Molecular evidence of francisella noatunensis sub sp. Orientalis in tilapia oreochromis spp. in yunnan province, south-western china

Abstract

© 2020, Indian Council of Agricultural Research. All rights reserved. Francisella sp. is an emerging bacterial pathogen affecting tilapia Oreochromis niloticus. This study surveyed presence of Francisella sp. in tilapia raised in Yunnan Province, south-western China along with water quality parameters and management practices. A total of 224 tilapia specimens were sampled from 28 farms between June and September 2017. Necropsy of the sampled fish revealed no granulomatous lesions and the standard bacterial isolation protocols proved negative for Francisella sp. However, the presence of Francisella sp. was confirmed by polymerase chain reaction in 18 samples (8%) from 8 of the 28 farms (28.6%) sampled, though no increasing mortality was reported from these farms. The 16S ribosomal RNA gene sequences revealed 99.7% identity with F. noatunensis sub sp. orientalis. The presence of Francisella sp. infection showed significant association with water temperature.