Comparative analysis of the hyomandibula during respiration in anabantoid teleost fishes:Macropodus opercularis in relation toCtenopoma acutirostre andAnabas testudineus

Abstract

The hyomandibula is an important element of the head and has been influenced in its structural features by different functions. It is roughly T-shaped with vertical and horizontal ridges. In fish, such asMacropodus opercularis, the deep curve at the antero-dorsal end of this ridge may be correlated with the concentrated force applied by the adductor mandibulae muscles. InMacropodus opercularis, the hyomandibula is shorter and broader than that ofAnabas testudineus andCtenopoma acutirostre. In the latter two genera, almost the entire anterior surface of the vertical ridge is uniformly curved, which may be explained by the distributive force applied by the adductor muscles perpendicularly. InMacropodus, the hyomandibulo-interhyal articulation is not straight along the axis of the interhyal as inCtenopoma, but the interhyal makes an angle of 45‡ to the hyomandibula. This difference might be functional as well as due to the oblique orientation of the hyomandibula. InCtenopoma, the articulating facet of the symplectic is located slightly below the interhyal articulating facet. This might be caused by the location of the hyomandibulo-interhyal articulation. The hyomandibulo-interhyal articulation also helps in the depression of the lower jaw when the latter is depressed by the hyoid bar. Thus, a structural analysis of the hyomandibula and its relationships with functions depict the interrelation between form and function.