Seasonal patterns of feed intake and growth of Hammerfest and Svalbard Arctic charr maturing at different ages

Age at maturity, feed intake and growth were monitored in two strains (Hammerfest, 70 degrees N and Svalbard, 80 degrees N) of Arctic charr, Salvelinus alpinus, held under comparable rearing conditions for 2 years (age 9 to 32 months after hatching). Feed intake of individually tagged fish was measured using X-radiography, and growth rates and timing of maturation were monitored for the same individuals. There were differences in age at first maturity, both between strains and between sexes. In the Hammerfest charr, 56% of the males matured at age 1 + , bur no male Svalbard charr matured at this age. At age 2 + , 94% of the Hammerfest males were mature, compared to 14% of the Svalbard males. No females matured at age if, while 71% of the Hammerfest females matured at age 2 +. No Svalbard females matured during the study. There were no differences between strains in weight, feed intake and growth before the first reproductive season at age 1 + . When fish were held at constant temperature (7 degrees C), seasonal variations in feed intake and growth were observed in fish of both strains and sexes. Svalbard charr were significantly larger than Hammerfest charr from age 19 months onwards, and by the end of the experiment, the Svalbard charr were 25% larger than Hammerfest charr. The differences between the strains were largest in 2 + mature males. Prior to maturation, maturing fish were significantly larger than immature fish, but in the weeks immediately prior to maturation, the maturing fish grew significantly less than the immatures. (C) 1999 Elsevier Science B.V. All rights reserved.