The increasing use of antibiotics in aquaculture, notably sulfamethoxazole (SMX) and trimethoprim (TMP), has raised environmental concerns due to their persistence and potential toxicity to non-target aquatic species. These compounds are frequently used in combination as a composite (co-trimoxazole), which may demonstrate distinct biological effects relative to the individual compounds. Evaluating the risks associated with their presence in the environment requires understanding their ecotoxicological profiles and potential interactions.

This study examined the effects of SMX, TMP, and their combination on the green microalga Chlorococcum sp., selected as a representative aquatic species. Cultures were subjected to environmentally relevant concentrations of each compound and their combinations under controlled laboratory conditions to evaluate potential toxic responses.

The purpose of this research is to elucidate the individual and combined detrimental effects of SMX and TMP and to propose alternative approaches to mitigate their environmental impacts. The work advances our understanding of the environmental behaviour of antibiotic combinations and their relevance to sustainable aquaculture methods.

Acknowledgements: "The research project is implemented in the framework of H.F.R.I call "3rd Call for H.F.R.I.'s Research Projects to Support Faculty Members & Researchers" (H.F.R.I. Project Number: 26141)".