Abstract: Behavior is becoming an increasingly important field of study in aquatic ecology and ecotoxicology. It has long been known that aquatic organisms show a rich and subtle behavioral repertoire, which is vital for their survival and reproductive success. The increasing pressure on marine ecosystems leads to a renewed interest: researchers realize that pollutants, sound and climate change may influence the organism's environment as well as the organism itself. Seemingly small changes in behavior may have strong effects on population level due to changes in competitive balance, predation pressure or reproduction. Studying behavior has become easier due to the increasing availability of tools and technologies. Video tracking and other image processing techniques add power and speed to the researchers' work, and there are also tools that support classical human observation. There is also a growing number of standardized behavioral paradigms for fish, such as novel tank diving and shoaling. This seminar will give an overview of available techniques and tools.