Body pigmentation is an important factor for shrimp prices, reflecting the freshness and quality of the product. Shrimp and other crustaceans are unable to biosynthesize carotenoid pigments, which makes it essential for them to obtain carotenoids from their diet to achieve and maintain body pigmentation.
Previous studies have mainly focused on supplementing astaxanthin pigment into the diet of farmed shrimp, which also helps enhance the stress resistance of crustaceans by acting as an effective antioxidant, as well as an additive to improve the growth performance and pigmentation of many aquatic animals. However, supplementing astaxanthin into the diet can significantly increase shrimp feed costs due to the expensive synthetic production process of this carotenoid pigment. Therefore, it is necessary to identify other cost-effective additives to replace astaxanthin in shrimp diets.
Crustaceans can convert various carotenoid pigments such as beta carotene into astaxanthin. For example, lutein, one of the natural carotenoid pigments significantly cheaper than astaxanthin, can be extracted from several plants such as marigolds. To support this, recent studies have shown that dietary supplementation with 200 mg/kg lutein enhanced growth performance, immunity, and total carotenoid pigment content in various tissues of the oriental river prawn Macrobrachium nipponense.
Pacific whiteleg shrimp (Litopenaeus vannamei), one of the most profitable farmed shrimp species in Vietnam, is highly favored by consumers for its delicious meat and high nutritional value. Previous studies have demonstrated that both lutein and astaxanthin play essential roles in the growth performance, resistance, and pigmentation of aquatic animals. However, knowledge regarding whether lutein can replace astaxanthin for L. vannamei has not yet been documented.
Study Setup
Whiteleg post-larvae were obtained and cultured at the Chinese Academy of Fishery Sciences (Lingshui, China). Before the feeding trial, shrimp were fed a control diet (C) for two weeks to acclimate them to the experimental conditions. At the start of the feeding trial, 800 shrimp (initial body weight: 0.64 ± 0.04 g) were randomly distributed into twenty 300-liter tanks in a recirculating aquaculture system. Each diet was randomly assigned in quadruplicate, and shrimp were fed to apparent satiation three times daily at 5-8% of body weight for 8 weeks. During the feeding trial, water temperature was maintained at 26.9-28.2°C, pH at 7.6-7.8, salinity at 30-32 ppt, dissolved oxygen above 7 mg/L, total ammonia nitrogen below 0.1 mg/L, and sulfide below 0.05 mg/L.
Five experimental diets included: no lutein or astaxanthin (control group, C); lutein groups (L), L1-L3, containing 0; 62.5 ppm; 75 ppm and 87.5 ppm lutein, respectively; and astaxanthin group (A) containing 50 ppm astaxanthin. All diets contained approximately 405 g/kg crude protein and 71 g/kg crude lipid.
Research Results and Discussion
All carotenoid-supplemented groups in the study, except for group L3, showed significantly higher growth performance (weight gain rate, WGR, and SGR) of L. vannamei than group C. There are two main reasons why carotenoid pigments can improve the growth performance of crustaceans. One is that carotenoid pigments can regulate the metabolism of animals and thus promote their nutrient digestion. The other is that carotenoid pigments can shorten the molting cycle period of crustaceans and regulate metabolism to reduce energy consumption, leading to enhanced growth performance.
Furthermore, we observed growth performance (WGR and SGR), feed conversion ratio (FCR), and survival rate (SR) in groups L1-2 and group A, indicating that dietary lutein supplementation from 62.5 to 75 ppm can adequately replace astaxanthin in the diet of L. vannamei.
The ability to digest and metabolize nutrients in aquatic animals are also important parameters for evaluating an additive. In this study, no significant differences in various digestive enzymes were found between the four carotenoid pigment treatment groups and group C, indicating that dietary carotenoid pigments could not alter the protein digestibility of L. vannamei, although relevant data suggest that lutein and astaxanthin can improve the lipid synthesis ability of this shrimp species.
The results also showed that, compared to the control group, significantly lower levels of various antioxidant parameters appeared in the four carotenoid-supplemented groups, indicating that lutein and astaxanthin can act as antioxidants and protect cells from oxidative stress, while also improving the antioxidant capacity of L. vannamei. These results are similar to previous findings reported by other researchers.
The antioxidant properties of lutein and astaxanthin have been widely reported in several previous studies, but very few studies have focused on the anti-inflammatory capacity and other immune functions of these carotenoid pigments. This result also demonstrates that dietary supplementation with lutein or astaxanthin can inhibit apoptosis (programmed cell death occurring in multicellular organisms) in L. vannamei.
Perspective
Overall, the research results indicate that dietary lutein supplementation ranging from 62.5 to 75 ppm led to similar growth performance, antioxidant capacity, and immune responses in L. vannamei compared to a diet supplemented with 50 ppm astaxanthin. Therefore, dietary lutein is suggested to be sufficient in the diet of Pacific whiteleg shrimp to replace astaxanthin.
Adapted from an article by GSA – Global Seafood Alliance.
