Organismal stoichiometry at the temporal scale: Seasonal variability shapes interspecific differences in fish

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