In vivo assessment of fat composition in Senegalese sole (Solea senegalensis) by real-time ultrasonography and image analysis of subcutaneous fat

An ultrasound and image analysis non-invasive and non-destructive method for predicting skin fat, filet muscle fat, and whole body fat depots in live Senegalese sole (Sole senegalensis) was evaluated. The experiment was conducted with Senegalese sole of commercial market size (n=46, mean weight 278±78g). The fishes under a mild anesthesia were placed in a rectangular metallic container and were scanned with a real time ultrasound (RTU) scanner equipped with a linear array transducer of 7.5MHz. For all fish, four cross-sectional RTU images of the dorsal anterior filet was obtained. The RTU images were analyzed using ImageJ software to determine the fish subcutaneous fat (SF) at each section. After this, fish were killed, and the right dorsal filet of each fish was dissected in muscle and skin. These two components and the remaining of the fish were ground and homogenized for chemical analysis. The skin fat, filet muscle fat and whole body chemical fat contents were obtained. The relationships between the SF obtained from image analysis and skin fat, filet muscle fat and whole body fat were computed using simple regression and partial least squares regression (PLSR). The skin and filet muscle had lower fat than the whole body (1.5 and 4.5 versus 6.6%, respectively). Filet muscle presents the lowest fat depot (1.5%). The SF obtained from RTU and image analysis shows a mean value between 2.8 and 3.5%. All fat depots were significantly correlated with SF obtained by RTU and image analysis, with R2 values ranging from 0.707 to 0.851 for skin fat, 0.725 to 0.802 for filet muscle fat and 0.664 to 0.760 for whole body fat. The PLSR models explained accurately the skin fat (R2=0.875 and RMSEP=0.506), filet muscle fat (R2=0.800 and RSMEP=0.117) and whole body fat (R2=0.785 and RSMEP=0.586). Our results suggest that RTU and image analysis is a practical and feasible non-invasive and non-destructive technique for in vivo fat depots prediction in Senegalese sole fish.In aquaculture, the knowledge of the body composition in live fish, particularly fat content, is important for feeding, reproduction and genetics programs. However, all those programs depend critically on quick, accurate, and above all, non-invasive methods to predict body composition in live fish. Traditionally fish body composition was determined by comparative slaughtering followed by chemical analysis. Comprehensive studies using image techniques such as real time ultrasonography (RTU) show the ability of this technique to predict fish body composition traits. This technique is non-invasive and non-destructive and therefore is very useful for use in vivo for fish body composition examinations. Our present work investigated the ability of RTU and image analysis to predict in vivo fat composition of Solea senegalensis. Through this work monitoring fat variations with time and the possibility of repeated measurements on the same individuals and on a high number of live fish throughout the life-cycle is possible. Therefore our present study has close relevance to aquaculture particularly to nutrition status of farmed fishes.