The results of fertilisation rate of MGC sperm in HBSS extender are shown in Table 4. This
result suggests that the higher the sperm volume of MGC is, the greater the fertilisation yield is
achievable. From Table 4, an extended sperm volume of at least 2 ml is needed to achieve a
satisfactory fertilisation. The decrease in sperm quality and consequent reduction in fertilisability of
cryopreserved sperm was also observed in Cyprinus carpio [12] and Misgurnus anguillicaudatus [13].
However, Ding et al. [14] showed that the fertilisation rate and hatching rate of Mandarin fish
(Siniperca chuatsi) by sperm cryopreserved for 1 week or even 1 year in liquid nitrogen were similar
to those obtained when fresh sperm was used. Thus, this cryopreservation technique should be further
improved to get a better fertilisation rate for MGC sperm.
For hybrid artificial breeding in different extenders, the best fertilisation rate (89.7%) of MGC
sperm with P. hypophthalmus eggs was observed with 2 ml of the control (fresh sperm) in HBSS. This
was followed by the 2-week-cryopreserved sperm in HBSS at 2 ml (36.2%), while at 0.5 ml volume no
fertilisation was observed (Figure 5). An unsatisfactory rate was obtained at 1.0 ml while at 2-ml
volume, fertilisation rate was highest among all treatments including fresh sperm. In a similar study
involving interspecific fertilisation, a fertilisation rate of 26-45% from MGC sperm and P.
hypophthalmus oocytes was obtained [3]. The fertilisation rate of 30.9% by one-year-old cryopreserved MGC sperm and fresh P.
hypophthalmus eggs proved to be satisfactory (Table 5). This finding confirms all previous
experiments involving the suitability of HBSS extender for MGC sperm cryopreservation.
Theoretically, extended sperm can be kept for many years and according to the findings of this study,
cryopreserving for a period of one year can be considered suitable for achieving a reasonable rate of
fertilisation. The availability of cryopreserved MGC sperm can now be increased since the viability of
preserved sperm can be maintained for a considerably long period. More consideration should be given
to the mass application of the cryopreservation process for endangered species. However, cryopreservation
technique still needs to be improved in a further study to increase the fertilisation rate.
Moreover, the proper ratio of cryopreserved sperms and eggs will also be evaluated in the further
study.