fish swimming prediction model

Critical swimming speed (Ucrit) is a key factor in assessing the swimming ability of fish in different flow conditions. However, the existing Ucrit prediction models lack inconsistencies in unit and physical significance. We hypothesized that the thrust provided by fish to resist the force introduced by water flow at a critical swimming state was balanced and that the fish’s gravity was balanced with its buoyancy in water. Through mathematic derivation, we established a new Ucrit prediction model and evaluated the influences of various factors on Ucrit results. The new theoretical model considers Ucrit as a function of the comprehensive coefficient α, gravitational acceleration g, and body length L, and uses a unified expression Ucrit =α(gL) 0.5 to predict the Ucrit of fish. We have validated the model using previous research data and found that the predictive results of the new theoretical model are more consistent with other empirical models. This new model provides a universal Ucrit prediction method for various fish species, addressing the issue of inconsistency in the application of experimental results by different researchers, and offering a solid reference for fish stocks protection, fishway construction, and habitat restoration.