Abstract: The body composition of cultured live large yellow croaker (Pseudosciaena crocea) is extremely difficult to detect. In order to solve this problem, we analyzed the relationship between the impedance measured at 2, 5, 20, 50, 100 kHz for the dorsal and ventral muscles of live large yellow croaker and their key components (protein, fat and moisture). The optimal models (r = 0.830–0.922, P < 0.001) for non-destructive evaluation of the muscle protein and water contents as well as the fat content in live fish was established using the impedance at 2 and 100 kHz frequencies, and their accuracy was verified by experiments (r ≥ 0.900). The correlation among muscle composition, microstructure and impedance indicated that the average area of muscle fiber increased with increasing protein content and decreasing moisture content and was positively correlated with the impedance at 2 kHz; in contrast, the density of muscle fiber and the area of extracellular space decreased with increasing protein content and decreasing moisture content and was negatively correlated with the impedance at 2 kH. The diameter and volume of adipocytes increased with the deposition of fat, and had a significant relationship with the impedance at 100 kHz. This study can rapidly evaluate the composition of fat, protein, water and so on of cultured live large yellow croaker by using biological impedance, and clarify the internal reasons for predicting the composition of live fish by impedance. The findings of this study can help aquaculture enterprises with targeted breeding and and help consumers to choose the optimal products.

Key words: live fish; bioimpedance; components; non-destructive determination