Comparative study of growth in Carassius gibelio (Bloch, 1782) and Rutilus rutilus (L., 1758) from two Serbian reservoirs: Multi-model analysis and inferences

• Application of multi-model analysis in modeling Prussian carp and roach growth patterns.
• The most commonly used von Bertalanffy model was not the best fitting in all cases.
• Model-averaging provided a more stable inference and reduced model selection bias.
• Comparison of Prussian carp and roach growth patterns between two types of reservoirs.
• Both species from the lowland reservoir attained larger asymptotic lengths.

We assessed growth patterns of Prussian carp Carassius gibelio (Bloch, 1782) and roach Rutilus rutilus (L., 1758) from two different types of reservoirs (lowland type vs highland type) through multi-model analysis. We applied three different fish growth models: von Bertalanffy (VBGF), Gompertz (GGF) and Robertson (RGF) growth functions and assessed the best fitting model using the Akaike's Information Criterion (AIC). Additionally, we calculated deviations from the best fitting model (Δi) and Akaike weights (wi) for all models. The VBGF was not the best fitting model in all cases. Furthermore, in many cases more than one model was significantly supported (Δi < 2) and Akaike's weight displayed no ‘clear winner’ (wi < 0.9). Therefore we applied multi-model inference through model-averaging in order to provide more stable inferences, reduce model selection bias and achieve higher precision compared to the selected best model. Since most studies that applied multi-model analysis in modeling fish growth were conducted on elasmobranchs and other marine fish species, we suggest that these analyses should also be applied to freshwater species in order to achieve improved conservation strategies for endangered species and improved management strategies for invasive species. When comparing growth patterns between the two reservoirs, the F-statistic displayed significant differences in the best fitting growth functions between the Gruža and Međuvršje Reservoirs for both species. As hypothesized, individuals inhabiting the calm, shallow lowland reservoir with a large surface area attained higher asymptotic lengths than individuals inhabiting narrow highland reservoir with high water flow. Fish inhabiting narrow water bodies with high water flow need to adapt specifically to these conditions since water current affects the movement of fish as well as prey encounter rate, thus smaller bodies which allow higher maneuverability appear to be favored when compared to bulkier body forms in such environments. Therefore, we assume that differences in growth patterns observed in this study predominantly present a response to the highly differential environmental conditions from the two reservoirs.