Abstract Changes in organismal stoichiometry (OS) may be driven by seasonal changes
in lipid reserves (i.e. energy) and gonadal development in fish. However, these relationships
are understudied. Hence, we investigated how seasonal changes in body lipid content
and gonadal development can drive the seasonal variability of OS traits at the example
of three coexisting freshwater fish species. Furthermore, we aimed to assess the importance
of seasonal OS alteration in comparison with interspecific differences. Carbon (%C),
nitrogen (%N) and phosphorus (%P) contents, and the molar ratios of these elements
(C:N, C:P and N:P) were examined in rudd (Scardinius erythrophthalmus), pumpkinseed
(Lepomis gibbosus) and Amur sleeper (Perccottus glenii). We consider the sex and seasonal
changes in body size as a potential factor in shaping OS. Substantial seasonal intraspecific
variability occurred in all OS traits. Its extent exceeded interspecific differences
in %C, %N and C:N, while %P and C:P, N:P were determined primarily by species identity.
The effect of sex occurred sporadically and was considerable in some cases. Seasonal
changes in total length did not contribute to intraspecific variability of OS. Intra-annual
changes in body lipid content affected seasonal variability of OS traits substantially,
but the strength of this effect was species-specific. The regulatory role of lipid
reserve alterations worked only for those species that exhibited considerable seasonal
variation in body fat content. Gonado-somatic index proved to be marginal in shaping
seasonal changes in OS, presumably because a substantial portion of the essential
elemental demand for gonadal growth is supplied by rearrangements within the body,
without notable changes in the entire elemental composition. In the light of our findings,
we suggest that more attention should be given to the influence of seasonal variability
in OS traits, and sex should be considered as a taxon-dependent effect. Ignoring this
substantial degree of variability might lead to inaccuracies in assessing the extent
of both intra- and interspecific OS differences. We conclude that seasonal OS variability
might shape consumer-driven nutrient dynamics.
