| Summary: | The growth hormone (Gh)/insulin‐like growth‐factor (Igf) axis is important to growth regulation of fishes, including responses to food restriction. The role of Igf binding proteins (Igfbps) in the regulation of Igf function during food restriction is unresolved. We examined changes in the circulating levels of Gh and Igf1 and hepatic igfbp expression during food restriction of Atlantic salmon ( Salmo salar ) smolts. Smolts were fasted for either 3 or 10 days at the peak of smoltification (late April to early May). Branchial Na + , K + ‐ATPase activity, which increases during smoltification, was not altered by food restriction. Condition factor (weight:length ratio) of food restricted fish was significantly lower than controls after 10 days. We measured the expression levels of igfbps that exhibit robust expression in Atlantic salmon liver, including igfbp1a1 , ‐1b1 , ‐1b2 , ‐2a , ‐2b1 and ‐2b2 . We observed a marked increase in the expression of igfbp1a1 following both 3 and 10 days of food restriction. No other investigated hepatic igfbps responded to food restriction. We will also present information on igfbp transcription in muscle and circulating levels of Gh, Igf1, cortisol and thyroid hormones. We will discuss the relationship between hepatic igfbp expression and circulating Igf1 with an aim to resolve how the activities of the Gh/Igf axis are modulated during food restriction of juvenile Atlantic salmon.
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