This chapter intends to give a comprehensive coverage about sperm features in salmonids. After a briefl y presenting the structure of a typical salmonid spermatozoon, the chapter goes on to cover different aspects of sperm quality assessment including motility and its mechanism of activation, energetic metabolism, as well as environmental aspects such as seminal or ovarian fl uid, swimming solutions composition or temperature. Evaluation of sperm quality includes DNA or cell membrane integrity as well as adverse factors such as reactive oxygen species or pollutants are also discussed. Ultimately, the ability for sperm to fertilize an egg constitutes a crucial test for spermatozoa integrity.