7. Role of Lipids in Fish Populations
141
an adaptive size-specific tactic to maximize fecundity (Schultz et aI., 1991). Late
breeding places less demand on stored energy, and postponement enables individuals with low initial lipid reserves to breed without starving. By delaying reproduction, females breed at a larger size and are more fecund (Bell, 1980). By
delaying reproduction, greater numbers of offspring are produced; however, offspring survival may be decreased because the young would not have sufficient
time and food resources to grow and store adequate lipid reserves for overwinter
survival. The yellowtail rockfish, Sebastes flavidus, also uses an intermediate
resource allocation strategy. In lean years this species retains lipids in mesenteries
until the time of breeding or even until later in the year. This strategy increases the
prospects of maternal survival and greater production of progeny in future, more
optimum (higher food production) years, perhaps at the expense of the present
year class (MacFarlane et aI., 1993). In walleye, Stizostedion vitreum, females
elaborate gonadal tissue only if there is sufficient fat to do so. Energy for gonadal
development may cease, however, if visceral fat supplies drop below a critical
level (Henderson et aI., 1996).
Among most fish species there is a strong selection pressure to make the
appropriate gonadal responses at the correct times of the year in predictable or
more stable environments (Munro, 1990). Such pressure occurs because gonadal
growth and maturation are associated with considerable energy investment at the
expense of somatic growth, and this high energy drain can ultimately result in
increased mortality and a reduction in future fecundity (Myers, 1984; Lamon and
Ward, 1983). Thus, even after maturation, natural selection should favor those
genotypes that respond to the appropriate environmental factors in a manner that
permits the most efficient sequential distribution of resources between somatic
and gonadal compartments. Ideally, somatic growth should be continued for as
long as possible to maximize the potential fecundity for that season and before
diverting energy to the gonads (Munro, 1990). If an individual diverts, therefore,
energy from somatic growth to gonadal investment too early, then it must either
breed early and jeopardize survival of that brood or wait until optimal breeding
conditions. Conversely, fish that postpone gonad growth mature later in the
spawning season and must either undergo gonad regression and recycle gonadal
material back to the body (with associated energy losses) or attempt a later and
probably unsuccessful spawning. Individuals that attempt to increase potential
fecundity by postponing gonad development too long in a particular season will
also be selected against.
Summary and Future Initiatives. Reproduction and growth in fishes do not occur
without some compromises. Fish employ a variety of strategies for allocating
available energy such that the trade-offs between these basic functions tend toward optimization. At the core of these allocation strategies are lipid reserves that
function as a connector or a "common currency" between environmental resource
availability and various uses by the organism such as reproduction. If reproductive function is maximized, some other component such as growth is usually
compromised. The energy allocation strategies used by each species are the prod-
141
an adaptive size-specific tactic to maximize fecundity (Schultz et aI., 1991). Late
breeding places less demand on stored energy, and postponement enables individuals with low initial lipid reserves to breed without starving. By delaying reproduction, females breed at a larger size and are more fecund (Bell, 1980). By
delaying reproduction, greater numbers of offspring are produced; however, offspring survival may be decreased because the young would not have sufficient
time and food resources to grow and store adequate lipid reserves for overwinter
survival. The yellowtail rockfish, Sebastes flavidus, also uses an intermediate
resource allocation strategy. In lean years this species retains lipids in mesenteries
until the time of breeding or even until later in the year. This strategy increases the
prospects of maternal survival and greater production of progeny in future, more
optimum (higher food production) years, perhaps at the expense of the present
year class (MacFarlane et aI., 1993). In walleye, Stizostedion vitreum, females
elaborate gonadal tissue only if there is sufficient fat to do so. Energy for gonadal
development may cease, however, if visceral fat supplies drop below a critical
level (Henderson et aI., 1996).
Among most fish species there is a strong selection pressure to make the
appropriate gonadal responses at the correct times of the year in predictable or
more stable environments (Munro, 1990). Such pressure occurs because gonadal
growth and maturation are associated with considerable energy investment at the
expense of somatic growth, and this high energy drain can ultimately result in
increased mortality and a reduction in future fecundity (Myers, 1984; Lamon and
Ward, 1983). Thus, even after maturation, natural selection should favor those
genotypes that respond to the appropriate environmental factors in a manner that
permits the most efficient sequential distribution of resources between somatic
and gonadal compartments. Ideally, somatic growth should be continued for as
long as possible to maximize the potential fecundity for that season and before
diverting energy to the gonads (Munro, 1990). If an individual diverts, therefore,
energy from somatic growth to gonadal investment too early, then it must either
breed early and jeopardize survival of that brood or wait until optimal breeding
conditions. Conversely, fish that postpone gonad growth mature later in the
spawning season and must either undergo gonad regression and recycle gonadal
material back to the body (with associated energy losses) or attempt a later and
probably unsuccessful spawning. Individuals that attempt to increase potential
fecundity by postponing gonad development too long in a particular season will
also be selected against.
Summary and Future Initiatives. Reproduction and growth in fishes do not occur
without some compromises. Fish employ a variety of strategies for allocating
available energy such that the trade-offs between these basic functions tend toward optimization. At the core of these allocation strategies are lipid reserves that
function as a connector or a "common currency" between environmental resource
availability and various uses by the organism such as reproduction. If reproductive function is maximized, some other component such as growth is usually
compromised. The energy allocation strategies used by each species are the prod-