Scale diversity in bigeye tuna (Thunnus obesus): Fat‐filled trabecular scales made of cellular bone. (14th March 2018)

• Record Type: Journal Article
• Authors: Wainwright, Dylan K.; Ingersoll, Sam; Lauder, George V.
• Is Part Of: Journal of morphology. Volume 279:Number 6(2018)
• Page Start: 828
• Page End: 840
• Publication Date: 2018-03-14
• Subjects: bone -- fish -- lipid -- locomotion -- skin; Morphology -- Periodicals; Physiology -- Periodicals; Anatomy -- Periodicals; 571.3
• DOI: 10.1002/jmor.20814
• Languages: English
• ISSNs: 0362-2525

Abstract

Abstract: Tunas of the genus Thunnus possess many morphological and physiological adaptations for their high‐performance epipelagic ecology. Although Thunnus anatomy has been studied, there are no quantitative studies on the structure of their scales. We investigated the scales of bigeye tuna ( Thunnus obesus ) from ten regions of the body using micro computed tomography (µCT)‐scanning and histology to quantitatively and qualitatively compare regional scale morphology. We found a diversity of scale sizes and shapes across the body of bigeye tuna and discriminant function analysis on variables derived from µCT‐data showed that scales across the body differ quantitatively in shape and size. We also report the discovery of a novel scale type in corselet, tail, and cheek regions. These modified scales are ossified shells supported by internal trabeculae, filled with fat, and possessing an internal blood supply. Histological analysis showed that the outer lamellar layers of these thickened scales are composed of cellular bone, unexpected for a perciform fish in which bone is typically acellular. In the fairing region of the anterior body, these fat‐filled scales are stacked in layers up to five scales deep, forming a thickened bony casing. Cheek scales also possess a fat‐filled internal trabecular structure, while most posterior body scales are more plate‐like and similar to typical teleost scales. While the function of these novel fat‐filled scales is unknown, we explore several possible hypotheses for their function. Abstract : Scales of bigeye tuna ( Thunnus obesus ) are modified on certain parts of the body. Here on the fairing near the pectoral fin, scales are thickened with a three‐dimensional bony shell supported by internal trabeculae‐like struts. The space inside these thickened scales is filled with fat (adipocytes) and includes arterioles and venules.