NON-INFECTIOUS DISEASES Pigment Aberrations in Fish

I. Causative Agent and Disease III. Clinical Signs Pigment aberrations of flesh, oc- Aberrant external pigmentation in casionally observed in salmonids and fish is generally confined to the epider- other fish species, are not caused by any mis. Complete albinos have no melanin known infectious agents. In unpolluted pigment within any tissue. Marbled or waters, the abnormal pigmentation is completely white-fleshed Chinook or often due to genetic or congenital defects other salmon require observation of fil- resulting in abnormal overall body leted skeletal muscle. color or localized epidermal discolor- ation, most often yellow in salmonids. IV. Transmission Other abnormal pigmentation occurs Aberrant pigmentation has no infec- in Chinook salmon where the skeletal tious cause and cannot be transmitted. muscle is white rather than orange due Coloration is most likely due to pigments to a genetic inability to retain carotenoid obtained from food consumed, the pigments from consumed prey. Partial or natural environment or is hereditary complete albinism may also cause yel- allowing parent fish to pass the trait on low/green to white body color. Certain to some of their offspring, as is the case prey species and natural plant materials for some stocks of “white” king salmon. in the environment can influence body Albinism is caused by a genetic defect in color, as observed in the blue-green flesh tyrosinase that metabolizes tyrosine to of lingcod inhabiting kelp forests. Indus- the black pigment melanin. trial pollution also affected flesh color of Atlantic salmon in Scotland causing a V. Diagnosis yellow/orange to red pigmentation from Diagnosis is based on the observa- exposure to paper mill effluent. This tion of uncomplicated aberrant pigmen- caused hemolytic anemia and hyper- tation. Yellow pigmentation extending bilirubinemia resulting in jaundice, into the internal body fat suggests jaun- both externally and within the internal dice that is symptomatic of a systemic mesenteric fat. disease process that is not related to uncomplicated pigment aberration. II. Host Species In Alaska, albinism is common in VI. Prognosis for Host cultured chum salmon fry while adult Abnormal pigmentation from natural white king salmon occur occasionally food and plant materials or hereditary or frequently, depending on the fish defects causes no physical harm to stock. Varying degrees of white and red affected fish except that the unnatural skeletal muscle can produce a marbled coloration may be more conspicuous to appearance. White flesh also occurs in predators. sockeye and coho salmon while yellow pigmented epidermis occurs in cutthroat VII. Human Health Signifcance trout, Chinook salmon, pink salmon There are no human health concerns and most frequently in sockeye salmon. associated with uncomplicated aberrant Other aberrations include epidermal yel- pigmentation in fish from unpolluted low/green marbling in pink salmon, pink waters. flesh in halibut and pike, and blue-green pigmentation in lingcod.

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Left: Marbled white fesh of sockeye salmon; Center: Marbled white-feshed coho salmon compared to normal red on right; Right: Blue-green pigmented lingcod.

Left: Yellow pigmented sockeye salmon; Center: Yellow pigmented ventral foci on cutthroat trout; Right: Yellow pigmented area in the epidermis of a Chinook salmon.

Left: Pink feshed halibut; Center: Pink feshed northern pike; Right: Yellow-green marbled epidermis of pink salmon likely due to partial albinism.

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