Effect of water containing Lactobacillus rhamnosus PTCC 1637 on survival rate and water quality for rainbow trout (Oncorhynchus mykiss) fingerling

As an alternative to chemicals and antibiotics, probiotics have proven to be effective in promoting successful aquaculture. They can improve water quality and generate high-quality livestock. The current study aimed to investigate the effect of adding Lactobacillus rhamnosus PTCC 1637 to the rearing water on survival rate and water quality during spawning on juvenile stages of rainbow trout of Oncorhynchus mykiss. This study has been implemented in three groups (1: eyed eggs, 2: alevin, and 3: fry) and three treatments (1 × 106, 1 × 107 bacteria per mL of water, and a control group). The abovementioned bacterial concentrations in group 1 were added on the days 1, 3, and 5; in group 2, every other day; and in group 3, from the days 1 to 20 on every other day, and from 20 to 60 once every four days. The results showed that the direct addition of L. rhamnosus to the rearing water improved the water quality parameters (DO, pH, ammonia and ammonium; p<0.05). Also, according to the results of the second part, the highest survival rate (%) was observed in the eyed egg group (the days 1-20). The highest survival rate in the third part was found in the treatments receiving bacteria in the eyed egg (the days 1-60) and alevin (the days 8-60) groups. In general, the use of bacteria in the eyed eggs group (107 CFU/mL) that received bacteria from the first day exhibited a more favorable result. Finally, probiotics added directly into the rearing water is an effective method that causes increases survival and improves water quality parameters in O. mykiss.