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Application of L-tryptophan in aquatic feed

Tryptophan is a neutral, aromatic amino acid that is a precursor of metabolites such as serotonin, melatonin, and niacin. It is also an essential amino acid for the growth and health of aquatic animals. In addition to its protein synthesis function, tryptophan also has physiological and biochemical functions such as regulating food intake, alleviating stress reactions, and enhancing immune and antioxidant abilities.
Tryptophan is an important component of feed protein, the first limiting amino acid of high-fat meat and bone meal, the second limiting amino acid of corn protein meal, blood meal, poultry offal, and broad bean, and the third limiting amino acid of lupine and feather meal. Lack of tryptophan leads to decreased growth performance, scoliosis, lordosis, and cataracts in rainbow trout, as well as increased levels of calcium, magnesium, sodium, and potassium in the liver and kidneys.
Tryptophan, as a precursor of the neurotransmitter serotonin, can regulate the feeding and aggressive behavior of aquatic animals.
1. The demand for tryptophan in aquatic animals
Tryptophan is the lowest amino acid in the protein composition of aquatic animals, therefore, the demand for tryptophan in aquatic animal feed is also lower than other essential amino acids. The tryptophan requirement of aquatic animals is related to various factors such as breeding variety, feed composition, and initial body weight of experimental animals. In addition, the digestibility of protein, amino acids, and energy in feed can also affect the tryptophan requirement of aquatic animals. The tryptophan requirements vary among different aquaculture varieties, and the overall range of research results is 0.13% -0.48% (percentage of tryptophan in feed dry matter).
Lack or excess of tryptophan can inhibit the growth of aquatic animals, reduce digestive enzyme activity and immune function. An appropriate amount of tryptophan can increase the intestinal length, weight, index, and fold height of aquatic animals, as well as the activity of proteases, lipases, and amylases in the liver, pancreas, and intestines, thereby improving the apparent digestibility of proteins, amino acids, and dry matter. At the same time, it can increase the deposition rate of other essential and non essential amino acids, thereby promoting the growth of aquatic animals. An appropriate amount of tryptophan improves the growth performance of aquatic animals by improving intestinal morphology and structure, increasing digestive enzyme activity, promoting the synthesis of insulin-like growth factor - I, and muscle growth.
2. The effect of tryptophan on the food intake of aquatic animals
An appropriate amount of tryptophan can promote the feeding of aquatic animals. When the tryptophan content in grass carp feed is 0.07% -0.31%, the feed intake and weight gain rate significantly increase with the increase of feed tryptophan content, and the weight gain rate is significantly positively correlated with the feed intake.
3. The effect of tryptophan on stress response in aquatic animals
An appropriate amount of tryptophan can alleviate stress stress caused by nitrite, high copper content, netting, bacterial infections, crowding, etc. At the Saw Edge Green
The addition of 0.75% or 1.00% tryptophan in crab feed significantly reduced the attack intensity and attack frequency, and the addition of 0.50%, 0.75% or 1.00% tryptophan significantly increased the content of 5-hydroxytryptamine in hemolymph and the survival rate of crab.
To increase the yield of aquatic animals per unit area, high-density farming is the most commonly used farming mode. However, high-density farming usually brings crowding stress, leading to increased cortisol release and long-term stress affecting the health of aquatic animals. Specific characteristics of high-density aquaculture group sea cucumber The specific growth rate of sea cucumber in high-density aquaculture group is significantly lower than that in low-density aquaculture group. Adding 1% or 3% tryptophan to the feed changes the body's energy distribution, increases the energy used for growth, reduces the content of cortisol, glucose, and lactate in the body, and significantly improves the specific growth rate of sea cucumber.
4. The effect of tryptophan on the disease resistance, antioxidant and immune function of aquatic animals
Tryptophan metabolites have a wide range of physiological effects. In addition to relieving stress mentioned above, tryptophan also has functions such as improving disease resistance, antioxidant and immune function. The possible mechanisms by which tryptophan regulates the disease resistance, antioxidant and immune function of aquatic animals are: 1) As a precursor of 5-hydroxytryptamine and melatonin, tryptophan can be added under stress conditions in aquatic animals to increase their synthesis, thereby enhancing the activity of downstream antioxidant enzymes and exerting antioxidant effects. 2) Tryptophan catabolism can be induced by IDO γ- Interferons, release cytokines, activate immune cells, enhance the body's antioxidant and antibacterial activities, thereby enhancing the body's immune function. The regulation of body health by tryptophan is also related to intestinal immunity.
Reference: Wang Liansheng, Zhang Yuanyuan, Li Jinnan, Yang Zhe, Research progress on tryptophan in aquatic animals [J], Journal of Animal Nutrition, 2021, 33 (9): 4801-4809.