Meeting Abstract
Tunas have an area of enlarged scales behind the gill opening called the corselet. We find that these scales are not only larger in length and height, but also in thickness compared to scales more posterior on the body. Fish scales are normally a single ossified plate, but tuna corselet scales appear as hollow scales, with ossification on the top and bottom as well as ossified struts in the middle. This bizarre morphology looks similar to trabeculcated bone, and has not been previously described in the literature. In this study we examine tuna scales using µCT scans of scale patches from different areas on the bigeye tuna (Thunnus obesus). The thickened scales occur mostly on the anterior part of the body, on corselet and cheek areas, and small but thickened scales also occur on the tail. These thickened tail scales may be for helping to shape and stiffen the keels on the tail of tuna. Scales elsewhere on the body do not show the thickened morphology. Cheek and tail scales are modified into elongate, spindle-like shapes, although cheek scales are an order or magnitude larger than cheek scales. Scales are embedded under epidermis over the corselet and perhaps the entire body, allowing the surface of the tuna to be smooth despite the large scales. We hypothesize that the function of these corselet scales may have to do with heat conservation.
