Feed intake, growth and ionoregulation in Atlantic salmon (Salmo salar L.) smolts in relation to dietary addition of a feeding stimulant and time of seawater transfer

Summary

Feed intake, growth and ionoregulation of Atlantic salmon (Salmo salar L.) were studied in fish fed diets either with or without squid extract supplementation in combination with transfer from fresh water to seawater (SW) at different times during parr–smolt transformation (10 April, 3 May and 19 June). Water temperature was held at approximately 8 °C. All groups of fish showed a temporary depression in feeding and growth after SW transfer. The depression was most severe in fish transferred in April, intermediate in fish transferred in May and shortest in fish transferred in June. Nevertheless, squid extract resulted in increased feeding and growth, especially in fish transferred to SW in June, providing evidence that squid extract contains substances that serve as feeding stimulants. The results indicate that there may be a potential to improve SW performance of salmon by adding squid extract to feed. The results also indicate that Atlantic salmon may be transferred to SW over a relatively long period during spring, but to minimise the duration of appetite depression, late transfer may be preferable. Individual feeding rates following short-time SW exposure were not correlated with plasma chloride concentrations in any of the groups, indicating that appetite suppression is not a direct result of osmo-ionoregulatory failure.