The effects of concentration and supplementation time of natural and synthetic sources of astaxanthin on the colouration of the prawn Penaeus monodon

The purpose of this study was to quantify and model the combined effects of dietary concentration of astaxanthin (32.5-102.5 ppm) and time of supplementation (29-69 days) on the growth, survival, and colouration of Penaeus monodon (Black tiger prawn), using natural (Haematococcus pluvialis) and synthetic (Carophyll Pink®) astaxanthin. A model was used to determine the optimal combination of concentration and supplementation time required to obtain a commercial colour standard, based on the minimum quantity of astaxanthin required for each source. The provision of astaxanthin, as either natural or synthetic, at any concentration or supplementation time, had no effect on growth or survival. However, the colour of boiled prawns supplemented with natural astaxanthin had a small, but significant, improvement in colour (CIE2000 L*a*b* colour distances between 0.74 ± 0.22 and 1.79 ± 0.63), when compared with supplementation with synthetic astaxanthin. The astaxanthin concentration and supplementation time also had a significant effect on the colour of boiled prawns, where higher concentrations of astaxanthin for longer supplementation times resulted in improved colouration up until a plateau of 98 ppm for 66 days for natural astaxanthin, and 90 ppm for 63 days for synthetic astaxanthin. An additional model was used to predict the minimum usage of astaxanthin for each source during three annual commercial production cycles (Christmas, Summer, and Restock). Compared with the current commercial standard, the natural source would require 21.0%, 21.6%, and 21.3% less total astaxanthin, and the synthetic source would require 0.7%, 0.2%, and 0.3% less total astaxanthin, for the Christmas, Summer, and Restock production cycles, respectively. The predictive models developed here were able to explain the combined effects of dietary concentration of astaxanthin, time of supplementation, and effects of source on the colouration of boiled prawns, thereby predicting the minimum usage required at the commercial pond scale.