Wainwright Dylan K, Ingersoll Sam, Lauder George V
Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts.
J Morphol. 2018 Jun;279(6):828-840. doi: 10.1002/jmor.20814. Epub 2018 Mar 14.
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.
金枪鱼属的金枪鱼具有许多形态和生理适应性，以适应其高效的海洋上层生态。尽管已经对金枪鱼的解剖结构进行了研究，但尚未对其鳞片结构进行定量研究。我们使用微计算机断层扫描（µCT）和组织学方法，对大眼金枪鱼（Thunnus obesus）身体十个部位的鳞片进行了研究，以定量和定性地比较不同部位鳞片的形态。我们发现大眼金枪鱼全身的鳞片大小和形状各不相同，对µCT数据导出变量的判别函数分析表明，全身鳞片在形状和大小上存在定量差异。我们还报告了在胸甲、尾部和脸颊区域发现的一种新型鳞片。这些经过改良的鳞片是由内部小梁支撑的骨化外壳，内部充满脂肪，并具有内部血液供应。组织学分析表明，这些增厚鳞片的外层薄片由细胞骨组成，这对于典型的骨通常为无细胞的鲈形目鱼类来说是出乎意料的。在前部身体的整流罩区域，这些充满脂肪的鳞片层层堆叠，深度可达五层，形成一个增厚的骨质外壳。脸颊鳞片也具有充满脂肪的内部小梁结构，而后部身体的大多数鳞片更像板状，类似于典型的硬骨鱼鳞片。虽然这些新型充满脂肪的鳞片的功能尚不清楚，但我们探讨了几种关于其功能的可能假设。
