Description of the dermal armor plates of Pterygoplichthys pardalis

[bekateen]

Ebenstein, D., Calderon, C., Troncoso, O. P., & 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, 175–182. http://dx.doi.org/10.1016/j.jmbbm.2015.02.002

ABSTRACT

Dermal plates from armored catfish are bony structures that cover their body. In this paper we characterized structural, chemical, and nanomechanical properties of the dermal plates from the Amazonian fish

Pterygoplichthys pardalis

. Analysis of the morphology of the plates using scanning electron microscopy (SEM) revealed that the dermal plates have a sandwich-like structure composed of an inner porous matrix surrounded by two external dense layers. This is different from the plywood-like laminated structure of elasmoid fish scales but similar to the structure of osteoderms found in the dermal armour of some reptiles and mammals. Chemical analysis performed using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) results revealed similarities between the composition of P. pardalis plates and the elasmoid fish scales of

Arapaima gigas

. Reduced moduli of P. pardalis plates measured using nanoindentation were also consistent with reported values for A. gigas scales, but further revealed that the dermal plate is an anisotropic and heterogeneous material, similar to many other fish scales and osteoderms. It is postulated that the sandwich-like structure of the dermal plates provides a lightweight and tough protective layer.

[bekateen]

After reading the paper, I found no mention of where the fish came from or how they were ID'd; the materials and methods are silent in this regard. The paper includes two images of what the authors call

Pterygoplichthys pardalis

, although it is not clear to me that the photo of a live fish is actually of a fish used in the study, and the preserved fish shown is basically just dark colored. Do these photos look like they are of pardalis? The fin coloration just doesn't look right to me, but to be fair, I am not well experienced with these fish at mature sizes.

[Bas Pels]

The fish in fig 1 does not resemble P pardalis to me. It looks much more like the flow-loving L number, L095 if I remember the number right

[bekateen]

That was exactly my thought, although I couldn't remember which species or L number looked like that. Unfortunately, it is not clear from the paper that the fish in Figure 1 was actually used in the study, versus the authors simply using this photo as a "representative" photo of pardalis (which as you also suggest it is not). Alas, the preserved specimen, which I presume WAS actually used in the study, is so darkened by preservation that I can't tell if it is pardalis, L095, or something entirely different. To be honest, based upon the size and number of armor plates shown in the preserved photo, I suspect the preserved specimen is also L095 (or something like it) rather than pardalis. I would expect that for the length of body shown, there should be more rows of narrower plates on pardalis than are evident in the photo.

[matthewfaulkner]

I agree with you both that the 'Fig 1' picture is definitely not

Pterygoplichthys pardalis

, and is actually from the 1999 redescription of

Pseudorinelepis genibarbis

by Armbruster and Hardman. Maybe someone got Pterygoplichthys and Pseudorinelepis confused?

Although, I do think that the dead/preserved fish in 'Fig 2', on a generic level, is a Pterygoplichthys. To me, the general body shape conforms to what I'd expect.

[bekateen]

Why, Matthew, you are spot on with regard to figure 1: http://www.auburn.edu/academic/science_ ... elepis.pdf

And the paper doesn't even cite the Armbruster & Hardman publication. Yikes.

Regards, Eric