454
MALCOLM S. GORDON
recent geological findings have led some workers to doubt this. They
suggest that the environment has undergone substantial changes within
geologically relatively recent times (Menzies et al., 1961).
111. EXPERIMENTAL STUDIES
A. General Remarks
The following survey of the experimental literature on pressure effects
on fishes emphasizes work done since the thorough review of Cattell
( 1936). Behavioral studies are de-emphasized, since they have recently
been summarized by Knight-Jones and Morgan ( 1966). Morita (1967)
provides a useful listing of various types of apparatus which have been
used in studies of biological effects of pressure.
B. Low Pressures
Studies of the effects of low pressures ( u p to 5 atm) on fishes
have been directed solely toward intact organisms, with most effort
expended on behavioral studies. A variety of freshwater and marine
species have been tested with respect to their ability to detect and
behaviorally respond to small changes in pressure. All species tested
respond, those having swim bladders showing lower response thresholds
than those lacking swim bladders. Fish with swim bladders generally
have thresholds in the range of 5-10 mbars, those without bladders at
about 25 mbars ( Knight-Jones and Morgan, 1966).
The tolerance of developing fish eggs, larvae, and various ages of
juvenile fishes for changes in pressure has been studied by several
workers. The majority of the eggs and larvae of several species of
shallow water, freshwater, and marine fishes, at their normal environmental temperatures, can tolerate both rapid and gradual changes in
pressure. Developing eggs of bream and pike perch showed no significant
effects of being maintained for 5 days at 1.5-2.0 atm pressure instead
of more normal pressures near 1 atm (Belyi, 1963). Larvae of these
two -species (1-6 days old) subjected to 3.5-5.0 atm pressure for 5-6
days also were unaffected as long as the release of pressure at the end
of the experiment was relatively slow (reduced over 65 min). More
rapid pressure release (25 min) raised mortality to three times control
levels. Larvae of both species developed normal gas-filled swim bladders
MALCOLM S. GORDON
recent geological findings have led some workers to doubt this. They
suggest that the environment has undergone substantial changes within
geologically relatively recent times (Menzies et al., 1961).
111. EXPERIMENTAL STUDIES
A. General Remarks
The following survey of the experimental literature on pressure effects
on fishes emphasizes work done since the thorough review of Cattell
( 1936). Behavioral studies are de-emphasized, since they have recently
been summarized by Knight-Jones and Morgan ( 1966). Morita (1967)
provides a useful listing of various types of apparatus which have been
used in studies of biological effects of pressure.
B. Low Pressures
Studies of the effects of low pressures ( u p to 5 atm) on fishes
have been directed solely toward intact organisms, with most effort
expended on behavioral studies. A variety of freshwater and marine
species have been tested with respect to their ability to detect and
behaviorally respond to small changes in pressure. All species tested
respond, those having swim bladders showing lower response thresholds
than those lacking swim bladders. Fish with swim bladders generally
have thresholds in the range of 5-10 mbars, those without bladders at
about 25 mbars ( Knight-Jones and Morgan, 1966).
The tolerance of developing fish eggs, larvae, and various ages of
juvenile fishes for changes in pressure has been studied by several
workers. The majority of the eggs and larvae of several species of
shallow water, freshwater, and marine fishes, at their normal environmental temperatures, can tolerate both rapid and gradual changes in
pressure. Developing eggs of bream and pike perch showed no significant
effects of being maintained for 5 days at 1.5-2.0 atm pressure instead
of more normal pressures near 1 atm (Belyi, 1963). Larvae of these
two -species (1-6 days old) subjected to 3.5-5.0 atm pressure for 5-6
days also were unaffected as long as the release of pressure at the end
of the experiment was relatively slow (reduced over 65 min). More
rapid pressure release (25 min) raised mortality to three times control
levels. Larvae of both species developed normal gas-filled swim bladders