Comparative evaluation of two chronic stress models in zebrafish for advancing depression research

Depression is a debilitating neuropsychiatric disorder, and the failure of many antidepressants in clinical trials reflects the limited predictive validity of preclinical models. Therefore, a comparative evaluation of animal models that recapitulate the behavioral and molecular features of depression is essential for improving translational relevance. This study evaluated the utility of two chronic stress paradigms in zebrafish for modeling depression-like states. A modified Chronic Stress model termed Chronic Aggression Stress (CAgS) was developed and compared with the established Chronic Unpredictable Stress (CUS) model. In the CAgS paradigm, zebrafish were subjected to daily encounters with an aggressive cichlid for five days, while the CUS paradigm involved ten distinct stressors administered unpredictably twice daily for 10 days. Behavioral outcomes were assessed using the novel tank test, scototaxis, and threat response test. Molecular changes were examined by RT-qPCR, western blotting, and immunofluorescence. Both stress models induced robust depression-like phenotypes in adult zebrafish. CAgS produced consistent behavioral deficits, including reduced locomotion, increased anxiety-like behavior, and enhanced passive defensive responses across sexes, whereas CUS elicited divergent behavioral trajectories. At the molecular level, CAgS triggered a pronounced pro-inflammatory state characterized by elevated microglial activation and disrupted neurotrophic signaling. In contrast, CUS produced a more heterogeneous response, including sex-specific regulation of inflammatory cytokines and neurotrophic pathways. Both stress paradigms also showed astroglial activation and altered cellular proliferation. These findings demonstrate that both CAgS and CUS paradigms induce depressive-like phenotypes in zebrafish, with CUS uniquely revealing sex-specific behavioral and molecular alterations, highlighting their complementary utility for investigating depressive pathophysiology.