1. Used as a food attractant to promote animal feeding
 
Most fish discover and determine food mainly through vision, and ultimately whether the facility still relies on smell and taste. The perception of smell and taste by fish is achieved through the olfactory epithelium and taste buds. The olfactory epithelium is located in the olfactory sac. There are about 100,000 taste buds in fish. There are taste buds in the mouth, tongue, tentacles, gills, body sides, and tail, making it the most sensitive taste bud among animals. Based on the responses of the anterior palatal nerves innervated by the facial nerve, scholars from Mie University in Japan have studied the taste and sensitivity of five species of marine teleosts to amino acids, betaine and nucleotides. The results show that the taste receptors of all fish are sensitive to 10- 4M of betaine which has the reaction. Israeli scholars have used behavioral testing to study the chemical susceptibility of adult freshwater shrimp. The threshold concentration of betaine reaches 10-5M-10-8 M, and the animal attracting behavior is ≥50%. Adding 0.5% to 1.5% betaine to fish feed has a strong stimulating effect on the smell and taste of all fish and crustaceans such as shrimps and crabs (Zheng Jucao et al., 1995).

Yan Xizhu (1996) reported that when 0.8% and 1.0% betaine were added to the feed, the daily weight gain of tilapia increased by 28.68% and 29.48%, respectively, compared with the control group, and the feeding time was shortened by 1/3. The carp test of Chaoyang District Fisheries Bureau in Beijing showed that the daily weight gain of carp was different from that of the control group when betaine and 0.1% betaine compound were added to the same basic feed. The increase of 16.5%, 17.4%, 21.5% and 34.6% indicated that adding betaine and its compound agent to the feed had a growth-promoting effect on carp, and the compound agent had better effect. Yan Li et al. (1994) reported that when betaine was added to the carp feed at a ratio of 0.3%-0.5%, the weight gain was increased by 41.78%-49.32%, and the feed coefficient was decreased by 14.13%-24.16%, respectively.

Betaine can not only improve the palatability of the feed, increase the food intake of fish, but also greatly shorten the feeding time and reduce the bait coefficient. Yan Xizhu et al. (1996) showed that Nile tilapia feeding with betaine feed would increase the activities of protease and amylase in the intestine and liver, which not only improved the utilization rate of the feed but also reduced the pollution of the water quality by the residual bait. In addition, betaine can accelerate the physiological molting of shrimps and crabs, which is beneficial to the production performance of shrimps and crabs (Nelson, 1989). Xu Zirong, et al. (1998), Wang Yizhen, et al. (1999) conducted a study on Du grown pigs at different growth stages. Adding 1000mg/kg betaine to the diet increased the daily weight gain of growing pigs by 13.20% (P<0.01), and the feed conversion rate by 7.93% (P<0.05). The weight gain increased by 13.3% (P<0.01). In addition, there were significant gender differences in the effect of promoting the growth of finishing pigs. The effect on barrows was better than that of sows. and feed conversion ratio were not significantly affected.

2. Relieve stress and improve the ability of animals to resist stress
 
Various stress responses seriously affect the feeding and growth of aquatic animals, reduce the survival rate, and even cause death. Betaine reduces the content of homocysteine ​​in the body by promoting the conversion of homocysteine ​​to methionine in the body. Homocysteine ​​is an excitatory amino acid and an inhibitor of gamma-aminobutyric acid (GABA) synthase in the brain, glutamate decarboxylase (GAD) (Hammond et al., 1981). The content of homocysteine ​​can reduce its inhibition of GAD activity, which is conducive to the synthesis of GABA in the brain, thereby strengthening the central inhibition effect, thereby relieving stress.

Freed et al (1979) found that betaine had anti-homocysteine, pentylenetetrazole and electroconvulsive effects in mice. The pharmacological study of Xu Deyi et al. (1986) showed that betaine has obvious sedative effect. Hall (1995) reported that betaine can reduce the stress response of long-haul cattle and increase the speed of weight recovery after transport. Cinton (1989) reported that the addition of betaine to the feed can promote the feeding of aquatic animals under disease or stress. Nelson (1991) test showed that betaine helps salmon resist cold stress below 10°C, and is an ideal feed additive for overwintering fish. Wang Yan et al. (1998) found that betaine helps fish resist the stress caused by long-distance transportation. Wang et al. put 1,000 grass carp fry after long-distance transportation into Pond A and Pond B with the same conditions. The grass carp feed in Pond A added 0.3% betaine, and the grass carp feed in Pond B did not add betaine. The results found that A The grass carp fry in pond were active in water and fed quickly, and no fry was found to die; while the fry in pond B fed slowly and the mortality rate was 4.5%.


3, Adjust the osmotic pressure
 
In the case of osmotic pressure changes, in order to maintain the osmotic pressure balance and prevent the ion concentration in the cells from changing rapidly, the presence of osmotic pressure buffer substances is required. Studies have shown that high concentrations of betaine contained in mitochondria and chloroplasts play an important role in maintaining normal cellular metabolism during osmotic stress.

Betaine is an effective osmotic pressure buffer substance, which can be used as an osmotic protective agent for cells, which can improve the tolerance of biological cells to drought, high humidity, high salt and hypertonic environments, and prevent the loss of cell water and the entry of salts ( Ko et al., 1994), improve the function of the Na-K pump of the cell membrane (Biggers, 1993), stabilize the enzyme activity and the function of biological macromolecules, adjust the osmotic pressure and ion balance of tissue cells, maintain the nutrient absorption function, and enhance the osmotic pressure of fish and shrimp. Tolerance during cataclysm (caused by shrimp metamorphosis, fish transport, etc.) and increase the survival rate.

Virtanen et al. (1989) reported that adding 1.5% betaine/amino acid to carp feed can reduce the water content in carp muscles; and when the concentration of inorganic salts in the water increases, it is beneficial to maintain the balance of electrolytes and osmotic pressure in the fish body; Diao Xin Equal (1990) reported that betaine is beneficial for marine organisms to maintain a lower salt concentration in the body, continuously replenish water, play an osmotic adjustment role, and enable freshwater fish to adapt to the transition to a seawater environment. Clarke (1994) reported that adding 1% betaine to the feed of 1-month-old chinook salmon had no significant effect on the growth and death of the fish in freshwater, but could significantly promote the growth of the fish in seawater.