A novel bacterium, designated strain Ruye-53(T), was isolated from a freshwater pond used to rear tilapiine cichlid fish in Taiwan. The taxonomic position of the novel strain was determined using a polyphasic approach. Strain Ruye-53(T) was Gram-reaction-negative, aerobic, cream-white coloured, rod-shaped, non-motile and poly-�]-hydroxybutyrate-accumulating. Growth occurred at 10-37 �XC (optimum between 20 and 25 �XC), at pH 6.0-9.0 (optimum between pH 8.0 and pH 9.0) and with 0-1 % (w/v) NaCl (optimum 0 %). Phylogenetic analyses based on 16S rRNA gene sequences showed that strain Ruye-53(T) belonged to the genus Gemmobacter and that its most closely related neighbour was Gemmobacter aquatilis DSM 3857(T) (97.6 % sequence similarity). The novel strain's predominant fatty acid was C18 : 1�s7c, its major respiratory quinone was Q-10 and its genomic DNA G+C content was 61.2 mol%. The polar lipid profile consisted of a mixture of phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, one uncharacterized aminolipid and four uncharacterized phospholipids. The DNA-DNA relatedness value between strain Ruye-53(T) and Gemmobacter aquatilis DSM 3857(T) was about 45.5 % (48.2��0.4 % in the reciprocal experiment). On the basis of the genotypic, chemotaxonomic and phenotypic data, strain Ruye-53(T) represents a novel species in the genus Gemmobacter, for which the name Gemmobacter tilapiae sp. nov. is proposed. The type strain is Ruye-53(T) (= BCRC 80261(T) = KCTC 23310(T)).