Stocking density and water temperature as modulators of aggressiveness, survival and zootechnical performance in matrinxa larvae, Brycon amazonicus

The matrinxa (Brycon amazonicus) presents zootechnical potential for commercial production, it is considered a species of interest due to its rapid growth and high-quality meat. However, one of the difficulties this species faces in the breeding system is the reduced supply of juveniles, mainly due to aggressiveness during larviculture. The purpose of the study was to evaluate the effect of stocking density and water temperature on the aggressiveness, survival and performance of matrinxa larvae. Two experiments were carried out Experiment I: 12 h after hatching (HAH) were kept at three stocking densities (low: 20 larvae/l, intermediate: 40 larvae/l and high: 60 larvae/l), up to 72 HAH, with 5 replicates each. During the experimental period, 10-min videos were made in both periods (12 and 72 HAH) to quantify the behavior of the larvae and to evaluate the zootechnical performance. Experiment II: the 72 HAH larvae were submitted to six experimental treatments for up to 132 HAH. These derived from the association of three stocking densities (low: 20 larvae/l, intermediate: 40 larvae/l and high: 60 larvae/l) with two temperatures levels (low: 24.09 +/- 0.15 degrees C and high: 28.33 +/- 0.12 degrees C). The same procedure used in experiment I was used here in order to analyze the aggressiveness, survival and zootechnical performance. The results showed that the higher stocking density increased the aggressiveness, however, without affecting the other parameters up to 72 HAH. Nevertheless, after 72 HAH, the density did not affect the aggressiveness, it stimulated increased biomass and production instead. It was observed that the lowest temperature of the water reduced the aggressiveness and provided more homogeneous sizes among the animals in the group, nonetheless, it reduced the growth of the larvae. The results obtained indicated that the use of different densities is recommended depending on the period of larval development, that is, the density of 40 larvae/1 in the initial stages of life (up to 72 HAH) and 60 larvae/1 after this period; the maintenance of larvae at temperatures close to 24 degrees C is also recommendable since it provides less aggressive individuals with lower differential growth within the group, which may increase the survival rate in the medium and long term during the matrinxa larviculture.