Aggressivity expressed as cannibalism in fish larvae is a problem that limits the development of many species in aquaculture, therefore, understanding it and generating strategies to reduce its impact is important. This study described cannibalistic attacks behavior in Tropical gar (Atractosteus tropicus) larvae. The larvae were exposed to different tank colors and shelters (rocks and plastic vegetation), in pairs (2 larvae) and in groups (10 larvae). In addition, attacks behavior, types of attacks, and morphometric aspects related to cannibalism were described. In pairs, attacks occurred in greater numbers with white background color (8.50 ± 0.70) and fewer for yellow and purple (0.66 ± 0.57, p < 0.05). The largest number of group attacks was observed with the background colors pink, blue and yellow, and purple to a lesser extent. The presence of shelters (artificial vegetation) decreased the attacks in pairs and in groups compared to the use of rocks as refuge. A. tropicus larvae show a clear preference for artificial vegetation. It was found that morphologically, both juveniles and larvae (10 Days after hatching (DAH)) can consume prey greater than their own body depth (1.59 ± 0.22, 1.00 ± 0.12) and body width (1.74 ± 0.29, 0.94 ± 0.12). The mouth depth angle was significantly higher in larvae (10 DAH) (85.63 ± 6.41°), which decreases as age increases. A total of 452 events were recorded, four behaviors were described: interaction (214 events, 47 attacks, effectiveness of the attack (EA) 21.96%), chasing (127 events, 44 attacks, EA 34.64%), escape (62 events), and fast swimming (47 events). Three types of attacks were recorded: frontal (41.24%), lateral (29.94%), and posterior (28.81%), with three attack regions: head (31.64%), body (10.72%), and tail (57.63%). The most frequent attack was posterior tail with 70 events (39.55%). Attacker presented a S-like curvature prior to the attack (30.50%). Differences were determined in the percentage of weight (g) and total length (cm) between the attacker larvae and the attacked larvae 16.39 ± 10.86% and 15.23 ± 5.68%, respectively. In conclusion, A. tropicus larvae show cannibalism Type I, II, and two variants of Type III. It is suggested that this species is a more efficient cannibal than an interspecific predator. The relation of the greater number of attacks in the white color tanks could be related to the contrast with the bottom, thus, there is a less preference for this color. This information is essential to carry out a more efficient sorting of the larvae during their culture and reduce cannibalism in the larval stage in A. tropicus. The results of this study could be useful to understand this behavior in other species.