Operculum characteristics, functions, anatomy, examples

The operculums of fish are bones that have the main mission of protecting the gill structures or gills. They are also responsible for ensuring the circulation of water through the gills in a single direction, in order to comply with the respiratory process of the body..

The operculum in many species of fish is the broadest bone lamina of the skeleton, for this reason it is frequently used by scientists in biological research as a measurement parameter for estimating the age of the individual..

Cranial skeletal malformations, specifically those suffered in the glands, have been reported mainly in captive-bred fish, occurring in the first stages of growth and attributed to unfavorable conditions of the environment in which they are found..

Fighting fish Betta splendens, Originally from the Asian continent, they have been widely studied due to the common aggressive reaction that male individuals develop towards other males, showing striking aptitudes such as the extension of the fins and the particular opening of the gills, where the gills even protrude.

Article index

• 1 General characteristics
• 2 Functions
• 3 Anatomy
• 4 Malformations
• 5 Examples in different species
• 6 References

General characteristics

The gills, being soft structures in constant contact with water and the environment, need to be protected by the gills that are formed by a calcareous composition. Bony fish have four pairs of gills, each supported by a gill arch.

The process of respiration or gas exchange between oxygen O_two and carbon dioxide CO_two of blood in fish begins with the opening of the mouth, allowing water to enter the body.

Subsequently, they close it, conducting the water towards the gills for its filtration and extraction of oxygen, and finally it is expelled without it being able to return through the gills..

The circulation of the blood is against the current of the water, thus achieving that the exchange of gases is approximately 80%, otherwise it would only be 50%, fulfilling the capture of oxygen and the elimination of carbon dioxide.

Compared with air-breathing organisms, energy expenditure is very high, especially when oxygen concentrations in the water are low, for this reason the respiratory system must be highly efficient..

The determination of the age of the fish is generally more exact in the operculum than in the scales, with the exception of older specimens. Growth rings can be clearly seen on its surface.

Operculums are unique to bony fish, so cartilaginous fish such as sharks and rays lack these.

Features

Operculums serve two primary functions in bony fish:

1. Protect the gills, which are very sensitive organs and prone to physical damage or diseases caused by bacteria, parasites and fungi.
2. Actively contribute to the respiratory process, where they function as pumps and gates that regulate the exit of water from the body, prevent its entry and establish a single flow direction.

Anatomy

The covers are located in the anterior part of the fish, establishing the limit of the head. They are mostly trapezoidal or rectangular in shape, having a slightly concave inner face.

They are divided into four margins: the anterior or preopercular, the superior, the posterior and the inferior or subopercular.

To achieve its constant movement, the operculum has three powerful muscles inserted on its surface dorsally.

Malformations

Skeletal malformations that have occurred in caps have been identified mainly in cultivation practices and are not common in natural populations..

Therefore, they are associated with unfavorable circumstances of captivity such as the physical-chemical conditions of the water, nutritional imbalances, diseases and genetic factors..

These malformations are observed at different stages of larval development, but the earlier they appear, the greater the degree of severity..

Among the negative effects that fish suffer with these alterations in the size and shape of the operculum are: the decrease in pumping of water, directly affecting respiration; and the exposure of the gills to the external environment, having as a consequence that they are more susceptible to being injured and to infections caused by parasites, bacteria and fungi.

Larval survival is also adversely affected by reduced growth and possible cannibalism of larger individuals..

These malformations of the operculum in some cases, despite their severity, it is possible that they will be recovered, provided that the deficient conditions are adapted and the correct treatment is applied..

Examples in different species

Below you can see some examples of the shape and size of the caps present in different species of marine and freshwater bony fish:

Snake fish, Channa striata

Sun fish So great

Angiliform fish, family Muraenidae

Seahorse Hippocampus sp.

Salmon Psalm sp.

Betta fish Betta splendens

Gold carp fish Carassius auratus

Shaker Electrophorus electricus

Piranha Pygocentrus sp.

References

1. rguello, W., M. Bohórquez and A. Silva. (2014). Cranial malformations in larvae and juveniles of cultured fish. The t. Am. J. Aquat. Res. Vol. 42 (5): 950-962.
2. Bioinnova. Gaseous exchange in fish. Innovation group on teaching in biological diversity. Recovered from: https://www.innovabiologia.com/
3. Mancini, M. (2002). Introduction to the biology of fish. Introductory courses on animal production and animal production I, FAV UNRC. 19 pp.
4. Martínez, I. (2008). Aggressive behavior in Siamese fighting fish (Betta splender). University Annals of Ethology. Vol. 2: 98-105.
5. Miranda, R. and M. Escala. (2002). Identification guide for cyprinid bone remains. Publ. Biol. Univ. Navarra, Ser. Zool. Vol. 28: 98-114.
6. Werlinger, C. (2005). Marine biology and oceanography: concepts and processes. Volume I. 253-285 pp.