Comparative analysis of intestinal microbiota of discus fish (Symphysodon haraldi) with different growth rates

Discus fish (Symphysodon haraldi) is an important ornamental species. There are significant individual growth differences in the same batch of fry under the same feeding conditions. Such differences can greatly influence the efficiency and profitability of discus farming. Gut microbiota plays an important role in fish nutrition metabolism and growth. Studies on the relationship between intestinal microbiota and growth rates are scarce to the present. Here, we investigated the community diversity and function of intestinal microbiota of juvenile and adult discus from the same parents but with different growth speeds under the same conditions. The results showed that, for juvenile (40 days post-hatch (DPH)) and adult (270 DPH) discus, the OTUs (856 vs. 657 and 1408 vs. 1222, respectively) of bacterial community of the slow-growing discus were both higher than those of the fast-growing ones. No significant differences in microbial community diversity between fast- and slow-growing juveniles or adults were observed. However, for 40 DPH discus, relatively higher content of Plesiomonas (2.53% vs. 0.6%) was observed in the intestines of slow-growing juveniles while relatively higher levels of Bacillus (2.95% vs. 1.83%) and Lactococcus (0.86% vs. 0%) were found in those of fast-growing ones. For 270 DPH discus, relatively higher content of Enterococcus (5.62% vs. 0%) was observed in the intestines of slow-growing adults but relatively higher level of Lactococcus (7.06% vs. 1.27%) was found in those of fast-growing ones. Although no significant divergences in bacterial communities and in functional profiles between fast- and slow-growing juveniles or adults were observed, the bacterial species (e.g., Bacillus and Lactococcus) mentioned above might account for discus distinct growth performance.