Unintended Consequences of Aquatic Enrichment in Experimental Biology

Enrichment in aquatic animal studies is important for promoting welfare and maintaining animal health and can be categorized by physical, sensory, social, occupational, and dietary enrichment. However, the risk of potential chemical leaching associated with physical enrichment items has been largely overlooked (i.e., artificial plants or shelter). Most enrichment items lack information on their chemical composition and have not undergone testing for plastic or metal leachates that can alter water chemistry and impair animal physiology. In fish and invertebrate research, these leachates have the potential to modify the health of aquatic animals or their reproductive processes. Moreover, in toxicology research, altered chemical exposure concentrations and interactive effects with leachates could invalidate toxicity assays and lead to misleading results. We identify key contaminants associated with common enrichment items and highlight the substantial lack of empirical research focusing on the confounding factors associated with aquatic enrichment. We explore the mechanisms through which relevant leachates can complicate experimental outcomes, detailing the pathways by which these substances may interact with both the experimental environment and the animals themselves. We conclude that there is widespread potential for serious complications to research outcomes and chronic toxicity from enrichment materials. Therefore, we advocate for the establishment of standardized regulations and a global certification system for aquatic enrichment items to ensure the validity of studies and to safeguard animal welfare. We encourage researchers to critically consider the implications of leaching from aquatic enrichment when designing experimental systems.