Food consumption and growth in maturing Atlantic salmon (Salmo salar)

Circulating levels of the steroid hormones 11-ketotestosterone (11-KT) and 17 beta-estradiol (E2), voluntary food intake, and growth performance were measured in individual Atlantic salmon (Salmo salar) over the year precedin g their maturation as grilse. 11-KT and E2 were measured by radioimmunoassa y, and X-radiography was used to measure food consumption rates. Two phases of sexual maturation were identified: the early phase (October 1992 - Apri l 1993) was characterized by slowly rising steroid hormone levels concomita nt with relatively high rates of food consumption and growth, and in the la te phase (May-October 1993), steroid hormone levels increased more rapidly and growth rates decreased in association with inappetence. Significant lin ear relationships were observed between food consumption and specific growt h rates of fish throughout the study (ANCOVA, p < 0.05). Slopes and interce pts of regressions were similar for fish during early maturation, while a l ower intercept and steeper slope (ANCOVA, p < 0.05) was observed during the later stages of maturation. In November, January, February, and April, fis h in which steroid hormone levels were elevated were significantly heavier than those in which hormone levels were basal. There were no significant di fferences in specific growth rates (except in February), food consumption, or weight-specific food conversion ratio (except in August and October) ass ociated with maturation status.