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Shrimp production has been affected by disease outbreaks caused by Vibrio sp. bacteria. Using a polyculture system has been proposed as preventive management, but until now, the mode of action by which the organisms in polyculture obtain some benefits was unknown. Some studies indicate that these benefits are related to the immune system in the skin mucus. The present study aimed to determine the antibacterial potential of skin mucus in two tilapia varieties, Oreochromis sp. (marine adapted) and O. niloticus (freshwater), against Vibrio bacteria that affect the shrimp Penaeus vannamei. Skin mucus extracts were obtained from both varieties of tilapia during spring and winter. The extracts were: acidic, aqueous and two organics. In total, 16 extracts were obtained. During the winter season, no antibacterial activity was detected; however, in the spring, the acidic extract from the marine-adapted tilapia inhibited V. parahaemolyticus. Additionally, V. harveyi was inhibited by the acidic and organic extracts from both varieties. The aim of this study was confirmed: tilapia skin mucus has antibacterial activity against Vibrio bacteria, which depends on the tilapia variety, bacterial strain, season and the concentration of colony forming units. SDS-PAGE revealed a protease of 96 kD present in all extracts, even in those without antibacterial activity.

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Probiotics and co-culture of shrimp and tilapia are two strategies to improve yield and ecoefficiency of both species. However, only few studies have analyzed the combination of these two strategies. This study analyzes the effect of a mixture of potential probiotics supplied in the diet at different frequencies in a system of shrimp (10/m2) and tilapia (5/m2) in a trial lasting 84 days. The probiotics mixture was composed of four lactic acid bacteria and one yeast strain that were supplied either daily, every 5 days, or every 10 days in the diet and compared with a control without any supply of probiotics. At the end of the experiment, blood chemistry and hematology of shrimp and tilapia were analyzed as an index of physiological condition. Water quality did not differ between treatments. The final weight, feed conversion ratio, and yield of shrimp were significantly higher with daily supply of probiotics compared to shrimp that did not receive probiotics supply, with intermediate values for treatments with probiotics supply every 5 or 10 days. However, level of supplementation every 5 days could be considered as optimal because no significant differences with daily supply were observed for any variable, whereas the supply each 10 days resulted in a significantly lower yield. Significantly higher final weight, feed conversion ratio, and yield of tilapia occurred with daily supplements. Blood cholesterol in tilapia significantly decreased with increasing frequency of probiotics supplementation. These results indicate that probiotics supplements for shrimp and tilapia cultivated simultaneously improved yields and physiological condition.