A preliminary study on tailoring of fillet iodine concentrations in adult Atlantic salmon (Salmo salar L.) through dietary supplementation

The present study was performed to assess to what degree supplemented dietary iodine (I) was retained in selected tissues, including the fillet of adult Atlantic salmon (Salmo salar) reared in sea water. Atlantic salmon weighing approximately 1.5 kg were randomly assigned to three net pens per treatment and fed moist pellets (based on minced saithe and herring) supplemented with 0, 40 or 80 mg iodine (as KI) kg(-1) on dry weight basis for 150 days. The iodine concentrations in the experimental feeds were analysed to be 10, 54 and 86 mg kg(-1) dry weight, respectively. Growth, mortality and blood haemoglobin concentration (Hb) were recorded. Iodine concentrations were measured in muscle, liver and kidney after 90 and 150 days of feeding by inductively coupled plasma-mass spectrometry. In addition, plasma thyroxine (T-4) and triiodo-thyronine (T-3) were determined. The weight gain during the period was approximately 1 kg for all treatments. There were no mortalities, and blood Hb levels were within normal ranges. The iodine concentration in muscle, liver and kidney were all affected by the dietary iodine level, despite wide intratreatment variation. After 150 days, fillets of fish fed 10, 54 and 86 mg I kg(-1) showed mean concentrations of 0.4, 0.5 and 0.9 mg I kg(-1) wet weight, respectively, whereas the iodine concentration in the liver and the kidney increased approximately three times in the dietary groups. Similarly, plasma T-4 and T-3 showed great variation within the treatments. No significant correlations were found between individual tissue iodine concentration and thyroid hormone concentration in any of the groups at any sampling time. This preliminary feeding experiment showed that fillet iodine in adult Atlantic salmon can be increased up to 1.4 mg I kg(-1) wet weight by dietary iodine 80 times the minimum requirement for salmonids, without impacting health, performance or plasma thyroid hormone status.