Factors Influencing Milt Quality in Fishes and Its Usefulness to Cryopreservation

Sperm quality is primarily defined as its capability of fertilising an egg and consequently allowing for the development of a normal embryo. Sperm quality can be highly variable; therefore, gamete quality assessment is a prerequisite for fertilisation trials. Fish semen analysis includes several methods, such as measurements of sperm motility parameters, sperm concentration and viability, mitochondrial potential and chromatin structure integrity. Recently, ‘omics’ methodologies, including genomics, transcriptomics, proteomics and metabolomics, have been utilised to search for potential molecular indicators that predict sperm quality, which could be used in practice. Several analytical parameters appear to be useful for the evaluation of changes in sperm quality during cryopreservation. Major factors that influence sperm quality are related to genetics, biology and environmental effects, both natural and anthropogenic. Among the genetic factors, inbreeding is the most common factor that usually leads to a decrease in sperm quality, and biological factors include, for example, social status and the age of the fish. Environmental factors markedly shape fish reproduction and encompass season, water temperature and salinity, nutrition, living conditions in captivity, fish handling and the effects of various environmental contaminants. Factors securing the high quality of fresh sperm usually determine its usefulness for predicting cryopreservation success.