Dermal Plates of the Armored Catfish - Pterygoplichthys Pardalis

The Pleco fish, also commonly called the suckermouth fish, was also called by another name which is the armored catfish. The term “armoured” was given primary because the Place fish has a rather tough skin surface at the top of the fish. Because of that, Ebenstein (2015) have carried out a research on the dermal plates of this so called armored catfish. In her research paper, Ebenstein analysed the dermal plates of the Amazonian fish Pterygoplichthys pardalis (Pleco fish) which then characterized it into the structural, chemical and nanomechanical properties. Among the analysis performed by Ebenstein, the most significant discovery was from the scanning electron microscope (SEM) that reviewed that the dermal plates have a sandwich-like structure, it is made up of an inner porous matrix surrounded two external dense layer (Ebenstein et al., 2015).

            For most fishes, their outer skin layer are covered by scales. These scales found on their body are much like the other college-based natural structure such as bones, teeth and mineralized materials (Torres et al., 2008). On the contrary, the armored catfish does not have scales compared to the majority of the fishes, but instead have a rather distinct type of dermal elements such as odontodes, teeth, dermal denticles (like sharkskin) or dermal plates as Ebenstein described it in her research paper. However, a little was known about the structural, chemical and mechanical properties of this dermal plate until Ebenstein’s research in 2015.

            Based on the results obtained in the research of Ebenstein, she discussed that the dermal plates from the Pterygoplichthys pardalis are not flat like those of elasmoid fish scales, but have a 3-dimentional “V” shape as shown in Figure 1. It was measured that the dermal plates are around 15 mm in length and 1.5 mm in thickness (Ebenstein et al., 2015). The internal surface of the plates that are not exposed to water is actually smooth, whereas the external surface has a rough surface due to the presence of tubercles (see Figure 1). The tubercles are referred to as dermal denticles that are tooth-like element. On the other hand, the sharkskin is also referred to as dermal denticles but microscopic observation showed that the structure is not the same as those of the armored catfish.

Figure 1. Dermal plate of armored catfish Pterygoplichthys pardalis 

It was also reported that the tubercles on the dermal plates provided the armored catfish against penetration resistance as well as hydrodynamics (Ebenstein et al., 2015). With that said, the penetrating tooth of the catfish’s predator such as aquatic snakes, freshwater turtles or other predatory fish would have to indent the tubercles first before penetrating the external layer of the dermal plate. When the predator tooth penetrate on its dermal plate, the outer dense layer act as a shield to resist penetration while the inner matrix will deform to absorb the shock from the forces of the predator teeth during the attack, thus this help to increase the toughness of the dermal plate to prevent the fracture and penetration of the soft inner tissue beneath the dermal plates (Ebenstein et al., 2015).

Apart from that, it was also analysed that the tubercles also modify the viscous drag forces of the flowing water, surface shear stress and skin friction of the Pterygoplichthys pardalis (Ebenstein et al., 2015). So even though the dermal denticles of the armored catfish is different from that of the sharkskin, it was debated that both their dermal denticle served the same purpose of reducing drag as they swim.

Apart from structural analysis using SEM, Ebenstein also studied on the chemical properties on the dermal plates of Pterygoplichthys pardalis using FTIR, DSC and XRD that reviewed on the composition of the dermal plates, these results can be referred in the research paper as they are not the main discussion of this literature topic.

Thus, to conclude this literature review, the Pterygoplichthys pardalis does not have scales but rather a dermal plates that has a 3-dimasional “V” shape structure. The main findings from Ebenstein reviews that the tubercles on the external surface of the dermal plate served to provide protection for the Pterygoplichthys pardalis against predator in its habitat and also reviewed that it also modify the water flow across the surface of the fish which provided hydrodynamics.

Be sure to CHECK OUT our NEXT POST where we share how the skin of the fish INSPIRED the development of a NEW TYPE of BODY ARMOUR!!!

Reference

1. Ebenstein, D., Calderon, C., Troncoso, O.P. and Torres, F.G., 2015. Characterization of dermal plates from armored catfish Pterygoplichthys pardalis reveals sandwich-like nanocomposite structure. Journal of the Mechanical Behavior of Biomedical Materials, 45(February), pp.175–182.
2. Torres, F.G. et al., 2008. Characterization of the nanocomposite laminate structure occurring in fish scales from Arapaima Gigas. Materials Science and Engineering C, 28(8), pp.1276–1283.