Can Otolith Nucleus Elements Differentiate Antarctic Fish Species in the Southern Ocean? A Case Study of Three Nototheniidae Species

The otolith nucleus captures a fish’s life history during egg and hatching stages, offering insights into species-specific differences in element types and concentrations as well as the endogenous and exogenous factors shaping these variations. This study aimed to investigate the variation in the types and concentrations of elements within the otolith nuclei of three Antarctic fish species, including Pagothenia borchgrevinki, Trematomus hansoni, and Trematomus bernacchii, collected from Prydz Bay, East Antarctica. Nine elements, ²³Na, ²⁴Mg, ²⁹Si, ³¹P, ³⁹K, ⁵⁷Fe, ⁶⁶Zn, ⁸⁸Sr, and ¹³⁷Ba, were selected for analyses because of their concentrations and ecological significance. Ratios of each element to Ca (Me/Ca) were used for analysis, and Me/Ca in the otolith nuclei of these species were analyzed to explore species-specific variations in element types. Significant differences in element composition, except for Fe/Ca and Ba/Ca, were found in different species. Temperature, salinity, reproduction, pelagic larval lifestyle, and diet composition were considered as key endogenous and exogenous factors influencing these differences. Decision tree discriminant analysis, based on the variation of the types and concentrations of elements, was used to identify P. borchgrevinki, T. hansoni, and T. bernacchii with accuracy rates of 86.54%, 82.61%, and 73.33%, respectively. Principal component analysis showed overlapping 95% confidence ellipses for the three species at 79.96%, 67.31%, and 56.71%, respectively. As these species belong to the Nototheniidae family and share a similar hatching period, the accuracy of species discrimination is reduced. Considering the high probability of error in distinguishing species using otolith nucleus elements, we recommend otolith shape should also be considered to improve identification accuracy.