Monitoring the gut microbiota of rainbow trout during seawater acclimation

Abstract In seawater aquaculture of rainbow trout, deaths and poor growth may occur after seawater acclimation, so it is necessary to establish a satisfactory seawater transfer method. To understand more about the problems affecting fishes around the time of acclimation, the gut microbiota composition of rainbow trout was monitored by regular serial collection of fecal samples from the same individuals to determine any relationship between changes in gut microbiota and the health of the fish after seawater acclimation. Although there were some differences in the bacteria detected depending on the production lots of fish that were used, Mycoplasma species dominated most of the gut microbiota regardless of salinity, suggesting that the presence of this genus is characteristic of the rainbow trout gut. In addition, bacteria of the family Vibrionaceae, mainly Vibrio sp. and Aliivibrio finisterrensis , appeared at salinities higher than 18 psu. In particular, there was a negative correlation between trout growth and the relative abundance of Vibrio sp. It is concluded that the gut microbiota change drastically on transferring trout from freshwater to seawater aquaculture systems, and that the abundance of Vibrionaceae species may be a useful general health indicator of trout in seawater aquaculture.