What are the effects of astaxanthin on growth, color and antioxidant of Pelteobagrus fulvidraco?

 Pelteobagrus fulvidraco has tender flesh, delicious taste, no interstitial spines and high nutritional value, which is favored by consumers and is a characteristic freshwater aquaculture species in the 13th Five-Year Plan of China. Under the intensive pond culture mode, due to the high culture density, when the supply of pigment in the feed is insufficient, it is very easy to cause abnormal body coloration of Pelteobagrus fulvidraco, resulting in the phenomena of "fading" and "black body", which will affect the quality of Pelteobagrus fulvidraco. Therefore, adding colorants to improve the body color of Pelteobagrus fulvidraco through feed is a common measure, but there are many varieties of colorant additives in the market with different qualities, and farmers often overfeed them, which results in Pelteobagrus fulvidraco being susceptible to the phenomena of "banana fish" and "flower spots". Based on the above problems, finding a suitable feed additive for body color improvement is important. Astaxanthin is a kind of carotenoid, also known as zooxanthin and astaxanthin, which mainly comes from microorganisms (e.g. microalgae, yeasts and bacteria, etc.) and marine organisms (shrimps, crabs, salmonids, etc.).

 

 Studies have shown that astaxanthin is commonly used to improve the body color of aquatic animals, such as ornamental fish, Plectropomus leopardus, shrimps and crabs. With the deepening of research, astaxanthin also plays corresponding functions in other aspects, and astaxanthin is also effective in improving the survival rate of aquatic animals, and promoting the growth, reproduction and development of the organism. There are few studies on the effects of astaxanthin on the growth, body color and antioxidant of Pelteobagrus fulvidraco. In this experiment, we took Pelteobagrus fulvidraco as the research object to investigate the effects of different levels of astaxanthin on the growth, body color and antioxidant of Pelteobagrus fulvidraco, so as to provide basic data for the healthy development of Pelteobagrus fulvidraco aquaculture industry.

 

1 Materials and Methods

1.1 Test fish

The juvenile Pelteobagrus fulvidraco was purchased from an aquatic market in Changchun City in the same batch, and was temporarily reared in the aquaculture system of the Aquaculture Laboratory of Jilin Agricultural University for 15 d to adapt to the experimental aquaculture environment after the observation of the naked eye to confirm that there was no obvious injury on the surface of the body and that the fish was swimming actively. During the period of temporary culture, basic feed was fed twice a day (9:00 and 16:00) to adapt to the experimental feed. The water temperature was maintained at 23~25 ℃, the dissolved oxygen was maintained at ≥5 mg/L, the pH was maintained at (7.1±0.1), and the ammonia nitrogen was <0.5 mg/L.

 

1.2 Formulation and preparation of test feeds

The astaxanthin used in the experiment was supplied by Xi'an Zebang Bio-technology Co., Ltd. and the astaxanthin was mainly extracted from Rhodococcus pyrenoidus at a concentration of 2%. Fish meal and corn protein powder were used as the main protein sources to formulate the basal feed, and the composition and nutritional levels of the main ingredients are shown in Table 1. The main ingredients and nutrient levels were shown in Table 1. 0, 50, 100, 150 and 200 mg/kg of astaxanthin were added to the basic feeds, and the feeds were manually produced according to the method of Yao JM et al. (2019), so that five kinds of experimental feeds were formulated, preserved and stored.

 

1.3 Experimental design and daily management

After 15 d of temporary rearing, 450 Pelteobagrus fulvidraco of the same size with an initial weight of about 8 g were selected, weighed and randomly divided into 15 buckets of 30 fish each, randomly divided into 5 groups with 3 replicates in each group, and each bucket was labeled. After fasting for 24 h, the fish were fed with five kinds of experimental diets for 8 weeks. The feeds were fed manually twice a day (9:00 and 16:00) in the form of satiation feeding, and the specific feeding amount was adjusted according to the food intake. The frequency of water change, water temperature, dissolved oxygen, pH and ammonia nitrogen conditions were the same as those in the temporary rearing period.

 

1.4 Sample Collection and Indicator Measurement

Weighing was performed in buckets before the beginning and at the end of the feeding trial, and the average weight gain rate, specific growth rate, feed efficiency and protein efficiency were calculated according to the recorded initial and final weights of Pelteobagrus fulvidraco and the daily recorded intake according to the method of Yao JM et al. (2019).

Subsequently, five Pelteobagrus fulvidraco fish were randomly selected from each replicate, dried, and the colorimetric values of the skin on the back and abdomen of Pelteobagrus fulvidraco were measured with a colorimeter (CR-400), and the brightness (L*), redness (a*), and yellowness (b*) were recorded.

After the colorimetric value was measured, blood was drawn from the tail vein, and the serum was placed in static position for the measurement of antioxidant indexes, and the total superoxide dismutase (T-SOD) and catalase (CAT) activities and the levels of GSH and MDA were measured by using the kit (Nanjing Jianjian Bioengineering Research Institute, Nanjing, China).

Finally, Pelteobagrus fulvidraco was dissected on ice and the dorsal and abdominal skin was taken to determine the total carotenoid content. Total carotenoids were determined according to the method of Yao JM et al. (2019).

 

1.5 Statistics

All data were recorded in an Excel spreadsheet and analyzed using SPSS 20.0 to determine the significance of the differences between the experimental groups at the P<0.05 level of significance. All the experimental data were expressed as "mean ± standard deviation".

 

2 Results and analysis

2.1 Effects of astaxanthin on growth performance of Pelteobagrus fulvidraco (see Table 2)

As shown in Table 2, the final weight of Pelteobagrus fulvidraco in the 100, 150 mg/kg and 200 mg/kg groups was significantly higher than that of the control group (P<0.05), and the final weight of Pelteobagrus fulvidraco in the 150 mg/kg and 200 mg/kg groups was significantly higher than that of the control and 50 mg/kg groups (P<0.05). The average weight gain rate and specific growth rate of Pelteobagrus fulvidraco in the 100, 150 mg/kg and 200 mg/kg groups were significantly higher than those in the control and 50 mg/kg groups (P<0.05). The feed efficiency and protein efficiency of Pelteobagrus fulvidraco in the 100, 150 mg/kg and 200 mg/kg groups were significantly higher than those of the control group (P<0.05), and the feed efficiency and protein efficiency of Pelteobagrus fulvidraco in the 150 mg/kg and 200 mg/kg groups were significantly higher than those of the control and 50 mg/kg groups (P<0.05).

 

2.2 Effects of astaxanthin on body color of Pelteobagrus fulvidraco (see Tables 3 and 4)

As shown in Table 3, the brightness and redness of the skin on the back of Pelteobagrus fulvidraco in the 150 mg/kg and 200 mg/kg groups were significantly higher than those in the control group (P<0.05). The yellowness of the skin on the back of Pelteobagrus fulvidraco in the 100 mg/kg, 150 mg/kg and 200 mg/kg groups was significantly higher than that of the control group (P<0.05). The brightness and yellowness of the abdominal skin of Pelteobagrus fulvidraco in the 100 mg/kg, 150 mg/kg and 200 mg/kg groups were significantly higher than those in the control group (P<0.05). The redness of the abdominal skin of Pelteobagrus fulvidraco in the 150 mg/kg and 200 mg/kg groups was significantly higher than that of the control group (P<0.05).The total carotenoid content of the dorsal skin of Pelteobagrus fulvidraco in the 100, 150 and 200 mg/kg groups was significantly higher than that of the control group (P<0.05).The total carotenoid content of the abdominal skin of Pelteobagrus fulvidraco in the 150 mg/kg and 200 mg/kg groups was significantly higher than that of the control group (P<0.05). The total carotenoid content of the abdominal skin of Pelteobagrus fulvidraco in the 150 mg/kg and 200 mg/kg groups was significantly higher than that of the control group (P<0.05).

 

2.3 Effects of astaxanthin on antioxidant indexes of Pelteobagrus fulvidraco (see Table 5)

As shown in Table 5, the serum T-SOD activity of Pelteobagrus fulvidraco in the 150 mg/kg group was significantly higher than that of the control group (P<0.05). The serum CAT activity and GSH level of Pelteobagrus fulvidraco in the 150 mg/kg and 200 mg/kg groups were significantly higher than those in the control group (P<0.05). The serum MDA levels of Pelteobagrus fulvidraco in the 100, 150 mg/kg and 200 mg/kg groups were significantly lower than those of the control group (P<0.05).

 

3 Discussion

3.1 Effects of astaxanthin on the growth of Pelteobagrus fulvidraco

The growth performance and feed utilization of Pelteobagrus fulvidraco in the 100 mg/kg, 150 mg/kg and 200 mg/kg groups were significantly improved under the present experimental conditions, which indicated that 100-200 mg/kg of astaxanthin had a significant effect on the growth of Pelteobagrus fulvidraco. Addition of astaxanthin to the feed increased the average weight gain and specific growth rate of Paramisgurnus dabryanus. Similarly, astaxanthin's growth-promoting effects have been demonstrated in juvenile ovate pompano (Trachi⁃ notus ovatus), colorful fairy fish (Symphysodon aequifas⁃ ciata), and blood parrot (Amphilophus citrinellus × Cichlasoma synspilum), among others. The growth-promoting effect of astaxanthin has been demonstrated in The growth-promoting effect of astaxanthin has also been demonstrated in shrimps, such as South American white shrimp (Penaeus vannamei), Macrobrachium rosenbergii, and Penaeus monodon. However, the results of the studies on the appropriate levels of astaxanthin in different fish species varied, e.g., the optimal level of astaxanthin was 50 mg/kg in the Chinook salamander and the colorful fairy fish, the optimal level of astaxanthin in the oviparous pomfret was 200 mg/kg, and the optimal level of astaxanthin in the blood parrot was 100~150 mg/kg, which may be attributed to dose-dependence, species-specific, growth-dependent, or species-specific. The reason for this is that there may be a dose-dependent relationship, which is related to the differences in species, growth stage, culture environment and astaxanthin source, but further analysis is needed.

 

3.2 Effects of astaxanthin on body color of Pelteobagrus fulvidraco

Under the present experimental conditions, with the increase of astaxanthin addition level, the brightness, redness and yellowness of the skin of Pelteobagrus fulvidraco dorsal and abdominal skin increased significantly, as well as the total carotenoid content of the skin of dorsal and abdominal skin, which indicated that astaxanthin had a significant effect in improving the body color of Pelteobagrus fulvidraco. In the study of Pelteobagrus fulvidraco, it was also found that astaxanthin at the level of 100-200 mg/kg significantly improved the body color of Pelteobagrus fulvidraco. The best coloration effect was observed in Trichogaster microlepis when 100 mg/kg of astaxanthin was added to the diet, and it was found that the pigment was mainly deposited on the skin, scale and fin surfaces.

 

In a study on Chinese goldfish (Carassius auratus), a dose-dependent effect of pigment accumulation was found, i.e., as the concentration of astaxanthin was increased, the amount of pigment in the fish body gradually increased. In studies on blood parrots, Mou Wenyan et al. (2014), Sun Xueliang et al. (2017), Li Xiaohui et al. (2008), and Zhang Xiaohong et al. (2009) found that the addition of appropriate amounts of astaxanthin to the feed could significantly increase the amount of pigmentation in the body of blood parrots, and improve the coloring effect of the fish, but the effect varied with different methods of adding astaxanthin. The results of body coloration studies on pink-white, red-spotted and black-spotted red tilapia (Oreochromis niloticus) also showed that astaxanthin additions had a certain degree of tissue and organ variability in body coloration deposition, and through cluster analysis, it was found that carotenoids deposition was highest in the fins, followed by gills and eyeballs, and the lowest deposition was in the skin and muscle tissues of the red tilapia. In conclusion, the above studies showed that astaxanthin has the function of improving body color in aquatic animals, which is attributed to the fact that astaxanthin itself is a carotenoid, but there are differences in pigment deposition among different species, different methods of addition, and different organs, which need to be further investigated and analyzed.

 

3.3 Effects of astaxanthin on antioxidant indexes of Pelteobagrus fulvidraco

It was hypothesized that the appropriate level of astaxanthin could promote the growth of Pelteobagrus fulvidraco, which might be related to the improvement of its antioxidant capacity. Natural astaxanthin is a highly efficient natural antioxidant. Fish are subjected to oxidative stress induced by various factors during the aquaculture process, resulting in the decline of production performance, and improving the antioxidant capacity of the organism can help to promote the growth of fish. Currently, the antioxidant capacity of the organism is generally evaluated by some antioxidant-related enzymes or substances. Under the present experimental conditions, the serum T-SOD activity, CAT activity and GSH level of Pelteobagrus fulvidraco in the 150 mg/kg group were significantly higher than those of the control group, and the MDA content was significantly lower than that of the control group, which indicated that the addition of astaxanthin did promote the antioxidant capacity of Pelteobagrus fulvidraco, and that the addition of astaxanthin in the 150 mg/kg group significantly improved the antioxidant capacity of juvenile snakehead (Channa argus), The antioxidant capacity, immunity and disease resistance of juvenile Channa argus were significantly improved by 50~100 mg/kg astaxanthin. Meanwhile, the total superoxide dismutase, glutathione peroxidase and total antioxidant capacity of larvae of Larimichthys crocea tended to increase with the increase of astaxanthin level. However, the study on astaxanthin's regulation of antioxidant activity in aquatic animals only involves the study of antioxidant enzymes and other related indexes, and its specific mechanism still needs to be further investigated.

 

4 Conclusion

Under the present experimental conditions, the addition of astaxanthin at 150~200 mg/kg could effectively improve the growth performance of Pelteobagrus fulvidraco, improve its body color, and enhance the antioxidant capacity of Pelteobagrus fulvidraco.