三种不同游泳习性鱼类骨骼肌的快、慢肌纤维组织学特性

Histological characteristics of fast and slow muscle fibers in skeletal muscle of fishes with three different swimming habits

关键词:  骨骼肌  快、慢肌纤维  组织学特征  游泳习性

Key words:  Skeletal muscle  Fast and slow muscle fibers  Histological features  Swimming habits

摘要:

硬骨鱼类的骨骼肌可为其游泳运动提供动力。为认识不同游泳习性鱼类的骨骼肌肌纤维组织学特征，本研究选取3种具有不同游泳习性的鱼类：鲐(Scomber japonicus)、大黄鱼(Larimichthys crocea)和褐牙鲆(Paralichthys olivaceus)，采用石蜡切片苏木精–伊红染色法和形态计量法，以形状、直径和密度作为评价指标，对其骨骼肌的快、慢肌纤维组织学特性进行表征，比较3种不同游泳习性鱼类的快、慢肌纤维组织学特征差异。组织学观察发现，3种类型鱼类的骨骼肌快、慢肌纤维横切面均呈不规则形状。营持续式游泳的鲐的快肌纤维呈多角状，慢肌纤维呈多边柱形；营延长式游泳的大黄鱼的快、慢肌纤维呈长椭圆形；营爆发式游泳的褐牙鲆的快、慢肌纤维呈扁椭圆形。形态计量结果显示，3种鱼类的快肌纤维直径均极显著大于其慢肌纤维(P<0.01)。大黄鱼的慢肌纤维直径在3种鱼类中最大，约为鲐的1.34倍、褐牙鲆的1.14倍；鲐的快肌纤维直径在3种鱼类中最大，约为大黄鱼的1.41倍、褐牙鲆的1.35倍。3种鱼类的快肌纤维密度均极显著小于其慢肌纤维(P< 0.01)，其中，快肌纤维密度大小排序为褐牙鲆[(274.60±9.07)根/mm2]>大黄鱼[(205.43±12.63)根/mm2]>鲐[(118.92±10.74)根/mm2]，慢肌纤维密度大小排序为鲐[(1 442.33±28.25)根/mm2]>褐牙鲆[(1 073.92±39.40)根/mm2]>大黄鱼[(945.74±19.53)根/mm2]。进一步分析发现，鱼类的肌纤维形状、直径和密度与鱼类的游泳习性密切相关。上述对不同游泳习性硬骨鱼类骨骼肌的肌纤维形状、直径和密度等组织学特征的描述与差异分析结果，可为进一步开展硬骨鱼骨骼肌的适应性进化和运动生理学研究提供基础性资料。

Abstract:

Swimming is of great significance for the survival of fish and directly affects their ability to avoid predators and enemies, hunt and capture prey, carry out mating and reproduction, and migrate. The skeletal muscles of bony fish, which provide power for swimming and account for approximately 40%–60% of the body mass, can be divided into red and white muscle fibers. Red muscle fibers have a slow contraction, strong endurance, high mitochondria content, glycogen, and myoglobin; mainly employ aerobic metabolism; and effectively use oxygen to produce ATP. They are also known as slow-twitch muscle fibers, whose main function in fish is to provide stable and continuous power for the swimming process. White muscle fibers contract quickly but also tire rapidly and mainly use glycolic metabolism. They are also known as fast-twitch muscle fibers and, in fish, provide power for fast swimming behaviors (such as predation and escape). Many studies have indicated a strong correlation between fish swimming habits and the composition of slow and fast-twitch muscles. Most of these studies focused on the correlation between swimming motion and muscle fiber types, but differences in the histological characteristics of fast- and slow-twitch muscle fibers of fish with different swimming habits have rarely been reported. The histological characteristics of muscle fibers include shape, diameter, and density, which are important indicators describing the histological structure of the skeletal muscle in fishes. In this study, we selected three species (Scomber japonicus, Larimichthys crocea, and Paralichthys olivaceus) representing different swimming styles, to clarify the histological characteristics of fast- and slow-twitch muscle fibers, and compared them using hematoxylin-eosin staining of paraffin sections and morphometric methods. The staining showed that the transverse sections of the fast- and slow-twitch skeletal muscle fibers were irregular and the diameter of the fast-twitch muscle fibers was larger than that of the slow-twitch muscle fibers. In S. japonicus, a species engaged in sustained swimming, the fast-twitch muscles were multi-angular, whereas the slow-twitch muscle fibers were multi-columnar. In L. crocea, a species swimming in an extended style, the muscle fibers were long, oval, and had cells with round edges. In P. olivaceus, a species engaged in prolonged swimming, the fast-twitch muscle fibers were oblate and had more connective tissues than the slow-twitch fibers. The slow-twitch muscle fibers of S. japonicus and the fast-twitch muscle fibers of P. olivaceus were finer than the slow-twitch and fast-twitch muscle fibers of these two species, respectively. The longitudinal section of the muscle fibers in the three species were distributed in strips alternating with connective tissue. In addition, the muscle fibers in S. japonicus occupied a larger space and were more loosely arranged than those in the other two species. However, the muscular space between fibers of both types was smaller in P. olivaceus and the muscle cells were more closely arranged. Morphometric results showed that the diameters of fast-twitch muscle fibers were significantly larger than those of slow-twitch muscle fibers (P<0.01). The fast-twitch muscle fibers in S. japonicus were 4.84 times the diameter of slow-twitch muscle fibers, while that ratio was approximately 2.57 in L. crocea and 3.07 in P. olivaceus. The diameter of slow-twitch muscle fibers in L. crocea was the largest among the three species, approximately 1.34 and 1.14 times that of S. japonicus and P. olivaceus, respectively. In contrast, S. japonicus had the largest fast-twitch muscle fiber diameter, approximately 1.41 and 1.35 times that of L. crocea and P. olivaceus, respectively. The slow-twitch muscle fiber density in all three species was significantly greater than that of fast-twitch muscle fibers (P<0.01). The density of slow-twitch muscle fibers was 12.13, 4.60, and 3.91 times than that of fast-twitch fibers, in S. japonicus, L. crocea, and P. olivaceus, respectively. The order of the fast-twitch muscle fiber density was P. olivaceus [(274.60±9.07) unit/mm2] > L. crocea [(205.43±12.63) unit/mm2] > S. japonicus [(118.92±10.74) unit/mm2]. The density of the fast-twitch muscle fiber of P. olivaceus was 2.31 and 1.34 times that of S. japonicus and L. crocea, respectively. The order of slow-twitch muscle fiber density was S. japonicus [(1 442.33±28.25) unit/mm2] > P. olivaceus [(1 073.92±39.40) unit/mm2] > L. crocea [(945.74±19.53) unit/mm2]. Furthermore, the slow-twitch muscle fiber density of S. japonicus was 1.53 and 1.34 times that of L. crocea and P. olivaceus, respectively. The above-described methodology and analysis of differences in the shape, diameter, and density in the skeletal muscle fibers of teleost fish with different swimming habits will provide basic data for further studies on the adaptive evolution and movement physiology of this taxonomic group.