In order to understand the the nutritional requirement of juvenile tawny puffer(Takifugu flavidus) during the bait conversion period, the growth, body lipid content and its fatty acid composition of tawny puffer juvenile before, during, and after the domestication were detected and analyzed by biochemical analysis methods. The results show that the phenomenon of body weight compensatory growth of tawny puffer juvenile has been found after the domestication; the highest condition factor of juvenile was found before the domestication(10.02), the lowest condition factor was found during the domestication(5.43), and it increased significantly after the domestication(6.00). The dry matter contents of tawny puffer juvenile increased significantly after the domestication. 8 saturated fatty acids(SFA), 7 mono-unsaturated fatty acids(MUFA), and 12 poly-unsaturated fatty acids(PUFA) were found in the dry sample before, during, and after the domestication. From the percent content, during the bait conversion period, the C16:0 content of tawny puffer juvenile was the highest and stable(21.26%-23.81%), the C18:0 content decreased significantly, and the C16:1 and C18:1n9c contents increased significantly; the C22:6n3(DHA) content was rich(11.95%-13.05%), it decreased faintly during the bait conversion period;the C20:5n3(EPA) percent content of juvenile decreased faintly during the domestication, and increased faintly after the domestication; the C22:5n3(DPA) percent content decreased significantly during the bait conversion period. During the bait conversion period of tawny puffer juvenile, the SFA was relatively stable(38.13%-42.52%), the MUFA increased significantly, however, PUFA decreased significantly, especially∑n3PUFA. And more notably, the C18:2n6c percent content of the compound feed was particularly high(21.29%), however, the C18:2n6c content of juvenile fed with compound feed was very low(2.47%);On the contrary, the C16:1 percent content of the compound feed was particularly low(3.87%), however, the C16:1 content of juvenile fed with compound feed was very high(9.25%). Therefore, tawny puffer juvenile had a higher demand for n3PUFA(especially DHA and EPA), but didn't need too much C18:2n6c, and part of the C16:1 in juvenile body was from transformation of other nutrients. In order to improve the survival rate of tawny puffer juvenile during the bait conversion period, it is suggested that:1) Before the domestication of tawny puffer juvenile, enhancing live bait, especially seawater copepods enriched with n3PUFA;2)Increasing the additive amount of DHA and EPA, reducing the proportion of C18:2n6c, and increasing the proportion of C16:1, in the compound feed of tawny puffer juvenile during the bait conversion period.