Swimming pool granuloma,The Swimming pool granuloma is a chronic skin

infection caused by Mycobacterium marinum (atypical

mycobacteria). The bacteria are found in fresh, aquarium and

sea waters and in some fish species. They cause an infection

in fish and humans. It permeates broken skin, and 3 – 4

weeks after the injury the infection develops, usually on the

injured spots /upper and lower limbs/.

Thank you very much professor Yang Xiaoliang 

Fish (teleost or elasmobranchs) have a limited clinical spectrum of gross clinical signs in most organ systems. In 20 years as an aquatic veterinarian you learn not to make snap assumptions about the aetiology of a condition, it is highly dangerous. You need to find an aquatic veterinarian to examine your animals, carry out appropriate diagnostic tests including skin scrapes and examination of wet and stained preparations, if very valuable specimens even doing a skin biopsy for histopathological evaluation and bacteriology. Pale skin patches in fish could be parasitic, fungal, bacterial, traumatic, etc. etc. Please seek appropriate local veterinary assistance.

Thanks vet. Colin Johnston we take already skin biopsy for histopathological evaluation and wet mount from lesions for parasitological examination and we make microbiological examination and waiting the results   and I am aquatic veterinarian and Currently, the pathogen is being diagnosed in my laboratory of the Fish Diseases Lab. at the National Institute of Oceanography and Fisheries.We excluded the fact that the pathogen was a parasite or fungi

Good glad that you are working through a diagnostic cascade.