Sex Determination in Young and Adult Rainbow Trout Using Geometric Morphometrics Analysis

Sex determination in rainbow trout generally involves the subjective evaluation of body shape and color in sexually mature individuals. The present study aimed to evaluate sex differences in body geometry in both young and adult individuals of rainbow trout using geometric morphometry. A total of 80 rainbow trout (Oncorhynchus mykiss) individuals were studied, including 40 young individuals (20 females and 20 males) and 40 adult individuals (20 females and 20 males). Sixteen homologous landmarks were evaluated in the left lateral images of the studied trout. Geometric morphometrics procedures were applied separately to young and adult fish to determine the sex differences. The results revealed that in young male trout individuals, the origin point of the pelvic fin was posteroventral, and the anterior tip of the nose was anterodorsal, compared to females. When adult male trout fish were compared to their female counterparts, the anterior tip of the nose was observed to be anterodorsal, and the anterodorsal corner of the dorsal fin was dorsal. In the Principal Component Analysis (PCA), PCA 1–2 explained 61.49% of the total variance between the sexes in young trout and 43.48% of the total variation in adult trout. The use of geometric morphometry enabled easy determination of sex differences, particularly in young rainbow trout and partly in adult rainbow trout. Therefore, geometric morphometry could serve as a cost-effective, non-invasive, and feasible approach for the sex determination of fish in trout farms to achieve simple, sustainable, economical, and high-value-added fish farming within a short duration.