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Cantharidin, a toxic monoterpene secreted by blister beetles, has long been used in traditional Chinese and modern medicine for its unique properties. However, despite its widespread use, its effects on fish have not been studied. The aim of this study was to evaluate the potential therapeutic applications of cantharidin in fish by examining its antioxidant, hemagglutinating, hemolytic, and cytotoxic activities at different concentrations (0, 0.625, 1.25, 2.5, 5, and 10 μg mL−1) in three different cell lines. In addition, the study explored the bactericidal and bacteriostatic properties of cantharidin against various fish pathogenic bacteria. The results revealed that there were no significant differences in antioxidant, hemagglutinating, or hemolytic activities between the different concentrations of cantharidin tested. However, the study found that cantharidin exhibited dose- and time-dependent cytotoxicity in seabream (Sparus aurata) erythrocytes and in SAF-1, PLHC-1, and Hela cell lines, resulting in morphological changes indicative of apoptosis. Interestingly, the highest dose of cantharidin tested demonstrated potent bactericidal activity against four marine fish opportunistic bacteria, including Vibrio harveyi, V. anguillarum, Photobacterium damselae, and Tenacibaculum maritimum, but no statistically significant changes in bacteriostatic activity were observed against any of the bacteria tested. Overall, these results provide valuable information on the potential therapeutic applications of cantharidin in fish aquaculture. Further research is needed to fully understand the mechanisms of action and to explore possible preventive uses of cantharidin in fish.

Gilthead seabream is bred mainly in fish farms in the Mediterranean Sea. One important factor responsible for the deterioration of fish quality is lipid oxidation. Moringa oleifera leaves have been described as having high antioxidant content. This work investigates the effect of dietary supplementation with Moringa leaves on the antioxidant activity of seabream. Gilthead seabream specimens were divided into four groups, the control group (fed a commercial diet) and three other groups fed diets enriched with Moringa (5%, 10% and 15%). The antioxidant capacity was measured by assays of free radical scavenging (OH·, H2O2, lipoperoxyl and ABTS), Rancimat test and linoleic acid system in muscle and skin of gilthead seabream, commercial diet, enriched diet and Moringa. Finally, the polyphenol content of Moringa and the fatty acid composition of seabream fed diets with and without Moringa were determined. Results showed an increase in antioxidant activity in gilthead seabream fed with diets enriched with a higher percentage of Moringa; therefore, Moringa could be considered a functional ingredient in diets for fish bred in fish farms and. The antioxidant potential of Moringa leaves could be mainly attributed to the presence of polyphenolic compounds.

Disease outbreaks continue to represent one of the main bottlenecks for the sustainable development of the aquaculture industry. In marine aquaculture, many species from the Vibrio genus are serious opportunistic pathogens responsible for significant losses to producers. In this study, the effects on the immune response and the skin microbiota of European sea bass (Dicentrarchus labrax) were studied after a natural disease outbreak caused by V. harveyi. Data obtained from infected and non-infected fish were studied and compared. Regarding the local immune response (skin mucus) a decrease in the protease activity was observed in infected fish. Meanwhile, at a systemic level, a decrease in protease and lysozyme activity was reported while peroxidase activity showed a significant increase in serum from infected fish. A clear dysbiosis was observed in the skin mucus microbiota of infected fish in comparison with non-infected fish. Moreover, V. harveyi, was identified as a biomarker for the infected group and Rubritalea for healthy fish. This study highlights the importance of characterizing the mucosal surfaces and microbial composition of the skin mucus (as a non-invasive technique) to detect potential disease outbreaks in fish farms.

Biocides are chemical substances that can deter or kill the microorganisms responsible for biofouling. The rapid expansion of the aquaculture industry is having a significant impact on the marine ecosystems. As the industry expands, it requires the use of more drugs, disinfectants and antifoulant compounds (biocides) to eliminate the microorganisms in the aquaculture facilities. The use of biocides in the aquatic environment, however, has proved to be harmful as it has toxic effects on the marine environment. Organic booster biocides were recently introduced as alternatives to the organotin compounds found in antifouling products after restrictions were imposed on the use of tributyltin (TBT). The replacement products are generally based on copper metal oxides and organic biocides. The biocides that are most commonly used in antifouling paints include chlorothalonil, dichlofluanid, DCOIT (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one, Sea-nine 211®), Diuron, Irgarol 1051, TCMS pyridine (2,3,3,6-tetrachloro-4-methylsulfonyl pyridine), zinc pyrithione and Zineb. There are two types of risks associated with the use of biocides in aquaculture: (i) predators and humans may ingest the fish and shellfish that have accumulated in these contaminants and (ii) the development of antibiotic resistance in bacteria. This paper provides an overview of the effects of antifouling (AF) biocides on aquatic organisms. It also provides some insights into the effects and risks of these compounds on non-target organisms.