Effect of water temperature on aggressiveness and physiological parameters of juvenile matrinxã, Brycon amazonicus (Spix and Agassiz, 1829)

Abstract

The matrinxã (Brycon amazonicus) is one of the species with the greatest rates of commercialization in the Amazon region, however, it has a high frequency of aggressiveness and cannibalism, and these traits are considered a major obstacle to the aquaculture sector. Environmental factors (e.g., water temperature) are known to impact fish behavior and, thus could contribute to reducing fish aggressiveness and improve production conditions. Therefore, we tested the effect of water temperature on aggressive behavior and stress parameters in juvenile B. amazonicus. Aggressive behavior and stress indicators (haematological indices and glucose) were compared in 24 individuals that were isolated for eight days and submitted to one of three temperatures: low (24.33 ± 0.33 °C), intermediate (29.49 ± 0.43 °C) and high (34.48 ± 0.56 °C); eight fish were used per treatment. The experimental period was divided into three phases: A. Initial- the average temperature was equivalent to the acclimatization period (29.49 ± 0.70 °C) and lasted for 60 h; B. Transition- a gradual increase/decrease in temperature over a period of 36 h (∼2.55 °C/day) was implemented; and C. Final- temperatures corresponded to the respective experimental treatments, to which the fish were exposed for 96 h. Aggressive behavior was monitored from the 5th to 8th days of the experiment, and blood was collected for physiological analysis on the 1st and 8th days. At the end of the experiment, the fish submitted to the higher temperature showed less aggressive interactions compared to fish maintained at the lower temperature (Fisher LSD, P = 0.025). For all temperatures tested, a reduction in hematocrit, red blood cell counts, hemoglobin concentration and plasma glucose was observed at the end of the experiment, but the reductions in most of these parameters did not differ among the treatments (Kruskal-Wallis, X² = 1, P = 0.61, ANOVA, F = 0.84, P = 0.17). In conclusion, the higher temperature did indeed cause a reduction in the aggressiveness of the juvenile B. amazonicus, though it did not act as a stressor. These findings may contribute to the improvement of social conditions during the farming of this species and, consequently, to the development of new technologies for the productive sector.