Regulation of color morphic patterns in the giant kelpfish, Heterostichus rostratus Girard: genetic versus environmental factors

Abstract

Color choice experiments tested preferences of red, green, and brown color morphs of giant kelpfish, Heterostichus rostratus Girard, for matching versus non-matching colored backgrounds. Kelpfish were determined to prefer matching colors, these results being most pronounced with live plant backgrounds and progressively less significant with backgrounds of artificial plants and flat plastic panels, respectively. Adult kelpfish demonstrated a stronger preference for matching backgrounds than did juveniles. Kelpfish larvae whose parents colors were known were reared on red, green, or brown colored backgrounds. They developed brown or green juvenile color morphic patterns, apparently independently of parent color. These rearing experiments indicated that development of juvenile color is determined by plant background. Long-term color change abilities of juvenile and adult kelpfish color morphs on colored habitats were tested in laboratory and in situ experiments. It was found that juveniles readily changed on both artificial and live plant backgrounds from green to brown, and vice versa. Changes in color of adults were less pronounced and slower, particularly in laboratory experiments, and largely confined to females. In situ experiments yielded the greatest magnitudes of color change, some adult females changing between red, brown and green. Male and juvenile kelpfish were incapable of becoming red, corresponding to color morph frequency collection data. Adult males also apparently lost the capability to change to true green. These differences indicate that color change ability and assumption of red color may be governed by sex hormones.