Otoliths of Pterophyllum scalare

By Juan Fco. Fernández Roca
(Atreyu on The Angelfish Society Forum)

Publications:
FinTAStic Issue-29
http://www.theangelfishsociety.org/newsletters/2013_June_LowRes_2.1.pdf (Baja resolución)
http://www.theangelfishsociety.org/newsletters/2013_June_HighRes_v2.1.pdf (Alta resolución)
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Summary: We present otolith morphometric characteristics of the  species  Pterophyllum scalare , making a tour of the otoliths, “Lapillus” “Asteriscus” and “Sagitta”. This presentation will help us understand and publicize the importance of these elements of our Angelfish bone.

 

Introduction: When looking for previously published material on  the otoliths of our Angelfish, I must admit that I only found one publication. “New contributions to the knowledge of the current fish” by Juan Bauza and Manuel Compte, pages 79, 80 and 92. So our work is to develop and expand specific information on Angel - fish Otoliths.

 

The Otoliths

 

For those who are new to this world inside our fish, several questions will arise, but perhaps the most immediate, “What are they and what are they for?”.


Figure 1
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The otoliths are one of the most important parts of the inner ear of fish, particularly bony fish (teleosts) are calcareous forms constituted largely by deposition of aragonite (calcium carbonate CaCO3) and protein conchiolin.

These are found within a few bags located in an area near the braincase and are known as “Otic Capsules.” To be precise, there are three pairs of members (six in total), known as Lapillus (2), Asteriscus (2), and Sagitta (2), one set of each of the pieceslocated in each sachet and on both sides of the fish.

Otoliths keep a similar characteristic shape in each species, taking into account that each however allow for identification and therefore categorization due to their main forms.

The Lapillus Otolith

Its size is very small and is the tiniest otolith, in some cases barely the size of a pinhead. These otoliths “Lapillus” P. scalare correspond to a standard size 5cm. Its shape resembles that of a kidney. These Otolith are included in a camera called “Utricle” and the same as the rest of the otic capsule it is submerged in a liquid that is the endolymph. The primary function of these otoliths is to act as informing level of position.


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The Asteriscus Otolith

Another otolith is the “Asteriscus,” in most cases it is some what larger in size than the “Lapillus,” the otoliths correspond to specimen about 5cm standard length. The “Asteriscus” are located in a chamber called “Lagena.” These, together with the last otolith called “Sagitta,” are actually responsible for the heaving, being this otolith “Asteriscus,” who communicates the vibrations to the brain organs.


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The Sagitta Otolith

The otolith “Sagitta” is the most interesting and under research, yielding valuable information on P. scalare growth and the stages through which it has passed through its life. Nowadays it is known that the endolymph liquid keeps on depositing these calcareous layers in a concentric way that creates some rings which corresponds to the different growth serials, so that observing the number of rings, we can guess the age of the fish.

Perhaps a common mistake is to think that the size will always correspond with the age of P. scalare, however it has been found that the size and deposit of these calcareous layers are influenced by the environment in which they develop. If this is more or less favorable, there will be more space between the rings. If the fish has gone through stages in which the habitat has not been favorable (including food of course), the rings will be closer together than in times of splendor.

The “Sagitta” is located in the camera called “Saccule” and it is the otolith that first receives the vibrations, therefore it will be the one that transmits the vibrations to the otolith “Asteriscus”.

The following sagittas belong to species whose standard length 5cm round.


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At this point, we will look into more details related to otolith “Sagitta” and its morphology. The otoliths “Sagitta” are described morphologically in some publications, their names are applicable to all species and in this case it will apply to Pterophyllum scalare.


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The contour of the otolith from an external point of view allow us to establish comparisons, studies, etc. On the left we can identify the first element, “Face” and “Antirostrum,” between which a hollow is created called “Escotadura.” These prominences and depressions vary from ones to other otoliths, but we have observed that these patterns are always the same.

The top following with the “Antirostrum” is called “Dorsal Edge” and the bottom below the “Face” is “Edge Belly.” In the previous photos of otoliths “Sagitta” we can see the “Face” and “Antirostrum” keep some parallelisms, in the case of the regions “Edge Dorsal” and “Ventral edge” rather significant differences can appear. The differences highlight the presence in many of these otoliths, of a shape in the area called “Edge Belly”.


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The next element we see in these otoliths is a depression in the limestone formation, running it from the “cutout” until almost the opposite region of the otolith. This depression is known as “Groove” (Sulcus Acusticus), is in contact with the “Mácula,” constituted by nerve endings, connected to the auditory nerve.


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In the groove we can also identify some parts, starting from the area “Rostrum” and “Excisura major” we find the region called “Ostium.” In our Pterophyllum it is wide, narrowing as it starts the channel calling this area “Collum” , moving the channel it forms the area known as “Peaks,” where small salient are formed. The “Sulcus” will end up in an area called “Cauda.” This area increases significantly in size, presenting a depression over the face of the otolith and acquiring an oval shape.


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Discussion

Otolith “Sagitta” has a moderate thickness, oblong and shaped with not deep Sulcus. It presents perfectly differentiated the Cauda concavity (being oval), shows the edges in most analyzed sagittas in a rounded shape.

Conclusions

The otoliths “Sagitta” both left and right, have little difference, keeping symmetry in their formation.

References Graphics

Fig.1 – Otoliths Pterophyllum scalare
Fig.2 – Otolith Lapillus, exemplary measures 04e.
Fig.3 - Otolith Lapillus, exemplary measures 04f.
Fig.4 - Otolith Lapillus, exemplary measures 01e.
Fig.5 - Otolith Lapillus, exemplary measures 01f.
Fig.6 – Otolith Asteriscus, exemplary measures 03c.
Fig.7 – Otolith Asteriscus, exemplary measures 03d.
Fig.8 – Otolith Asteriscus, exemplary measures 04c.
Fig.9 – Otolith Asteriscus, exemplary measures 04d.
Fig.10 – Otolith Asteriscus, exemplary measures 02c.
Fig.11 – Otolith Asteriscus, exemplary measures 02d.
Fig.12 – Otolith Asteriscus, exemplary measures 01c.
Fig.13 – Otolith Asteriscus, exemplary measures 01d.
Fig.14 – Otolith Sagitta, exemplary measures 01b.
Fig.15 – Otolith Sagitta, exemplary measures 01a.
Fig.16 – Otolith Sagitta, exemplary measures 02a.
Fig.17 – Otolith Sagitta, exemplary measures 02b.
Fig.18 – Otolith Sagitta, exemplary measures 03a.
Fig.19 – Otolith Sagitta, exemplary measures 03b.
Fig.20 – Otolith Sagitta, exemplary measures 04a.
Fig.21 – Otolith Sagitta, exemplary measures 04b.
Fig.22 – Otolith Sagitta, exemplary measures 05a.
Fig.23 – Otolith Sagitta, exemplary measures 05b.
Fig.24 – Otolith Sagitta, measures.
Fig.25 – Otolith Sagitta, morphology_1.
Fig.26 – Otolith Sagitta, morphology_2.
Fig.27 – Otolith Sagitta, morphology_3.

Acknowledgments

I would like to thank the Newsletter Committee for the great efforts in adaptations and translations from texts trying to bridge differences between English and Spanish and the deference shown.

References

Gallardo Cabello, M. 2012. Study of the otoliths of Stripped Mullet Mugil cephalus Linnaeus, 1758 in Mexican Central Pacific. Journal of Fisheries and Aquatic Science 7 (6). pp: 346-363. ISSN: 1816-4927

Nelly Aloisi, Patricia. 1990. Características morfológicas y morfométricas de los otolitos de tres especies de Pejerrey de la Costa Marplatense. Universidad Nacional De Mar Del Plata. Facultad de Ciencias Exactas y Naturales. págs: 25.

Romero, Aldemaro. El lenguaje de los peces. Museo de zoología de Barcelona. Departamento de Hidrozoología. pp: 439-442 págs.

Simmons John E. 2005. Cuidado manejo y conservación de las colecciones biológicas. Universidad Nacional de Colombia. Págs: 146. ISBN: 938-39-6969-1.

Tuset Andújar, Víctor Manuel. Morfología del otolito sagitta y determinación del crecimiento en especies del género serranus (osteichthyes, serranidae). Universidad de la Laguna. Departamento de Biología animal. págs: 234.

Tuset, Victor M. 2008. Otolith atlas for the western Mediterranean, north and central eastern Atlantic. Scientia Marina 72S1.
Barcelona. págs: 192. ISSN: 0214-8358

Viera, Martina. 2011. Características ecomorfométricas de los otolitos Sagitta de Genypterus blacodes y Genypterus brasiliensis provenientes de la zona común de pesca Argentino-Uruguaya. Universidad de la República Uruguay. Facultad de ciencias. Págs: 36