Morphometric Ratio-Based Discrimination of Six Triglidae Species from the Eastern Coast of Libya Using Discriminant Function Analysis

Abstract Accurate discrimination of closely related species remains a fundamental challenge in fish taxonomy and biodiversity assessment. This study investigates interspecific morphological differentiation among six Mediterranean Triglidae species using morphometric ratios and discriminant function analysis (DFA). A total of 100 specimens representing Chelidonichthys cuculus (n = 10, TL = 179.51 ± 3.754 mm), C. obscura (n = 29, TL = 184.869 ± 2.672 mm), C. lastoviza (n = 27, TL = 178.377 ± 4.744 mm), Lepidotrigla cavillone (n = 10, TL = 107.3 ± 1.977 mm), C. lucerna (n = 14, TL = 167.142 ± 7.092 mm), and Trigla lyra (n = 10, TL = 365.3 ± 14.038 mm) were analyzed using eight morphometric ratios expressed as being relative to total length or head length. All morphometric ratios differed significantly among species (P < 0.001), indicating substantial interspecific morphological differentiation. Among the examined variables, ED/TL made the strongest contribution to species discrimination (Wilks’ lambda = 0.070, F = 251.346), whereas CPDL/TL showed the weakest discriminatory contribution (Wilks’ lambda = 0.667, F = 9.395). DFA revealed pronounced morphological structuring among species, with the first discriminant function accounting for 70.7% of the total discriminant variation (Wilks’ lambda = 0.001, canonical correlation = 0.975, P < 0.001). The first three functions collectively accounted for 91.8% of the discriminant variation. Classification accuracy was 97.0% for the original cases and remained high under leave-one-out cross-validation (92.0%), indicating strong discriminatory performance and limited morphological overlap among the examined species. Most misclassifications involved C. lastoviza, whereas the remaining species showed complete or near-complete discrimination. These findings demonstrate that morphometric ratios expressed relative to total length or head length can provide high discriminatory power for distinguishing closely related Mediterranean Triglidae species. The results support the use of standardized morphometric approaches as useful complementary tools for taxonomic discrimination and biodiversity assessment.