Evaluation of fresh sperm quality indicates that depik sperm was condensed and had a white-milky color. The pH ranged from 7.4-8.0, spermatozoa density was 23.58 × 10
9 cells ml
-1, the initial motility and viability were 71.83% and 75.00%, respectively. Sperm abnormality was 11.00% (Table 1).
ANOVA test showed that FBS gave a significant effect on the sperm motility and fertility as well as egg hatching rate of the depik (P<0.05). The highest motility was found in 60% FBS (58.33% motility) and significantly different from those in other concentrations. The highest fertility and hatching rate were also recorded at 60% FBS, but the values were not significantly different with those at 50% FBS (69% vs 66.33% and 47% vs 45.67%, respectively) (Table 2).
The DNA electrophoresis results showed the presence of smears in both fresh and post-thawed sperm indicates the occurrence of DNA fragmentation. However, the application of 40% FBS showed thick and long smears, thereby, indicating a high degree of DNA fragmentation whereas the bright and short smears detected at 50% and 60% FBS applications showed low degree DNA fragmentation (Fig 1).
The results showed that the addition of FBS had a positive effect on the sperms motility and fertility and egg hatching rate of depik fish. This is presumably that FBS can protect sperm during freezing due to its protein, hemoglobin, glucose, insulin, cortisol, parathyroid hormone and prostaglandin E compositions
(Hayman et al., 1985; Chen et al., 1992; Garzon et al., 2008).
According to
Reyes-Morino et al., (2000), protein and glucose play an essential role in protecting sperms from excessive damage during cooling, freezing and thawing. The protecting effect of glucose presence in extender for better semen quality after freezing and thawing has been proved by better post-thawing and post-freezing motilty of Turkey sperms diluted in glucose 5% containing dimethyl sulphoxide over those diluted in other extenders (tris-glucose, lactated Ringer and lactated Ringer’s glucose) (
Kuzlu and Taskin, 2016).
In general, serum has multifunctional effects on sperms due to its high macromolecules and antioxidants contents
(Alcay et al., 2019). It can act as an extracellular cryoprotectant for frozen spermatozoa by protecting the plasma membrane from crystallization, recrystallization or ice melting during different phases of freezing and thawing processes (
Watson,1995). Besides, serum can induce capacitation (
Xia and Ren, 2009) and acrosomal reactions
(Hossain et al., 2007). This similar positive effect was reported by
Kusuda et al., (2005) in Sakhalin taimen fish and by
Yusoff et al., (2018) in groupers
. However, these authors used a higher concentration of FBS (90% and 85%, respectively). Meanwhile, 50-60% was found optimal for short preservation of depik sperms without suppressing the results.
The study showed that there was a correlation between sperms motility and sperm fertility and egg hatching rate of depik as fertility and hatching rates increase proportionally to sperm motility rate. Similar results were reported by
Ohta et al., (1995) in post-thawed sperm of masou salmon and turbot fish
(Dreanno et al., 1998), indicating motility is an important indicator of sperm quality. Contrarily,
Mutmainnah et al., (2018) reported no correlation between motility and fertility in cryopreserved sperms of seurukan fish when using glutathione as an antioxidant. The unclear relationship was also found in the sperms of brook and rainbow trout fish
(Lahnsteiner et al., 2011), African catfish
(Muchlisin et al., 2015) and muskellunge
(Ciereszko et al., 1999). According to
Ohta et al., (1995), several factors might reduce fertility including low post-thawing motility and egg stimulation. The ability of inactive sperms to fertilize egg is assumably related to hormones contained in it (
Gilkey, 1981). The teleosts egg produces pheromones for example to attract sperm (
Stehr and Hawkes, 1983). Gimnogamon hormone produced by egg can activate and draw spermatozoa
(Yanagimachi et al., 2017). In addition, glycoprotein contained in the herring egg can activate spermatozoa
(Griffin et al., 1996; Cherr et al., 2008).
The analysis of sperm DNA fragmentation after cryopreservation revealed the presence of smears in both fresh (column 2 in Fig 1) and preserved sperm (column 3, 4 and 5 in Fig 1 for 40%, 50% and 60% FBS, respectively). These results were in agreement with
Zilli et al., (2003) who found DNA damage in both fresh and frozen sperms of sea bass. The long smear of DNA bands after electophoresis show fragmentation whereas clear DNA bands without smears indicate purity or integrity
(Karp et al., 2012).
The results of this study showed the addition of concentrated FBS (line 3 and 4) could maintain DNA integrity of frozen depik sperms which is similar to that of fresh sperm (line 1). This might be responsible for the high fertilization and hatching rates of the sperm. The similar findings were reported by
Yusoff et al., (2018) when analyzing DNA of groupers sperm cryopreserved in a combination of polyethylene glycol 15% and FBS 85% that a slight DNA smear did not affect fertilization and hatching rates.