452
MALCOLM S. GORDON
including representatives or, in many cases, all known species of over 60
families of teleost fishes (Greenwood et al., 1966). There are also several
families of chondrichthyan fishes represented ( Bigelow and Schroeder,
1948, 1953).
Most types of deep-sea fishes are small. The most abundant species
are usually less than 5 cm in length. However, species reaching 20 cm
or longer are not rare, and some forms regularly attain lengths of many
meters.
The deep-sea fishes most often seen in pictures or described in the
popular literature are members of the abundant mesopelagic, diurnally
vertically migratory, deep scattering layer communities ( Taylor, 1968).
These fishes are typically black and silver in color, have luminescent
photophores of various types, and often have large mouths with long,
sharp teeth. About 50% of the species have gas-filIed swim bladders
(Marshall, 1960). Their vertical migrations take them toward the
surface at night, back into the depths during the day. Some species
appear to migrate more than 1000 meters vertically in each direction.
Different species have different ranges for migration. Some occur at the
surface at night, while others approach no nearer the surface than 100200 meters in depth. Daytime depths also vary between species. Scattering layer communities occur in all the oceans,, most often between
latitudes 40"N and 40"s.
The scattering layer fishes are not only the shallowest of the true deepsea fishes, but also are the deep-sea groups encountering the greatest
environmental variability. In all areas their migrations take them twice
daily between pressures of 50-100 atm and pressures of only one or a few
atmospheres. In thermally stratified regions, like most of the tropics, they
undergo twice daily changes in temperature, which often are in the
range of 10"-15"C. In substantial regions (e.g., much of the eastern
North Pacific) their migrations also either take them through, or their
daytime depths lie within, well-developed oxygen minimum layers. Dissolved oxygen concentrations in these layers are often well below 0.5
ml/liter ( 5 1 0 % saturation; Childress, 1968; Lavenberg and Ebeling,
1967; Longhurst, 1967). Vertical stratification of salinity is usually small,
variations generally being less than 0.59&,.
Vertical migrations also appear to occur among truly bathypelagic
fishes, but the frequency and extent of these migrations are very poorly
known. The environmental changes encountered in a move between,
say, 4000 and 3000 meters are, in any case, much smaller than the
changes just described for mesopelagic species. In this really deep-sea
situation, pressure would change by only about 25%, temperature by
no more than a fraction of 1"C, oxygen probably by less than 0.1 ml/
liter, and salinity probably not at all ( Menzies, 1965).
MALCOLM S. GORDON
including representatives or, in many cases, all known species of over 60
families of teleost fishes (Greenwood et al., 1966). There are also several
families of chondrichthyan fishes represented ( Bigelow and Schroeder,
1948, 1953).
Most types of deep-sea fishes are small. The most abundant species
are usually less than 5 cm in length. However, species reaching 20 cm
or longer are not rare, and some forms regularly attain lengths of many
meters.
The deep-sea fishes most often seen in pictures or described in the
popular literature are members of the abundant mesopelagic, diurnally
vertically migratory, deep scattering layer communities ( Taylor, 1968).
These fishes are typically black and silver in color, have luminescent
photophores of various types, and often have large mouths with long,
sharp teeth. About 50% of the species have gas-filIed swim bladders
(Marshall, 1960). Their vertical migrations take them toward the
surface at night, back into the depths during the day. Some species
appear to migrate more than 1000 meters vertically in each direction.
Different species have different ranges for migration. Some occur at the
surface at night, while others approach no nearer the surface than 100200 meters in depth. Daytime depths also vary between species. Scattering layer communities occur in all the oceans,, most often between
latitudes 40"N and 40"s.
The scattering layer fishes are not only the shallowest of the true deepsea fishes, but also are the deep-sea groups encountering the greatest
environmental variability. In all areas their migrations take them twice
daily between pressures of 50-100 atm and pressures of only one or a few
atmospheres. In thermally stratified regions, like most of the tropics, they
undergo twice daily changes in temperature, which often are in the
range of 10"-15"C. In substantial regions (e.g., much of the eastern
North Pacific) their migrations also either take them through, or their
daytime depths lie within, well-developed oxygen minimum layers. Dissolved oxygen concentrations in these layers are often well below 0.5
ml/liter ( 5 1 0 % saturation; Childress, 1968; Lavenberg and Ebeling,
1967; Longhurst, 1967). Vertical stratification of salinity is usually small,
variations generally being less than 0.59&,.
Vertical migrations also appear to occur among truly bathypelagic
fishes, but the frequency and extent of these migrations are very poorly
known. The environmental changes encountered in a move between,
say, 4000 and 3000 meters are, in any case, much smaller than the
changes just described for mesopelagic species. In this really deep-sea
situation, pressure would change by only about 25%, temperature by
no more than a fraction of 1"C, oxygen probably by less than 0.1 ml/
liter, and salinity probably not at all ( Menzies, 1965).