Hormonal manipulations for the enhancement of sperm production in cultured fish and evaluation of sperm quality

Abstract

This article reviews the use of hormonal treatments to enhance sperm production in aquaculture fish and the methods available for evaluating sperm quality. The different types of testis development are examined and a brief review is presented of the endocrine regulation of spermatogenesis in fishes, including the increasing evidence of the existence of spermatozoa subpopulations. Hormonal manipulations are employed to induce spermatogenesis in species such as the freshwater eels, to synchronize maximal sperm volume to ovulation for in vitro fertilization and to enhance sperm production in species with poor spermiation. The hormones that are employed include gonadotropins (GtH) of piscine or mammalian origin, and gonadotropin-releasing hormone agonists (GnRHa) administered by injections or controlled-release delivery systems, with or without dopaminergic inhibitors. Pheromones in the culture water and hormones added to the sperm in vitro have also been employed to enhance spermiation and sperm quality, respectively, in some fishes. Hormonal therapies usually do not affect sperm quality parameters, except in cases where fish fail to spermiate naturally or produce very small volumes of high-density sperm. Different parameters have been used to evaluate fish sperm quality, including sperm volume and density, spermatozoa motility and morphometry, and seminal plasma composition. The development of Computer-Assisted Sperm Analysis (CASA) systems made possible the estimation of a higher number of sperm motion parameters using an objective, sensitive and accurate technique. The development of Assisted Sperm Morphology Analysis (ASMA) software has introduced a new approach for sperm evaluation studies, demonstrating changes in the spermatozoa related to reproductive season, hormonal treatments or the cryopreservation processes, and how these may be related to changes in sperm motility and fertilization capacity. The article concludes with a few practical protocols for the enhancement of sperm production in aquaculture species.

Time of response to hormonal treatment but not the type of a spawning agent affects the reproductive effectiveness in domesticated pikeperch, Sander lucioperca

“…Results of the present study suggest either that 'early responders' should be excluded from the broodstock, since fish responsiveness to hormones appears to be a potentially important selection trait -especially since the 'early responders' had lower body weight than the best performing group ('timely responders')or that only fish with the highest body weight should be selected for the broodstock. Considering the fact that selective breeding for fast growth may have deleterious effects on teleost reproductive capacity (Mylonas et al, 2016), special care should be taken when deciding on such a selection strategy. Nonetheless, it can be speculated that fish exhibiting lower growth rate are probably having problems in the production of highest-quality eggs.…”

Fish sperm motility assessment as a tool for aquaculture research: a historical approach

“…; Mylonas et al . ). In fact, high correlations have been reported between sperm motility and fertilization and hatching rates in some fish species ( reviewed by Gallego et al .…”

“…is not good enough for hatchery operations; and (ii) in some fish species in which it is impractical or even impossible to simulate the environmental factors of the breeding process (i.e., spawning migration, depth), so gonadal maturation does not occur in captivity (Mylonas et al . ). In both situations, hormonal stimulation could provide several advantages for the aquaculture industry, and breeding males can be induced to produce more sperm of higher quality for a longer period, avoiding hatchery problems such as the gamete synchronization or limitation.…”

“…Recently, studies have examined the production and use of recombinant (re) GtHs of piscine origin, which have been successfully produced for zebrafish, channel catfish ( Ictalurus punctatus ), goldfish, Japanese eel, European seabass, Senegalese sole, cinnamon clownfish ( Amphiprion melanopus ) and European eel (reviewed by Mylonas et al . ). However, although the in vitro effect of these hormones was relatively good in most of these species (stimulating both FSH and LH receptors, steroids production, etc.…”

Reproductive performance of asian catfish (Hemibagrus wyckii Bagridae), a candidate species for aquaculture

“…Motility duration (DMO) was determined as the period between movements of the sperm to cessation of any progressive movement expressed in seconds. Sperm concentration (SC) was measured under a microscope using Neaubeaur’s hemocytometer and calculated as the number of sperm mlˉ¹ 16 . Semen pH was determined with a hand pH meter (HI8424 Hanna Instruments, USA).…”