How Is Astaxanthin Used in Shrimp and Crab Farming?

Carotenoids (terpenoids) include more than 700 (Zhang et al., 2021) structurally diverse organic, fat-soluble pigments (Lu et al., 2021) that are produced in plants (Fu et al., 2021), plankton phytoplankton, algae (Pereira et al., 2021; Li et al., 2021), bacteria and some fungi (Merhan, 2017), which can help aquatic animals (Cao et al., 2021), fruits and plant leaves to display colors (red, orange and yellow). Different carotenoids are closely related to each other (Dong Hongchun et al., 2021), coexist in many cases, can be converted into each other, and jointly exhibit many functional properties and physiological characteristics.

Crustacean aquatic products such as shrimp and crab have high protein content and are rich in nutrients. China has abundant resources of crustacean aquatic products and a wide variety of species, and is the world's main supplier of crustacean aquatic products. With the high-quality development of aquaculture in China, the aquaculture volume of crustaceans, mainly shrimps and crabs, reached 6.03 million tons in 2020, an increase of 6.32% compared to 2019. The growth rate is higher than that of fish and shellfish, showing a trend of rapid growth. The body color of shrimp and crab species, as well as the color of the gonads and hepatopancreas of crabs, all determine to some extent their value as economically important aquatic species. On this premise, carotenoids that can be colored can be promoted in the cultivation of shrimp and crabs.

1 Structure and function of astaxanthin

Astaxanthin is one of the most well-studied carotenoids (Peng Yongjian et al., 2017). It is widely distributed in nature and is found in large quantities in the marine environment. Its chemical name is 3,3′-dihydroxy-4,4′-dione-β,β′-carotene, and its molecular formula is C40H52O4. The C-3 and C-3′ ring structures at the ends of the astaxanthin molecule are two chiral centers, both of which have the existence forms of R or S. Therefore, astaxanthin has three stereoisomers, namely astaxanthin (3S, 3S'), astaxanthin (3R, 3R') and astaxanthin (3R, 3S').

Compared with other carotenoids, astaxanthin has unique properties, namely a more polar configuration, stronger esterification ability and higher antioxidant properties, which are largely due to the hydroxyl group (OH) and ketone group (C = O) present on each violone ring in its molecular structure (Lin et al., 2016; Yuan et al , 2011; Peng et al. , 2008; Hussein et al. , 2006; Martin et al. , 1999).

The strong antioxidant capacity of astaxanthin is related to its strong electron-donating ability as a reducing agent, which can neutralize endogenous free radicals (hydrogen peroxide, hydroxyl radicals and superoxide anions), neutralizing them and converting them into more stable products, while also terminating the chain reaction of free radicals in living organisms (Dhankhar et al., 2012; Guerra et al., 2012; Ranga Rao et al., 2010; Hussein et al., 2006). In nature, astaxanthin is mainly esterified with one or two fatty acid units (monoesters and diesters) or bound to proteins, for example in the exoskeleton of crustaceans and salmon muscle, to provide stability to the molecule (Higuera-Ciapara et al., 200 6; Storebakken et al., 2004; Coral-Hinostroza et al., 2002), astaxanthin therefore has great potential for use in animal health and nutrition, thanks in large part to its function in protecting organisms from a wide range of stressors and infectious diseases.

2 Sources of astaxanthin

Currently, almost all commercially available astaxanthin is synthetic (Nunes et al., 2021). It can be produced industrially using astaxanthin precursors (lutein, canthaxanthin, etc.) or by synthesizing astaxanthin from scratch (Sin et al., 2019). Chi et al., 2019), which has a relatively high yield (Wang Duoren, 2011). However, industrially synthesized astaxanthin is a mixture of multiple conformations and will also mix in by-products, and its safety and bioavailability are lower than that of natural astaxanthin (Cui Haihui, 2019).

Natural astaxanthin is mainly obtained by cultivating astaxanthin-producing algae (Fang et al., 2019), yeast (Leyton et al., 2019) and other microorganisms (Asker et al., 2018) or extracted from by-products rich in astaxanthin such as shrimp shells and crab shells. The astaxanthin obtained in this way is of high purity, has a clear structure, can be more efficiently utilized by organisms, and also puts less pressure on the environment. However, the current fermentation cost is high, the yield is low, and there is an urgent need to find a high-yielding special strain of bacteria. The use of alkaline extraction (Tan Junxiao, 2018), enzymatic hydrolysis, and organic solvent extraction (Tan Junxiao et al., 2018) to extract from by-products is a relatively complex process that requires significant investment. The technology needs to be continuously improved.

In addition, there are also studies on the large-scale extraction of astaxanthin from wastewater. At the current level, 10 to 13 μg of astaxanthin can be extracted from every milliliter of shrimp cooking wastewater (Gecim et al., 2021), which not only provides a revenue from astaxanthin, but also improves the wastewater to a certain extent. It can be seen that with the development of new technologies, the sources of astaxanthin are becoming more and more extensive.

3 Application of astaxanthin in shrimp farming

3.1 Vannamei shrimp

Vannamei shrimp, scientific name Litopenaeus vannamei, also known as white shrimp (Lin Liyun, 2021), has the characteristics of low feed requirements (Zhou Xinghua et al., 2002), high meat yield (Chai Zhan et al., 2015), fast growth rate (Tang Yang et al., 2018 ), and a wide salinity tolerance range (Yuan Jianbo, 2014). The economic benefits of farming are significant, and production areas are concentrated in coastal provinces such as Guangdong, Fujian, and Shandong. In 2020, China's production of marine white shrimp was about 1.2 million tons, accounting for 80.52% of the total production of marine farmed shrimp. In recent years, academia has widely explored the addition of astaxanthin to feed to improve its farming results.

Wang Haifang et al. (2016) found that adding 50 mg/kg astaxanthin to the feed can improve the stress resistance of Litopenaeus vannamei juveniles, resulting in an increase in growth rate, survival rate and feed conversion rate. Liu et al. (2018) also proved that astaxanthin can improve the growth performance, while also increasing the mRNA expression level of antioxidant enzymes. Nunes et al. (2021) demonstrated in experiments that a moderate amount of astaxanthin can increase the tolerance of white shrimp to osmotic and thermal stress. Yu et al. (2020) found that by adding a certain amount of astaxanthin to the diet, astaxanthin can reduce hepatopancreatic damage and protect the hepatopancreas of white liver and pancreas of white shrimp. Wang et al. (2020) showed that the addition of astaxanthin to the feed significantly up-regulated the expression of a large number of genes related to pyruvate metabolism and the glycolysis/gluconeogenesis pathway in the bodies of white South American shrimp, which initially explains the positive effect of astaxanthin on the growth of white South American shrimp.

3.2 Penaeus monodon

Penaeus monodon is a warm-water shrimp (Lin, 1988). Its optimum temperature is 15–35 °C. It is the largest species in the genus Penaeus, with the largest individuals reaching 350 mm (Gu Yu et al., 2020). Its astaxanthin content is about 20% higher than that of ordinary shrimp (Wen Weigeng et al., 2011). It is deeply favored by consumers and is a best-selling variety in the market. Its production in China is second only to that of the white leg shrimp.

Wen Weigeng et al. (2011) found that after adding astaxanthin to the feed of Penaeus monodon, although there was no significant effect on the activity of alkaline phosphatase (AKP), peroxidase (POD) and superoxide dismutase (SOD), the survival rate of Penaeus monodon was improved, and the weight gain rate, specific and phenoloxidase activity were significantly increased. Angell et al. (2018) also demonstrated that astaxanthin promotes the growth of Penaeus monodon, and that higher concentrations and longer supplementation times of astaxanthin can lead to improved color and visual effects of cooked P. monodon, increasing its commercial value.

3.3 Japanese tiger prawn

The Japanese tiger prawn (Marsupenaeus japonicus), also known as the Japanese prawn, is one of the most important crustaceans in Japan (Bulbul et al., 2014). In 2020, the aquaculture production of Japanese tiger prawns in China reached 4 22,930 tons. However, the color and luster of shrimp under artificial cultivation are quite different from those in the natural state, which greatly affects their commercial value. Therefore, some experiments have explored the use of astaxanthin in feed to improve their color (Dose et al., 2016).

Mos et al. (2018) evaluated the effects of chemically synthesized astaxanthin on the growth performance, survival rate, stress resistance, immune response, fatty acid content and pigmentation of Japanese tiger prawn (Penaeus vannamei) juveniles. The results showed that a dietary supplement of 400 mg/kg astaxanthin can improve the growth performance of Japanese tiger prawns and increase their blood cell count (THC) and viable cell count (VC), thereby enhancing their immune function. At the same time, as the level of astaxanthin supplementation increases, the redness and yellowness of the shrimp increased. After cooking, the shrimp fed with astaxanthin-containing feed appeared a beautiful dark red color, while the control group appeared a pale pink color, which to some extent increased their commercial value. Maoka et al. (2018) found that feeding Japanese tiger prawns with feed containing different levels of astaxanthin resulted in higher survival rates during the development and metamorphosis of the prawns to late larvae.

3.4 Other shrimps

Cheng et al. (2019) studied the effects of dietary astaxanthin on the growth performance and non-specific immunity of Procambarus clarkii (commonly known as small crawfish). It was found that adding 200, 400 mg/kg and 800 mg/kg astaxanthin to the feed for 8 weeks increased the weight, weight gain rate, survival rate, serum lysozyme (LYZ) activity, protein level, AKP activity, liver and pancreas SOD activity and glutathione peroxidase (GPx) activity of crayfish, demonstrating that astaxanthin can be used as a dietary supplement for crayfish. Hung et al. (2010) found that adding astaxanthin to Panulirus ornatus with cholesterol peroxidase (GPx) activity, demonstrating that astaxanthin can be used as a dietary supplement for crayfish.

Hung et al. (2010) found that adding astaxanthin and cholesterol to the diet of the spiny lobster (Panulirus ornatus) can significantly improve the growth rate, survival rate and pigment deposition of the spiny lobster, improve feed efficiency and commercial value. Barclay et al. (2006) found that with the addition of astaxanthin in the feed, the carotenoid content of the tissues of the lobster increased, and the pigmentation of the exoskeleton increased, visually darkening the lobster. These studies show that the addition of astaxanthin to the feeding of lobsters may be of great significance for their immune function and marketing.

4 Application of astaxanthin in crab farming astaxanthin in crab farming

4.1 Chinese mitten crab

The Chinese mitten crab (Eriocheir sinensis, commonly known as the river crab) is one of the most important freshwater farmed crabs in China (Zu Lu, 2020). It has tender meat and is rich in nutrients (Qi Ziyuan et al., 2021; Peng Jing et al., 2019), especially its mature gonads and liver and pancreas, which are beautiful in color, delicious and fragrant (Fu et al., 2021; Peng Jingwen et al., 2019), are traditional Chinese aquatic treasures. Although the production of river crabs is huge, but the products of pond farming have the problem that the color of the shell, the liver and pancreas, and the gonads are relatively light after cooking, which affects their market value (Kumar et al., 2021; Shiby et al., 2021; Wang et al., 2020; Kong et al., 2017). Astaxanthin is considered to improve the quality of crabs and the color and nutrition of crab roe and crab paste, and has been widely tested in the farming of river crabs.

Ji et al. (2020) found that adding 60 mg/kg microalgal astaxanthin to the diet can significantly improve the growth performance and survival rate of river crabs, and also enhance antioxidant capacity, non-specific immunity, tissue astaxanthin content and resistance to ammonia nitrogen stress. Ma et al. (2017) added synthetic astaxanthin to the fattening feed of river crabs, and after feeding, the total amount of carotenoids, color and antioxidant capacity in the carapace, hepatopancreas and ovaries of the crabs were significantly improved. Wang et al. (2018) conducted experiments on the susceptibility of river crab pond culture to high pH stress. The results showed that when astaxanthin was supplied, the symptoms caused by high pH stress, such as hemocyte apoptosis and structural damage to the hepatopancreas, were generally improved. These studies fully demonstrate the application potential of astaxanthin in the farming of Chinese mitten crabs.

4. 2. Three-spine horseshoe crab

The three-spine horseshoe crab (Portunus trituberculatus) is one of the most popular marine crustaceans in China. It is known for its tender taste and rich nutrition (Yuan et al., 2020), and has great potential for expanding the scale of aquaculture and improving nutritional value. In coastal areas have already carried out the artificial breeding of the three-spined horseshoe crab, and it mainly comes from pond breeding. Due to the growth environment and feeding structure, the color of the crab shell and ovaries is lighter than that of the wild horseshoe crab (Sun et al., 2022), which objectively restricts the improvement of the quality of pond-bred horseshoe crabs. In response to this problem, the academic community has carried out a series of experiments.

Ha n et al. (2018) demonstrated that the addition of astaxanthin to the feed enhanced the redness of the cooked crabs and also increased the astaxanthin concentration in the whole body, shell and hepatopancreas of the crabs. At the same time, astaxanthin supplementation can reduce oxidative stress and increase the concentration of n-3 highly unsaturated fatty acids (HU-FA) in the whole body, thereby improving the nutritional value of the product and promoting health. Yu Xiao Jun (2018) and Wu Renfu et al. (2018) also showed that astaxanthin has a positive effect on the pigmentation of the swimming crab, but the former experiment supplemented the feed with an appropriate amount of astaxanthin to improve the total antioxidant capacity (T-AOC), GPx and acid phosphatase (ACP) activity of the blood lymph of the swimming crab, and improve the total lipid and carbohydrate content of edible tissues.

4. 3 Other crabs

Daly et al. (2013) added astaxanthin to the diet of juvenile Kamchatka rock crabs (Paralithodes camtschaticus, commonly known as king crabs) in stages C1 to C4. After feeding for 56 days, it was found that astaxanthin can significantly improve the survival rate of juvenile king crabs, provide provide nutrition or enhance their immune systems. At the same time, analysis of digital photos found that feeding astaxanthin can improve the saturation of the king crab shell color and improve its quality. Thien et al. (2017) found that adding 500 mg/kg astaxanthin can significantly improve the maturity rate, spawning rate, gonadal index, and oocyte diameter of female crabs, which has a significant effect on the reproductive performance of the purple crab, and can significantly improve the survival rate of its second-stage amoeboid larvae and increase the survivability of the larvae.

5 Summary and outlook

Aquatic animals generally exhibit poor de novo synthesis of astaxanthin (Kong et al., 2012), which is the main pigment in shrimp (86%–98% of total carotenoids) and other crustaceans (Okada et al., 1994). The body color of crustaceans is closely related to the content and composition of carotenoids in their bodies. Although  crustaceans cannot synthesize astaxanthin from scratch (Najoan, 2021), but can use exogenous carotenoids in the feed and convert them into astaxanthin through the synthesis of canthaxanthin (Nguyen, 2013) or directly store other carotenoids and astaxanthin in the body to achieve proper coloring.

Therefore, the color of crustaceans is greatly affected by the feed composition. Studies have shown that (Nguyen, 2013) or by directly storing other carotenoids and astaxanthin in the bait in the body to obtain appropriate coloring. Therefore, the composition of the feed has a greater impact on the color of crustaceans. Studies have shown that astaxanthin can improve the color of shrimp and crab and make the liver and pancreas more bright and beautiful. In salmon trout, cichlids and ornamental fish are also often supplemented with astaxanthin to improve their color.

For example, supplementing the feed with astaxanthin can significantly improve the muscle coloration and total carotenoid content of rainbow trout (Kumar et al., 2021) (Dong et al., 2021). Adding natural astaxanthin to the bait can effectively improve the body color and increase its redness value (Jiang Jufeng et al., 2021). Adding an appropriate amount of astaxanthin to the feed of red ornamental fish such as koi and blood parrot fish (Mou Chunyan, 2015; Wu Songqing et al., 2014) and rainbow tetra (Song Xuelu, 2017) can significantly improve body color and enhance ornamental value.

At the same time astaxanthin can reduce oxidative stress by activating the Nrf2/Keap1 pathway and inhibiting the NF-kappa B pathway (Chen et al., 2020), and some studies have also reported the DNA repair properties of astaxanthin (Singh et al., 2020; Davinelli et al., 2018). In addition astaxanthin is also considered to be an essential growth factor in the early development of some shrimp species (Dall, 1995).

However, high doses of astaxanthin may not be beneficial for growth performance because they can inhibit the expression of some important genes or promote the abnormal expression of other important genes (Saleh et al., 2018), which may disrupt normal growth and metabolism. Therefore, astaxanthin has been shown to have a positive effect in shrimp and crab farming, but the amount of additive, feeding time, and usage methods need to be adjusted according to the specific species and actual farming conditions.

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