SUPPRESSION OF MATURATION IN MALE ATLANTIC SALMON (SALMO-SALAR L) PARR BY REDUCTION IN FEEDING AND GROWTH DURING SPRING MONTHS

Four sibling populations of Atlantic salmon parr were subjected to seasonal variations in feeding opportunity, from February to September. Growth was restricted relative to a control population by increased density. During 2-month periods growth was increased by reducing density. Consequently different populations grew faster than controls at different times of year. In September the mean size of fish did not differ between populations, but percentage maturation did. Populations growing relatively fast during spring had high percentages of mature males, similar to the control population, while those growing relatively fast in winter and summer, but slowly in spring, had fewer mature males. In experiments where growth was suppressed by fasting fish in alternate weeks during different 2-month periods, maturation was suppressed by fasting in the spring. It is concluded that if spring growth is inadequate, maturation is switched off physiologically. This growth-related suppression of maturation may contribute to the correlation between growth and maturation rates in salmonids. We suggest it is adaptive, preventing maturation when the growing season starts late, and is too short for fish to acquire sufficient reserves for spawning. © 1990.