Abstract: A study to determine the effect of varying dietary probiotic levels on the reproductive performance of a freshwater ornamental species, the swordtail (Xiphophorus helleri) was carried out. The commercial probiotic, Primalac were mixed thoroughly with the artificial feeds at concentration of 0.0% (A), 0.04% (B), 0.09% (C) and 0.14% (D) and fed to healthy fish for a period of 26 weeks. Results showed that supplementation of feed with probiotic increased significantly (p<0.05) the Gonadosomatic Index (GSI), fecundity and fry production of female broodstock. Fry production, fecundity and fry survival were significantly higher in group B as compared to the group A (control) (p<0.05). The highest significant Gonadosomatic Index (GSI) and fry weight were observed in group B (p<0.01). The fish of experimental groups B and A recorded the lowest and highest deformed fry (%), respectively. Based on these data, it is concluded that female swordtail broodstocks benefit from inclusion of primalac in diet during their reproductive stages. Further study in needed into the mechanism (s) of action for probiotics such as Primalac and their application in aquaculture.