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

Abstract

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 (T4) and triiodo‐thyronine (T3) 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 T4 and T3 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.

Fecal Excretion and Whole-Body Retention of Macro and Micro Minerals in Atlantic Salmon Fed Torula Yeast Grown on Sugar Kelp Hydrolysate

“…The I level in both liver and kidney was close to five times higher compared to muscle and whole body. This is in line with Julshamn et al [ 45 ], who described lower incorporation of I in muscle than in liver and kidney of Atlantic salmon that had been raised for 150 days in seawater and fed 54 or 86 mg I kg −1 diet. In accordance with the present results, experiments with rainbow trout in freshwater have shown increased I levels in the fish after feeding different seaweeds and that the I concentration in muscle was dependent on the dietary level of I and the length/percent body weight increase obtained [ 46 , 47 ].…”

Iodine content of six fish species, Norwegian dairy products and hen’s egg

“…The difference may be due to a higher fat content in muscle of farmed halibut compared to wild halibut, but may also be caused by a low iodine content or bioavailability in the fish feed used for Atlantic halibut in fish farms. For salmon, it has been shown that fish muscle is responsive to iodine supplementations in feed to a certain degree ( 24 ). Furthermore, there was a general trend of declining concentrations of iodine in fish feed in Norway during 2000–2006, probably due to reduced use of fish meal in feed production ( 25 ).…”

Natural fortification of trout with dietary macroalgae and selenised-yeast increases the nutritional contribution in iodine and selenium

“…Within this scenario, a new perspective towards consumers' dietary needs must be considered when designing aquafeeds. Fillets traits have already been effectively changed by modulating fish feeds in terms of bioactive fatty acids (Kennedy, Bickerdike, Berge, Dick & Tocher, 2007;Ramos et al, 2008;Rosa, Andrade, Bandarra & Nunes, 2010), selenium (Lorentzen, Maage & Julshamn, 1994;Schram, Schelvis-Smit, Van Der Heul & Luten, 2010) and iodine (Julshamn, Maage, WaagbØ, & Lundebye, 2006;Ramalho Ribeiro et al, 2015). However, the efficacy of muscle fortification seems to be dependent on supplemental dose, feeding strategies and also important the supplement product form (inorganic vs. organic).…”