Increased supply of astaxanthin in the diet of rainbow trout (Oncorhynchus mykiss) prior to maturation – effects on muscle pigmentation

Summary

The primary aim of this project is to increase the value of rainbow trout (Oncorhynchus mykiss) fish farming through combined production of high quality rainbow trout and roe for consumption. Earlier experiments, done at Svanøy Havbruk AS, showed a pronounced decline in the fillet colour (content of astaxanthin) of rainbow trout, just prior to the roe being suitable for caviar production. The trout spawners morphological changes (colour and shape) and pale muscle, both contribute to the downgrading of the overall fish quality. The rainbow trout cannot, on its own, make astaxanthin (asta.). Therefore, it is dependent on a steady supply of asta. through food. To improve the colourization of the muscle, a feeding experiment was conducted in 2018. An increased level of asta. (90 mg asta./kg feed) was compared to a control group that received fish feed containing 60 mg asta./kg. The fish used in this experiment was purchased as “all female”. Unfortunately, it turned out that a mistake had been made and the rainbow trout in the trial was in fact a mixed group. Subsequently, the experiment was repeated in the spring of 2019, this time with of “all female”. The results from this experiment show that the extra supply of asta (90 mg asta./kg feed) did not have any effect on the muscle colour compared to the control group. The results also showed that towards the end of the maturation period, the «all female” and the control group, both kept under similar farming conditions in the sea, had approximately the same gonadosomatic index (GSI) and muscle colour at slaughter. The only difference in this experiment was that the “all female” group was smaller in size and somewhat delayed in the final maturation period, compared to the control group.