How age, captivity and cryopreservation affect sperm quality and reproductive efficiency in precocious Atlantic salmon (Salmo salar L. 1758)

In order to restore an extinct population in a river basin, enough biological material for restocking purposes needs to be produced which requires male semen of good quality but also in large quantities. For sperm production in Atlantic salmon, it is possible to rely on (i) early matured males or (ii) sperm cryopreservation. However, the quality of both, fresh and cryopreserved spermatozoa can be influenced by biological factors such as the age of the fish or factors linked to their environment (captive vs. wild fish). this study investigates the impact of these factors to ensure good reproductive success. For this purpose, spermatozoa viability (SYBR-14/PI) and mitochondrial membrane potential (JC-1) were evaluated with flow cytometry staining techniques. Motility as well as velocity and trajectory parameters were evaluated using the Computer Assisted Sperm Analysis system (CASA). DNA integrity was assessed with the help of the Comet assay. After assisted reproduction, the reproductive success was determined at two developmental stages (i.e. eyed stage and hatching). For the first time, spermatozoa quality and reproductive success were compared between adult males and early parr of different ages and origins. Spermatozoa quality and reproductive success of fresh semen was similar for anadromous males and early parr regardless of their age and origin. This observation further supports the use of highly available young parr from captivity for reproduction purposes. Cryopreservation on the other hand, affected spermatozoa quality differently in the different conditions tested. The mitochondrial potential and motility of parr from captivity was more severely affected by cryopreservation, which directly translated into reduced reproductive success. This is the first report of decreased cryoresistance of spermatozoa of precocious salmon induced by captivity. It is therefore recommended that only the semen of anadromous males should be cryopreserved.