In flounder affected by UDF, the ul

In flounder affected by UDF, the ulcers have been described as open, dark red, rounded, and superficial (Wiklund & Bylund 1993). Ulcer size varied from small lesions (1 to 2 mm) to large eroded areas (10 to 20 mm in diameter). The development of the ulcers was divided into 3 stages: (1) initially weak haemorrhage in the skin which developed into (2) a white lesion surrounded by a red rim of haemorrhagic inflammatory tissue； (3) in the final, true ulcer stage the skin tissue was eroded and the muscle tissue was exposed (Wiklund & Bylund 1993). Unfortunately, there are no reports on histological studies of skin ulcers in flounder.