Morfometria anchoa

JOURNAL OF MORPHOLOGY 267:750 –757 (2006)

Is Geometric Morphometrics Efficient for Comparing Otolith Shape of Different Fish Species?
Dominique Ponton*
IRD, BPA5, 98848 Noumea, New Caledonia ´ ABSTRACT The 2D shape of sagittae of Encrasicholina devisi, E. heteroloba, E. cf. punctifer, and Stolephorus indicus, four tropical Engraulididae of New Caledonia, was studied with 1) dimensionlessshape descriptors (form factor, roundness, and aspect ratio); 2) elliptic Fourier analysis (EFA) and Fast Fourier Transform (FFT) of 2D outline; and 3) geometric morphometrics (GM) based on four standard landmarks and nine semi-landmarks. The largest sagittae of E. cf. punctifer were lacier, i.e., had a smaller form factor, than the sagittae of the other species. The sagittae of E. devisi and S.indicus were more roundish, and presented a lower aspect ratio, than those of E. heteroloba and E. cf. punctifer. Between-class correspondence analysis (COA) indicated that between-species inertia was the lowest when based on the 96 Fourier coefficients originating from EFA, and the highest when based on the 22 partial warps originating from GM. As otoliths of different sizes from different speciespresented similar shapes, relative between-species inertia increased markedly when length, width, perimeter, and area were added to the set of variables originating from EFA, FFT, or GM. Despite otoliths having only a few, sparsely located, homologous landmarks, GM appeared slightly more efficient in distinguishing the sagittae of the four species and allowed visualization of the modification of otolithshape as they grow. J. Morphol. 267:750 –757, 2006.
© 2006 Wiley-Liss, Inc.

KEY WORDS: Engraulididae; sagittae; size; form factors; Fourier analysis; thin-plate spline

The labyrinth system of the inner ear of teleost fishes is a complicated structure of canals, sacs, and ducts filled with endolymph: semicircular canals detect accelerations when sensory tissue in otic sacs detects both linearaccelerations and sounds (Wright et al., 2002). In both ears, each of the three otic sacs contains an otolith, a calcareous structure acting as a mechanoreceptor stimulating the kinocilia of the sensory tissue (Popper et al., 2000). These three otoliths differ in size and shape, the sagitta being the larger in non-ostariophysean fishes (Secor et al., 1992). Otolith shape has been widely used foridentifying past (Nolf, 1995) and present fish species (L’AbeeLund and Jensen, 1993; Tuset et al., 2003a) as well as populations or stocks (Castonguay et al., 1991; Campana and Casselman, 1993; Begg and Brown, 2000; DeVries et al., 2002; Watkinson and Gillis, 2003; Stransky, 2004). Compared to the traditional
© 2006 WILEY-LISS, INC.

approaches based on morphometric and meristic characters of thefish body, measurements made on otoliths have the advantage of being unaffected by short-term changes in fish condition or by preservation, as long as acidic preservatives are avoided (Campana and Casselman, 1993). Otolith shape has also been widely used as an aid in identification of fish species consumed by birds (Bugoni and Vooren, 2004) or mammals (Tollit et al., 2004a; Zeppelin et al., 2004),although digestion can be an issue (Jobling and Beriby, 1986; Tollit et al., 2004b). Sagittae are generally laterally compressed, left– right symmetrical, elliptical on their sagittal plane, compressed on their internal– external axis, and present a main axis of growth oriented in the anterior–posterior direction (Wright et al., 2002). Most morphometric studies of otoliths have thus concentrated onsize-dependent measurements made on their sagittal plane and on sizeindependent shape analyses of contour. Morphometric measurements of the depression in the internal face where the sensory tissue connects, the sulcus acusticus, have also been used (Torres et al., 2000) as well as measurements of internal structures (Begg et al., 2000). The size-dependent variables most often recorded from an...