The fish fanning industry has been more focused on the quality of eggs or larvae rather than that of sperm, even though the quality of both gametes may affect fertilisation success and larval survival, in some species, poor sperm quality can be a limiting factor in their culture, however, even when fertilisation success is high, differences in sperm quality between males when mixed sperm from multiple males is used may severely reduce the apparent population size and may affect the future genetic integrity of the stock. Sperm quality in fanned fish may be affected by different components of broodstock husbandry, during collection and storage of sperm prior to fertilisation or the fertilisation procedure. Although other approaches for quantification of sperm quality have been suggested, motility is most commonly used since high motility is a prerequisite for fertilisation and correlates strongly with fertilisation success. The assessment of sperm motility has historically relied on subjective estimates of motility characteristics, the value of which is questionable in predicting fertility. Computer-assisted sperm analysis (CASA) systems that were initially developed to examine sperm quality in mammals and birds have only recently been applied to fish sperm. CASA can play an important role in aquaculture since it can rapidly and objectively quantify the effects of husbandry conditions and sperm handling on sperm motility and hence, fertilising capacity in fanned fish. This paper reviews existing methods of sperm quality assessment in fish, surveys the factors affecting quality and shows how the application of computer-calculated motility analysis may achieve a better understanding and quantification of the impact of aquaculture practices on sperm quality and fertilisation success. The review focuses primarily on teleost fish which predominate in both aquaculture and research, but also includes some of the studies on sturgeon which are of increasing interest in aquaculture. (C) 2004 Elsevier B.V. All rights reserved.