Microstructural architecture of the bony scutes, spine, and rays of the bony fins in the common pleco (Hypostomus plecostomus)

Abstract

Studying scute and fin morphology are advantageous approaches for phylogenetic identification and provide information on biological linkages and evolutionary history that are essential for deciphering the fossil record. Despite this, no prior research has precisely characterized the histological structures of scutes in the common pleco. Therefore, this research investigated the microstructure and organization of bone tissue within the dermal skeleton, including the scutes and fins, in the common pleco, using light microscopy, stereomicroscopy, and scanning electron microscopy. The dermal scutes were organized in a pentagonal shape with denticular coverage and were obliquely aligned with the caudal portion pointing dorsally. The dermal scutes consisted of three distinct portions: the central, preterminal, and terminal portions. Each portion comprised three layers: a superficial bony plate, a basal bony plate, and a mid-plate. Both the superficial and basal bony plates were composed of lamellar bone and lamellar zonal bone, whilst the mid-plate consisted of secondary osteons and woven bone. In the terminal portion, the superficial and basal bony plates became thinner. The pectoral fin consists of spines and rays composed of lepidotrichium (two symmetrical hemi-rays). The spine contained centrifugal and centripetal lamellar and trabecular bones. A centripetal fibrous bone was implanted between the lamellar bones. Besides being oriented in a V shape, the hemi-rays were also composed of thin centrifugal and centripetal lamellar bones and trabecular bones. A fibrous bone was identified between the centrifugal and centripetal bones. The trabecular bone and lamellar bone were made up of bone spicules.

Keywords: Hypostomus plecostomus; bony fins; bony scutes; light microscope; scanning electron microscope; stereoscope.

Figure 1.

Demonstration of the structurally investigated fields of common pleco fish with general view of scutes covering the body.

Figure 2.

The histological structure of the central portion of the dermal scute on the dorsal side of the common pleco head. Semi-thin sections stained with toluidine blue.

Figure 3.

The histological structure of the preterminal portion of the dermal scute on the dorsal side of common pleco head stained with toluidine blue.

Figure 4.

The histological structure of the terminal portion of the dermal scute on the dorsal side of the common pleco head.

Figure 5.

Connections between the dermal denticles and the bony scutes on the lateral side of common pleco head.

Figure 6.

The histological structure of the spine in the dorsal fin of common pleco, semithin sections stained with toluidine blue.

Figure 7.

The histological structure of the rays of the dorsal fin of common pleco – semithin sections stained with toluidine blue.

Figure 8.

The histological structure of the dermal scute on the dorsal side of the common pleco head.

Figure 9.

The histological structure of the spine of the common pleco dorsal fin.

Figure 10.

The histological structure of the rays of the dorsal fin in common pleco.

Figure 11.

The histological structure of the common pleco scute using safranin O-fast green on the lateral side of the fish dorsal fin.

Figure 12.

The histological structure of the spine of the common pleco dorsal fin using safranin O fast green.

Figure 13.

The histological structure of the longitudinal view of the hemisegment in the dorsal fin ray of common pleco using safranin O-fast green.

Figure 14.

The histological structures of the fin spine and scute of common pleco fish using PAS.

Figure 15.

Histological structure of the scute on the lateral side of the common pleco head using the Mallory’s triple stain.

Figure 16.

The histological structure of the spine of the pectoral fin of common pleco fish demonstrated with Crossman’s trichrome.

Figure 17.

Histological structure of the spine of the dorsal fin in common pleco fish – silver stain.

Figure 18.

Identification of the surface features of the bony scutes in common pleco fish.

Figure 19.

Identification of fibrillary organization of the lamellar, lamellar zonal bone, and osteonal lamellae of the scute using SEM on the lateral side of the common pleco fish.

Figure 20.

Scanning electron microscopy identification of vascular channels and fibrous bone in the common pleco scute.

Figure 21.

Stereoscope structure features of the pectoral fin rays in the common pleco.

Figure 22.

Scanning electron microscopy structure of pectoral fin rays in the common pleco fish.