Application of algal powder in aquatic feed

In recent years, the scale of aquaculture in China has been expanding, the degree of intensification and industrialization has become higher and higher, the pollution of aquaculture waters has become increasingly serious, diseases occur frequently, seriously disturbing the healthy development of aquaculture industry. Algae powder has the advantages of non-toxic, no residue, no drug resistance, etc. The application of algae powder as an additive in aquatic feed can improve the growth performance of aquatic animals and body immunity, and improve the phenomenon of drug abuse in aquaculture in China. Meanwhile, artificial cultivation of algae can improve the ecological environment of waters and protect aquatic biological resources.

1. Application status and effective ingredients of algal powder in aquatic feed

From tiny single-celled algae to giant algae dozens of meters long, algae species are various, including green algae, brown algae, blue algae, red algae, etc. At present, the main cultured algae in China is macroalgae, with an annual output of about 1 million t, which is mainly used for food and industrial glue extraction. Algal powder is rarely used in aquatic compound feed which is processed in China, which makes it difficult for algal powder, a rich resource, to be fully exploited and utilized. Algae powder, however, contain more protein, carbohydrate, lipid, a variety of vitamins, calcium, phosphorus, sodium, magnesium and other minerals and trace elements like iron, zinc, copper and manganese, can promote the growth of aquatic animals, in addition, kelp powder also contains a variety of biological active substances (such as unknown growth factor, the pigment, the thermal stress of the material) and antibacterial, antiviral substances (seaweed polysaccharides, mannitol, nucleoside, terpenoids, macrocyclic lactones, alkaloids), etc., can improve the body color of the aquatic animals and disease resistance. Superoxide dismutase (sod) and polyamine contained in algal powder can delay cell senescence. Polysaccharides (dai-1, 3-glucan, etc.) and beta-carotene can significantly enhance the immune function of the body. Unsaturated fatty acids such as omega-linolenic acid can promote the reproduction and development of aquatic animals, improve the survival rate and metamorphosis rate of juveniles. Most algae contain different biogels, such as alginate, alginate brown, etc. Therefore, algal powder can be used as a binder for feed.

2.Effects of algal powder on growth performance of aquatic animals

Using algal powder as feed additive can supplement the deficiency of nutritive components of compound feed and meet the nutritional requirements of aquaculture animals. Pan guo-ying and wang ning-zhu (1997) added 2% ulva algae powder to the diet of Japanese prawn cystis japonicus, and found that the survival rate and weight gain rate of prawn increased by 8.69 % and 173 % compared with the control group, and the feed coefficient decreased from 4.05 to 3.64. Zhou qichun and zhao huachao (2001) added algal powder (mixed algal powder consisting of crabgrass, nori and kelp) to the feed of macrobrachium rosenbergii, and the weight gain rate of the algal powder group was significantly higher than that of the control group. When fed the same compound feed, the growth rate of prawns bred in outdoor cement pond (algae such as endogenous margin platform) was significantly higher than that in indoor cement pond. In shore, shrimp feed add 0%, 3%, 6%, 9%, 12%, different levels of algae powder (hybrid alga of wakame, seaweed and kelp powder), after 30 d, the results show that the 3% set of prawn weight gain and protein efficiency is significantly higher than other groups, did not add the group to grow the worst (Zhou Qi deposit and shaw, 2003). Spirulina powder can significantly promote the growth of abalone when it is used as an additive in artificial compound feed. When the shell length of abalone is 2.1-3.5cm and the shell length is 3.5-4.5cm, 5% and 10% spirulina powder are added to the feed, respectively, which can achieve ideal feeding effect (Chen quanxia et al., 2004). The addition of algal powder (rhamnosum) to the feed had a significant effect on promoting the growth of young ginseng, and the average daily growth and weight gain were more than twice that of the pure algal powder group (xu zongfa et al., 1999).

When spirulina powder was added to carassius auratus carp feed, the weight gain rate and feed efficiency increased by 8.91 % and 8.46 % respectively at 6 weeks. At 16 weeks, the increase was 19.17% and 3.86%, respectively (CAI chunfang et al., 2002). Spirulina (2 %, 4 %) was added to the feed to promote the growth, improve the survival rate and reduce the feed factor of the crucian carp (liu huazhong et al., 2004). Adding 1 % ~ 2 % spirulina to the feed of juvenile turtle had a significant promoting effect on the weight gain of juvenile turtle, and increased the feed intake of juvenile turtle by 18.6 % ~ 23.5 %. Adding 1 % ~ 8 % spirulina to the feed of juvenile turtle could significantly promote the lateral growth of juvenile turtle, deepen the bluish green color of the abdomen of juvenile turtle, and increase the disease resistance (ning yuwang et al., 2000).

Zheng Xianchang etc. (2003) found that spirulina in different feed additives on South America white shrimp have no obvious effect on growth performance, the reason may be that in feed ingredients for prawn requirements under the premise of adding a certain amount of spirulina powder, its growth promoting effect completely may be concealed by other factors, may even be caused by adding spirulina nutrition surplus.

3. Effects of algal powder on immune function of aquatic animals

Algal powder contains algal polysaccharides, alkaloids, mannitol, riboids, terpenes, macrolides and other bioactive substances, which have the functions of enhancing immunity, anti-bacterial, anti-virus and promoting growth. At present, algae polysaccharides in aquatic animals more research. In vivo and in vitro experiments showed that the seaweed polysaccharides extracted from brown algae could activate the activities of the forekidney cells and white blood cells of the Atlantic salmon and the bluefish perch, and enhance the resistance of the bluefish perch to hydrophilia monospora. In vitro experiments, the polysaccharide stimulation effect of sulfated seaweed is more significant than that of unsulfated polysaccharide

Macrophages produced more peroxides and higher activity of acid phosphate esters (ACP), which may be due to the increased solubility of sulfated seaweed polysaccharides in water (Dalmo et al., 1998,Samuel et al., 1996). Polysaccharides from sea algae can improve the immune function of penaeus chinensis and scallop chlamys farreri (liu shuqing et al. 1999; Mou haizin et al.,1999). Adding spirulina powder to carassius auratus gibelio feed can improve the activities of lysozyme (LSZ) and superoxide dismutase (SOD) in serum (CAI chunfang et al., 2002).

Other functions of algal powder in feed

Spirulina is added to the feed of ornamental fish, because spirulina is rich in pigment, making ornamental fish colorful. Spirulina can improve the body color and texture of koi because of the combined effects of chlorophyll a, carotenoids, lutein, cyanin and cyanin (yuan feiyu et al., 2003). The content of eicosapentaenoic acid (EPA) in the body of penaeus vannamei showed a good linear relationship with the addition of 0 % ~ 1.5 % spirulina. The content of docosahexaenoic acid (DHA) in shrimp was significantly higher than that in shrimp(cao yutao et al., 2004).

Algal powder is rich in minerals sodium, potassium, vitamin A, vitamin E, vitamin C and other nutrients, these substances have different degrees of resistance or alleviate stress. Algal powder is rich in a variety of amino acids, and some amino acids on aquatic animals have a strong role in attracting prey, such as l-alanine is rainbow trout, Atlantic salmon, river trout and other seedlings as well as carp, goldfish effective food attractant; L-methionine can stimulate the foraging activity of river trout, while histidine, arginine and ornithine can induce the prey of loach.

 C.B.N. Bio-engineering Co., Ltd