Microbiome manipulation
We manipulated the gut microbiome of the fish in the tanks using control (untreated) feed, antibiotic treated feed and probiotic treated feed:
Antibiotic treatment : Oxytetracycline (OTC), and Chloramphenicol (CAP), two broad spectrum antibiotics, were selected for the trial. Twenty-four tanks (for 12 (families)*2 (replicates)) were labelled as antibiotic and were treated with OTC (83 mg/kg/day concentration) (Kokou et al., 2020; Rosado et al., 2019) for six days. After six days the fish were switched to a combination of Chloramphenicol (CAP) (42 mg/kg/day) (Bilandzic et al., 2012) plus the OTC for four more days, for a total of 10 days of antibiotic treatment. Fish were fed three times a day at approximately 3% of their body weight.
Probiotic treatment : Twenty-four tanks (for 12 (families)*2 (replicates)) were labelled as probiotic treatment and fed commercially available Jamieson Probiotic Complex with 60 billion colony forming units (CFU) (Jamieson Laboratories, Canada; Supplementary Table S1). Specifically, the probiotic-treated feed (3 capsules per 100 gram of feed) was coated with 10 mL of sodium alginate (1%) and 10 mL of 0.5 % calcium chloride prior to mixing with the probiotic powder. Fish were fed three times a day at approximately 3% of their body weight.
Control : Twenty-four tanks (for 12 (families)*2 (replicates)) were labelled as control group and fish were fed with regular feed without probiotic or antibiotic for ten days. Fish were fed three times a day at approximately 3% of their body weight (Fig. 1).