Adriaens D, Aerts P, Verraes W
Ghent University, Vertebrate Morphology, Ghent, Belgium.
J Morphol. 2001 Mar;247(3):197-216. doi: 10.1002/1097-4687(200103)247:3<197::AID-JMOR1012>3.0.CO;2-S.
During ontogeny, larval fish have to deal with increasing nutritional and respiratory demands as they grow. As early ontogeny is characterized by an increasing complexity of moving structural elements composing a fish skull, some constraints will have to be met when developing mechanisms, which enable feeding and respiration, arise at a certain developmental stage. This article focuses on the presence/absence of a possible functional response in mouth opening during ontogeny in Clarias gariepinus. Some reflections are given, based on morphological data, as well as related function-analysis data from the literature. Starting shortly after hatching, a total of up to five different mouth opening mechanisms may become functional. Of these, three may remain functional in the adult. As could be expected, the apparatuses that enable these mechanisms show an increase in complexity, as well as a putative improvement in mouth opening capacity. Initially, two consecutive mechanisms may allow a restricted depression of the lower jaw (both passively and actively). Synchronously, two more mechanisms may arise, which involve the coupling of the hyoid depression to the mouth opening. At about 11 mm SL a fifth mechanism becomes established, better known as the opercular mouth opening mechanism. An overlapping chronology of functionality of the different mechanisms, as well as differences in efficiencies, could be an indication of the absence of a true critical period in C. gariepinus (at least in relation to mouth opening), as well as the possible presence of a shift in feeding type. Finally, the coupling of the chronology of the shift in mouth opening mechanisms and several morphological, behavioral, and physiological changes during ontogeny, related to feeding and respiration, make it possible to distinguish five important phases in the early life history of C. gariepinus.
在个体发育过程中，幼鱼随着生长需要应对不断增加的营养和呼吸需求。由于早期个体发育的特点是构成鱼头骨的运动结构元素日益复杂，在发育出能够实现摄食和呼吸的机制时，在某个发育阶段必须满足一些限制条件。本文重点研究了非洲鲶鱼个体发育过程中张口是否存在可能的功能反应。基于形态学数据以及文献中的相关功能分析数据进行了一些思考。孵化后不久，总共多达五种不同的张口机制可能开始发挥作用。其中，三种机制在成年后可能仍起作用。正如预期的那样，实现这些机制的结构显示出复杂性增加，以及张口能力可能有所提高。最初，两种连续的机制可能允许下颌有限地下降（被动和主动）。同时，另外两种机制可能出现，这涉及到舌骨下降与张口的耦合。在体长约11毫米时，第五种机制确立，即鳃盖张口机制。不同机制功能的重叠时间顺序以及效率差异，可能表明非洲鲶鱼不存在真正的关键期（至少与张口有关），以及摄食类型可能发生转变。最后，张口机制转变的时间顺序与个体发育过程中与摄食和呼吸相关的一些形态、行为和生理变化的耦合，使得区分非洲鲶鱼早期生活史中的五个重要阶段成为可能。
