Crossbreeding between green genetically modified and wild zebrafish generates a more anxious and less sociable strain.

Behavioral differences can be artificially selected through the selection of morphological traits, particularly for the ornamental trade. Zebrafish (Danio rerio) genetically modified for ornamental purposes may accidentally hybridize, leading to the emergence of novel strains. Here, we evaluated potential behavioral differences between wild-type (WT) zebrafish and green wild-type (G-WT) zebrafish, a hybrid resulting from the crossbreeding of WT with a genetically modified green ornamental strain. We conducted a novel tank diving test, a sociability test, and an open field test, to assess anxiety-like behavior and locomotor activity, sociability, and establishment of homebase, respectively. The behavioral tests were chosen based on the zebrafish behavioral repertoire, a very active fish, highly social and explorative. Twenty-six hybrid fish were used, with 13 exhibiting normal color patterns (WT) and 13 showing greenish color patterns (G-WT). No difference was observed in locomotor in the novel tank patterns (average speed, distance traveled) and open field (homebase occupation and exploration) tests between the WT and G-WT groups. G-WT zebrafish presented higher anxiety-like behavior in the novel tank (increased time spent at the bottom). In the sociability test, the G-WT group spent less time in the conspecific area and kept higher distance from the social area, indicating reduced sociability compared to WT zebrafish. In conclusion, our results suggest that the hybridization between genetically modified and wild zebrafish may impact population dynamics, compromising social stability and increasing individual stress levels.