Sperm cryopreservation of Japanese eel, Anguilla japonica

Abstract

In the present study, methods for the cryopreservation of Anguilla japonica spermatozoa were examined. Spermatozoa were collected from artificially matured males and incubated in Japanese eel K30 artificial seminal plasma (K30 ASP) before experiments. Sperm motility was investigated using computer-assisted sperm analysis (CASA). 10% and 15% MeOH as cryoprotectant was the most successful cryoprotectant with percentage of the initial motility of 59.7±12.1%; the combination of 5% MeOH and 5% DMA was also viable. DMSO was unsuitable as a cryoprotectant with K30 ASP as it showed no cryopreservation properties and was toxic to sperm, causing sperm to be immotile immediately after dilution. Japanese eel spermatozoa had a narrow range of optimal cooling rates (6.3–28.6°Cmin−1) and immersion temperatures of −40 to −70°C were effective. The different fetal bovine serum (FBS) concentration in extender, temperature of milt before cooling, dilution rates (3–100 times) and equilibrium time showed no significant difference. The results indicate that the type of extender media greatly influenced the suitability of cryoprotectant. The establishment of a protocol to cryopreserved Japanese eel sperm will benefit the artificial seed production of Japanese eel and provide an important tool for genetic and breeding studies. Statement of relevanceThe development of the sperm cryopreservation protocol for Japanese eel will ensure a stable supply of high quality seed for experimental and commercial purposes.