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S.M. Adams
assumed to be limited, which forces fish to use different energy allocation strategies depending on the short- and long-term availability of these food resources.
The three-spined stickleback, Gasterosteus aculeatus, is an example of a species that sacrifices body weight and condition to maintain egg production in the
face of food restriction. Relatively high levels of hydration of the carcass and liver
and the comparatively small size of the liver in spawning females, even at high
rations, provide evidence that egg production has a priority over somatic growth
(Wootton, 1977). Both the observed increases of water in body tissues and the
smaller liver size are indicative of lipid utilization and mobilization to support
gonad development. Several other aspects of the stickleback life history suggest
that investment in reproduction is more profitable than growth. For example,
small size at maturity, short life expectancy, multiple spawnings, and poor
postspawning survival indicate emphasis on short-term reproductive success.
Decreased postspawning survival, in particular, indicates mobilization of lipids
from body tissues, which weakens fish and renders them vulnerable to mortality
from numerous sources (Shul'man, 1974).
Another extreme in energy allocation strategy is represented by the winter
flounder, Pseudopleuronectes americanus. which typically sacrifices gonad
development or egg production to maintain body weight (Tyler and Dunn, 1976).
This strategy channels energy that is not used for maintenance or lipid storage into
increasing body size so that when a good year of food resources occurs, fish will
be able to develop larger ovaries. Evidence for use of this strategy in this species
includes positive correlations between calories consumed and body condition,
liver weight, percentage of lipid in the liver, percentage of fish with yolk-bearing
ovaries, and ovary weight. Under reduced rations, fewer fish initiate yolk development, and for those fish that do produce yolk, fewer eggs actually receive
yolk. Therefore, the fact that fish maintained body condition including levels of
fat in the liver and that reproductive development was hindered during reduced
feeding indicate that this species placed a higher priority on maintaining body size
than on producing reproductive products.
The bluegill sunfish, Lepomis macrochirus, employs an energy allocation strategy that is somewhat intermediate between that of the stickleback and the winter
flounder. For juvenile bluegill the strategy for maximizing survival, at least in the
northern part of its range, is to divert as much energy as possible into somatic
growth while maintaining some lipid reserves for overwinter survival (Booth and
Keast, 1986). Rapid growth of juveniles is important because female fecundity
and male success in competition for breeding space are weight-dependent (Gross,
1982). Maximizing growth in length is also critical for enhancing abilities to
capture prey (Werner, 1979) and maintaining growth refuge from predators (Keast
and Eadie, 1984). The energy allocation dilemma for bluegill, therefore, is that
enough energy has to be channeled into growth to maximize survival during the
growing season for minimizing the risk of predation while conserving enough
energy as lipids to maximize overwinter survival.
Many fish species balance somatic growth with reproductive output. In the
dwarf surfperch, Micrometrus minimus, small females postpone reproduction as
S.M. Adams
assumed to be limited, which forces fish to use different energy allocation strategies depending on the short- and long-term availability of these food resources.
The three-spined stickleback, Gasterosteus aculeatus, is an example of a species that sacrifices body weight and condition to maintain egg production in the
face of food restriction. Relatively high levels of hydration of the carcass and liver
and the comparatively small size of the liver in spawning females, even at high
rations, provide evidence that egg production has a priority over somatic growth
(Wootton, 1977). Both the observed increases of water in body tissues and the
smaller liver size are indicative of lipid utilization and mobilization to support
gonad development. Several other aspects of the stickleback life history suggest
that investment in reproduction is more profitable than growth. For example,
small size at maturity, short life expectancy, multiple spawnings, and poor
postspawning survival indicate emphasis on short-term reproductive success.
Decreased postspawning survival, in particular, indicates mobilization of lipids
from body tissues, which weakens fish and renders them vulnerable to mortality
from numerous sources (Shul'man, 1974).
Another extreme in energy allocation strategy is represented by the winter
flounder, Pseudopleuronectes americanus. which typically sacrifices gonad
development or egg production to maintain body weight (Tyler and Dunn, 1976).
This strategy channels energy that is not used for maintenance or lipid storage into
increasing body size so that when a good year of food resources occurs, fish will
be able to develop larger ovaries. Evidence for use of this strategy in this species
includes positive correlations between calories consumed and body condition,
liver weight, percentage of lipid in the liver, percentage of fish with yolk-bearing
ovaries, and ovary weight. Under reduced rations, fewer fish initiate yolk development, and for those fish that do produce yolk, fewer eggs actually receive
yolk. Therefore, the fact that fish maintained body condition including levels of
fat in the liver and that reproductive development was hindered during reduced
feeding indicate that this species placed a higher priority on maintaining body size
than on producing reproductive products.
The bluegill sunfish, Lepomis macrochirus, employs an energy allocation strategy that is somewhat intermediate between that of the stickleback and the winter
flounder. For juvenile bluegill the strategy for maximizing survival, at least in the
northern part of its range, is to divert as much energy as possible into somatic
growth while maintaining some lipid reserves for overwinter survival (Booth and
Keast, 1986). Rapid growth of juveniles is important because female fecundity
and male success in competition for breeding space are weight-dependent (Gross,
1982). Maximizing growth in length is also critical for enhancing abilities to
capture prey (Werner, 1979) and maintaining growth refuge from predators (Keast
and Eadie, 1984). The energy allocation dilemma for bluegill, therefore, is that
enough energy has to be channeled into growth to maximize survival during the
growing season for minimizing the risk of predation while conserving enough
energy as lipids to maximize overwinter survival.
Many fish species balance somatic growth with reproductive output. In the
dwarf surfperch, Micrometrus minimus, small females postpone reproduction as