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Novel structure in sciaenid fish skulls indicates continuous production of the cephalic neuromast cupula

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ABSTRACT

The presence of a conspicuous and frequent but never-described structure in the skull cavities of sciaenid fish was noted during population studies in an urbanized bay. The ultrastructure closely resembles the cupula of neuromasts, an organ associated with the perception of the environment in teleost fish. The bodies were recorded detached in both preserved and freshly sampled individuals and without associated cilia. Prominent characteristics are acellularity, the elliptic-conic shape composed of stack-like protein lamellas, and a mesh-like appearance in cross section. These acellular lamellar cephalic bodies (ALCBs) were more abundant in larger individuals and showed temporal peaks of abundance independently of the fish size. The conic and lamellar features suggest that the deposition of protein layers follows fish growth, and the bimodality of the size of these structures in individuals indicates temporal peaks of production. These results indicate that these ALCBs are a consequence of the accretion of the cupula of neuromasts at a faster rate than they degrade. Given the novelty of this structure and the increasing records of diseases of marine organisms worldwide, an important question is whether these bodies occur subsequently to some environmental change and whether their accumulation in the skull cavities has consequences to fish health.

No MeSH data available.


Ultrastructure of upper and lower surfaces.Ultrastructure of upper and lower surfaces of the Acellular Lamellar Cephalic Bodies (scanning electron microscopy). Each row of figures represents a different structure. The upper rows show details of the upper surface of two different ALCBs (scales: (A) 500 μm; (B) 50 μm; (C) 200 μm; (D) 30 μm); lower rows (scales: (E) 500 μm; (F) 50 μm; (G) 200 μm; (H) 20 μm) show details of the lower surface of two different ALCBs.
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f4: Ultrastructure of upper and lower surfaces.Ultrastructure of upper and lower surfaces of the Acellular Lamellar Cephalic Bodies (scanning electron microscopy). Each row of figures represents a different structure. The upper rows show details of the upper surface of two different ALCBs (scales: (A) 500 μm; (B) 50 μm; (C) 200 μm; (D) 30 μm); lower rows (scales: (E) 500 μm; (F) 50 μm; (G) 200 μm; (H) 20 μm) show details of the lower surface of two different ALCBs.

Mentions: In the ultrastructure analysis, the SEM revealed that the upper surface of the structure was in an advanced process of decomposition, also denoted by the presence of abundant bacteria; while the lower view showed a flat, smooth surface (Fig. 4), which indicates that it is more recent. Considering that this undamaged surface is also always the larger, we suggest that the lower surface was most recently in contact with the fish body, i.e., a neuromast surface. The results presented so far suggest that the ALCB is a detached neuromast cupula, which was sequentially produced from the top (older surface) to the bottom (newer surface). If so, this may also explain an important feature, described for the cupula structure, that was not observed for the ALCB: the presence of spherical structures that correspond to associated cilia of the neuromasts. We suggest that the cilia would be associated only with a functional cupula, and the ALCB would represent a non-functional cupula derivative; as new layers are constructed to enclose the cilia, the previous base loses the association with it.


Novel structure in sciaenid fish skulls indicates continuous production of the cephalic neuromast cupula
Ultrastructure of upper and lower surfaces.Ultrastructure of upper and lower surfaces of the Acellular Lamellar Cephalic Bodies (scanning electron microscopy). Each row of figures represents a different structure. The upper rows show details of the upper surface of two different ALCBs (scales: (A) 500 μm; (B) 50 μm; (C) 200 μm; (D) 30 μm); lower rows (scales: (E) 500 μm; (F) 50 μm; (G) 200 μm; (H) 20 μm) show details of the lower surface of two different ALCBs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120346&req=5

f4: Ultrastructure of upper and lower surfaces.Ultrastructure of upper and lower surfaces of the Acellular Lamellar Cephalic Bodies (scanning electron microscopy). Each row of figures represents a different structure. The upper rows show details of the upper surface of two different ALCBs (scales: (A) 500 μm; (B) 50 μm; (C) 200 μm; (D) 30 μm); lower rows (scales: (E) 500 μm; (F) 50 μm; (G) 200 μm; (H) 20 μm) show details of the lower surface of two different ALCBs.
Mentions: In the ultrastructure analysis, the SEM revealed that the upper surface of the structure was in an advanced process of decomposition, also denoted by the presence of abundant bacteria; while the lower view showed a flat, smooth surface (Fig. 4), which indicates that it is more recent. Considering that this undamaged surface is also always the larger, we suggest that the lower surface was most recently in contact with the fish body, i.e., a neuromast surface. The results presented so far suggest that the ALCB is a detached neuromast cupula, which was sequentially produced from the top (older surface) to the bottom (newer surface). If so, this may also explain an important feature, described for the cupula structure, that was not observed for the ALCB: the presence of spherical structures that correspond to associated cilia of the neuromasts. We suggest that the cilia would be associated only with a functional cupula, and the ALCB would represent a non-functional cupula derivative; as new layers are constructed to enclose the cilia, the previous base loses the association with it.

View Article: PubMed Central - PubMed

ABSTRACT

The presence of a conspicuous and frequent but never-described structure in the skull cavities of sciaenid fish was noted during population studies in an urbanized bay. The ultrastructure closely resembles the cupula of neuromasts, an organ associated with the perception of the environment in teleost fish. The bodies were recorded detached in both preserved and freshly sampled individuals and without associated cilia. Prominent characteristics are acellularity, the elliptic-conic shape composed of stack-like protein lamellas, and a mesh-like appearance in cross section. These acellular lamellar cephalic bodies (ALCBs) were more abundant in larger individuals and showed temporal peaks of abundance independently of the fish size. The conic and lamellar features suggest that the deposition of protein layers follows fish growth, and the bimodality of the size of these structures in individuals indicates temporal peaks of production. These results indicate that these ALCBs are a consequence of the accretion of the cupula of neuromasts at a faster rate than they degrade. Given the novelty of this structure and the increasing records of diseases of marine organisms worldwide, an important question is whether these bodies occur subsequently to some environmental change and whether their accumulation in the skull cavities has consequences to fish health.

No MeSH data available.