Slowly-sinking Feed Processing Of Bighead Carp And Its Appropriate Protein Requirement

This paper studied on the parameters of producing the slowly-sinking feed ofbighead carp by the twin-screw extruder. Basing on this, the different protein leveldiets were produced for researching the appropriate protein requirement of bigheadcarp (Aristichthys nobilis). The results were as follows:1. According to the single-factor design, the starch gelatinization，sinkingspeed and expansion ratio of the compound feed were used to evaluate the influenceof the material moisture content, barrel temperature, fat content and protein contentof the material on the quality of diets. The results showed that：(1) With thematerial moisture content changing from20%to30%, the starch gelatinizationincreased significantly (P<0.01), then kept stably (P>0.05); with increasingmaterial moisture content，sinking speed was significantly slower (P<0.01)，theexpansion ration firstly increased and then decreased (P>0.05).(2) With theincreasing of barrel temperature，the starch gelatinization degree of the diet wassignificantly increased (P<0.01)，and then kept stably (P>0.05), sinking speed wassignificantly slower (P <0.01), the impact of the expansion ratio was not significant(P>0.05).(3) With the fat content of the material changing from5%to11%, thegelatinization of the diet increased firstly and then decreased (P<0.01), sinkingspeed was significantly lower (P<0.01)，the expansion ration increased firstly andthen decreased (P>0.05).(4) With the increasing of protein content of material, thegelatinization of the diet increased firstly and then decreased (P<0.01), theexpansion ration firstly decreased and then increased (P<0.01), the protein contenthad no significant effect on the sinking speed of the diet (P>0.05).The above results suggested that the befitting process parameters forslowly-sinking feed could be described as: material moisture content was25%,barrel temperature was90-115-130℃, and material fat content was7~9%.2. A90-day growth experiment was conducted in a recirculated filtered rearingsystem to research the appropriate protein requirement of bighead carp (Aristichthys nobilis) and the effects of dietary protein levels on growthperformance, digestive enzyme activities and body composition of bighead carp(6.00±0.02g). White fishmeal and casein were used as dietary protein sources toproduce the slowly-sinking powder feedstuff at six protein levels (18.77%,23.60%,29.20%,34.24%,39.93%and46.00%). The results were as follows:(1) Withdietary protein levels increased, weight gain ratio and specific growth rate of thefish improved, and peaked at34.24%.(2) There were no significant effects onfatness, hepatosomatic index among fish fed different diets (P>0.05).(3) Thechanges of diet protein level did not influent the activity of protease or lipase inintestine significantly (P>0.05), but the intestinal protease activities increased andthen decreased with the increase in dietary protein level, and reached a peak at34.24%(P>0.05).(4) Crude protein content and ash content in whole bodyincreased with the protein level increasing in dietary (P<0.05), whereas crude lipidcontent decreased with the protein level increasing in dietary (P<0.05).Results of the experiment indicated that protein levels had a positivelypromotion to the growth performance, the secretion of digestive enzyme anddeposition of body protein of bighead carp. Quadratic curve model was used toanalyze weight gain ratio and special growth rate, respectively. It showed that theappropriate protein requirement for bighead carp was34.65%~34.88%.