Sperm Morphology, Physiology, Motility, and Cryopreservation in Percidae

Abstract

In percids, the spermatozoon is acrosomeless and asymmetrical in shape. The head of the spermatozoon is spherical and contains the genomic material. Mitochondria and proximal and distal centrioles are located in the midpiece of the spermatozoon. The flagellum consists of an axoneme with a “9 + 2” microtubule structure surrounded by a plasma membrane. The length of spermatozoa flagella is between 30 and 35 μm. The volume of sperm and spermatozoa concentration highly differs among species and individuals. Seminal plasma is composed of both mineral and organic compounds and has osmolality about 300 mOsmol kg−1 to maintain the spermatozoa in the quiescent state. A hypo-osmotic shock is required to trigger initiation of spermatozoa motility after discharge into an aquatic environment. The duration of sperm motility lasts from several seconds to a few minutes, however sperm motility kinetics (percentage of motile spermatozoa, spermatozoa velocity and beating frequency of flagella) rapidly decrease after initiation of sperm motility due to rapid depletion of energy source required for the axonemal beating. The environmental osmolality, pH and ionic concentrations affect sperm motility kinetics. The highest percentage of spermatozoa motility and spermatozoa velocity are observed in an activation medium with osmolality of 100 mOSmol kg−1. There are various factors that affect semen quality in male broodfish including photoperiod and seasonal regimes, nutrition and antinutritional factors, rearing condition and age and size of broodfish. For short-term storage, it is essential to dilute semen in an ionic extender (300 mOsmol kg−1) with or without antibiotics. Methanol (6–10 %) and dimethyl sulfoxide (10 %) can be used as cryoprotectant for sperm cryopreservation.