Investigating the metabolic and oxidative stress induced by biofouled microplastics exposure in Seriola lalandi (yellowtail kingfish).

Microorganisms quickly colonise microplastics entering the ocean, forming a biofilm that, if ingested, is consumed with the microplastics. Past research often neglects to expose fish to biofouled microplastics, opting only for clean microplastics despite the low likelihood that fish will encounter clean microplastics. Here, we investigate the physiological impacts of biofouled polyethylene microplastic (300-335 μm) exposure in juvenile fish. Intermittent flow respirometry, antioxidant enzyme activity, and lipid peroxidation were investigated after fish were exposed to clean, biofouled, or no microplastic beads. Fish exposed to biofouled microplastics had a wider aerobic scope than those exposed to clean microplastics while antioxidant enzyme and lipid peroxidation levels were higher in clean microplastics. Clean microplastic exposure indicated higher fitness costs, potentially due to a nutritional advantage of the biofilm or varying bioavailability. These findings highlight the importance of replicating natural factors in exposure experiments when predicting the impacts of increasing pollutants in marine systems.