VII. DESERT FISHES
409
with whitened, sloughing tissue on their dorsolateral surfaces, and with
severely damaged caudal and dorsal fins, presumably as a result of sunburn,
drying, or both (Minckley and Barber, 1971, and subsequent observations).
Pupfishes, afflicted with gaseous distension of their digestive tracts which
forced them to the surface (Minckley and Itzkowitz, 1967), were similarly
injured. Sunburn has been demonstrated in hatchery-maintained salmonid
fishes at various latitudes (DeLong et al., 1958; Allison, 1960; Corson
and Brezosky, 1961), and cataracts of the eyes in salmonids also have
been related to sun exposure (Allison, 1962). Direct damage usually is
followed by secondary infection by bacteria or fungi, and death often ensues in desert fishes we have studied.
Certain wavelengths of light (ultraviolet) are lethal to the embryos of
killifish (Fundulus) exposed at early stages of development (Hinrichs,
1925); exposure of older e m b r e i resulted in delayed hatching. Haempel
and Lechler (1931) theorized ffiat summer levels of ultraviolet in nature
would be lethal at midday to exposed salmonid embryos and larvae. Most
wavelengths of radiation that contact fishes, however, are in the visible
spectrum, since water allows only poor transmission of ultraviolet or infrared. Inhibition of hatching of eggs or growth of larvae by visible light
has been widely reported (Perlmutter, 1961; Breder, 1962), and some
pelagic ova of marine species rise at night and sink in the day, possibly
as an adaptation toward limiting exposure to radiations (Breder, 1962).
On the other hand, the total absence of light may also inhibit hatching
of eggs of fishes of epigean habit (Rasquin and Rosenbloom, 1954; Breder,
1962). Breder proposed that the transparency of eggs and larvae of some
fishes were adaptations allowing radiations to pass through (i.e., not to
be absorbed), and therefore not to influence sensitive tissues or enzyme
systems. Pigments, colored oils or fat globules, or physical placement of
ova in sheltered places away from light, are other presumed means of
avoiding radiation exposures. Almost all the shallow-water fishes with
which we are familiar in deserts deposit their eggs beneath the surface
of the substrate, on or within aquatic vegetation, or on debris.
Most cyprinodontids have pigmented larvae, with melanophores heavily
investing the dorsum of the head and visceral cavity, at least. Cyprinoids,
on the other hand, are essentially transparent and have darkened areas on
the midline of the back and over the cranial vault. In general, fishes with
permanently exposed pineal areas of the brain usually produce transparent
eggs and larvae, and those which produce heavily pigmented eggs have
thick skulls or heavy pigmentation over the pineal region. Many intermediate groups can control pineal exposure to light. Unexpectedly, they
expose the region in light and tend to cover it in darkness (Breder, 1962).
Therefore, the protective nature of some of these features, along with an
409
with whitened, sloughing tissue on their dorsolateral surfaces, and with
severely damaged caudal and dorsal fins, presumably as a result of sunburn,
drying, or both (Minckley and Barber, 1971, and subsequent observations).
Pupfishes, afflicted with gaseous distension of their digestive tracts which
forced them to the surface (Minckley and Itzkowitz, 1967), were similarly
injured. Sunburn has been demonstrated in hatchery-maintained salmonid
fishes at various latitudes (DeLong et al., 1958; Allison, 1960; Corson
and Brezosky, 1961), and cataracts of the eyes in salmonids also have
been related to sun exposure (Allison, 1962). Direct damage usually is
followed by secondary infection by bacteria or fungi, and death often ensues in desert fishes we have studied.
Certain wavelengths of light (ultraviolet) are lethal to the embryos of
killifish (Fundulus) exposed at early stages of development (Hinrichs,
1925); exposure of older e m b r e i resulted in delayed hatching. Haempel
and Lechler (1931) theorized ffiat summer levels of ultraviolet in nature
would be lethal at midday to exposed salmonid embryos and larvae. Most
wavelengths of radiation that contact fishes, however, are in the visible
spectrum, since water allows only poor transmission of ultraviolet or infrared. Inhibition of hatching of eggs or growth of larvae by visible light
has been widely reported (Perlmutter, 1961; Breder, 1962), and some
pelagic ova of marine species rise at night and sink in the day, possibly
as an adaptation toward limiting exposure to radiations (Breder, 1962).
On the other hand, the total absence of light may also inhibit hatching
of eggs of fishes of epigean habit (Rasquin and Rosenbloom, 1954; Breder,
1962). Breder proposed that the transparency of eggs and larvae of some
fishes were adaptations allowing radiations to pass through (i.e., not to
be absorbed), and therefore not to influence sensitive tissues or enzyme
systems. Pigments, colored oils or fat globules, or physical placement of
ova in sheltered places away from light, are other presumed means of
avoiding radiation exposures. Almost all the shallow-water fishes with
which we are familiar in deserts deposit their eggs beneath the surface
of the substrate, on or within aquatic vegetation, or on debris.
Most cyprinodontids have pigmented larvae, with melanophores heavily
investing the dorsum of the head and visceral cavity, at least. Cyprinoids,
on the other hand, are essentially transparent and have darkened areas on
the midline of the back and over the cranial vault. In general, fishes with
permanently exposed pineal areas of the brain usually produce transparent
eggs and larvae, and those which produce heavily pigmented eggs have
thick skulls or heavy pigmentation over the pineal region. Many intermediate groups can control pineal exposure to light. Unexpectedly, they
expose the region in light and tend to cover it in darkness (Breder, 1962).
Therefore, the protective nature of some of these features, along with an