Use of common salt affects aggressiveness in matrinxã larvae (Brycon amazonicus)

Aggressiveness is potentiated during the production of fish of commercial interest due to the densification and confinement, and this may affect the welfare and health of these animals. We compared the effect of salinity on aggressiveness, locomotor activity and body cortisol level in matrinxã larvae (Brycon amazonicus) submitted to three experimental treatments: 0, 2 and 4 g of common salt/L. For each treatment, the larvae were collected at 24, 36, 48, 60 and 72 HAH (hours after hatching) and then transferred to 5‐L aquariums for 30 min to analyse behavioural categories. The use of common salt increased the frequency of aggressive interaction, cannibalism, mortality and locomotion in all observation periods. Body cortisol levels did not differ between treatments until 48 HAH, but showed a significant increase at 72 HAH in the 4 g salt/L. There was a positive correlation between aggressive interactions and locomotor activity. Negative correlation was observed between these parameters and cortisol up to 60 HAH; however, they were positively correlated at 72 HAH. We concluded that the use of common salt stimulates the display of aggressive behaviour and locomotor activity and that the effect of salt is dependent on the developmental phase of the larvae of B. amazonicus.