Seleção da estrutura etária, idade e as relações de crescimento de Hoplias aff. malabaricus (Bloch, 1794) na região sul do Rio Grande do Sul, Brasil.

Abstract

Determining the age of fish through calcified structures composed one of the most important basic information that allow the assessment of fish stocks. This type of study is vital for understanding the population dynamics of the species, especially when these populations are subjected to environmental influences and/or anthropogenic. The trahira Hoplias aff. malabaricus is a species of freshwater fish of most importance for artisanal fisheries in southern Rio Grande do Sul, but in recent years, its natural stocks have declined drastically. This study examined the scales and otoliths betrayed to select the structure that affixing provides better results as the visualization of their brands growth and determined the age and growth relationships of the species. We tested several methods for both structures, as indicated in literature. The results of the observations of scales and otoliths and the comparison between the structures showed that the scales of trahira taken from the middle region of the body of the fish and examined under transmitted light and low light, provide better clarity in the identification of growth rings. The otoliths, even undergoing various visualization methodologies are not suitable for reading the marks of growth in this species. It was possible to determine the age of both populations analyzed, data validation was performed by Von Bertalanfy equation. Were found up to 9 years of age in fish at the dam of Chasqueiro and up to 5 years in Lagoa Mirim. The average size, both in length and weight were statistically higher in specimens of the Chasqueiro Dam. The results suggest that the population of traíras of the Mirim Lagoon is suffering from the fishing activit, especially larger fish and more susceptible to capture by the nets of fishermen. This information is evidenced by the average size of the specimens in each age class and the growth parameters of the species in each environment studied.