A Fish of a Different Color

The red porgy, Pagrus pagrus, is a valuable food fish in Mediterranean and Atlantic waters. Because it grows well and has no significant disease problems in captivity, it seems to be a good candidate for commercial aquaculture. However, there is a drawback: When the fish is farmed, its skin darkens and loses its characteristic red and silver coloration, decreasing its market appeal.

European researchers, led by Michael Pavlidis at the Institute of Marine Biology of Crete in Iraklion, Greece, set about to find out what muddies the creature’s complexion and how to bring back its natural blush. They raised the fish in tanks with dark and light backgrounds and with different lighting conditions -primarily full- spectrum fluorescent lights and aquarium lamps with predominantly blue spectra. For skin color measurements, they used a MiniScan spectrophotometer from Hunter Associates Laboratory Inc. in Reston, Va.

A wild porgy has characteristic red and silver coloring (left); farm-raised fish have darker, less attractive skin color (right).

They observed higher skin melanin in fish reared in dark backgrounds and under high light intensity, especially in heavily stocked tanks. Overall results indicate that the differences in skin lightness are related to how the melanophores are distributed; they are dispersed in wild fish but tend to collect in farmed ones.

The findings, which are pending publication in Aquaculture, should help the fishing industry teach “homeschooled” fish how to color properly.