Cohen Karly Elizabeth, Hernandez L Patricia
Department of Biological Sciences, The George Washington University, Science and Engineering Hall, Washington DC.
J Morphol. 2018 Nov;279(11):1615-1628. doi: 10.1002/jmor.20891. Epub 2018 Oct 22.
Hypophthalmichthys molitrix, silver carp, is an invasive Asian carp that has become increasingly widespread and ecologically destructive within the upper Mississippi River Basin. Its complex trophic anatomy may help explain the apparent efficiency with which they consume phytoplankton, outcompeting native filter feeders. This cypriniform species is characterized by trophic synapomorphies that include a palatal organ, loss of upper pharyngeal jaws, and a hypertrophied lower pharyngeal jaw. However, in silver carp these structures have become greatly modified and diverge from the more basal condition that characterizes species such as goldfish. The trophic apparatus of silver carp is composed of discrete structures that are functionally coupled: filtering plates, paired epibranchial organs (EBO), a modified palatal organ composed of large muscular folds that interdigitate with the filtering plates, and hypertrophied lower pharyngeal jaws and teeth. The filtering plates fill a significant portion of the buccal cavity, especially since the distal parts of these filtering plates make up a key component of the EBOs. EBOs, food aggregating structures found in many teleosts, are thought to have independently evolved at least six times. Ranging in complexity from small slits on the dorsal wall of the pharyngeal cavity to exceedingly intricate spiraling structures, EBOs are morphologically diverse among filter-feeding fishes. Despite this morphological diversity and broad taxonomic distribution, little is known regarding the functional anatomy of the EBO. Moreover, the EBO in silver carp is distinct from the organs previously described in other species, being created by four independent pharyngeal involutions (instead of the more typical one or two) that form spiral-shaped pharyngeal tubes surrounded by circumferential muscle. On each side of the head greatly hypertrophied hyomandibulae and opercles are connected to the anterior cartilaginous caps of the bilateral EBOs via enlarged muscles. Given that these fish are pump filter feeders we hypothesize that the opercula may compress and expand the EBOs during pumping causing food to be moved posteriorly toward the pharyngeal jaws.
鳙鱼，即鲢鱼，是一种入侵性亚洲鲤鱼，在密西西比河上游流域日益广泛分布且具有生态破坏性。其复杂的营养解剖结构或许有助于解释它们消耗浮游植物的显著效率，从而胜过本地滤食性动物。这种鲤形目物种具有一些营养共源性状，包括腭器官、上咽颌的缺失以及肥大的下咽颌。然而，在鲢鱼中，这些结构已发生了极大改变，与金鱼等物种所具有的更为原始的状态有所不同。鲢鱼的营养器官由功能耦合的离散结构组成：滤板、成对的鳃上器官（EBO）、由与滤板相互交错的大型肌肉褶皱构成的改良腭器官，以及肥大的下咽颌和牙齿。滤板占据了口腔的很大一部分，特别是因为这些滤板的远端部分构成了EBO的关键组成部分。EBO是许多硬骨鱼中发现的食物聚集结构，据认为至少独立进化了六次。从咽腔后壁上的小裂缝到极其复杂的螺旋结构，EBO在滤食性鱼类中形态多样。尽管存在这种形态多样性和广泛的分类分布，但关于EBO的功能解剖学却知之甚少。此外，鲢鱼的EBO与其他物种中先前描述的器官不同，它由四个独立的咽内陷（而非更典型的一两个）形成，这些咽内陷形成了由环形肌肉包围的螺旋形咽管。在头部两侧，极大肥大的舌颌骨和鳃盖通过增大的肌肉与双侧EBO的前软骨帽相连。鉴于这些鱼是泵吸式滤食者，我们推测鳃盖在泵吸过程中可能会压缩和扩张EBO，从而使食物向后朝着咽颌移动。
