The predominant carotenoid in prawn tissues is astaxanthin (Axn) and its role in pigmentation has been well studied. However, the effects of dietary Axn on other prawn physiological performance measures are uncertain and dietary carotenoid uptake and tissue deposition are poorly understood. This study fed juvenile prawns (Penaeus monodon) diets that contained 0, 25, 50 or 100 mg kg -1 Axn for 6 weeks. Animals fed carotenoid free diets had significantly reduced growth than those fed carotenoids, but survival was unaffected. Carotenoid uptake (digestibility) improved as dietary carotenoid levels increased, and was 98.5% in animals fed 100 mg kg -1 Axn. After 6 weeks, whole body carotenoid levels were significantly depleted in 0 or 25 mg kg -1 fed animals, compared with those fed 50 or 100 mg kg -1 . Specific fatty acid esters of Axn accumulated in epithelial tissue, with mono-esters enriched saturated fatty acids, while di-esters were enriched with monounsaturated and polyunsaturated fatty acids. These data suggest a minimum dietary requirement of 25 mg kg -1 Axn in clear water systems to maintain growth performance, and 50 mg kg -1 or more to avoid depletion of body carotenoid levels and improve efficiency of utilisation. These results also implicate specific fatty acids in the function of carotenoid esters within prawn tissues.

Crustaceans form their distinct patterns and colours through the interaction of the carotenoid astaxanthin with a protein called crustacyanin (CRCN). Presently, the expression of just two genes is thought to provide the protein subunits that combine to form the crustacyanin complex and associated carotenoid colour change from red to blue. This study aimed to explore the genetic complexity underlying the production of pigmentation and camouflage in penaeid shrimp. We isolated 35 new genes from 12 species, and their sequence analysis indicated that this gene family has undergone significant expansion and diversification in this lineage. Despite this duplication and sequence divergence, the structure of the CRCN proteins and their functional role in shrimp colour production has been strictly conserved. Using isoforms from as an example, we showed that isoforms were differentially expressed, and that subtle phenotypes were produced by the specific downregulation of individual isoforms. These findings demonstrate that our knowledge of the molecular basis of pigmentation in shrimp was overly simplistic, and suggests that multiple copies of the genes within species may be advantageous for colour production. This result is of interest for the origin and evolution of pigmentation in crustaceans, and the mechanisms by which gene function is maintained, diversified or sub-functionalized.

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