Otolith Morphology and Population Discrimination of Triplophysa yarkandensis

Abstract

To study the classification, identification, and discrimination between different geographical populations of Triplophysa yarkandensis and explore the related otolith morphology and fish life history, this study statistically analyzed the morphological otolith indices and fish bodies of 734 T. yarkandensis from the Yarkand River, Hotan River, and Tarim River using otolith morphology and fish ecology methods. The results showed that otoliths were small in T. yarkandensis, approximately elliptic, thicker in the middle, gradually thinning to the outer edge, and with a prominent protrusion in the center of the external surface. Otolith length was obviously larger than otolith width while the excisural notch was not obvious, wherein the rostrum was developed, the ventral otolith edge was smooth with a shallow arc, and the otolith dorsal had a crest-like ridge. No significant difference between left and right lapillus morphology was observed (P > 0.05). The otolith morphological indices followed a logarithmic function with the body length and weight (R2=0.48~0.62). It reflects the ontogenetic adaptation to the environment, and migration behavior mainly affects the relationship between otolith morphology and fish body morphology. The SHAPE software was used to extract the outer otolith contour of T. yarkandensis, revealing morphological differences between T. yarkandensis populations. The parameter with the largest discriminant coefficient, i.e., the one in which the morphological difference has the greatest significant effect, was screened. Therewith, the discriminant formula was set up to calculate the discriminant accuracy. Discriminant analysis between groups using fish morphology, otolith morphometry and elliptical Fourier analysis, respectively. The discriminant accuracy of the Hotan River and Tarim River populations was 96.0%, 61.4%, and 82.2%; the Yarkand River and Hotan River was 93.0%, 79.5%, and 87.9%; the Yarkand River and Tarim River populations was 96.5%, 77.5%, and 86.8%. Environmental factors such as water temperature, spatial niche adaptation, and habitat depth were the main causes of the otolith morphological changes, also affecting the behavior characteristics of typical T. yarkandensis life history, especially fish migration. In this study, the T. yarkandensis was found to live in high altitude, low habitat temperature, and high salinity and alkaline waters, so the fish body growth and the elements deposition rate onto otoliths were low. T. yarkandensis belongs to the sub-cold water and benthic fish group, which only enters deep water during overwintering in winter. In other seasons, it swims along the edge and rests in shallow depth waters, so the otolith grows slowly and has a small size. The relationship between otolith and body growth reflected the T. yarkandensis ontogenetic adaptability to its habitat. As the T. yarkandensis residence time is short in the migration area, mineral elements in the water body cannot be rapidly deposited in a short period of time, and the accelerated body growth is not completely reflected in the otolith growth. Therefore, the short-distance migration behavior under habitat fragmentation mainly affects the correlation between otolith and fish growth in T. yarkandensis. The fish otolith morphology is highly species-specific and population-specific. T. yarkandensis otolith morphology was significantly different among the geographically different populations (P 90.0%) was slightly higher than that of elliptic Fourier analysis (> 80.0%), both of which could be used as the discrimination basis parameter. However, the traditional fish otolith morphology is easy to record, as repetitive operations are robust and less affected by the environment, especially in the contents of a carnivorous fish feeding analysis; therefore, vertebrate paleontology explore has a useful application prospect in these aspects. Moreover, it could serve as an effective tool to identify fish intraspecific differences in the case of growth restriction or bodily injury. Therefore, it is of great research value to introduce the otolith morphology into the population identification of T. yarkandensis. This study explored the T. yarkandensis morphological characteristics and compared otolith morphologies to effectively identify the geographically different population, co-relating otolith shape with T. yarkandensis growth (i.e., body length and quality) and resource management, providing theoretical support to further researches about the composition and migratory population growth. The T. yarkandensis intraspecies differences in different rivers were also compared concerning fish body morphology, otolith measurements, and elliptic Fourier analysis, providing strong evidence for traditional morphological classification. The effective utilization and cost control of incomplete fish samples was greatly favored by this study. Otolith morphology was applied for the first time in the classification and population identification of T. yarkandensis, which laid a foundation for the development and research of its microchemical features and life history strategy, presenting a reference for further identification and evolutionary classification of Triplophysa, strengthening the taxonomic foundation of aquatilia, and providing scientific basis for protecting the plateau fishery germplasm resources.

Keywords

• triplophysa yarkandensis
• otolith
• morphological difference
• discriminant analysis