▪️  Edwardsiella piscicida (old name Edwardsiella tarda (E. tarda) is a gram-negative rod-shaped bacterium (1 μm in diameter and 2–3 μm long) and motile.

▪️ The genus Edwardsiella has previously contained three species; E. tarda isolated from humans and animals, E. hoshinae isolated from reptiles and birds, and E. ictaluri isolated from channel and white catfish.

▪️ Recently, according to molecular and phylogenetic assay, the genus Edwardsiella was reclassified into five species; three fish pathogens (E. piscicida, E. anguillarum, and E. ictaluri) and two non-fish pathogens (E. tarda and E. hoshinae) (Buján et al., 2018).

▪️  E. piscicida is the new name for the previously isolated E. tarda which possesses the type III and type VI secretion systems (T3SS and T6SS). Meanwhile, E. tarda recovered from human or environment do not have any of the previous secretion system (Shao et al., 2018).

Table 1: Differential phenotypic characteristics among Edwardsiella species (Buján et al., 2018)

▪️ The severity of fish Edwardsiellosis has been influenced by many predisposing factors, such as environmental stressors (high temperature, high ammonia and carbon dioxide, low dissolved oxygen), high organic matter, heavy parasitic infestation, and improper use of antibiotic chemicals in aquaculture.

▪️  It was reported that the bacteria can be isolated from sterile pond water over 76 days at 20°C, indicating that the bacterium can remain alive for long time in the environment. E. tarda was isolated from both fresh and salt water, mud, and fouling material in nets. Moreover, it can stay alive at 0–4% sodium chloride, pH 4.0–10.0, and 14–45°C.