Effect of butylated hydroxytoluene (BHT) on the cryopreservation of common carp (Cyprinus carpio) spermatozoa

• BHT is an antioxidant widely used in the cryopreservation of animal spermatozoa.
• BHT has been used for spermatozoa of a fish species for the first time.
• BHT within the defined concentrations improved post-thaw spermatozoa characteristics.

The aim of the present study was to test the effects of butylated hydroxytoluene (BHT) on the cryopreservation of common carp spermatozoa. BHT is widely used in the cryopreservation of the spermatozoa of different animal species and successfully sustains the characteristics of spermatozoa during freezing and thawing, but it has not previously been used with fish. After sampling, common carp spermatozoa were diluted with an extender composed of modified Kurokura's extender, 10% DMSO, and 10% egg yolk containing 0.0001, 0.001, 0.01, 0.1, 1, 2.5, 5, or 10 mM BHT and subsequently frozen in liquid nitrogen. The post-thaw spermatozoa characteristics (i.e., progressive motility percentage (%), duration of progressive motility (s), fertilization rate (%), and eyed-eggs rate (%)) were evaluated and compared with those of the control group. There were significant increases in the percentage of progressive motility and the duration of progressive motility at the concentrations of 0.1 and 0.001 mM BHT (P < 0.05). The duration of post-thawed spermatozoa progressive motility at 0.001 mM BHT was significantly greater than that of the other groups (39.6 ± 0.4 s, P < 0.05), and the fertilization rates and eyed-eggs rates were also higher following the 0.1 and 1 mM BHT treatments. BHT at concentrations of more than 1 mM caused sperm immobility during the preparatory stages of the sperm freezing. We concluded that 0.001–0.1 mM BHT can be beneficial for the cryopreservation of common spermatozoa.