Apparent Digestibility Coefficient Of 21 Feed Ingredients And Dietary Tryptophan Requirement For The Large Yellow Croaker, Pseudosciaena Crocea R.

Apparent digestibility coefficients of dry matter, crude protein, energy, phosphorous and amino acid in 21 feed ingredients were determined respectively for large yellow croaker. Furthermore, another feeding experiment was conducted to estimate the dietary tryptophan requirement for the large yellow croaker. Results of the experiment are presented as follows:1. Apparent digestibility coefficients (ADC) were determined using a reference diet with 0.04% Y2O3 indicator and test diets that contained 70% reference diet, by weight, and 30% of the test feed ingredient being evaluated. The feed ingredients included fish meal, blood meal, shimp shell powder, squid visceral ointment, feather meal, chicken meal, expanded soybean, zymotic soybean meal, double-low rapeseed meal, expanded soybean, wheat middling, rice bran, corn grain meal, yeast, beer yeast, wheat gluten, corn gluten meal, tapioca, a-starch, casein and gelatin. ADC of dry matter,crude protein,phosphorus and Energy in fish meal for large yellow croaker were highest (70.17%,93.22%,61.98% and 88.30% respectively). The ADC of dry matter and crude protein in wheat gluten, casein, squid visceral ointment, fish meal, zymotic soybean meal and bread flour ranged from 65% to 85%, lower than those in fish meal. All the dry matter ADC ranged from 47.72% to 70.17%, and that in maize protein was the lowest (P<0.05). ADC of crude protein ranged from 70.98% to 93.22%, and lower digestibility coefficients were found in rice bran (P<0.05). ADC of energy ranged from 59.22% to 88.3%, and lower digestibility coefficients were found in expanded soybean. ADC of phosphorus ranged from 18.45% to 61.98%, and lower digestibility coefficients were found in maize protein. ADC of amino acid for large yellow croaker obviously varied between various materials and various amino acid of one material, and the regularity was not notable. Wherese, ADC of total amino acids and ADC of crude protein kept the same trend.2. A feeding experiment was conducted to estimate the quantitative requirement of tryptophan in juvenile large yellow croaker. The results showed that dietary tryptophan significantly affected the growth and survival of large yellow croaker. The weight gain (WG) and specific growth ratio (SGR) in fish group fed without adding tryptophan (0.23% Trp, Dietl) were obviously lower than those in other groups (p<0.05). WG and SGR increased with the increasing tryptophan up to 0.8%(Diet 4), thereafter, declined (P<0.05). The results indicated that for growth of large yellow croaker, tryptophan is essential and large yellow croaker is able to utilize crystalline forms of tryptophan, but there was a marked decline in growth response and feed utilization beyond the optimum requirement level for tryptophan. On the basis of SGR, the optimum dietary tryptophan requirement of juvenile large yellow croaker was estimated using 0.82% of tryptophan diet (1.73% of dietary protein). Survival ratio of large yellow croaker increased with increasing tryptophan. No significant differences in body composition were found by dietary tryptophan levels (P>0.05).3. A series of experiments were conducted with the macrophages isolated from head kidney of large yellow croaker, Pseudosciaena crocea. Graded concentration of tryptophan with 0.00,0.03,0.06,0.12,0.24 and 0.48mM were added to the culture medium for a 6h incubation. After then, samples were taken for the measurements of respiratory burst, losozyme activity, superoxide dismutase activity and catalase activity. The results show that as the concentration of tryptophan increased, the respiratory burst activity first increased then decrease, and the value of respiratory burst activity at 0.12mM group was significantly higher than the control (P<0.05). With increasing concentration of tryptohan, SOD also first increased then decreased. When the tryptophan concentration was 0.06-0.48mM, the values of SOD were significantly higher than the control (P<0.05). However, CAT and lysozyme activity were independent of the tryptophan concentration (P>0.05). This result indicated that moderate concentration of tryptophan enhanced the nonspecific immune response of kidney macrophage of large yellow croaker in vitro.