Protein Requirement Of Mandarin Fish (Siniperca Chuatsi) In Three Different Size

Siniperca chuatsi,as a typical representative of carnivorous fish,has a higher demand for protein in bait than herbivorous,omnivorous or even partial carnivorous fish.Different aquatic animals have a great difference in their demand for protein in bait and their species characteristics.With the continuous breakthrough and improvement of the feed breeding mode and technology of the mandarin fish,it is very important to explore and clarify the appropriate demand for protein in different growth stages of the mandarin fish in order to better reduce the breeding cost,improve feed utilization efficiency and reduce tail water discharge.In this study,three different sizes of mandarin fish were taken as the research objects,and the eight-week growth experiment was conducted to study the appropriate dietary protein requirements of the mandarin fish at different growth stages,as well as the change rules of feed utilization rate and ammonia nitrogen excretion after feeding diets with different protein levels.The initial body weight of the three different sizes of mandarin fish were 11.58 ± 1.34g(small size),94.77 ± 2.59g(medium size)and245.26 ± 3.59g(large size),respectively.Five protein levels(40%,45%,50%,55%and 60%)were set for small size,and six protein levels(35%,40%,45%,50%,55%and 60%)were set for medium size and large size.The results showed that the weight gain rate(WGR)and specific growth rate(SGR)of the mandarin fish were significantly increased with the increase of dietary protein level(P < 0.05).The SGR of small size and medium size mandarin fish reached the maximum value of 2.71 ±0.11% /d and 1.61 ± 0.11% /d when the dietary protein level was 50%,and the SGR of large size mandarin fish reached the maximum value of 0.88 ± 0.04% /d when the dietary protein level was 45%.The feed coefficient(FCR)of the three different sizes of the mandarin fish showed an opposite trend.In the high-protein diet group(55%and 60%),all three specifications showed lower protein deposition rates(PDR).The survival rate of small size and medium size mandarin fish fed diets with low protein level(35% and 40%)was significantly lower than that of other groups(P < 0.05),but the dietary protein level had no significant effect on the survival rate of large size mandarin fish(P > 0.05).The fatness(CF),hepatopancreas somatic indices(HSI)and visceral somatic indices(VSI)of small and medium sized mandarin fish showed a decreasing trend with the increase of dietary protein level(P < 0.05).With the increase of dietary protein level,HSI of large size Mandarin fish showed a significant decrease(P < 0.05).The apparent digestibility(ADC)of feed crude protein for the three specifications of the mandarin fish increased significantly with the increase of feed protein to a certain level(P < 0.05),and tended to be stable when the protein level reached 50%.When the dietary protein level reaches 55%,the ADC of small size mandarin fish to crude fat is the highest,but there is no significant difference between medium size and large size mandarin fish to Crude fat(P > 0.05).The trypsin activity of foregut of the three sizes of mandarin fish was significantly increased with the increase of feed protein level(P < 0.05),and reached a certain value when the feed protein level reached a certain value(small size and medium size: 50%;Large size: 45%)tends to be stable.The amylase activity in foregut of small and medium sized Mandarin fish was significantly increased with the increase of dietary protein level(P < 0.05),but the amylase activity in foregut of large sized mandarin fish was significantly decreased with the increase of dietary protein level(P < 0.05).The activities of alanine aminotransferase(ALT)and aspartate aminotransferase(AST)in liver of three specifications of mandarin fish were significantly increased with the dietary protein level increasing(P < 0.05).The excretion rate of ammonia nitrogen reached the peak 6h after feeding,and the excretion rate of ammonia nitrogen of mandarin fish increased significantly with the increase of dietary protein level(P <0.05).When feeding high protein diet,the ammonia nitrogen excretion rate of large size mandarin fish was significantly higher than that of small size mandarin fish(P <0.05).SGR linear regression model analysis of different sizes of mandarin fish showed that the optimal protein levels for three different sizes of mandarin fish were49.71%,45.19% and 44.60%,respectively.