364
KJELL JOHANSEN
parts involved with purely aquatic breathing have become reduced or
modified for the new purpose of breathing air.
Table I lists representative species of air-breathing fishes arranged
according to the type of their structural adaptation. The list is not exhaustive, and the interested reader is referred to more specialized morphological texts (Rauther, 1910; Carter and Beadle, 1931b; Das, 1940;
Saxena, 1963).
A. Structural Derivatives of the Mouth and
Pharynx as Air-Breathing Organs
By far the most common and yet the most diversified structural adjustments for air breathing are those associated with the branchial,
opercular, and pharyngeal cavities.
Piscine gills are designed to function in water where lack of net
gravitational forces prevents collapse of the fine filaments and lamellae.
However, the collapse of these in air makes the gills of most fishes useless
as organs of aerial gas exchange. A very few fishes, such as Symbranchus
and Hypopomus, are able to use their gills for air breathing. They fill the
buccal cavity with air regularly at the surface, and the used air is voided
from the mouth or the opercular openings (Taylor, 1913; Carter and
Beadle, 1931b; Johansen, 1966). The gills of these fishes are structurally
modified to prevent their collapse in air. Most notably they show a high
ratio between the breadth and height of the secondary lamellae. The
ratio is more than twice that in purely aquatic fishes or fishes possessing
other types of structural adaptations for air breathing (Carter and
Beadle, 1931b ) . The epithelium of the buccal and pharyngeal cavities
of these two fishes is richly vascularized and plays a supporting role
in aerial gas exchange.
The common eel, Anguilla anguilla (Berg and Steen, 1965), and
species of Periopthalmus (Schottle, 1931) also employ gill breathing successfully during air exposure.
A further development of aerial mouth breathing is seen in fishes
with foldings and papillations of the buccal epithelia projecting into the
buccal cavity and forming extensive vascular surfaces for aerial gas exchange. The electric eel, Electrophorus electricus, offers a striking example (Evans, 1929; Boker, 1933; Richter, 1935; Carter, 1935; Johansen
et al., 1968). In this fish the papillated projections are distributed over
both the floor and the roof of the mouth, while smaller prominences are
present on the branchial arches and the lateral branchial walls. The
system of papillae forms a labyrinth of air passages. Studies on formalin-
KJELL JOHANSEN
parts involved with purely aquatic breathing have become reduced or
modified for the new purpose of breathing air.
Table I lists representative species of air-breathing fishes arranged
according to the type of their structural adaptation. The list is not exhaustive, and the interested reader is referred to more specialized morphological texts (Rauther, 1910; Carter and Beadle, 1931b; Das, 1940;
Saxena, 1963).
A. Structural Derivatives of the Mouth and
Pharynx as Air-Breathing Organs
By far the most common and yet the most diversified structural adjustments for air breathing are those associated with the branchial,
opercular, and pharyngeal cavities.
Piscine gills are designed to function in water where lack of net
gravitational forces prevents collapse of the fine filaments and lamellae.
However, the collapse of these in air makes the gills of most fishes useless
as organs of aerial gas exchange. A very few fishes, such as Symbranchus
and Hypopomus, are able to use their gills for air breathing. They fill the
buccal cavity with air regularly at the surface, and the used air is voided
from the mouth or the opercular openings (Taylor, 1913; Carter and
Beadle, 1931b; Johansen, 1966). The gills of these fishes are structurally
modified to prevent their collapse in air. Most notably they show a high
ratio between the breadth and height of the secondary lamellae. The
ratio is more than twice that in purely aquatic fishes or fishes possessing
other types of structural adaptations for air breathing (Carter and
Beadle, 1931b ) . The epithelium of the buccal and pharyngeal cavities
of these two fishes is richly vascularized and plays a supporting role
in aerial gas exchange.
The common eel, Anguilla anguilla (Berg and Steen, 1965), and
species of Periopthalmus (Schottle, 1931) also employ gill breathing successfully during air exposure.
A further development of aerial mouth breathing is seen in fishes
with foldings and papillations of the buccal epithelia projecting into the
buccal cavity and forming extensive vascular surfaces for aerial gas exchange. The electric eel, Electrophorus electricus, offers a striking example (Evans, 1929; Boker, 1933; Richter, 1935; Carter, 1935; Johansen
et al., 1968). In this fish the papillated projections are distributed over
both the floor and the roof of the mouth, while smaller prominences are
present on the branchial arches and the lateral branchial walls. The
system of papillae forms a labyrinth of air passages. Studies on formalin-