Larvae cannibalism is a problem in aquaculture, therefore, understanding it and generating strategies to reduce it, is important. This study described cannibalism in A. tropicus larvae and its mitigation with the addition of tryptophan in the diet. Larvae were exposed to different tank colors and shelters. Attacks behavior, types of attacks, and morphometric aspects related to cannibalism were described the effect of tryptophan (Trp) was evaluated (10, 20, and 30 g/kg) and a control diet (CD) regarding growth, survival, cannibalism, behavior, digestive enzymatic activity, and genes related to aggressiveness and/or cannibalism.
Most of the attacks occurred in white bottom (8.50 ± 0.70) and fewer for yellow and purple (0.66 ± 0.57, p < 0.05). The artificial vegetation decreased the attacks in pairs and in groups compared to the use of rocks as refuge. Using tryptophan, in the first stage, no differences were observed in growth parameters. Cannibalism was lower with the use of Trp, with the lowest percentage being the 10 g/kg Trp treatment (56.75 ± 2.47%) compared to CD (64.75 ± 1.76%). In the second stage, survival was greater in 10 g/kg Trp (75.00 ± 7.07%) than in CD (23.33 ± 5.77%). Thus, cannibalism was lower with 10 g/kg Trp (20.0 ± 10.0%) compared to CD (76.66 ± 5.77%). Cannibal larvae fed with 10 g/kg Trp had a greater enzymatic activity in acid and alkaline proteases and leucine aminopeptidase, as well as the overexpression of avpi1, crh, and htr1a and the subexpression of tph1, th, sstr1, and hdc (p < 0.05). No aggressive behaviors were recorded in the larvae fed with the 10 g/kg Trp treatment, unlike those fed with CD. In conclusion, it is suggested that this species is a more efficient cannibal than an interspecific predator and the use of 10 g/kg Trp improves survival and reduces cannibalism in A. tropicus larvae