ABSTRACT
Atlantic halibut, Hippoglossus hippoglossus L., is the largest flatfish and one of the largest farmed fish species with body weight exceeding 300 kg [1]. Atlantic halibut show a discontinuous reproductive pattern reaching reproductive readiness in the springtime. Females are batch spawners and males show prenuptial spermatogenesis, with spawning readiness at the peak of gonadal activity [2]. The quantity and quality of sperm decrease toward the end of the reproductive season, likely resulting from low spermiogenesis activity, intensive dehydration and ageing processes to spermatozoa [3-5]. Changes in semen quality towards the end of the season include: lowered fertilization ability [5] and poor resistance to cryopreservation [3]. Asynchrony in gamete quality occurs at the end of the reproductive season when quality eggs are still produced by females [6,4]. One of approaches to overcome the problem of poor quality of sperm late in the season is to cryopreserve the sperm when it is of the best quality. Atlantic halibut semen has been successfully cryopreserved [7,8].
