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Autumn smolts utilise astaxanthin better than spring smolts

NORWAY - Trine Ytrestyl of AKVAFORSK recently defended her doctoral dissertation entitled "Factors affecting utilisation of carotenoids in salmonid fishes".

Autumn smolts utilise astaxanthin better than spring smolts - NORWAY - Trine Ytrestyl of AKVAFORSK recently defended her doctoral dissertation entitled "Factors affecting utilisation of carotenoids in salmonid fishes".

Her research lays the groundwork that may be used in future efforts to adjust the levels of astaxanthin in salmon feed. Ytrestyl has documented several important factors that affect the utilisation of astaxanthin. These include water temperature, digestibility, retention and the muscle concentration of astaxanthin.

The low utilisation of the carotenoids known as astaxanthin and canthaxanthin, which are pigments in salmon muscle, may be explained by low absorption from the intestines, metabolic conversion, and limitations in uptake in muscle cells. Only 5-10% of the amount eaten by fish is retained in the muscle. Consequently, Ytrestyl has focused on factors that affect digestibility, metabolism and the deposition of carotenoids in the muscle of salmon.

Important findings

The research findings show that the digestibility of astaxanthin in Atlantic salmon was negatively affected by increased feed intake, but positively affected by increased water temperature.

Studies of metabolism and deposition in the muscle show that autumn salmon smolts utilise astaxanthin more effectively than spring salmon smolts. This finding is positive since a growing number of the smolts produced are put out to sea in the autumn. In connection with this research, a metabolite of canthaxanthin known as 4-hydroxyechinenone was documented for the first time in the muscle of Atlantic salmon. The compound was identified and quantified using modern chemical methods.

An alternative method for distributing astaxanthin was tested. Different doses were administered by injection into the abdomen of salmon, rainbow trout or cod to investigate the effects on uptake, metabolism and deposition of astaxanthin in various tissues. Following injections of 50 mg astaxanthin, an unusually high level of astaxanthin was found in the muscle of salmon (up to 30 mg/kg) whereas the level in cod was low (max. 1mg/kg). These results indicate that the deposition of carotenoids in muscle is regulated by uptake in the cells. The blood levels in both salmon and cod were extremely high. The injection of carotenoids into the abdomen may be suitable as a model for studying uptake, deposition and metabolism of carotenoids in fish, and it has potential for use as a commercial pigmentation method.

Ytrestyl was born in 1971 and grew up in Trondheim. In 1991 she completed a Norwegian hovedfag (comparable to a master's degree) in general zoology at NTNU, Trondheim, and in 2001 she was employed as a research fellow at AKVAFORSK, where she now holds a permanent position as Researcher II. Her doctoral research was funded by the Research Council of Norway, EWOS and Nutreco ARC. The defence was held at the Norwegian University of Life Sciences. Dr. ing. Bjrn Bjerkeng of AKVAFORSK was her adviser.

Further Information

To read the dissertation, click here

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