Assessment of body shape variation using Elliptic Fourier descriptors and ellipse fitting estimators and their genetic estimates in the flatfish Senegalese sole

Body shape is an important morphological trait in aquaculture. This study investigates the use of Elliptic Fourier descriptors (EFDs) analysis and ellipse fitting estimators to assess shape variation in Senegalese sole and their genetic variance components. A total of 2271 fish were individually photographed and body contours reconstructed using 20 Elliptic Fourier harmonics. Principal component analysis identified four symmetric components that explained the 68.6% of the total variation. They were mainly related to the adjustment of the body to an ellipse (PC1s and PC3s) and caudal fin morphological features (PC2s, PC3s, PC4s). Moreover, four asymmetric components related to caudal fin (PC1a, PC2a, PC3a) and head orientation (PC4a) that explained 24.5% of the total variation were also found. In addition to EFDs, body perimeter and five ellipse fitting estimators including the maximum body height to caudal peduncle height ratio (MBH/CPH), body aspect ratio (AR), ellipticity (ELL), AR from theoretical ellipse (ARe) and solidity (SOL) were calculated. PC1s was strongly correlated with ARe, AR and ELL (>= 0.75), PC2s with SOL (-0.79) and PC3s with AR and ELL (0.48-0.49). Males appeared more elliptic than females as revealed by all ellipse descriptors with a tendency to caudal fins with obtuse angles (PC3a) and heads orientated toward the abdominal cavity (PC4a). Overall, heritabilities for symmetric components were higher than for asymmetric. Heritabilities for body ellipse fitting estimators including PC1s were high or very high with the highest values for AR (0.80) and ARe (0.78) for body and whole-body, respectively. Heritability for MBH/CPH was high (0.51) with low genetic correlation with other morphological traits. Heritabilities for symmetrical and asymmetrical features of caudal fin were moderate or low and indirect selection using other highly correlated traits such as PC2s through SOL and PC3a through PC4a or PC1s would facilitate progress in the selection. Perimeter showed a moderate heritability and it was more genetically correlated with growth than shape-related traits. The data provided represent a valuable tool to assess body shape in sole and in the design of genetic breeding programs in Senegalese sole.

Automated summary

This study examines the use of EFDs analysis and ellipse fitting estimators to assess shape variation and genetic variance components in Senegalese sole. The results show that both symmetric and asymmetric components are related to body shape and fin features, with higher heritabilities for symmetric components. The findings can be applied to the design of genetic breeding programs for Senegalese sole.