Brazilian aquaculture is expanding, also because of the production of native species¹. One of these species is the yellowtail lambari (Astyanax altiparanae), that is a promising one in the current production scenario². However, it presents aggressive behavior in the artificial environment with negative impact in the production. One promising strategy to reduce the aggressiveness is the diet supplementation with tryptophan (L-TRP), precursor of serotonin, neurotransmitter involved in behavioral control. In this sense, the objective of this study was to determine whether dietary supplementation with L-TRP can reduce aggression in female yellowtail lambari.
Female juvenile yellowtail lambari (±11,78g) were used, divided into three 310 L tanks for the acclimatization and feeding period. The diet was prepared by aspersion of diluted L-TRP in a commercial feed. Three diets were prepared: D1 without L-TRP, D2 with 0.6912 g L-TRP/100 g feed and D3 with 1.3824 g L-TRP/100 g feed. The fish were fed the diets at 3% of live weight for 10 days. At the end, fish were anesthetized, measured, weighed, and given a blue methylene tag in the anterior region of the body, and then isolated in a 19L aquarium for three days to become the resident fish. Other fish, the intruders, that were not fed the experimental diets were also anesthetized, measured and weighed to form pairs of fish of the same size, and tagged with blue methylene in the posterior body region. After the isolation period of the resident fish, the same-sized intruder fish was transferred to the resident aquarium to initiate a direct confrontation, which was recorded for 20 minutes. The recorded confrontations were then analyzed by counting the number of head and body bites. The data obtained was analyzed using a one-way ANOVA, followed by a Duncan test for means comparison.
From the analysis of confrontations, a significant decrease in head biting (p = 0,0305) and body biting (p = 0,0533) behaviors was observed in females fed the D3 diet, indicating that supplementation with the amino acid reduced the aggressiveness of the yellowtail lambari females (see Fig. 01).
These results are consistent with the literature, which shows the same effect of TRP in other species, in which lower rates of aggressive behavior toward conspecifics were observed. The results indicate that the TRP was probably utilized to synthetize serotonin, neurotransmitter that probably have, in fish behavior, the same role described in mammals. Thus, TRP is a promising strategy to be used in farming of lambari to enhance productivity of the species.