Reproductive Characteristics of Precocious Male Parr in Salmonids: Morphology, Physiology, and Behavior

Morphological, physiological, and behavioral characteristics of precociously mature male parr were examined in the two representatives of salmonid species in Japan, masu salmon, Oncorhynchus rnasou and Miyabe charr, Salve linus rnalrna rniyabei. Selection on morphological characters during breeding activity was quantified on mature masu salmon parr. Larger body size was favored for sneaking success, contrary to the prediction that sneaking behavior favors small body size. This selection pressure was caused by the dominance hierarchy among parr and may have been facilitated by indifference of dominant migratory males to parr. No morphological characters other than body size contributed to the reproductive success of parr. This non-contribution may have been responsible for the lack of development of sexual characters in parr. Energy allocation to soma and testes of mature parr was compared with that of migratory males in masu salmon. Energy contents per unit mass of soma and testes did not show the consistent difference between mature parr and migrants; rather, they differed between two populations, likely reflecting the difference in food availability. By contrast, both relative testes investment in mass and energy were higher in mature parr than in migrants, consistently in the two populations. This result supports sper