Enhancing the colouration of the marine ornamental fish Pseudochromis fridmani using natural and synthetic sources of astaxanthin

Abstract

This study quantifies the effects of astaxanthin concentration as a dietary supplement (25, 50, 75, and 100 ppm) and supplementation time (0, 14, 28, 42, 56, and 70 days) on the colouration of the marine ornamental fish Pseudochromis fridmani (Orchid dottyback), using natural (as vegetative Haematococcus pluvialis) and synthetic (as Carophyll Pink®) sources. The colouration of experimental fish was quantified every two weeks and compared to a commercial standard, which had the desired colouration of an intense magenta/raspberry. A model was subsequently developed to quantify the predicted minimum colour distance to the commercial standard for each dietary source and concentration of astaxanthin, where shorter distances are desired. Although colour improved with increasing concentration and supplementation time for either astaxanthin source, natural astaxanthin improved colour more effectively and at the end of the feeding trial, the colour distances between the two sources at each concentration, ranged between 3.87 ± 0.60 and 4.90 ± 0.56, where a colour distance above 3.5 is noticeable to a standard observer. The most effective treatment was natural astaxanthin at a concentration of 100 ppm for 70 days (colour distance from the commercial standard of 4.91 ± 0.69). Importantly, the predicted minimum colour distances for each source could be quantified for all treatments except for concentrations of 100 ppm of both sources, where the distances were outside the concentrations tested. Therefore, increasing the concentration of astaxanthin beyond the highest level tested in this study is predicted to further improve the colour of the fish. Demonstrating the combined, interactive relationship between the dietary concentration and time of supplementation on the colour of P. fridmani, provides a fundamental understanding of how astaxanthin affects colour in marine ornamental species, and encourages a shift away from synthetic ingredients.