7. Role of Lipids in Fish Populations
149
Katti and Sathyanesan (1984) also found that liver lipids increased when the
catfish Clarias batrachus was exposed to cadmium chloride for up to 135 d. In
contrast to these two studies, Ram and Sathyanesan (1984) reported that freshwater fish subjected to 0.01 ppm mercuric chloride displayed decreases in liver and
ovarian lipids. Decreases in ovarian lipids and absence of yolk formation in the
oocyte could have been due to toxic effects of HgCl 2 on gonadotrophic secretion
that impaired liver vitellogenin synthesis. Freshwater fish subjected to 1-4 ppm
copper sulfate for 60-84 d demonstrated a gradual decrease in liver and muscle
lipids that was attributed to either oxidation or hydrolysis of these lipids (Pandey
and Pandey, 1994; Ansari, 1983). However, the lipid content of Atlantic salmon
exposed to four concentrations of aluminum for 60 d was not changed (McKee et
aI., 1989).
7.2.4.2. Thermal Effects
Varying thermal regimes can also alter the lipid dynamics and the health of fish by
(1) increasing metabolic activity, thereby increasing utilization of lipid stores;
(2) restricting fish from preferred feeding or breeding areas; (3) altering foraging
behavior; and (4) increasing susceptibility of fish to disease or parasites, which
could result in even greater metabolic costs.
The overall condition, lipid levels, and reproductive performance of striped
bass, Marone saxatilus, has been compromised in certain aquatic systems in
which preferred habitat for this species has been constricted by a combination of
high temperatures and low dissolved oxygen. Coutant (1987) hypothesized that
poor body condition of adult striped bass caused by habitat limitations early in
ovarian development ultimately reduced the reproductive potential of this species.
For some eutrophic systems that stratify during the summer, such as Cherokee
Reservoir in east Tennessee and Chesapeake Bay, warm upper-layer water combined with low dissolved oxygen in deeper cooler water forces or squeezes fish
into a narrow band of the water column. Temperatures in these constricted zones
are typically higher than preferred for the species, resulting in increased metabolic
demands, higher competition for limited food resources, and increased susceptibility to disease and other environmental stressors (Coutant and Benson, 1990).
This type of habitat restriction often results in poor performance as evidenced by a
reduction in the percentage of successfully spawning females and in embryo
survival. Even though the number of eggs was not affected, the survivorship of
eggs and larvae was reduced after spawning. Larval survival, as discussed in the
previous section, may have been impaired as a result of the lower concentrations of yolk and lipids derived from the malnourished parent. The survivorship
and vigor of larvae and reproductive success of the population can, therefore,
be linked to the environmental experience of the parent when the eggs were
developing.
Although summer habitat constriction was not as dramatic as that observed for
striped bass, northern pike, Esax lucius, also experienced habitat restriction and a
loss of condition over the summer in a stratified Ohio reservoir (Headrick and
Carline, 1993). This species was also squeezed into a narrow zone of unfavorable
149
Katti and Sathyanesan (1984) also found that liver lipids increased when the
catfish Clarias batrachus was exposed to cadmium chloride for up to 135 d. In
contrast to these two studies, Ram and Sathyanesan (1984) reported that freshwater fish subjected to 0.01 ppm mercuric chloride displayed decreases in liver and
ovarian lipids. Decreases in ovarian lipids and absence of yolk formation in the
oocyte could have been due to toxic effects of HgCl 2 on gonadotrophic secretion
that impaired liver vitellogenin synthesis. Freshwater fish subjected to 1-4 ppm
copper sulfate for 60-84 d demonstrated a gradual decrease in liver and muscle
lipids that was attributed to either oxidation or hydrolysis of these lipids (Pandey
and Pandey, 1994; Ansari, 1983). However, the lipid content of Atlantic salmon
exposed to four concentrations of aluminum for 60 d was not changed (McKee et
aI., 1989).
7.2.4.2. Thermal Effects
Varying thermal regimes can also alter the lipid dynamics and the health of fish by
(1) increasing metabolic activity, thereby increasing utilization of lipid stores;
(2) restricting fish from preferred feeding or breeding areas; (3) altering foraging
behavior; and (4) increasing susceptibility of fish to disease or parasites, which
could result in even greater metabolic costs.
The overall condition, lipid levels, and reproductive performance of striped
bass, Marone saxatilus, has been compromised in certain aquatic systems in
which preferred habitat for this species has been constricted by a combination of
high temperatures and low dissolved oxygen. Coutant (1987) hypothesized that
poor body condition of adult striped bass caused by habitat limitations early in
ovarian development ultimately reduced the reproductive potential of this species.
For some eutrophic systems that stratify during the summer, such as Cherokee
Reservoir in east Tennessee and Chesapeake Bay, warm upper-layer water combined with low dissolved oxygen in deeper cooler water forces or squeezes fish
into a narrow band of the water column. Temperatures in these constricted zones
are typically higher than preferred for the species, resulting in increased metabolic
demands, higher competition for limited food resources, and increased susceptibility to disease and other environmental stressors (Coutant and Benson, 1990).
This type of habitat restriction often results in poor performance as evidenced by a
reduction in the percentage of successfully spawning females and in embryo
survival. Even though the number of eggs was not affected, the survivorship of
eggs and larvae was reduced after spawning. Larval survival, as discussed in the
previous section, may have been impaired as a result of the lower concentrations of yolk and lipids derived from the malnourished parent. The survivorship
and vigor of larvae and reproductive success of the population can, therefore,
be linked to the environmental experience of the parent when the eggs were
developing.
Although summer habitat constriction was not as dramatic as that observed for
striped bass, northern pike, Esax lucius, also experienced habitat restriction and a
loss of condition over the summer in a stratified Ohio reservoir (Headrick and
Carline, 1993). This species was also squeezed into a narrow zone of unfavorable