Effects of fasting on temporal changes in plasma concentrations of sex steroids, growth hormone and insulin-like growth factor I, and reproductive investment in Arctic charr

Summary

Proportions of maturing fish and reproductive output [egg size, relative fecundity, spermatocrit and gonado-somatic index (IG)] were studied in repeat-spawning (þ4 year old) male and female Arctic charr Salvelinus alpinus, subjected to periods of fasting. Groups of individually tagged Arctic charr were fasted for c. 3, 6, 7 and 9 months, from November 1998. In the period February to November 1999, size (fork length and mass), specific growth rate (G), condition factor (K) and plasma concentrations of growth hormone (GH), insulin-like growth factor I (IGF-I), oestradiol-17b (E2; females) and 11-ketotestosterone (11KT; males), were monitored monthly. Maturing fish in each group started to gain mass soon after food was made available, and both sexes reached the highest K and G c. 2 months after the onset of feeding. The fasting regimes resulted in different growth patterns during spring and summer when energy stores are normally replenished in Arctic charr, and K prior to the breeding season was significantly higher in the groups fasted for 3 and 6 months compared to the groups fasted for 7 and 9 months. There were significant positive correlations between K during the period prior to the breeding season and reproductive output in terms of the IG, spermatocrit and relative fecundity. There was, however, no clear relationship between the length of starvation and the proportion of maturing fish. Likewise, no clear relationships were found between reproductive development and plasma levels of GH and IGF-I, although both showed marked seasonal changes, being ‘down-regulated’ during winter months and ‘up-regulated’ throughout summer months. # 2004 The Fisheries Society of the British Isles