A novel bacterial isolate A520ᵀ (A520ᵀ = CBAS 737ᵀ = CAIM 1944ᵀ) was obtained from the skin of bandtail puffer fish Sphoeroides spengleri (Tetraodontidae Family), collected in Arraial do Cabo (Rio de Janeiro, Brazil). A520ᵀ is Gram-stain-negative, flagellated and aerobic bacteria. Optimum growth occurs at 25–30 °C in the presence of 3% NaCl. The genome sequence of the novel isolate consisted of 4.5 Mb (4082 coding genes and G+C content of 41.1%). The closest phylogenetic neighbor was Pseudoalteromonas shioyasakiensis JCM 18891ᵀ (97.9% 16S rRNA sequence similarity, 94.8% Average Amino Acid Identity, 93% Average Nucleotide Identity and 51.8% similarity in Genome-to-Genome-Distance). Several in silico phenotypic features are useful to differentiate A520ᵀ from its closest phylogenetic neighbors, including trehalose, D-mannose, cellobiose, pyrrolidonyl-beta-naphthylamide, starch hydrolysis, D-xylose, lactose, tartrate utilization, sucrose, citrate, glycerol, mucate and acetate utilization, malonate, glucose oxidizer, gas from glucose, nitrite to gas, L-rhamnose, ornithine decarboxylase, lysine decarboxylase and yellow pigment. The genome of the novel species contains 3 gene clusters (~ 66.81 Kbp in total) coding for different types of bioactive compounds that could indicate ecological roles pertaining to the bandtail puffer fish host. Based on genome-based taxonomic approach, strain A520ᵀ (A520ᵀ = CBAS 737ᵀ = CAIM 1944ᵀ) is proposed as a new species, Pseudoalteromonas simplex sp. nov.