7. Role of Lipids in Fish Populations
143
flounder the reduced fecundity and rate of oocyte recruitment was due to low food
supply and low fat reserves prior to the maturation period. Reduced fecundity in
this species was also linked to low energy availability through a mechanism of
increased oocyte resorption. In addition to oocyte resorption, follicular atresia has
also been observed in fish under conditions of reduced food supply (Hester, 1964;
Scott, 1962). Both Bagenal (1966) and DeVlaming (1971) found that low energy
reserves reduced fecundity by effecting a decrease in the rate of oocyte recruitment. Maturation of male Atlantic salmon (Salmo salar) parr was suppressed
when mesenteric fat failed to reach a critical level in May (Rowe et aI., 1991).
Shul'man (1974) introduced the concept that fish must attain a minimum fat
content before maturation can be initiated. In this regard, Atlantic salmon returning from sea required a minimum fat content of 12% in the spring if they were
likely to spawn the following autumn. Likewise, the onset of maturation in the
arctic char, Salvelinus alpinus, appears to be triggered by a critical level of lipids
during maturation (Rowe et aI., 1991).
The source of fat reserves for gonad growth and maturation depends on the fish
species and life history. In general, the primary energy reserve controlling maturation appears to be carcass or muscle fat in pelagic species such as clupeids; liver
fat in benthic species such as flatfish and the Gadidae (Cowey and Sargent, 1972);
and mesenteric fat in salmonids (Rowe et aI., 1991) and many of the Centrachids
(Adams et aI., 1982), Percids (Henderson et aI., 1996), and Cyprinids. Exceptions
to these generalizations may exist such as for plaice (a benthic species), in which
Dawson and Grimm (1980) found that the carcass was the main source of lipid
reserves. Some members of the family Scorpaenidae (scorpionfish) such as
the yellowtail rockfish, however, use both liver and mesenteric fat in ovarian
development.
The high energy demands that reproductive development places on stored
lipids is illustrated by a unique case of gizzard shad mortality in a southeast U.S.
reservoir during the mid-1980s. An unusually large die-off of mature female
gizzard occurred in the late spring and was attributed to severe starvation (Adams
et aI., 1985). These shad, which normally reproduce in the spring, failed to spawn
in the spring of the previous year because of a series of unusual environmental
conditions, primarily temperature related, during that period. Consequently, those
individuals that failed to spawn in the spring spawned the next fall and, in the
process, depleted their remaining lipid reserves. Delayed spawning in this situation eventually proved to be the main cause of mortality because the fall is
typically the period when energy reserves are accumulated and stored for overwinter survival and gonad maturation. Therefore, the late spawning not only
depleted available fat reserves, but also did not allow sufficient time for replenishment of lipid stores before the winter fasting period. The late-spawning individuals thus entered the winter period with depleted fat levels that were insufficient
for basic maintenance needs throughout the winter.
Lipids influence reproductive success not only through gonad development and
maturation but through viability of the progeny. Larval survival and success has
been linked to egg quality as expressed by stored energy in the egg (Kamler, 1992;
143
flounder the reduced fecundity and rate of oocyte recruitment was due to low food
supply and low fat reserves prior to the maturation period. Reduced fecundity in
this species was also linked to low energy availability through a mechanism of
increased oocyte resorption. In addition to oocyte resorption, follicular atresia has
also been observed in fish under conditions of reduced food supply (Hester, 1964;
Scott, 1962). Both Bagenal (1966) and DeVlaming (1971) found that low energy
reserves reduced fecundity by effecting a decrease in the rate of oocyte recruitment. Maturation of male Atlantic salmon (Salmo salar) parr was suppressed
when mesenteric fat failed to reach a critical level in May (Rowe et aI., 1991).
Shul'man (1974) introduced the concept that fish must attain a minimum fat
content before maturation can be initiated. In this regard, Atlantic salmon returning from sea required a minimum fat content of 12% in the spring if they were
likely to spawn the following autumn. Likewise, the onset of maturation in the
arctic char, Salvelinus alpinus, appears to be triggered by a critical level of lipids
during maturation (Rowe et aI., 1991).
The source of fat reserves for gonad growth and maturation depends on the fish
species and life history. In general, the primary energy reserve controlling maturation appears to be carcass or muscle fat in pelagic species such as clupeids; liver
fat in benthic species such as flatfish and the Gadidae (Cowey and Sargent, 1972);
and mesenteric fat in salmonids (Rowe et aI., 1991) and many of the Centrachids
(Adams et aI., 1982), Percids (Henderson et aI., 1996), and Cyprinids. Exceptions
to these generalizations may exist such as for plaice (a benthic species), in which
Dawson and Grimm (1980) found that the carcass was the main source of lipid
reserves. Some members of the family Scorpaenidae (scorpionfish) such as
the yellowtail rockfish, however, use both liver and mesenteric fat in ovarian
development.
The high energy demands that reproductive development places on stored
lipids is illustrated by a unique case of gizzard shad mortality in a southeast U.S.
reservoir during the mid-1980s. An unusually large die-off of mature female
gizzard occurred in the late spring and was attributed to severe starvation (Adams
et aI., 1985). These shad, which normally reproduce in the spring, failed to spawn
in the spring of the previous year because of a series of unusual environmental
conditions, primarily temperature related, during that period. Consequently, those
individuals that failed to spawn in the spring spawned the next fall and, in the
process, depleted their remaining lipid reserves. Delayed spawning in this situation eventually proved to be the main cause of mortality because the fall is
typically the period when energy reserves are accumulated and stored for overwinter survival and gonad maturation. Therefore, the late spawning not only
depleted available fat reserves, but also did not allow sufficient time for replenishment of lipid stores before the winter fasting period. The late-spawning individuals thus entered the winter period with depleted fat levels that were insufficient
for basic maintenance needs throughout the winter.
Lipids influence reproductive success not only through gonad development and
maturation but through viability of the progeny. Larval survival and success has
been linked to egg quality as expressed by stored energy in the egg (Kamler, 1992;