DEPOSITION REGULARITY OF THE DAILY INCREMENTS AND ANNULI IN SCHIZOPYGOPSIS MALACANTHUS

Schizopygopsis malacanthus is a highly specialized schizothoracine fish. Affected by changes in the external environment and human factors, the population size of S. malacanthus has declined sharply and has been listed as a vulnerable species (VU). Otolith microstructure is now regarded as a widespread phenomenon in teleost fishes and is widely accepted as a powerful tool for studying population dynamics during different stages of the life cycle. Therefore, studies on the characteristics of otolith in S. malacanthus will be helpful for better understanding the characteristics of otolith microstructure deposition, increasing the accuracy of growth characteristics, more fully reflecting the relationship between growth and environmental changes, and providing references for population dynamics research and fishery management policy formulation. In the present study, we analyzed the morphological changes of lapilli and sagittae, confirmed the deposition regularity of otolith daily increment and annuli by lapilli, calculated the formation time of the first annulus of the lapillus, and explored the relationship between its daily increment and annulus. It was found that the morphology of the lapilli was more stable than that of the sagittae, and it was more suitable for the age identification material of S. malacanthus. The breeding experiment confirmed that the first daily increment of lapillus was formed on the second day after hatching under the conditions of this experiment, the increment deposition had a daily periodicity in the larval period, and the growth increments were increments. The lapilli have an annual deposition pattern in the cultured adult fish, with an increase of one ring every year. The width of the increments in the annuli increased first and then decreased. The growth increments in width of cultured fish otoliths were larger than those of wild fish otoliths. Based on the otolith increment technique, it is calculated that the first annulus formation time of farmed and wild is from 28 Jan. to 13 Mar., 2021 (n=40) and from 8 Mar. to 10 May, 2017 (n=75) respectively. At the same time, analysis of otolith growth increments in farmed and wild samples over several years found that the number of growth increments and the annual growth width of lapilli decreased with increasing age and the annual growth area increased with increasing age. These results are helpful to improve the accuracy of age identification and provide references for the study of fish population dynamics and the formulation of fishery management policies.