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Biofouling in freshwater and marine environments developed on man-made aquatic surfaces causes significant economic losses. Still, this problem is magnified when it comes to invasive species, such as the golden mussel. One of the alternatives to combat it is the use of antifouling solutions; however, the vast majority focus on solutions for the marine environment. In this same context, natural antifouling solutions from macrophytes have been reported as promising to combat estuarine biofouling; however, trials with freshwater organisms are still incipient. Thus, this study evaluated the performance of 25 macrophyte extracts in inhibiting the formation and/or eradication of bacterial biofilms, settlement of the golden mussel (Limnoperna fortunei), as well as its toxicity effect on three different non-target model organisms of three trophic levels. Among the 25 extracts, nine demonstrated ≥ 60% inhibition of biofilm formation, with only the extracts of Typha domingensis and Eichhornia crassipes having a biofilm inhibitory effect of ≥ 70% for bacterial isolates and ≥ 60% for multispecies biofilms. Planktonic growth had distinct responses, ranging from induction, inhibition, and no effect on growth. The T. domingensis extract showed quorum sensing inhibition (QSI) with a dose-dependent relationship, while the E. crassipes extract showed QSI only at a dilution of 1.2%. These same extracts prevented the golden mussel from attaching and showed safe concentrations of 35.35% for Pseudopediastrum boryanum and Daphnia magna and 70.71% for Pimephales promelas. This study highlights the biotechnological potential of macrophyte extracts as a sustainable and environmentally harmless alternative for the control of micro and macrofouling in freshwater environments., Competing Interests: Declarations. Ethical approval: According to Brazilian legislation (Law 11,794 of October 8, 2008), research with invertebrates does not require authorization from any ethics or animal welfare committee. The collection of invertebrates was approved by the Brazilian Agency SisBio (process no. 77095–1). The assay with P. promelas was approved by the Consejo Nacional del Ética Animal (CNEA) – Ata n° 17/11. Consent to participate: Not applicable. Consent for publication: Not applicable. Competing interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Co-author Ng Haig received research support from the National Council for Scientific and Technological Development – CNPq (Process 404233/2021–0), and co-author Grasiela Lopes Leães Pinho received research support from the Mixed Technical Commission of Salto Grande and Latitud (Uruguay Technological Laboratory Foundation – LATU)., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The yellow clam is a sand-burrowing bivalve that inhabits the dissipative beaches from southern Brazil to the north coast of Argentina. In the last decades, populations of this species have been impacted by mass mortality events, overfishing and other anthropogenic activities. The production of juveniles in captivity would allow feasibility studies to be carried out to restore the natural stock as well as the production in aquaculture systems. Given the scarcity of studies on the maintenance of this species in captivity, a culture system and a management protocol were developed and tested. Wild-caught clams (total length ≥50 mm) were used in a series of 14 day-long trials. Survival was higher in clams that were allowed to bury into the sand. A permanent ink marker covered with a thin layer of a quick-hardening adhesive proved to be a reliable method to tag clams. The maintenance of yellow clams in this system resulted in high survival and growth, increases in the condition factor and oocyte diameter, and a relative advancement of gonadal development.