Sperm motility patterns as a tool for evaluating differences in sperm quality across gonad development stages in the sea urchin Paracentrotus lividus (Lmk, 1816)

Abstract Reproductive biotechnologies provide innovative support tools which are increasingly being applied to aquatic species. The development of tools for the assessment of changes in gamete quality as a function of gonad stage is a key issue in the establishment of species-specific protocols for gamete management and embryo production that guarantee the supply of high quality samples. The aim of the present study was to evaluate the sperm motility parameters, during the various phases of the gonad cycle, of Paracentrotus lividus specimens sampled from a population living along the mid-to-lower Adriatic coast of Italy. In this location, particularly favourable environmental conditions enable a prolonged reproductive period, and gonads containing mature gametes (whether developing or relict after spawning events) have been recorded nearly all year round. Specifically, each collected specimen was assigned a gonad stage following histological analysis and the sperm motility parameters, recorded by computerised analysis, were evaluated in relation to the assigned values. In addition, their fertilisation capacity was evaluated. Sperm motility was found to change during the gonad cycle: the highest motility percentages (> 90%) and sperm velocities (curvilinear velocity > 300 µm/s) were observed during the spawning stage. Conversely, no effect on the fertilisation capacity was observed (> 85%, regardless of the gonad stage). It can therefore be concluded that an objective assessment of sperm motility parameters, mainly velocity levels, is a helpful tool for evaluating the quality of P. lividus semen samples on collection, as it makes it possible to identify samples from mature and spawning individuals. Statement of relevance The development of reproductive biotechnologies in aquaculture depends on the continuous supply of viable gametes, and on the development of assessment tools able to discern among different gamete physiological conditions. Sperm velocity evaluations by computerised analysis proved to be able to discern samples coming from mature and in spawning sea urchins, those having the best physiological conditions and motility values.