Amelioration of gonadal development by increased expression of kisspeptin, GnRH and GTH subunit genes in Nile tilapia (Oreochromis niloticus) reared with probiotics

Nutrition plays an important role in influencing reproductive events spanning from puberty to gametogenesis in all vertebrates, including fish. To know the effects of probiotics on gonadal maturation, expression of genes representing kisspeptin (kiss2), kisspeptin receptor (kiss2r) GnRH (gnrh1, gnrh2 and gnrh3) in the brain and GTH subunits (fshb and lhb) and growth hormone gene (gh) in the pituitary as well as gonadal histology and gona-dosomatic index (GSI) were examined in Nile tilapia (Oreochromis niloticus) reared with probiotics. Male (n =20/ aquarium) and female (n =20/aquarium) fry were reared separately with two probiotics (commercial and lab-developed) treatments, including a control (without probiotics), each with three replications for 6 weeks (42 days). The commercial probiotics containing Bacillus subtillis, B. licheniformis, B. polymyxa, B. coagulans, B. megaterium, B. pumilus, B. amyloliquefaciens, Aspergillus niger, A. oryzae with a load of 3.2 x10(9) cfu/mL and lab-developed probiotics containing Bacillus subtilis, Lactobacillus buchneri and L. rhamnosus with a load of 2.5 x10(9) cfu/mL. Both probiotics were added directly in water of aquarium at a dose of 1.0 mL/L. The relative mRNA level of kiss2, kiss2r, gnrh1 and gnrhr in the brain of both sexes significantly increased in response to probiotic treatment compared to the fish without probiotic. In the pituitary, the gh and fshb in both sexes and lhb in females were also significantly increased in response to probiotic treatment. Histological analysis exhibited advanced development of gonad (higher proportion of spermatids and vitellogenic oocytes in male and female, respectively) with increased GSI due to probiotics application. Overall, the findings of this study suggest that probiotics have a stimulatory impact on gonadal development by up-regulating the kisspeptin/GnRH/GTH system in Nile tilapia.