Fish Immunotoxicity Research (2015 - 2025): A Systematic Review of Methodological Approaches, Progress and Data Gaps.

Although immunotoxicity is receiving increasing regulatory attention, it remains largely neglected in ecotoxicological hazard assessment. However, there are many indications for effects of substances on immune-related parameters in environmental organisms, for example in fish. This systematic review analyzes fish immunotoxicity research from 2015 to 2025 with three objectives: compiling available data, identifying research gaps in mechanistic and holistic assessments, and evaluating progress compared to earlier studies. From 1,078 screened articles, 238 were included. The analysis revealed that only few studies address immunomodulatory modes of action, limiting the linkage between molecular initiating events and apical effects. Experimental documentation is often insufficient, with missing rationales for test conditions, hindering comparability across studies. Furthermore, most studies report significant effects, restricting conclusions about endpoint specificity. Consequently, reliable and specific immunotoxicity markers in fish are still lacking, and differentiation from systemic toxicity remains difficult. Overall, little progress has been made compared to earlier findings.