Historically, Europe has been home to many pond landscapes, usually used for extensive fish farming (Aubin et al., 2017). This is the case for the Auvergne-Rhône-Alpes region of France, which contains several pond areas (Dombes, Forez, and Dauphiné). Fish farming persists in these areas but faces many challenges, including the impacts of climate change. In these extensive production systems, up to 70% of productivity comes from natural resources provided by the pond ecosystem (Robin et al., 2016). This natural productivity can be enhanced through several management practices (liming, fertilization, feeding, and a dry period every 4-5 years) (Wezel et al., 2013; Girard et al., 2024). However, stocking strategies (fish species composition and density) are not always adapted to the productive potential and ecological functioning of individual ponds.
Materials and Methods
The FISHMIX project (2023–2026) aimed to evaluate new fish species assemblages suited to ponds, their productive potential, and their biological functioning, in the context of climate change. Over a three-year period, we monitored 46 fish ponds in the Dombes region, in which five scenarios of fish species assemblages were implemented. These assemblages were designed in collaboration with fish farmers, removing species that are more vulnerable to climate change, adding species uncommon in the region, and adjusting the proportions of the species. Fish production (yields and economic margins) and ecological parameters (water and sediment physicochemistry, phytoplankton, zooplankton, macrophytes, and macroinvertebrates) of all ponds were measured. We also monitored meteorological parameters and water temperature throughout the production season.
Results and Discusssion
Temperature and precipitation varied greatly among the three years, which caused pond functioning to vary greatly as well, thus illustrating impacts of climate change. Low water levels in ponds, especially at the end of winter, and high temperatures during the summer limited fish production. Despite high variability among sites and years, one highly diversified species-assemblage scenario (called "resilience") showed promising performances, with a higher mean net fish yield (Figure 1) and economic margin.
The data generated by the project highlighted direct impacts of climate change on pond functioning and productivity potential. The increase in mean temperatures observed, along with prolonged droughts and heat waves, is forcing managers to rethink species assemblages. Introducing new species to the region such as largemouth bass (Micropterus salmoides), which is more resistant to high temperatures, or grass carp (Ctenopharyngodon idella), a herbivorous species that uses natural food resources not used by other fish species, may represent promising adaptation options. In light of these changes in production, market perspectives must also be adjusted. The scenarios tested provide potential pathways for sustainable pond aquaculture that combine acceptable farm income, production resilience, and ecosystem services such as biodiversity conservation.
Figure 1:
Violin plots of net fish yields of 46 ponds stocked with one of five scenarios of fish species assemblages: full carp (80-90% common carp), grass carp (traditional scenario + grass carp), resilience (5-6 species, with two size cohorts for each), profitability (tench, whitefish, and largemouth bass), and traditional (60-70% common carp, 20-30% tench and whitefish, and 10% pike or pikeperch). Whiskers equal 1.5 times the interquartile distance. The dashed horizontal line shows the mean net fish yield of all ponds.
Acknowledgments
The FISHMIX project was funded in the PEPIT programme by the Auvergne-Rhône-Alpes region.
References
Aubin, J., J. Robin, A. Wezel, & M. Thomas, 2017. Agroecological management in fish pond systems. In Agroecological Practices for Sustainable Agriculture: Principles, Applications, and Making the Transition. World Scientific Europe Ltd.
Girard, L., A. Wezel, & J. Robin, 2024. Drying out fish ponds, for an entire growth season, as an agroecological practice: maintaining primary producers for fish production and biodiversity conservation. Open Research Europe 3: 125. https://doi.org/10.12688/openreseurope.16363.1.
Robin, J., M. Guerin, B. Sarrazin, & A. Wezel, 2016. Stimuler la productivité naturelle des étangs de la Dombes. Comment optimiser la disponibilité des ressources alimentaires et améliorer la rentabilité économique de l'activité piscicole tout en conservant la biodiversité? Pôle d'Expérimentation et de Progrès Aquacole of the Rhône-Alpes region and the Ain department.
Wezel, A., Robin, J., Guerin, M., Arthaud, F., Vallod, D., 2013. Management effects on water quality, sediments and fish production in extensive fish ponds in the Dombes region, France. Limnologica 43, (3), 210–218. https://doi.org/10.1016/j.limno.2012.11.003