The influence of the individual variation, sex and spatial factor in somatic growth of Serrasalmus rhombeus, an Amazon predator fish species

The Amazon is one of the regions with the greatest fish diversity on the planet. In this vast biodiversity, there is Serrasalmus rhombeus, a predatory species that plays a vital ecological role in aquatic ecosystems. In order to generate biological data and valuable information to management efforts, we characterized the somatic growth pattern of S. rhombeus and identified its sources of variation. To achieve this, individuals of S. rhombeus were collected from two dams between October 2018 and November 2019. Analyzing the marginal increment based on data from 158 individuals revealed the formation of a single annual growth ring at the onset of the rainy season. Individual ages ranged from 1 to 6 years old. Among the considered models, the one that provided the best explanation for the variation in somatic growth of S. rhombeus integrated individual variation, sex, and sites. This highlights that the rate of an individual’s growth and the size it can attain are influenced by individual resource utilization, which is mediated by interindividual genetic diversity. Furthermore, this variation is associated with sex and the specific site where the individual is located.