Effect of dietary Saccharomyces Boulardii on growth performance and heat tolerance in guppies.

Guppies (Poecilia reticulata), are a major export in the ornamental fish industry. Challenges associated with intensive farming practices, suboptimal growth performance and reduced tolerance to elevated water temperatures. Saccharomyces boulardii, a well-documented probiotic yeast in food fish, remains relatively underexplored in ornamental fish species. Therefore, this study was conducted to evaluate the effects of dietary S. boulardii supplementation on growth performance, feed efficiency, heat tolerance, and reproductive output in guppies. A total of six experimental groups were used, comprising three control replicates (G0) and three probiotic replicates (G1), with 10 fish per tank. Fish were fed for four weeks, during which G0 received a commercial diet, while G1 was fed a diet supplemented with S. boulardii at 1 × 107 CFU/g feed. Growth parameters, including weight gain and feed conversion ratio (FCR), were assessed at the end of the feeding trial, while survival was monitored throughout the experiment. Following the feeding period, all groups were subjected to a 48-hour heat tolerance challenge at 32°C to evaluate thermal resilience. Guppies fed the probiotic-supplemented diet exhibited significantly higher mean weight gain (0.24 g; p < 0.05) and improved FCR (1.187; p < 0.05) compared to the control group. Survival rates during the feeding trial were comparable between groups. During the heat tolerance challenge, the probiotic group exhibited a 100% survival rate, slightly higher than that of the control group (96.67%), suggesting improved physiological resilience to thermal stress; however, the difference was not statistically significant. Additionally, a higher frequency of offspring production was observed in the probiotic group during the feeding period. Overall, this study demonstrates that dietary S. boulardii supplementation can improve feed efficiency, promote modest growth enhancement, enhance heat tolerance, and potentially stimulate reproductive output in guppies, highlighting its potential application in sustainable ornamental fish culture.