134
D. J. RANDALL
available. There are, however, still some areas in which there is a marked
paucity of data; for example, very little is known about the heniodynamics of blood flow in arteries and veins in fish.
Recently, Robb (1965) has reviewed the anatomy of the cardiovascular system and Johansen and Martin (1965) have discussed some comparative aspects of cardiovascular function in vertebrates. Randall ( 1968)
and Johansen and Hanson ( 1968) have discussed the functional morphology of fish and dipnoan hearts, respectively. Hunn (1967) has compiled a bibliography on the blood chemistry of fishes.
Fishes, including the Agnatha and Dipnoi, as well as the Chondrichthyes, Osteichthyes, Choanichthyes, and teleosts, represent a diverse
group including over 20,000 species, extending in space over a wide
variety of environments, and in time over widely divergent evolutionary
pathways. The requirements of an aquatic environment enforces limitations on various systems and maintains morphological and physiological
similarities between the groups. These Similarities, however, may be
superficial, and there is a danger of assuming conformity in function
simply because of a general structural resemblance.
There is an apparent conformity of structure in the circulatory
systems of fishes, with the exception of cyclostomes and lungfishcs, blood
pumped by the heart passes through the gill and systemic circulation
before returning to the hcart. Variations in the general scheme arc, first,
the large blood volume, low blood pressure, and the development of accessory hearts in the hagfish, and, second, the presence of a pulmonary
circulation and a partial separation of oxygenated and deoxygenated
blood in the heart of lungfish, associated with the transition from an
aquatic to an aerial environment. A numbcr of air-breathing fish have a
well-developed circulation to respiratory surfaces other than the gills.
The blood supply to these accessory respiratory organs is in parallel with
the systemic circulation but in series with the gill circulation.
Of the small number of species of fish used in studies of the circulation, only a few have been investigated estensively. These include hagfish, dogfish, skate, ratfish, Port Jackson shark, trout, salmon, carp, tench,
cod, lingcod, eel, and lungfish. The data have been collectcd using a
variety of techniques under a variety of conditions. In some instances
the fish were not intact and were cBither out of water, rcstrained,
or anesthetized; in other experiments the recordings were obtained from
intact, unanesthetized, and relatively unrestrained fish. The circulatory
system is of necessity vcry responsive to changes in the environment and
often adjusts rapidly to an experimental situation. The use of telemetry
and other techniques has permitted experimentation on the cardiovascular system with relatively little interaction between the animal and the
D. J. RANDALL
available. There are, however, still some areas in which there is a marked
paucity of data; for example, very little is known about the heniodynamics of blood flow in arteries and veins in fish.
Recently, Robb (1965) has reviewed the anatomy of the cardiovascular system and Johansen and Martin (1965) have discussed some comparative aspects of cardiovascular function in vertebrates. Randall ( 1968)
and Johansen and Hanson ( 1968) have discussed the functional morphology of fish and dipnoan hearts, respectively. Hunn (1967) has compiled a bibliography on the blood chemistry of fishes.
Fishes, including the Agnatha and Dipnoi, as well as the Chondrichthyes, Osteichthyes, Choanichthyes, and teleosts, represent a diverse
group including over 20,000 species, extending in space over a wide
variety of environments, and in time over widely divergent evolutionary
pathways. The requirements of an aquatic environment enforces limitations on various systems and maintains morphological and physiological
similarities between the groups. These Similarities, however, may be
superficial, and there is a danger of assuming conformity in function
simply because of a general structural resemblance.
There is an apparent conformity of structure in the circulatory
systems of fishes, with the exception of cyclostomes and lungfishcs, blood
pumped by the heart passes through the gill and systemic circulation
before returning to the hcart. Variations in the general scheme arc, first,
the large blood volume, low blood pressure, and the development of accessory hearts in the hagfish, and, second, the presence of a pulmonary
circulation and a partial separation of oxygenated and deoxygenated
blood in the heart of lungfish, associated with the transition from an
aquatic to an aerial environment. A numbcr of air-breathing fish have a
well-developed circulation to respiratory surfaces other than the gills.
The blood supply to these accessory respiratory organs is in parallel with
the systemic circulation but in series with the gill circulation.
Of the small number of species of fish used in studies of the circulation, only a few have been investigated estensively. These include hagfish, dogfish, skate, ratfish, Port Jackson shark, trout, salmon, carp, tench,
cod, lingcod, eel, and lungfish. The data have been collectcd using a
variety of techniques under a variety of conditions. In some instances
the fish were not intact and were cBither out of water, rcstrained,
or anesthetized; in other experiments the recordings were obtained from
intact, unanesthetized, and relatively unrestrained fish. The circulatory
system is of necessity vcry responsive to changes in the environment and
often adjusts rapidly to an experimental situation. The use of telemetry
and other techniques has permitted experimentation on the cardiovascular system with relatively little interaction between the animal and the