What is Hikui?

Hikui is a benign skin disease found in certain varieties of koi carp (Kohaku, Sanke, Showa). It affects individuals over 2 years old with a very good red quality and affects both males and females.

This disease initially affects red skin areas (Hi) but can spread to other colors (especially white).

Clinically, diseased individuals develop hyperplasia of the epidermis, then inflammation and finally skin erosion (Japanese breeders initially called it “Hi Kui Wa-mu” because of of the appearance of these lesions). These lesions are often associated with hemorrhage or erythema. Red areas often turn white, but white areas can also become pigmented (migration of erythrophores).

Lesions are generally located on the back and top of the head, more rarely on the stomach or sides of the lower abdomen. Fish rarely succumb to skin lesions, and eventually heal but associated with changes in skin coloring.

Many etiologies have been mentioned (chronic inflammation, neoplasia), but without scientific certainty. Seasonal recurrences are common.

Treatments

Unlike the raised lesions of carp pox (Pox Carp CyHV-1), Hikui can easily be scratched (with cotton balls).

Topical treatments (local disinfectant) tend to accelerate the healing of skin lesions (even without treatment, they eventually regress spontaneously).

Antibiotics can sometimes be administered to prevent secondary bacterial infections.

Differential diagnoses

Infectious:

• Parasites: red-eating worm,

• Other parasites: protozoa,

• Fungi: dermatophytes or aflatoxins,

• Bacteria,

• Virus: herpesvirus. Non-infectious :

• Environment: toxins, sunburn, nutrition, poor water quality, high organic load,

• Neoplasia: skin cancer, fibrosarcoma,

• Genetic (hereditary) susceptibility.