Toxicity induced by three antibiotics commonly used in aquaculture on the marine microalga Tetraselmis suecica (Kylin) Butch

• Antibiotics assayed cause adverse effects on the microalgae Tetraselmis suecica.
• The most affected parameters were those related to photosynthesis and growth.
• Based on the IC50 values obtained toxicity can be ranked as FLO > CHL > OTC.
• Flow cytometry provides additional and accurate information for this type of studies.

Aquaculture facilities are a potential source of antibiotics to the aquatic ecosystems. The presence of these compounds in the environment may have deleterious effects on non-target aquatic organisms such as microalgae, which are often used as biological indicators of pollution. Therefore, the toxicity induced by chloramphenicol (CHL), florphenicol (FLO) and oxytetracycline (OTC), three antibiotics widely used in aquaculture, on the marine microalga Tetraselmis suecica was evaluated. Growth inhibition and physiological and biochemical parameters were analysed. All three antibiotics inhibited growth of T. suecica with 96 h IC50 values of 11.16, 9.03 and 17.25 mg L−1 for CHL, FLO and OTC, respectively. After 24 h of exposure no effects on growth were observed and cell viability was also unaffected, whereas a decrease in esterase activity, related with cell vitality, was observed at the higher concentrations assayed. Photosynthesis related parameters such as chlorophyll a cellular content and autofluorescence were also altered after 24 h of antibiotics addition. It can be concluded that T. suecica was sensitive to the three antibiotics tested.