In the initial stages of production, fish are continually exposed to adverse conditions in the production system and their immune systems are not yet sufficiently developed. High concentrations of ammonia nitrogen in breeding water, due to excess organic matter, pose a threat to survival and growth in larviculture. Probiotics are alternatives that can maintain water quality in aquaculture in a simple and economical manner. However, studies on their application as food additives in the early stages of freshwater fish are scarce, and absent in B. amazonicus larviculture. Thus, our objective was to evaluate the use of potential autochthonous probiotics in feeding yamú larvae on survival after chronic exposure to ammonia.
In total, 3200 yamú larvae (0.0088 g) were distributed in 16 aquariums (20 L), in a continuously aerated closed system with partial water changes of 70% daily. The lyophilized (indigenous) probiotic was added directly to the commercial mashed feed (55% CB, Nutripiscis- PRESENCE®) in mixtures (1:1 ratio), with T1 - mix of three strains Bacillus pumilus, Lactobacillus plantarum, Lysinibacillus sphaericus; T2 - mix of three strains B. cereus, B. megaterium, Lactococcus lactis; T3 - (isolated strains of Colossoma macropomum) B. cereus, B. pumilus, B. subtilis; Tcontrol - commercial feed without probiotics, four replications per treatment. Fed from the food transition (co-feeding) 9–15 days after hatching (dah); therefore, only food plus probiotics, four times a day (15% of live weight), in a proportion of 10 g of probiotics for every 1 kg of feed, for 39 continuous days. On the 20th experimental day, the animals were measured, redistributed (20 fish/box), and transferred to a new system with 310 L boxes and continuous water flow. At the end of the experimental period, fish were exposed to ammonia ((NH4)2SO4) for 96 h at a concentration of 45.49 mg L-1, and their behavior and daily mortality were observed. The concentration was established based on the LC50. Mortality data were evaluated using log-rank survival analysis, with a significance level of p ≤ 0.05. The water parameters remained ideal, with few variations.
When comparing survival, fish treated with probiotics had greater survival (T1 = 15%, T2 = 50%, and T3 = 20%) than those of the control treatment (Tcontrol = 0%), and T2 showed the greatest resistance (p ≤ 0.05) throughout the stress period. During the first 24 h of exposure, Tcontrol resulted in more than 50% mortality (Figure 1).
The results showed that providing a beneficial probiotic mixture can effectively improve the survival of B. amazonicus in the face of chronic ammonia stress. To our knowledge, this study is the first to demonstrate these beneficial effects in larviculture. However, the mechanisms of action of these microorganisms in the early stages of life are enigmatic and require further investigation.