Ontogeny of Squamation in Swordfish, Xiphias gladius

Spinoid scales appear early in the development of Swordfish, Xiphias gladius, and are first discernable in the larval stage. Scales vary in form between two principal types: small single and multispined scales and large multispined scales. Unlike the typical teleostean condition, Xiphias scales are attached along their base, not at their proximal end within scale pockets. Scales persist in juveniles and adults, that is, scales are not shed or resorbed. Scales become more deeply embedded within the dermis as the dermis thickens in ontogeny; consequently only the tips of spines protrude through the dermis of adults. A network of mucous canals with regularly spaced pores to the exterior develop in the dermis of adults, and the mucus produced further insulates scales from the surface of the integument. The ontogeny of the squamation of Xiphias differs from that of the related Istiophoridae.

Fig. 1.

Photomicrographs of the integument and scales of Xiphias gladius. (A) The integument with scale (S), epidermis (Ed), and dermis with stratum spongiosum (SSp), stratum compactum (SCm) of a 22.2 mm SL larvae (scale bar = 63 μm). (B) The integument of a ∼330 cm SL adult (scale bar = 45 μm)

Fig. 2.

Gross morphology of the scales of Xiphias gladius. (A) Photograph of the ventral aspect of a preserved larvae 114 mm SL (scale bar = 1.5 mm). (B) Photograph of a cleared and stained biopsy of the lateral flank of a ∼150 mm SL larvae (scale bar = 0.3 mm). (C) Photograph of a cleared and stained biopsy of the lateral flank of a ∼102 cm SL juvenile (scale bar = 0.6 mm)

Fig. 3.

Photomicrograph of a scale of a ∼330 cm SL adult Xiphias gladius with growth increments (arrows) (scale bar = 27 μm)

Contributor Notes

(JJG, MAW) Center for Coastal Fisheries and Habitat Research, National Oceanic and Atmospheric Administration, 101 Pivers Island Road, Beaufort, North Carolina 28516–9722; (DZ) 15/5 Metudella Street, Jerusalem, Israel; (AZZ) Brain Science Program, Interdisciplinary Unit, Bar Ilan University, Israel; (PRB) aquatic Animal Health Program, Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853–6401; and (BBC) National Marine Fisheries Service Systematics Laboratory, Smithsonian Institution, P.O. Box 37012, NMNH Room WC-57, MRC 0153, Washington, DC 20013–7012. (JJG) jeff.govoni@noaa.gov

Accepted: 16 Jan 2004