9. AIR BREATHING IN FISHES
371
Members of the Anabantidae ( Anubas, Macropodus, Trichogaster, and
others) typically show the air labyrinths starting as outgrowths from
the epibranchial section of the first branchial arch. Laminated projections
contribute to the surface expansion inside the chambers. The detailed
structure of the labyrinthine organ is extremely complicated (Munshi,
1968). The diffusion distance from air to blood in Trichogaster has been
measured as the smallest of all recorded in respiratory organs, showing
a minimal value of 600 A, a medium range of 1300-1700 A, and a maximum value of 1.2 p (Schulz, 1960). Based on electron microscopy,
Schulz reported that capillaries of some areas of the labyrinthine organ
lack both basal membrane and endothelium, thus leaving only a thin
epithelium intervening between blood and air.
In CZurias the two remarkable vascular rosettelike trees which fill the
air chambers on each side receive structural support from gill arches 2
and 4 and their vascular supply from the first and fourth afferent
branchial arteries ( Moussa, 1956). Figure 2 shows the gross appearance
of the labyrinth in CZurias Zuzeru.
B. Structural Adaptations of the Gastrointestinal
Tract for Air Breathing
In some fishes portions of the gastrointestinal tract, notably the
stomach or part of the small intestine, have been modified to serve in
gas exchange between the blood and rhythmically swallowed air. The
used air is voided at the anus or the mouth. Members of the families
Loricaridae, e.g., Pkcostomus pkcostornus ( Carter, 1935), and Callichthyidae, e.g., Callichthys and Hoplosternum (Carter and Beadle, 1931b)
offer typical examples of gastrointestinal air breathers. Most fishes employing the gastrointestinal tract for gas exchange use it as an accessory
breathing organ when aquatic conditions become severely oxygen deficient. Others depend on it during short migrations over land (Plecostomus), and a few are obligate air breathers that need to supplement
the aquatic gas exchange with air breathing at all times.
C. The Air Bladder as a Respiratory Organ
It is now generally conceded that the air bladder in fishes originally
functioned as an accessory respiratory organ. In most extant actinopterygian fishes the air or swim bladder serves primarily in buoyancy
control or sound production or sound detection. In dipnoan fishes the air
bladder has retained and further evolved the respiratory function it
allegedly possessed in the crossopterygian fishes that also gave rise to
amphibians and land vertebrates. Members of the primitive orders
371
Members of the Anabantidae ( Anubas, Macropodus, Trichogaster, and
others) typically show the air labyrinths starting as outgrowths from
the epibranchial section of the first branchial arch. Laminated projections
contribute to the surface expansion inside the chambers. The detailed
structure of the labyrinthine organ is extremely complicated (Munshi,
1968). The diffusion distance from air to blood in Trichogaster has been
measured as the smallest of all recorded in respiratory organs, showing
a minimal value of 600 A, a medium range of 1300-1700 A, and a maximum value of 1.2 p (Schulz, 1960). Based on electron microscopy,
Schulz reported that capillaries of some areas of the labyrinthine organ
lack both basal membrane and endothelium, thus leaving only a thin
epithelium intervening between blood and air.
In CZurias the two remarkable vascular rosettelike trees which fill the
air chambers on each side receive structural support from gill arches 2
and 4 and their vascular supply from the first and fourth afferent
branchial arteries ( Moussa, 1956). Figure 2 shows the gross appearance
of the labyrinth in CZurias Zuzeru.
B. Structural Adaptations of the Gastrointestinal
Tract for Air Breathing
In some fishes portions of the gastrointestinal tract, notably the
stomach or part of the small intestine, have been modified to serve in
gas exchange between the blood and rhythmically swallowed air. The
used air is voided at the anus or the mouth. Members of the families
Loricaridae, e.g., Pkcostomus pkcostornus ( Carter, 1935), and Callichthyidae, e.g., Callichthys and Hoplosternum (Carter and Beadle, 1931b)
offer typical examples of gastrointestinal air breathers. Most fishes employing the gastrointestinal tract for gas exchange use it as an accessory
breathing organ when aquatic conditions become severely oxygen deficient. Others depend on it during short migrations over land (Plecostomus), and a few are obligate air breathers that need to supplement
the aquatic gas exchange with air breathing at all times.
C. The Air Bladder as a Respiratory Organ
It is now generally conceded that the air bladder in fishes originally
functioned as an accessory respiratory organ. In most extant actinopterygian fishes the air or swim bladder serves primarily in buoyancy
control or sound production or sound detection. In dipnoan fishes the air
bladder has retained and further evolved the respiratory function it
allegedly possessed in the crossopterygian fishes that also gave rise to
amphibians and land vertebrates. Members of the primitive orders