Effect of cold temperature pre-treatments on the European eel spermatogenesis and spermiation

Resumen del trabajo presentado en el XIII Congress of the Iberian Association of Comparative Endocrinology, celebrado en modalidad virtual del 16 al 17 de septiembre de 2021.The European eel (A. anguilla) is a valued species targeted for aquaculture production. However, it is considered a critically endangered species and its reproduction in captivity seems to be the only alternative to solve both economic and ecological problems. Although it is possible to obtain eel gametes for artificial fertilization, it requires longterm hormonal treatments. Recent studies found that cold seawater stimulates the brainpituitary-gonad axis in eel males, inducing the start of spermatogenesis. These results suggested that cold seawater could be used as a pre-treatment before the standard hormonal therapy applied to induce sexual maturation, to obtain higher sperm quantity and quality. Thus, our study evaluates the effects of cold seawater pre-treatments of different duration (1, 2 and 4-weeks) on reproductive performance of eel males. Biometric parameters from control and pre-treated fish were measured. Blood and testis samples were collected for steroid (T, 11-KT and E2) and histology analyses, respectively. Once eels were spermiating, sperm parameters were evaluated using a CASA system. Eel males pre-treated with cold temperature showed increased biometric indexes, androgens and E2 plasma levels. Males maintained at 10 ºC for 4-weeks showed a significantly higher percentage of differentiated type A spermatogonia in comparison to undifferentiated ones. However, the low sperm quality found in the pre-treated groups revealed that pretreatments followed by recombinant human chorionic gonadotropin (rechCG) treatment at high temperatures impairs spermatogenesis. Cold temperature pre-treated males had a time-dependent and fast response to rechCG treatment, but their spermiation period was shorter and sperm parameters were significantly lower. Further research is needed to study the effect of thermic pre-treatments on gene regulation controlling spermatogenesis.Funded by the Spanish MICIU (Project EELGONIA; RTI2018-096413-B-I00). LF and MM have contracts funded by Generalitat Valenciana (GRISOLIAP/2020/063 and APOSTD/2020/053). VG had a grant from the MICIU (IJCI2017-34200)