Effect of dietary lipid and astaxanthin level on pigmentation of arctic charr (Salvelinus alpinus)

Lin, Shujun (1997) Effect of dietary lipid and astaxanthin level on pigmentation of arctic charr (Salvelinus alpinus). Masters thesis, Memorial University of Newfoundland.

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Abstract

A 3 x 3 factorial design was used to study the effects of dietary lipid and astaxanthin levels on the pigmentation of Arctic charr (Salvelinus alpinus). Different groups of charr with mean initial weight of 70.16 ± 2.18 g were fed with diets containing 10, 18 or 26 % dietary lipid together with 40, 60 or 80 ppm synthetic astaxanthin for 24 weeks. The proximate composition of flesh, total carotenoid concentration in flesh and belly skin, and the Hunter colour values of filets, homogenized flesh and belly skin were determined at 4-week intervals. The apparent digestibility coefficient of carotenoid and specific growth rate (SGR) of the experimental fish at different dietary lipid and carotenoid levels were also investigated. Results indicated that: -- (1). The moisture content of flesh was inversely related to the level of dietary lipid, while there was a significant direct relationship between the content of flesh and dietary lipid. The protein and mineral content of flesh were not significantly influenced by the level of dietary lipid. -- (2). The total carotenoid concentration in flesh and belly skin of charr increased with time. The concentration of carotenoids in the flesh generally reached or exceeded 4 mg/kg wet tissue on week-16, 20 and 24 for the fish receiving 26, 18 and 10 % dietary lipid, respectively. This amount is considered as being sufficient for providing a satisfactory colour impression. The carotenoid concentration in the flesh and belly skin of fish was directly correlated with both dietary lipid and carotenoid levels. There was a significant interaction between dietary lipid and carotenoid levels on the total carotenoid concentration in flesh and belly skin of charr. A high correlation also existed between the carotenoid concentration and total lipid content in flesh. -- (3). The intensity of redness (Hunter a) and yellowness (Hunter b) of filet, homogenized flesh, and belly skin for all treatments increased with time on pigmented diets while their lightness (Hunter L) decreased. The Hunter L values of filet, homogenized flesh, and belly skin were inversely correlated with their carotenoid contents, whereas their Hunter a and b values correlated directly with the total carotenoid concentration. No significant relationship existed between any of the Hunter colour values and the lipid content in the flesh of charr. -- (4). The retention of carotenoids in charr flesh varied significantly among treatments, ranged from 4.13 to 10.66 %. The total amount of carotenoids retained in flesh was directly related to the content of dietary lipid, but inversely related to dietary carotenoid levels. There was a significant interaction of dietary lipid and carotenoid levels on the retention of carotenoids in flesh. -- (5). The apparent digestibility coefficient of carotenoids, ranging from 47.99 to 73.62 %, correlated directly with the content of dietary lipid, but inversely with dietary carotenoid levels. There was a high correlation between the amount of carotenoids retained in flesh and their digestibility. No interaction of dietary lipid and carotenoid on the carotenoid digestibility was observed. -- (6). The dietary lipid and carotenoid levels used in this study did not result in any abnormal growth of fish. The specific growth rate (SGR) of the fish fed 18 and 26% dietary lipid were significantly higher than that of the groups receiving 10% dietary lipid. In addition, at the same level of dietary lipid (18 %), the weight gains of fish on dietary carotenoids were faster than that of fish receiving no dietary carotenoids. However, these differences were not statistically significant. -- In conclusion, the results of the present study demonstrated that an increase in both lipid and carotenoid levels in charr diet enhances deposition of carotenoids in the fish flesh and skin. There was a significant interaction of dietary lipid and carotenoids on the pigmentation of Arctic charr. Thus, an increase in dietary lipid within a certain range may improve the pigmentation efficacy of charr.

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