The practice of intensive farming in the catfish industry has been increasing along with the odds of disease outbreaks. In addition, hybrid catfish size disparity is problematic for the processing plants, which may lead to financial penalties to farmers. A balanced intestinal microbiota can be beneficial for disease resistance and may assist on standardized growth performance. In this study, an autochthonous probiotic, Lactococcus lactis MA5, was tested in early life stage hybrid catfish. The egg and intestinal microbiota, embryo quality, and body indices were investigated after rearing the fish for 92-days in a pond-like environment.
Parent fish (female: channel catfish; male: blue catfish) were obtained from the Warmwater Aquaculture Research Unit (USDA-ARS), and used to obtain the gametes. Eggs were collected and divided into a control and two probiotic groups. The first probiotic group (TRT) was introduced to MA5 during fertilization; eggs and sperm were mixed with 1.03×107 CFU of MA5/mL, and incubated in individual McDonald type hatching jars in a flow-through system for 48 hours (N=3). Embryos were collected for microbiota characterization and tested for egg quality-related gene expression levels. After hatching, 3,000 fry were moved to an indoor aquarium system for an intermediate nursery with 500 fish/tank (70-L). Fish were fed with a commercial feed to satiation three times a day. The second probiotic group (IM) was exposed to MA5 at this point; 6 tanks of 15-day post-hatched naïve fish were immersed with 2.1×107 CFU/mL of MA5 in 10-L aquarium tanks for 20 mins. Finally, catfish fry (~0.5 grams) were moved to outdoor tanks operating as a recirculating system using pond water (n=3) and reared for 92 days. The body weight, total length, and intestinal microbiota were assessed. The result shows the TRT group has less body weight and total length variation compared to the other groups. No genes were found to be significantly differentially expressed, however there was a trend of lower hsp70 expression in the TRT group compared to the control. Relative abundances of approximately 23-39% were observed for Lactococcus spp. after 48 hours of fertilization in TRT embryos. Weight gain was not affected by MA5. In summary, the autochthonous probiotic MA5 may be a valuable for decreasing size disparity without affecting embryo quality, when introduced during egg fertilization.