Among the range of practices that promote aquaculture efficiency and sustainability, polyculture (i.e. production of two or more fish species in the same physical space at the same time, adapted from ), is one of the most ancient fish farming practice in the world. In Western Europe, intensive monoculture has been favored during the last decades instead of the traditional extensive pond polyculture production. Nevertheless, the recent theorization of long-standing productions as well as developments of new concepts (agroecology) and practices (integrated multi-trophic aquaculture, aquaponics, and integrated agriculture-aquaculture) reflect a renewed interest in polyculture for future aquaculture developments . Indeed, polyculture is seen as an opportunity to promote aquaculture by mitigating some of the negative impacts and unsustainable development of current aquaculture . In order to be efficient, polyculture requires that the involved species are compatible (i.e. species which can live in the same production system without detrimental interactions or competition for resources) and moreover complementary (i.e. species which can use different parts of the available resources or develop commensal/mutualist interactions) . Ensuring compatibility and complementarity requires to promote an optimal use of all resources; trophic (e.g. by combining species with different diets), spatial (by combining species occupying different areas in the living environment), and temporal (by combining species with different periods of activity; e.g., day and night) . Although long-standing polyculture are available, new species combinations are requested to maximize the benefits of polyculture, to address new socio-economic and environmental challenges (e.g. climate change, new technological developments and new consumer demand). For example, considering the context of climate change, new species combinations are needed since some species that were initially compatible in a given environment may no longer be so due to the resistance of some of them to variations in environmental parameters such as temperature and salinity. Moreover, considering a large number of species could maximize the chances to determine the best combination(s) of species to provide to fish farmers.
Problematic and objectives
Designing new species combinations involves considering a large number of possible species combination, which cannot be assessed by empirical methods. Indeed, such methods are based on trial-and-error essays, and are thus time-consuming and costly. They do not maximize the chances of identifying combinations of polyculture that respond to new socio-economic and environmental issues. Such empirical approaches are reasonably unlikely to be feasible for practical and ethical reasons . Moreover, considering only empirical methods cannot be regarded as the most efficient solution to develop new fish polyculture because the most useful species combination(s) for aquaculture purpose could be missed out. To overcome this problem, here we propose an integrative conceptual method to standardize and rationalize the choice of the best species combinations for future polyculture.
Background and steps of the in silico method
In order to reach an efficiency and sustainability aquaculture, a polyculture should (i) use optimally all available resources in the aquaculture system, (ii) to maximize fish welfare while addressing regulation, economic and environmental expectations. This implies to consider interspecific interactions to design new combinations, because the functioning of an agro(eco)system depends mainly on the nature of these interactions . Therefore, considering functional approach through species functional traits is necessary to understand how organisms interact with their environment and with other species .
Based on a functional approach, we propose the development of a new prospective and integrative method, divided into four successive assessing steps, requiring the intervention of scientists and stakeholders at several levels. The first step consists in theoretically predicting the compatibility of a wide number of fish species using their relevant functional traits (morphological: e.g., size, mass, physiological: e.g., growth rate, phenological: life span, and behavioral: e.g. swimming activity, predation, intra and interspecific relationships), available in different databases. The fish species compatibility is based on the calculation of an index, considering their stage of development, their abiotic requirements, the degree of competition for space/time/trophic resources and the risk of predation. This index is based on a contrasting gradient of compatibility ranging from 0 for incompatible species to 1 for highly compatible species. The second step aims to select one or more (new) species combination considering the stakeholder’s advices. The third step assesses species combinations performances from bioassays in Recirculated Aquaculture systems or in ponds. A fourth step corresponds to the transfer of technologies in real aquaculture exploitation conditions. During the conference, the presentation of the in silico method will be widely illustrated with examples of species combinations which have been tested in Recirculated Aquaculture systems.
This research program was funded by FEAMP SEPURE, INTERREG V A Perciponie and the ‘Zone Atelier Moselle’.
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