Aeromonas salmonicida grown aerobically in the presence of tyrosine produces a dark‐brown pigment, previously considered to be of a melanin type. However, this pigment is very water‐soluble in contrast to melanin's solubility. In addition, no evidence for the presence of key early reactions and intermediates of the melanogensis pathway has been obtained. Radioisotopic labelling experiments, spectral data and chromatographic analyses support the conclusion that pigment biosynthesis, from tyrosine by Aeromonas salmonicida differs substantially from that of melanogenesis, and strongly suggest that the first intermediate is 2,4‐dihydroxyphenylalanine and not 3,4‐dihydroxyphenylalanine.

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