age 8, and otoliths would be the most precise structure for age determination in G. firmispinatus. Vertebrae and otoliths matched closely up to age 4, while opercular bones could not be used for age estimation for the species.