Carotenoids are among the most widespread and important pigment classes in living organisms, and in marine animals, astaxanthin is the most commonly occurring red carotenoid. Carotenoids are vitamin A recursors and are fundamental in photosynthesis and light protection in plants. Increasing attention has fee, drawn to a possible light protection, cancer prevention and immune enhancement by carotenoids in mammals. Reported functions in fish range from a general enhancement of performance to specific functions in reproduction and metabolism. In this paper, we show that astaxanthin is essential for growth and survival of fish and crawfish, and discuss this fact in relation to the use of purified and semipurified diets in nutritional studies. The similarity in action of astaxanthin and canthaxanthin compared to a-tocopherol (vitamin E) and retinol (vitamin A) suggests that these two carotenoids should be listed among the fat soluble vitamins.

The degree of pigmentation in muscle of Atlantic salmon, Salmo salar L., fillets of fish that were fed eight diets fortified with 10, 20, 40, 60, 80.100, 150 and 200 mg astaxanthin kg−1 and a non‐supplemented control diet from 3 to 21 months was assessed using different methods. A tristimulus colorimeter (Minolta Chroma Meter) was used to measure the colour composition of the fillets instrumentally. The colour was also determined using the Roche Colour Card for Salmonids. The concentration of astaxanthin in the muscle was measured by chemical analyses. All measurements for colour were done directly on the epaxial muscle anterior to the dorsal fin. The lightness factor (L *). the red/green chromaticity (a*), the yellow/blue chromaticity (b*) and the saturation C* of the colorimetric readings and the Colour Card scores were compared with the chemical analyses. The astaxanthin concentration in the flesh varied from 1 to 10 mg kg−1 and the visual appearance of the fillets varied from yellowish‐white to red. The relationship between the a*, b* and C* values and the astaxanthin concentration in the muscle was non‐linear. Non‐linear regression lines were found between the a* value and the astaxanthin concentration in the flesh (r2= 0.974) and the b* value and the astaxanthin concentration in the flesh (r2= 0.984). The instrument was not able to detect differences in astaxanthin concentration at astaxanthin levels above 3‐4 mg kg−1 using the presented method directly on the fillet. The instrument might be useful for rejecting groups of salmon with poor pigmentation. A good linear regression was found between the Colour Card score and the mean astaxanthin concentration in the flesh (r2 ‐ 0.992). The Colour Card provided a better prediction of the astaxanthin concentration at higher astaxanthin levels than the Chroma Meter. None of the methods provided a satisfactory prediction of the astaxanthin concentration in the muscle of individual fish using the presented methods.

. Parr of Atlantic salmon, Salmo salar L., were fed semi‐purified diets supplemented with 60 mg astaxanthin kg−1 and without astaxanthin supplementation for 10.5 months. The astaxanthin concentration in the non‐supplemented diet was analysed to be 6–0 mg kg−1 The growth of the fish was significantly affected by the dietary treatment. The mean daily weight gain in the groups fed the supplemented diets was 0.39% throughout the period, whereas the groups fed the non‐supplemented diet had a mean daily weight gain of 0.18%. The dry matter and fat content were significantly higher in fish fed the supplemented diet. The astaxanthin concentration in the muscle of fish fed the astaxanthin‐supplemented diet was 2–7 mg kg−1 versus 0–3 mg kg−1 in the non‐supplemented fish. Antioxidant vitamins in the muscle (retinol, α‐tocopherol) and liver (retinol, α‐tocopherol and ascorbic acid) were two to 20 times higher in the fish in the supplemented group, suggesting antioxidant sparing effects. Blood haemoglobin and immunological parameters tended to be higher in fish fed the low astaxanthin diet although the difference was not significant. However, the resistance to challenge with Aeromonas salmonicida was higher in fish fed the astaxanthin supplemented diet. This may be due to a difference in weight at the time of the challenge which, in turn, may have influenced the body composition and smoltification of the fish. A relationship between dietary astaxanthin concentration and antioxidant status in both liver and muscle was observed, and this may also have had an influence on the observed differences in blood parameters and disease resistance.

Atlantic salmon fry hatched from pigment-free eggs and from eggs containing the pigment astaxanthin were fed eleven caseidgelatine-based purified diets with varying levels of astaxanthin, ranging from 0 to 3 17 mg kg-', to determine the optimum dietary astaxanthin level for satisfactory growth and survival during the start-feeding period. The fish were fed the experimental diets for a period of 11 weeks.No difference in performance was found between the two types of fry originating from the pigment-free eggs and those containing pigment. However, the dietary astaxanthin concentration was found to have a significant effect on both the growth and the survival of fry. Fish fed diets with astaxanthin concentrations below 5.3 mg kg-' were found to have marginal growth. In addition, mortality was high in the groups fed diets with astaxanthin concentrations below 1 .O mg kg-'. The specific growth rate (SGR) was also affected by the dietary treatment. The lipid content was higher and the moisture content was lower in the fish fed the diets containing astaxanthin concentrations above 5.3 mg kg-'. The vitamin A and astaxanthin concentrations in whole-body samples of the fry were significantly affected by the dietary level of astaxanthin. A plateau level in whole-body vitamin A concentration was observed at dietary levels of approximately 80 mg astaxanthin kg-' and higher, while no maximum astaxanthin concentration in whole-body samples was observed within the dietary levels used.The results suggest the need for a minimum dietary astaxanthin concentration of 5.1 mg kg-' to achieve maximum growth and survival during the start-feeding period. The results indicate a low bioavailability of vitamin A palmitate and acetate and the results also suggest a provitamin A function for astaxanthin during the same period.

An experiment with 2(7 − 3) reduced factorial design was conducted to study the biological effects of pro‐ and antioxidant micronutrients and lipid in Atlantic salmon. Vitamins C and E, astaxanthin, lipid, iron, copper and manganese were supplemented at high and low levels. For vitamins and minerals, high levels were chosen to be below the anticipated toxic level and the low levels were just above the requirement (vitamin C, 30 and 1000 mg kg−1; vitamin E, 70 and 430 mg kg−1; Fe, 70 and 1200 mg kg−1; Cu, 8 and 110 mg kg−1; Mn, 12 and 200 mg kg−1). For astaxanthin, the dietary levels were 10 and 50 mg kg−1 and for lipid, 150 and 330 g kg−1. The experiment was started with postsmolts (148 ± 17 g) and lasted for 5 months. The variation in micronutrients had only minor effects on growth, feed conversion and fillet quality, measured as lipid and astaxanthin deposition. High dietary lipid had a profound positive effect on growth and feed conversion but gave fillets nearly two times the fat content that was found in fish fed the low lipid diet. Astaxanthin deposition in the fillet was primarily affected by dietary astaxanthin with a positive effect of high dietary lipid in week 14 but not in week 23. Vitamin E protected the fillet against iron ascorbate stimulated oxidation, with no effect of the other nutrient variables.

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Atlantic salmon, Salmo salar L., juveniles, with a mean initial weight of 1.75 g, were fed casein‐based purified diets which had been supplemented with different levels of astaxanthin for a 10‐week period. The astaxanthin content of the diets ranged from 0 to 190 mg kg−1 dry diet. The growth and survival of the juveniles were recorded throughout the experiment. The proximate composition, astaxanthin and vitamin A content were determined from whole‐body samples at the start and termination of the experiment. The dietary treatment was found to affect growth significantly (P < 0.05). A reduction in the mean weight of the juveniles was observed in the groups fed the diets without astaxanthin supplementation. There was no difference in growth rate between the fish in the groups fed the diets containing 36 or 190 mg astaxanthin kg−1 dry diet, whereas the fish in the group fed the diet containing 5.3 mg astaxanthin kg−1 dry diet had a lower growth rate. There was a tendency to higher survival in the groups fed the diets containing astaxanthin when compared with the groups fed the non‐supplemented diets. The moisture and ash contents were significantly lower and the lipid content was higher in the groups fed the astaxanthin‐supplemented diets. The astaxanthin and the vitamin A concentrations in the fish were found to be dependent upon the dietary astaxanthin dose; the highest values were found in the fish fed the diet with the highest astaxanthin content. These results strongly indicate that astaxanthin functions as a provitamin A for juvenile Atlantic salmon. The body storage of vitamin A increased in the fish fed the diets containing astaxanthin. However, the increase was low in the fish fed the diet containing 5.3 mg astaxanthin kg−1 dry diet.

Abstract. The interactions of astaxanthin and vitamin A on the growth and survival of Atlantic salmon, Salmo salar L., during the first‐feeding period were examined using semi‐purified diets. Alevins, with a mean initial weight of 0.18g, were fed diets supplemented with 0, 20 and 40 mg astaxanthin/kg dry diet and 0, 750 and 1500 μg vitamin A/kg dry diet for 20 weeks. The weights of the fish were recorded throughout the experimental period and carcasses were collected for proximate composition, vitamin A and astaxanthin analyses at the beginning and end of the experiment. The feeds were analysed for proximate composition, vitamin A and astaxanthin levels. No interaction between astaxanthin and vitamin A was found in relation to the growth, survival or vitamin A content of the fry. Astaxanthin was found to strongly influence the growth, survival and vitamin A concentration in the fish. Poor growth and low survival rates were observed in groups fed diets without astaxanthin, including the group fed a diet with sufficient vitamin A. The results indicate both a provitamin A function of astaxanthin and a specific function of astaxanthin. Astaxanthin was found to be essential to alevins during the first‐feeding period.