Comparative morphology of the scales of roundscale spearfish Tetrapturus georgii and white marlin Kajikia albida

Abstract

The comparative morphology of the scales of roundscale spearfish Tetrapturus georgii and white marlin Kajikia albida was investigated. In addition, variation in scale morphology across different body regions within each species was analysed. Although considerable morphological variation was observed among scales from different body regions in both species, scales of K. albida generally have pointed anterior ends, fewer posterior points and are more heavily imbricated than those of T. georgii, which are frequently rounded anteriorly, often have many posterior points and are separated farther within the skin. In all sampled body regions and individuals, scales of T. georgii are significantly broader and have a lower length-to-width aspect ratio than those of K. albida. Superficial to the scales are denticular plates, which are ossified formations occurring on the surface layer of the epidermis; these were observed and described for T. georgii, K. albida and blue marlin Makaira nigricans. Detailed scale descriptions allow for a more accurate characterization of the variation within and differences between these two species and could potentially be a valuable tool for investigating istiophorid systematics.

High-resolution measurements of swordfish skin surface roughness

“…The results, of course, are not without limitation, and future work in this area should seek to address the lack of samples that are currently available. Targeted sampling strategies, in the spirit of Loose et al (2017), are preferred to properly identify intra-specific variations across the body of the fish as well as ontogenetic variations for fish of varying ages. Regardless, the information provided here should be sufficient in the first instance for developing representative synthetic surfaces which share the same statistical characteristics as the swordfish skin.…”