How to prevent and treat shell ulcer disease (brown spot disease) in prawns

(1) Pathogen The bacteria that can be isolated from the lesions include Vibrio, Pseudomonas and Flavobacterium, etc. They are Gram-negative bacilli. 

(2) Symptoms ① On the body surface shell and appendages of diseased prawns there are dark brown or black spot-like ulcers, forming brown depressions. The middle of the depression is deeper, and the surroundings of the depression are shallower and slightly white. ② In severe cases, the ulcers reach into the soft tissue beneath the shell, and some diseased prawns even have the rostrum (the frontal spine of the prawn, also called the prawn spear), appendages and tail fan completely rotted off, with the cut surface appearing black. Melanin is deposited around the ulcer site of the prawn to inhibit the rapid expansion of the ulcer, forming black spots. Pathogenic bacteria can invade the prawn's body through the wound, causing the prawn to become infected and die. 

(3) Diagnosis It can generally be diagnosed with the naked eye, but it must be distinguished from fusariosis. Fusariosis mainly appears in the branchial region of the carapace, while shell ulcer disease is more scattered in location, appearing everywhere on the dorsal shell, lateral shell, tail fan, antennal scales and rostrum. Secondly, fusariosis shows mycelium and conidia under microscopic examination, while brown spot disease mostly shows motile bacilli. 

(4) Epidemiology It is generally caused by poor water quality and bottom quality leading to massive Vibrio reproduction, which triggers the disease. Prawns are especially susceptible to infection when injured, and it is one of the common diseases in prawn disease prevention and treatment. 

(5) Prevention and treatment ① Feed high-quality feed. ② Ensure that the water environment has good water quality free from pollution. ③ Regularly splash disinfectants and water quality improvers to maintain a stable environment.