Shellfish hydrotherapy: plant-derived extracts enhance stress resilience in juvenile mussels (Perna canaliculus)

Currently the aquaculture industry is facing many challenges, such as more frequent and severe marine heatwaves and disease outbreaks. Prophylactic treatments can help mitigate specific issues within the aquaculture industry. In this study, we assessed the concept of “shellfish hydrotherapy” for juvenile green-lipped mussels, Perna canaliculus (1–2 mm), by exposing them to plant-derived extracts as antistress prophylactics to improve heat tolerance. Two experiments were performed using extracts derived from prickly pear (Opuntia ficus-indica) and beetroot (Beta vulgaris rubra), which contain similar bioactive compounds, including betalains and phenolics. In the first experiment, 41 treatments, including controls and extracts at different concentrations (1–6000 µg/ml), were scoped to identify beneficial extracts. A second experiment evaluated eight treatments, focussing on beetroot extracts at different concentrations (0.005–600 µg/ml) and controls, to validate improvements in heat tolerance. Testing involved bathing the mussels in the extract solutions for 2 h before they were exposed to a heat challenge, evaluating survival at 48 h after the stress. Results showed that survival to heat is significantly improved when mussels are treated with extracts derived from Opuntia (~ 2% increase) and beetroot (~ 7% increase), compared to untreated mussels. The mechanism of action of these treatments remains to be investigated, but it is likely that prophylactic treatments could have broader benefits beyond thermal tolerance. Hence, the use of plant-derived extracts as stress prophylactic treatments in aquaculture could have multiple advantages, also having the potential to be applied to different phases of production to increase general resilience of a target species at their most vulnerable stages.