Dinâmica do crescimento do pirarucu Arapaima gigas (Schinz, 1822) em cultivo

Abstract

The Arapaima gigas, known as pirarucu, is a fish native to the Amazon basin. Its captive breeding presents economic potential, especially in the northern region of Brazil, and growth studies are essential to understand population dynamics and ensure proper management. Therefore, the objective of this study was to analyze pirarucu growth in captivity through the analysis of age rings in rigid structures. For the growth study of pirarucu, samples were obtained in May, August, October, and December 2023 on properties in the municipalities of Benevides, Terra Alta, Castanhal, and Santa Izabel, and taken to the Laboratory of Ichthyology and Fish Population Dynamics (LAID) at UFRA. In the laboratory, the left and right otoliths of the pirarucus were extracted, and then otolith biometrics were recorded, measuring the length, width, thickness, and weight of the otoliths. After biometrics, the otoliths were embedded, cut on the metallographic saw, polished, and placed on slides for later reading. With the assistance of a LEICA DM 2500 polarized light optical microscope, images of the otoliths were captured for visualization and reading of the pirarucu age rings in the LAS v4.4 program. To verify the existence or not of significant differences between the left and right otoliths, the Student's "t" test was used. Otolith measurements were related in linear and power regressions for both sides. For the estimation of the Von Bertalanffy growth curve of pirarucu in captivity, the backcalculation method with marginal increment was used, followed by adjustment of the FordWalford relationship curve. Most morphometric relationships of the otoliths showed strong positive correlation, with the remainder showing moderate positive correlation. There was no difference between the lengths and weights of the left and right otoliths. For cultivated pirarucu, a growth rate of 0,0239 was analyzed, reaching a maximum size of 3,29 m over a period of 34 years with a t0 of -0,9167. In conclusion, the left and right otoliths of cultivated pirarucu showed no difference between them, and the determination of the periodicity of growth rings was marked monthly. Additionally, pirarucu growth in cultivation showed rapid growth during the first four months of cultivation. Keywords: Otolith, Growth curve, pisciculture.