Elimination of foreign material by epidermal malpighian cells during wound healing in fish skin

Cultured epidermal malpighian cells and experimental wounds of Atlantic salmon Salmo salar were challenged with a variety of particulate materials. Latex beads and the bacteria Carnobacterium piscicola, Pseudomonas fluorescens and Aeromonas salmonicida salmonicida were engulfed by cultured cells, whereas Staphylococcus intermedius were not. The cells engulfed bacteria that proliferated in culture medium devoid of antibiotics and melanin granules and other cellular debris. Cells at wound margins engulfed latex beads and C. piscicola, P. fluorescens and A. s. salmonicida, but not S. intermedius. Malpighian cells thus appear to be both phagocytic and discriminatory. The results support the hypothesis that malpighian cells remove foreign material from fish skin by sloughing after becoming laden with engulfed material.