Lactic acid bacteria viability and interactions in recirculating aquaculture systems for fish farming

In light of the growing demand for more sustainable aquaculture systems, this study evaluated the viability and interactions of the potentially probiotic lactic acid bacteria (LAB) strains Lacticaseibacillus paracasei GV17 and Lactococcus lactis GV103, either individually or in combination with a commercial bioremediator, in recirculating aquaculture systems (RAS). Eight treatments were tested to evaluate LAB viability under varying concentrations of nitrite (0.5-2.0 mg/L), ammonia (1.0-3.5 mg/L), pH levels (6.0-8.5), and temperatures (20 °C and 26 °C), as well as their effects on nitrite and ammonia concentrations in the system. Except for the bioremediator treatment at 26 °C, where no LAB viability was observed after 5 h at ammonia concentrations above 1.5 mg/L, all other treatments supported the growth of the strains under the tested conditions. The viability of LAB in recirculating aquaculture systems (RAS) was confirmed, with concentrations ranging from 13.0 to 14.0 log CFU/mL detected up to three days after inoculation in the presence of fish. After this period, reapplication was necessary. Additionally, ammonia and nitrite levels fluctuated over time, demonstrating the influence of LAB on water quality. These results indicate that Lbs. paracasei GV17 and Lactococcus lactis GV103 are capable of tolerating adverse environmental conditions and show potential for application in aquaculture systems as auxiliary agents in bioremediation.