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The mechanism by which tuna achieve very fast swimming speeds is not presently understood, and may involve delay of transition or an advanced propulsion mechanism (or both). The issue of whether the boundary layer on a tuna swimming at typical speeds (1 to 2 bodylengths/sec) is laminar, turbulent, or transitional is an open question. Using an arc-length Reynolds number (ReL) to estimate the nature of the boundary layer and predict when transition occurs only serves as a rough approximation. Uncertainties include the surface roughness of the skin, local favorable and adverse pressure gradients, and discontinuities such as the open mouth or juncture at the fins. The primary objectives of this project are to compute the approximate lateral location at which transition to turbulence occurs on the tuna for various swimming speeds, and to determinethe maximum speed at which laminar flow is retained on the tunas body. Two-dimensional (2D) and three-dimensional (3D) computer models are used to compute the boundary layer characteristics and predict the lateral location of turbulence onset. The computations cover speeds ranging from 2 to 22 m/s.