Data from: Integrating lipid storage into general representations of fish energetics

Fish, even of the same species, can exhibit substantial variation in
energy density (energy per unit wet weight). Most of this variation is due
to differences in the amount of storage lipids. In addition to their
importance as energy reserves for reproduction and for survival during
unfavourable conditions, the accumulation of lipids represents a large
energetic flux for many species, so figuring out how this energy flux is
integrated with other major energy fluxes (growth, reproduction) is
critical for any general theory of organismal energetics. Here, we
synthesize data from a wide range of fish species and identify patterns of
intraspecific variation in energy storage, and use these patterns to
formulate a general model of energy allocation between growth, lipid
storage and reproduction in fishes. From the compiled data we identified
two patterns: (1) energy density increases with body size during the
juvenile period, but is invariant with body size within the adult size
range for most species, and (2) energy density changes across seasons,
with depletion over winter, but increases fastest in periods of transition
between favourable and unfavourable conditions for growth (i.e. fall).
Based on these patterns we propose DEBlipid, a simple, general model of
energy allocation that is closely related to a simplified version of
Dynamic Energy Budget theory, DEBkiss. The crux of the model is that
assimilated energy is partitioned, with κ fraction of energy allocated to
pay maintenance costs first, and the surplus allocated to growth, and 1 −
κ fraction of assimilated energy is allocated to accumulating storage
lipids during the juvenile phase, and later to reproduction as adults.
This mechanism, in addition to capturing the two patterns that motivated
the model, was able to predict lipid dynamics in a novel context, the
migration of anadromous fish from low-food freshwater to high-food marine
environments. Furthermore, the model was used to explain intra and
interspecific variation in reproductive output based on patterns of lipid
accumulation as juveniles. Our results suggest that many seemingly
complex, adaptive energy allocation strategies in response to ontogeny,
seasonality and habitat quality can emerge from a simple physiological
heuristic.