Microstructure comparison of hard tissues (statoliths, beaks, and eye lenses) of Uroteuthis chinensis in the South China Sea

Abstract

In the present study, the microstructure features and the number of growth increments in the statoliths, beaks, and eye lenses of the mitre squid, Uroteuthis chinensis (Gray, 1849), were examined. Growth increments in three regions of the statolith [the dorsal dome (SDD), lateral dome (SLD), and rostrum] were observed; those of the SLD had the most stable increment widths. The SLD and SDD had a similar number of growth increments. Increment number in the rostrum sagittal section (RSS) of the upper beak was lower (about 30 increments) and that of the eye lens was many times higher (about 3–5 times) than those in the statolith and the beak. The best fits against mantle length were the number of growth increments of the beak, SLD, and eye lens. The relationship between mantle length and growth increments of SLD could be described with two separate equations, possibly indicating that two different cohorts were sampled. Based on the growth increments of SLD, the maximum age of U. chinensis in our study was inferred to be 169 d.