VII. DESERT FISHES
467
(1970) found some algae eaten by sheepshead pupfish showed cytoplasmic
streaming and were viable when removed from the hindgut. We have recovered living algae from the hindgut of threadfin shad and mosquitofish,
as have Velasquez (1939), Kutkuhn (1958), and Fish (1951) from various other species. In C. n. nevadensis at least, relatively heavy use of indigestible algae in summer, when the population is most dense, may indicate
a scarcity of other foods, or other interactions, that place the fish under
nutritional stress. Apparent starvation of some individuals in summer, but
not at other times, suggests that some population limitations may be
imposed.
Many pupfishes appear to feed almost exclusively on bottom sediments,
at least at certain sizes and at certain times of year. Some sediments of
springs are copropelic and may be quite high in various organic nutrients.
In Cuatro Ciénegas, copropel and included organisms in springs and
other habitats appear to be a major food material for pupfishes (Minckley
and Itzkowitz, 1967; Arnold, 1970) and for some cichlids. In Lake
Victoria, Africa, some bottom sediments are so high in organic materials
that they are used as food for domestic cattle and fowl (Hickling, 1961).
One of the most extreme, and unusual, feeding habits of a desert fish involves an endemic catfish, Clarias cavernicola, which lives in a deep, pitlike
spring in the Kalahari Desert and appears to subsist mostly on the excrement of a local colony of baboons (Jubb, in Cole, 1968).
Food eaten by a fish depends largely upon its abundance or availability
at the time of feeding and on the vulnerability of the prey species. The
loach minnow in Aravaipa Creek feeds exclusively on blackfly larvae
(Simuliidae) when they are abundant, but it rapidly shifts to mayfly nymphs
after blackfly emergences. Food habits may also display delayed shifts to
newly available food sources. Harrington and Harrington (1961), for
example, traced the prédation of a number of fishes upon a developing
mosquito hatch. Mosquitofish fed voraciously from the beginning, but the
typically herbivorous Poecilia only began to feed on the dipterans after the
hatch was well along in its development.
The Gila topminnow feeds mostly on amphipod crustaceans and plant
material (detritus) in Monkey Spring, Arizona (Schoenherr, 1970). Few
mosquitos are found in the restricted habitats where the fish now persists,
and their absence in stomachs must reflect intensive and almost complete
cropping. Under other conditions, P. occidental^ feeds avidly on mosquito
larvae. Aquatic plants, heterogenous bottoms, etc., may also protect prey
species. Various specializations such as open cephalic lateral line systems
in Poeciliidae (Rosen and Mendelson, 1960), a surface habit, and perhaps
even the generally small adult sizes of larvivorous fishes have occurred to
circumvent such problems.
467
(1970) found some algae eaten by sheepshead pupfish showed cytoplasmic
streaming and were viable when removed from the hindgut. We have recovered living algae from the hindgut of threadfin shad and mosquitofish,
as have Velasquez (1939), Kutkuhn (1958), and Fish (1951) from various other species. In C. n. nevadensis at least, relatively heavy use of indigestible algae in summer, when the population is most dense, may indicate
a scarcity of other foods, or other interactions, that place the fish under
nutritional stress. Apparent starvation of some individuals in summer, but
not at other times, suggests that some population limitations may be
imposed.
Many pupfishes appear to feed almost exclusively on bottom sediments,
at least at certain sizes and at certain times of year. Some sediments of
springs are copropelic and may be quite high in various organic nutrients.
In Cuatro Ciénegas, copropel and included organisms in springs and
other habitats appear to be a major food material for pupfishes (Minckley
and Itzkowitz, 1967; Arnold, 1970) and for some cichlids. In Lake
Victoria, Africa, some bottom sediments are so high in organic materials
that they are used as food for domestic cattle and fowl (Hickling, 1961).
One of the most extreme, and unusual, feeding habits of a desert fish involves an endemic catfish, Clarias cavernicola, which lives in a deep, pitlike
spring in the Kalahari Desert and appears to subsist mostly on the excrement of a local colony of baboons (Jubb, in Cole, 1968).
Food eaten by a fish depends largely upon its abundance or availability
at the time of feeding and on the vulnerability of the prey species. The
loach minnow in Aravaipa Creek feeds exclusively on blackfly larvae
(Simuliidae) when they are abundant, but it rapidly shifts to mayfly nymphs
after blackfly emergences. Food habits may also display delayed shifts to
newly available food sources. Harrington and Harrington (1961), for
example, traced the prédation of a number of fishes upon a developing
mosquito hatch. Mosquitofish fed voraciously from the beginning, but the
typically herbivorous Poecilia only began to feed on the dipterans after the
hatch was well along in its development.
The Gila topminnow feeds mostly on amphipod crustaceans and plant
material (detritus) in Monkey Spring, Arizona (Schoenherr, 1970). Few
mosquitos are found in the restricted habitats where the fish now persists,
and their absence in stomachs must reflect intensive and almost complete
cropping. Under other conditions, P. occidental^ feeds avidly on mosquito
larvae. Aquatic plants, heterogenous bottoms, etc., may also protect prey
species. Various specializations such as open cephalic lateral line systems
in Poeciliidae (Rosen and Mendelson, 1960), a surface habit, and perhaps
even the generally small adult sizes of larvivorous fishes have occurred to
circumvent such problems.