Fishes || Accessory respiratory organ

An accessory Respiratory Organ in Fishes

        A system of air chambers, formed by outgrowth from the mouth or gill region those fish that occasionally leave the water. The swim-bladder also may serve as accessory respiratory organ.

Type of Accessory Respiratory Organs

    Suprabrachial organ (Clarias batrachus), Branchial outgrowths (Anabas testudineus), pharyngeal Diverticula (Labeo rohita), etc.

Function of accessory Respiratory Organs

        The accessory respiratory organ contain a very high % of oxygen. Fish with such respiratory organs are able to live in water where oxygen levels are very low. Under this condition these fishes come to the surface of water to gulp in air far transmission to the accessory respiratory organs.

     1] Suprabrachial Organ :[e.g. Clarias batrachus]

        The morphology of the gas exchange organs of the African air-breathing Catfish (Clarias mossambicus)(peters) have been examined grossly, & by light, electron & scanning microscopes. The respiratory organs in Clarias consist of a gill system and accessory organs including a labyrinth organ and a suprabranchial chamber membrane. The similarity in the morphology of the marginal vessels and transverse capillaries (terminal respiratory elements) in the three respiratory organs suggests a strong developmental relationship between the gills and the accessory respiratory organs.

Fig. Suprabrachial organ in Clarias

    2] Branchial Outgrowth :[e.g. Anabas testudineus]

        The climbing perch [Anabas testudinus] has two large pouch-like outgrowths from the dorsal side of the branchial chambers. The epithelium lining these outgrowths is highly vascular & becomes folded to increase the respiratory area. Each chamber contains a characteristic rosette-like labyrinthine organ. Thus the organ develops from the first epibranchial bone and consists of several shells like concentric plates. The margins of the plates are wavy & the plates are covered with vascular gill-like epithelium.Each branchial outgrowth freely communicates not only with the opercular cavity but also with the buccopharyngeal cavity. Air enters the growth through the buccopharyngeal opening and exits through the valve.

    3]Pharyngeal Diverticula :[e.g. Labeo rohita]

        In the labio, the branch chamber covered with the operculum contains four pairs of gills. Each gill consists of a double row of gillnets or gillnets supported by a gill arch. Each gill filament bears numerous minute transverse lamellae covered with this epithelium. These lamellae contain capillaries of afferent and efferent nerve branches. A pair of four gills are carried over the openings of the first four branches. In Labeo and other teleosts, gill filaments are attached to very few interbranchial septa. Therefore, this type of gill is called pectinate or filamentous. The fifth gill arch bears no gill-filaments.