The digestive tract houses a consortium of microorganisms that plays critical roles in the nutrition and health of the host. Gut microbiota changes during the daily cycle, however, there is limited knowledge on absolute (vs. relative) temporal microbiota abundance variation (Vandeputte et al., 2021). Water temperature is a crucial factor in fish production, influencing among others feed intake and transit time. The aim of the present study was to assess the effect of rearing temperature and daily feeding rhythms on the fish gut microbiota. The greater amberjack (Seriola dumerili) was used as experimental species, a promising species for the diversification of Mediterranean aquaculture. Fish were randomly distributed in three independent RAS systems set to 18, 22 and 26°C. Juveniles were reared for 12 days and fed ad libitum three times daily with a commercial diet. Then, nine fish per temperature were sampled every 6 h for 24 h for fecal microbiota analysis. Results from 16S rDNA qPCR revealed no effect of temperature and sampling time on bacterial abundance per mg of gut content. By contrast, when focusing on the quantity of active cells (qPCR of 16S rRNA), differences with respect to sampling time but not temperature, were observed. The bacterial activity increased a factor 30 due to feeding but was reduced to prefeeding levels four hours after the last meal. This pattern was also observed in the specific bacterial activity (RNA:DNA ratio), with almost 2 orders of magnitude increase during the period of active feeding. At 18°C a higher dispersion in the results was observed, probably because of the slower gut transit time. Regarding community composition, feeding promoted an increase in the relative and absolute abundance of the order Vibrionales. In conclusion, this is the first study assessing the quantitative and qualitative effects of water temperature and daily feeding rhythm on the gut microbiota in fish. Feeding was the main driver modulating bacterial activity and suggest resource limitation of the gut microbiota during non-fed periods. However, low temperature seems to slow down the process, probably due to a slower digestive process.

Trabajo presentado en el XX International Symposium on Fish Nutrition and Feeding "Towards Precision Fish Nutrition and Feeding", celebrado en Sorrento (Italia) entre el 5 y el 9 de junio de 2022.

Project RTI2018-096134-B-I00 (MCIU-AEI, Spain + FEDER)