第286回 三崎談話会

第286回　三崎談話会

日時：２０１８年６月７日（木）１６時００分〜

場所：東京大学大学院理学系研究科・附属臨海実験所・セミナー室

講演者：Juan F. Asturiano, Luz Pérez, Víctor Gallego Albiach (Polytechnic University of Valencia)

懇親会： 18時30分〜　宿泊棟食堂にて

Juan F. Asturiano (Institute for Animal Science and Technology, Universitat Politècnica de València)

"Advances on the reproduction of European eel: where we are?"

First attempt to reproduce the European eel under captivity was carried out in 1964 in Paris. From then, several European research groups have tried to obtain viable eggs, but larvae were obtained only from a few groups from Belarus, Denmark, Italy, Spain and Hungary. The EU Project PRO-EEL (2010-14) established the protocols for the induction of massive spawnings and high production of larvae. Moreover, first experiments on larval feeding were carried out. However, the diet composition and rearing techniques must be improved as the maximum survival reached only 26 days after hatching. Obviously, research on this field has got some results, but has proved difficult due to the complex reproductive physiology of the eels. The required hormonal treatments are long and expensive, the use of wild animals (females) means to face pathologies and parasites, potential accumulated pollutants, as well as not optimal body composition (in especial PUFAs profile) which could limit the gametogenesis and the gamete quality. Improvements are crucial on the use of environmental factors, innovative hormonal treatments, broodstocks management, specific diets, gamete evaluation and handling, breeding and hatchery methods, and specific culture techniques for a self-sustained eel aquaculture. Moreover, the development of biotechnology techniques, such as production of recombinant hormones, spermatogonia and sperm cryopreservation and germ cell xenotransplantation could become complementary tools.

Luz Pérez (Institute for Animal Science and Technology, Universitat Politècnica de València)

"Ionic environment affects sperm motility in European eel sperm"

In general, fish spermatozoa are immotile in the testis. Movement is activated due to the osmotic shock (hypo- or hyperosmotic, depending on fish origin: freshwater or sea water species) experienced when they are released into the external medium. However, in marine fish, it is not clear how this process is happening and what ion exchanges are involved in. In the last years we have studied the importance of the environmental ions (Ca2+, K+, Na+, H+) on the activation of European eel sperm. For this purpose, the role of these ions was examined by removing each specific ion from the seminal plasma and the activation media, and studying sperm motility (by CASA systems) and intracellular changes in those conditions, by Flow Cytometry. When either Na+ or K+ were removed from the seminal plasma, sperm motility was strongly reduced, but that fact was not observed after removal of Ca2+. Regarding activation media, the absence of Na+, K+ or Ca2+ did not reduced sperm motility. In contrast, low seawater pH inhibited sperm motility. It was demonstrated that seawater activation induced a decrease in in sperm head area, what means a decrease in sperm volume upon activation. Such decrease was also observed after Na+ or K+ seminal plasma removal, thus it was shown that the presence of K+ and Na+ in the seminal plasma is important for the preservation of sperm motility in the European eel, at least in part by maintaining the right sperm cell volume in the quiescent stage. Intracellular calcium, sodium, pH and potassium were quantified in the sperm using Flow Cytometry. In quiescent conditions there is a gradient of both pH (pHi < pHe) and K+ ([K+]I > [K+]e) between the sperm cell and the environment, but Na+ is in equilibrium. In standard conditions, increases in intracellular Ca2+, Na+, K+ were observed, but its relation with motility was not clear. Regarding the ion Ca2+, our results strongly suggest that an increase in intracellular [Ca2+] ([Ca2+]i) is not a pre-requisite for the initiation of sperm motility in European eel sperm. Results are discussed and some hypothesis about eel sperm activation process are presented.

Víctor Gallego Albiach (Institute for Animal Science and Technology, Universitat Politècnica de València)

"Fish sperm motility as a tool for aquaculture research (with special emphasis on the European eel)"

Fish sperm motility is nowadays considered the best biomarker for the quality of fish spermatozoa, and sperm motion parameters from more than 300 fish species have been reported in more than 1500 scientific articles covering a wide range of topics, from molecular biology to ecology. The most studied topics have been (i) the sperm storage (involving both the use of chilled‐storage protocols for short‐term periods and sperm cryopreservation techniques for long‐term storage), (ii) the sperm physiology (fathom in the spermatozoa activation process and the whole propulsion machinery of the sperm cells) and (iii) the broodstock management (covering aspects such as rearing conditions, dietary requirements or hormonal induction treatments). In addition, other aquaculture and ecological topics, such as (iv) the knowledge of the breeding cycle of the species, (v) the phenomenon of the sperm competition and (vi) ecotoxicological studies for the evaluation of aquatic environments, have also been approached from the evaluation of sperm motion performance. Therefore, fish sperm motility assessment can serve as a potential tool for aquaculture and ecological purposes, covering key topics of fundamental and applied research. This review gives an overview of the major research areas in which fish sperm motility has been applied successfully, with special emphasis on the European eel.