Effects of protein restriction with subsequent realimentation on growth performance of juvenile Chinese shrimp (Fenneropenaeus chinensis)

The effects of protein restriction in the diet with subsequent realimentation on growth responses of juvenile Chinese shrimp, Fenneropenaeus chinensis (initial mean wet weight 1.347 g), were investigated. The control group (Group C) was fed an adequate diet containing 44.6% crude protein and 18.5 kJ gross energy/g dry matter throughout the experiment. For treatment Groups T₁₅ and T₃₀, in the restriction phase (weeks 1–2) dietary crude protein contents were reduced to 15.0% and 29.3%, respectively, with constant energy supply, while in the realimentation phase (weeks 3–6) they were supplied with the same diet as the control group. Protein restriction led to significant decrease in specific growth rates and body weight of shrimp. However, when the shrimp were transferred from protein restriction to realimentation, they had significantly increased specific growth rates in terms of dry matter, protein and energy (SGR_d, SGR_p and SGR_e) compared with the control shrimp. At the end of the experiment, the shrimp in Group T₃₀ achieved complete growth compensation, while those in Group T₁₅ were still significantly smaller than the controls. As dietary protein levels reduced, feed conversion efficiencies and apparent protein digestibility decreased, but feed intake and protein efficiency ratio increased. The shrimp responded to a change from protein restriction to realimentation by displaying improved feed conversion efficiencies (FCE_d, FCE_p and FCE_e) compared with the controls, although those in Group T₁₅ delayed in showing the enhanced FCE values. In the initial 2-week realimentation, the shrimp in Group T₁₅ showed significantly higher feed intake, and lower apparent digestibility of dry matter and protein than those of the controls. There was no significant difference in protein efficiency ratio among all groups in the realimentation phase. The above results suggest that compensatory growth in Group T₃₀ is mainly dependent on improved feed conversion efficiencies, while that in Group T₁₅ is attributable to both improved feed conversion efficiencies and increasing feed intake. After 2-week restriction, the shrimp showed lower body crude protein, lipid and energy content, and higher moisture and ash content than the controls. However, during the course of realimentation, the differences between the previously protein restricted shrimp and the controls diminished. This indicates that compensatory growth after a period of protein restriction in juvenile Chinese shrimp was accompanied by a complete recovery in body composition and energy content.