Aspectos populacionais e dieta natural do camarão Macrobrachium amazonicum (Decapoda: Palaemonidae) na represa do Funil (MG, Brasil)

Abstract

The species Macrobrachium amazonicum (Heller, 1862) is endemic to South America and extends from Venezuela and Argentina. The objective of the present work was to evaluate the population aspects of Macrobrachium amazonicum in the Funil dam, located in the city of Ijaci (MG, Brazil). The collections were carried out monthly from April 2021 to March 2022. The sampling effort was 30 minutes, where a person passed a sieve, in an upward movement, along the marginal vegetation. After collecting the shrimp, the physicochemical variables were measured: temperature, pH, dissolved oxygen and conductivity. The ovigerous females collected were individualized and all shrimp were frozen in a thermal bag with ice until transport to the Liminology and Carcinology laboratory at the Federal University of Lavras (UFLA). In the laboratory, subjects were stored in 70% alcohol until further analysis. Individuals were sexed and measured for cephalothorax length. Subsequently, they were classified into four demographic classes (Males, Females, Ovigerous Females and Juveniles). Eggs were removed from the females' abdomen and counted under a magnifying glass. Shrimp stomachs were removed to identify food items. To evaluate the relationship between the physicochemical variables (temperature, pH, conductivity and dissolved oxygen) and the demographic classes, a principal component analysis (PCA) was performed. Pearson's correlation was used to assess whether there is a relationship between the variables. The generalized linear model (GLM) was performed to assess whether there is a relationship between the abundance of individuals and the physicochemical variables and to assess whether there is a difference between the abundance of individuals between demographic classes. The fecundity of females was determined by the following formula: amount of eggs/abundance of females. The conductivity variable showed a negative correlation with the abundance of individuals and the other variables had no statistically significant correlation. Ovigerous and non-ovigerous females were the individuals with the longest cephalothorax length in the population and the highest abundance was observed in males of the population. Ovigerous females were present in 10 of the 12 months of collection, showing continuous reproduction, the peak of ovigerous females and eggs was observed between the months of September and October 2021. The shrimp diet was well diversified, and the most common items were digested organic matter, insect exoskeletons, microplastics and plant fragments. In general, it was observed in the population studied in the present work some similarities to other populations in other regions, such as continuous reproduction with a peak in the months with higher temperatures and omnivorous feeding habits. However, some differences were also observed, such as females being larger than males and males being the most abundant individuals in the population. These results will help to understand the wide plasticity of the species, especially in regions where there are still few studies about it, as is the case of the southern region of Minas Gerais.