414
JOHAN B. STEEN
I. INTRODUCTION
The swim bladder acts as a hydrostatic organ by replacing part of
the fish body, which is heavier than water, with gas. The specific weight
of the fish as a whole is thereby brought toward that of the ambient
water, and the fish becomes neutrally buoyant.
The function of the swim bladder rests on its ability to maintain a
gas space inside a fish and to vary this amount of gas according to
changing hydrostatic demands. The problems connected with this function are amplified by the fact that while most natural waters, and consequently the arterial blood of fishes, have a Po, and Px2 of about 0.2
and 0.8 atm, respectively, the partial pressure of 0, and N2 in the swim
bladder may be 100 and 20 atm, respectively. This ability of the bladder
to concentrate O? and N, some 500 and 30 times, respectively, is the
unique property of the organ. This aspect will therefore be the focus
of our interest throughout this chapter. In addition we shall discuss the
problems of hormonal and nervous regulation of its activities, as well as
the ?biological importance” of the organ.
In the swim bladder an intimate relationship between anatomy and
function is unusually evident. This holds true for the microstructures
but is particularly well displayed in the macroanatomy or, more properly,
the architecture of the organ. Since so much of the swim bladder
problem hinges on the anatomy, we shall describe this aspect in some
detail.
Various aspects of the swim bladder problem have been reviewed
at intervals. The articles by Fange (1953, 1966), Denton (1961), Marshall (1962), Kuhn et al. (1963), Steen (1963a,b,c), and Alexander
(1966) are of particular interest.
11. THE BIOLOGICAL SIGNIFICANCE
OF THE SWIM BLADDER
Marshall (1962) gives an excellent account of the distribution of
those marine fishes that have a swim bladder. The bladder is found most
frequently among fishes in the upper 200 meters and is less frequently
encountered down to lo00 meters. The organ is not found in fishes living
in free water below this depth, but it is found regularly in those living
near the bottom down to 2000 meters. The report by Nielsen and Munk
JOHAN B. STEEN
I. INTRODUCTION
The swim bladder acts as a hydrostatic organ by replacing part of
the fish body, which is heavier than water, with gas. The specific weight
of the fish as a whole is thereby brought toward that of the ambient
water, and the fish becomes neutrally buoyant.
The function of the swim bladder rests on its ability to maintain a
gas space inside a fish and to vary this amount of gas according to
changing hydrostatic demands. The problems connected with this function are amplified by the fact that while most natural waters, and consequently the arterial blood of fishes, have a Po, and Px2 of about 0.2
and 0.8 atm, respectively, the partial pressure of 0, and N2 in the swim
bladder may be 100 and 20 atm, respectively. This ability of the bladder
to concentrate O? and N, some 500 and 30 times, respectively, is the
unique property of the organ. This aspect will therefore be the focus
of our interest throughout this chapter. In addition we shall discuss the
problems of hormonal and nervous regulation of its activities, as well as
the ?biological importance” of the organ.
In the swim bladder an intimate relationship between anatomy and
function is unusually evident. This holds true for the microstructures
but is particularly well displayed in the macroanatomy or, more properly,
the architecture of the organ. Since so much of the swim bladder
problem hinges on the anatomy, we shall describe this aspect in some
detail.
Various aspects of the swim bladder problem have been reviewed
at intervals. The articles by Fange (1953, 1966), Denton (1961), Marshall (1962), Kuhn et al. (1963), Steen (1963a,b,c), and Alexander
(1966) are of particular interest.
11. THE BIOLOGICAL SIGNIFICANCE
OF THE SWIM BLADDER
Marshall (1962) gives an excellent account of the distribution of
those marine fishes that have a swim bladder. The bladder is found most
frequently among fishes in the upper 200 meters and is less frequently
encountered down to lo00 meters. The organ is not found in fishes living
in free water below this depth, but it is found regularly in those living
near the bottom down to 2000 meters. The report by Nielsen and Munk