Introduction
In recent decades, the monoculture farming of pikeperch (Sander lucioperca) has expanded, primarily in Europe and Central Asia, relying on recirculating aquaculture systems (RAS), land-based aquaculture systems (P��nka et al., 2025). However, while RAS farming offers many advantages (water savings, control of rearing conditions, etc.), this system also has drawbacks, notably high production costs that increase when energy prices rise. Furthermore, pikeperch remains a species highly sensitive to stress related to rearing conditions and various handling procedures (Baekelandt et al., 2018). This vulnerability can lead to greater susceptibility to pathogens, particularly opportunistic bacteria, and consequently necessitate the use of antibiotic treatment (survey towards the European Percid Fish Culture Group, 2024). Moreover, due to its specific behavior and biological preferences, pikeperch reared in monoculture does not make optimal use of available resources in tank (diet, water volume and depth) and polyculture, with another species, would have a benefit effect on rearing conditions and fish welfare. Therefore, the aim of our study is to evaluate the effects of antibiotic therapy and polyculture with the Russian sturgeon Acipenser gueldenstaedtii, a highly complementary species (P��nka et al., 2024), on zootechnical performances of both species reared in RAS and the consequences on bacterial communities of the system, which is influenced by fish species and play major roles in RAS (Changey et al., 2025).
Materials and methods
Our study was carried out at the Experimental Aquaculture Platform (PEA) of the University of Lorraine using 12 temperature-lighting-controlled independent RAS. The initial acclimatization of 110 kg of pikeperch (individual weigth of 200-300 g, from La Ferme Int��grale, La Baume-d'Hostun, France) and 50 kg of Russian sturgeon (individual weigth of 75-250 g from Belgium Quality Fish, Dottignies, Belgium) was done in separate specific tanks during september 2024. After this period, the batch of pikeperch was divided in two separate RAS which only one received an antibioc therapy for 10 days (15 g of Trisulmix per 100 kg of fish added to the diet). Then fish were transferred to experimental ecotrons on October 4th (10 kg/tank). Four experimental treatments were applied in triplicate: monoculture of pikeperch without previous antibiotic therapy (P), monoculture of pikeperch with previous antibiotic therapy (P+Ab), biculture of pikeperch without previous antibiotic therapy and russain sturgeon (PE) and biculture of pikeperch with previous antibiotic therapy and russain sturgeon (PE+Ab) with 50% of each species for biculture. The experiment lasted two months at a constant temperature (23-24°C) and fishes were fed at 1.2% feeding rate (Percid Grower Le Gouessant, 52% lipids, 15% proteins and 21,4 MJ/kg energy). Water quatity was controlled weekly and individual fish growth monthly (30 fish/species/ecotron), in order to characterize the growth performance of each species, biomass gains, and feed efficiency. Bacterial communities of gut, surfaces biofilm, and water was analyzed using 16S rRNA gene metabarcoding analysis.
Results and discussion
At the end of the experimental period, we observed that the mortality was very low and similar in all treaments. However, significant effects were observed on final biomass and biomass gain which were significantly higher in bicultures compared to monocultures. Lower food conversion rates were calculated in bicultures (IC = 1) compared to the monocultures among which the feed conversion ratio was significantly higher in the treatment group "pikeperch monoculture without antibiotic therapy" (IC = 2.5). Considering performances of each species, any significant difference was recorded in their final mean body weight, those of Russian sturgeon were exactly similar (1.15-1.20 kg) whereas for pikeperch, the final mean weight is close to be significantly higher in the mixed culture with antibiotic therapy" treatment compared to the pikeperch monoculture (P-value = 0.0629). We observed that pikeperch feeding behaviour was different in biculture compared to monoculture. Significant effects of antibiotic therapy and fish species on RAS bacterial communities were recorded. Antibiotic therapy induced a sharp reduction in alpha-diversity within the gut of all treated pikeperch, as well as in the water of the corresponding experimental groups. PERMANOVA results for planktonic and sessiles communities demonstrate that this effect significantly extends to beta-diversity in the water and in the biofilms (R2 = 0.3293 ; P-value=1e-4 ; R2 = 0.2778 ; P-value =1e-4 respectively). Notably, the polyculture with or without a previous antibiotic therapy for pikeperch, exhibited the highest similarity in terms of beta diversity for both water and biofilms, (despite remaining significantly different (R2 = 0.21758 p=0.01 for water ; and R2= 0.1116 ; p=0.047 for biofilms) suggesting a greater resilience of biofilms formed in polyculture compared to those in monoculture.
Acknowledgments
This work was funded by the research programme Interreg GR VA PolyRAS (INTGR0100025). We thank the members of the European Percid Fish Culture for their contribution to the survey on antibiotic therapy practices for pikeperch and Mr. A. Lautraite, the referring veterinarian for the PEA.
References
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