Caging is an active biomonitoring strategy that employs a sentinel species, sometimes a species naturally absent from the studied site, in the surveillance of water bodies to verify whether biota may be at risk. The main advantage of caging is the possibility to standardize several biotic and abiotic parameters. However, little knowledge is available about the effects of confinement on physiology and metabolism of caged organisms. The aim of this study is to characterize confinement and food access restriction effects, induced via caging experiments using a multi-biomarker approach (biometric data, immunity, antioxidant, metabolic detoxication, and digestive enzymes). The study has been undertaken using the same experiment conducted in ecosystem conditions using three-spined stickleback (Gasterosteus aculeatus) during two different periods: one in April, corresponding to breeding season, and the other in October, outside breeding season. Fifteen fish were maintained for 21 days in different conditions (caged or uncaged and with or without food supply). The main result was that confinement stress had little impact on the biological markers of sticklebacks. However, the stressors seemed to increase the negative effects of food restriction on these biomarkers, when sticklebacks needed more energy, that is, during their breeding period. Outside breeding period, most investigated biomarkers were not impacted by caging. This study showed a way to specify the conditions of application and interpretation of biomarkers during active monitoring to ensure an effective, reliable diagnosis of water body quality.
Keywords: Biomarkers; Biomonitoring; Caging; Fish; Food restriction.