For this purpose, zebrafish from three different genotypes (wild type, heterozygous BDNF+/− and knock out BDNF−/−) were kept for 21 days at 26 °C or 34 °C and then euthanized for brain molecular analyses or subjected to behavioural tests (Y-maze test, novel tank test, light and dark test, social preference test, mirror biting test) for assessing behavioural aspects such as boldness, anxiety, social preference, aggressive behaviour, interest for the novel environment and exploration. This evidence concerns the gene BDNF and Anxiety.