Stereovision and laser techniques allow for getting knowledge about fish, mostly when they are combined with computer vision. This kind of techniques avoid to use traditional procedures such as direct observation, which are impractical or can affect the fish behavior, in task such as aquarium and fish farm management or fishway, like vertical slot fishway, evaluation. This chapter describes in a first stage, the use stereovision join with computer vision to fish monitoring and measure size of fishes. In the second part, using laser technology and computer vision to fish detection, especially in slot fishways. Vertical slot fishways are structures that are placed in rivers to allow fish to avoid obstacles such as dams, hydroelectric plants. Then, it shows a results section and finally authors' conclusions.