Non-programmable cryopreservation of sperm from industrial-farmed Murray cod (Maccullochella p peelii)

Abstract

The high price of larvae is a major constraint for the expansion of Murray cod (Maccullochella p peelii) aquaculture. Sperm cryopreservation creates a ready supply of sperm for the production of larvae, reduces the number of males required by hatcheries and contributes to preserving desirable genetic traits for breeding programmes. For hatchery application, there is a requirement for easy-to-implement cryopreservation protocols. Important factors for the development of a practical non-programmable sperm cryopreservation method for industrial-farmed Murray cod were evaluated. The results showed that Murray cod sperm can be successfully cryopreserved using dimethyl sulfoxide (Me2SO), propylene glycol (PG) and methanol (MeOH) as cryoprotectant additives (CPAs). In 0.5 mL straws, 10% PG proved to be the most effective CPA (post-thaw motility 75 ± 7%), followed by 10% MeOH (62 ± 7%). At the same time, in 2 mL cryovials, 10% PG was significantly more effective than 10% MeOH at three chosen heights (P<0.05). In 0.5 mL straws, cooling rates of 11–22 °C/min from 20 °C to −5 °C provided better results than cooling rates of 4–6 °C/min in 2 mL cryovials. Post-thaw motility was greater, regardless of CPA, without a 5.0 min equilibration period (Me2SO, from 8 to 34%; PG, from 25 to 75%; MeOH, from 19 to 62%). Toxicity tests indicated a marked loss of sperm motility following dilution with cryoprotectants; MeOH was less toxic than Me2SO and PG and the toxicity of either Me2SO or PG increased according to exposure duration. Therefore, the results suggest that on-site non-programmable sperm cryopreservation with 10% PG is effective and efficient for industrial-farmed Murray cod, yielding an acceptable percentage of post-thaw motile sperm. However, minimising equilibration time before cooling and maintaining cooling rates of ~11 °C/min between 20 °C and − 5 °C may be crucial for reducing CPA-associated toxicity. Further research is required in order to confirm that the recovered sperm motilities which are shown in this study translate into fertility during the process of in vitro fertilisation.