Fish scale identification: From individual to species-specific shape variability

Abstract

Bräger Z., Staszny Á., Mertzen M., Moritz T., Horváth G. 2017. Fish scale identification: From individual to species-specific shape variability. Acta Ichthyol. Piscat. 47 (4): 331-338.Background. Species identification from recovered fish scales, e.g., from the sediment or stomach contents, has proven to be problematic for clupeid species. To ensure reliable species discrimination within Clupeidae, we attempted to reveal inter-and intra-specific, as well as, the intra-individual variability of scale shape in two sympatric clupeid species the European pilchard, Sardina pilchardus (Walbaum, 1792) and the round sardinella, Sardinella aurita Valenciennes, 1847. Our aim was to test, whether the landmark-based geometric morphometric method is reliable for species identification from mixed samples. Material and methods. The specimens of European pilchard and round sardinella were collected between May and October 2014 from the Gulf of Ambracia, Greece. The scale samples were taken from ten body areas (marked by letters A-J) of 487 specimens in total. A multiple-step analysis was conducted on randomly selected blind samples. The differences between body areas were assessed with canonical variate analysis (CVA) and discriminant function analysis (DFA) to compute generalized Mahalanobis distances (D) and discriminant functions (T 2 ), respectively. Results. The CVA based on the total scale samples showed that in sardinella, all body areas differed significantly from each other (D = 2.54 ± 0.79, P < 0.001) except for one (area I vs. J: D = 22.36, P = 0.085). In pilchard, two body area pairs represented non-significant group pairs (area D vs. G: D = 1.03, P = 0.12; and area F vs. G: D = 1.21, P = 0.06), whereas all other areas were significantly different (D = 2.43 ± 0.88, P = 0.003). At the last step of the blind sampling procedure, all scales were correctly classified by species with an average discrimination rate as high as 96.3%. Conclusion. In contrast to scale identification based merely on morphology, the geometric morphometric method is capable of detecting differences in scale shape from mixed samples that are unattainable with the former approach. Therefore, a more reliable and effective species identification can be accomplished from recovered scales, especially when discriminating species within the same family or genus.

Macro‐ and microscopic morphology of the flank scales of families Lutjanidae and Serranidae from the Persian Gulf Coral Reefs (Teleosts: Perciformes)

“…The findings of other authors such as Ibáñez and O’Higgins (2011) and Bräger et al. (2017) also underlined that scales of the mid‐section of fish are the most useful scale for fish species identification. Our results in the present study are also in agreement with previous studies.…”

“…The scales from the 3rd to 4th row below the dorsal fin above the lateral line are considered by previous studies as key scales (Esmaeili, 2001). The findings of other authors such as Ibáñez and O'Higgins (2011) and Bräger et al (2017) also underlined that scales of the mid-section of fish are the most useful scale for fish species identification. Our results in the present study are also in agreement with previous studies.…”

“…Moreover , Shackleton (1988) showed that scales from below the dorsal fin (i.e. "typical scales") were observed in high numbers in the sediments, as well as in samples collected during predatory behaviour of bottlenose dolphins (Bräger et al, 2017).…”

Scales surface topography: Comparative ultrastructural and decorative characteristics of a modern elasmoid fish scales in a cyprinid fish, Garra shamal (Teleostei: Cyprinidae) using digital optical light and scanning electron microscope imaging

“…The linear measurements used for the morphometric analyses and for the estimation of the focal index (Fi) as (a c/ a a 0 ) 100. "a c" is the distance from the outermost part of the anterior field to the focus, "a a 0 " is the distance from the outermost part of the anterior field to the outermost part of the posterior field, and "b b 0 " is dorsal-ventral height (Bräger et al, 2017;Echreshavi et al, 2021;Roberts & Aspy, 1993;Sabbah et al, 2020) T A B L E 1 The terminology of scale features and characters…”

“…Due to the fact that scale extraction does not kill fish, it is readily obtainable, its preservation is easy, and its preparation is easy for image processing, it has been used as essential hard structure applied as versatile research material in ichthyological studies for more than 200 years (Agassiz, 1833‐1843; Lagler, 1947; Roberts & Aspy, 1993; Viertler et al, 2021). The optical light microscopy (LM) and scanning electron microscopy (SEM) techniques, however, had particular contributions to our knowledge of fish scale morphology to be used sufficiently in fish and fisheries investigations to improve our knowledge to understand fish systematics and also to assess their phylogenetic relationships (e.g., Baudelot, 1873; Bräger et al, 2017; Chu, 1935; Cockerell, 1915; Lagler, 1947; Roberts & Aspy, 1993; Williamson, 1851). Therefore, since that time, fish scale morphology and their outer surface ornamentations and especially their surface microstructures have been widely studied in many fishes (Al Jufaili et al, 2021, 2022; Esmaeili et al, 2019; Esmaeili & Gholami, 2007; Ferrito et al, 2003; Jawad, 2005; Lanzing & Higginbotham, 1974; Purrafee Dizaj et al, 2020; Sadeghi et al, 2021; Seshappa, 1999).…”