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The present study aimed to comparatively evaluate the protein requirements of large yellow croaker (initial body weight: 17.03 ± 0.11 g) fed with five dietary protein sources including fish meal (FM), cottonseed protein concentrate (CPC), Clostridium autoethanogenum protein (CAP), Tenebrio molitor meal (TM) and Chlorella meal (CM). The basal diet contained 30% of FM. Based on it, each of the five dietary protein sources was used to formulate graded levels of dietary protein (35%, 40%, 45%, 50%, 55% and 60%, respectively). After a 56-day feeding trial, it was indicated that the protein requirement of large yellow croaker was 50.91%, 44.95%, 39.92%, 40.34% and 52.19%, when FM, CPC, CAP, TM and CM were used as the dietary protein source, respectively. Overall, the TM and CM groups showed lower weight gain rat, feed intake, feed efficiency, protein efficiency ratio, protein retention and in vitro digestibility of dietary protein compared to the FM, CPC and CAP groups at the same dietary protein level. Meanwhile, the FM groups showed the highest amylase, lipase and trypsin activities followed by CPC, CAP, CM, and TM. At the same dietary protein level, the FM groups showed the highest muscularis thickness, villus height and perimeter ratio of intestine, followed by the CPC, CAP, CM and TM groups. The fish fed with dietary TM showed severe liver damage compared to those in the FM, CPC, CAP and CM groups. In summary, the present study demonstrated that the dietary protein requirement of large yellow croaker could be different because of different protein source included into diets. The CPC and CAP were more suitable as the alternative dietary protein sources for large yellow croaker than TM and CM according to the growth, feed utilization, digestive and absorptive enzyme activities, intestinal and liver histology analysis.
Huangfu et al. (Wed,) studied this question.