Effects of Cryoprotectants and Diluents on the Cryopreservation of Spermatozoa from Far Eastern Catfish, Silurus asotus

A brief review of the methodology and cryoprotectants in selected fish and mammalian species

Cryopreservation is a valuable technique used to assist in the genetic improvement of cultured stocks and provide a continuous supply of good-quality semen for artificial insemination. Conserving semen by cryopreservation serves several purposes (e.g. artificial reproductive technologies and species conservation) and is also used in the clinical treatment of human infertility. However, the lifespan of cryopreserved semen is influenced by a range of factors, including storage temperature, cooling rate, chemical composition of the extender, the concentration of cryoprotectant, reactive oxygen species, seminal plasma composition and hygienic control. The choice of cryoprotectant is a vital factor underlying the success of animal semen cryopreservation. In this regard, extensive research has been carried out on various cryoprotectants, such as egg yolk, dimethyl sulfoxide, methanol, ethylene glycol and dimethylacetamide. Recent studies have also described the use of a range of new cryoprotectants for cryopreservation, including compounds of plant origin (soy), amino acids, antifreeze proteins, carbohydrates and cyclodextrins. Moreover, semen cryopreservation and storage require the use of liquid nitrogen or ultralow refrigeration methods for both long- and short-term storage. This review summarizes the general methods used for freezing semen and discusses the use of traditional and newly emerging cryoprotectants (permeable and non-permeable) for the cryopreservation of semen in selected fish and mammalian species.

Effect of cryopreservation on post-thaw motility and viability of Grey mullet, Mugil cephalus sperm (Linnaeus, 1758)

In this study, we optimized a simple method of cryopreservation for Mugil cephalus sperm based on post-thaw motility and viability. A series of experiments were conducted by changing the extender, cryoprotectant and freezing height above the liquid nitrogen (LN) surface. First, we carried out the cryopreservation using the extender V2E and cryoprotective agents (CPAs) namely, propylene glycol (PG), methanol (MeOH), glycerol (GLY), ethylene glycol (EG), dimethylsulfoxide (Me2SO) and dimethylacetamide (DMA) at a final concentration of 5% and 10%. We found that 10% of GLY, EG and Me2SO were more suitable compared to other CPAs. Then, different freezing heights (6, 8, 10 and 12 cm) above the LN surface were experimented with extender V2E and optimized CPAs. Then, 0.3 M of glucose, sucrose and trehalose were tested as extender along with optimized CPAs and freezing height. Additionally, the effect of fast-rate freezing and storage days (7, 30 and 180) on post-thaw sperm quality was documented using the factors optimized in earlier experiments. For all experiments, the fresh sperm was diluted at a ratio of 1:1 with cryomedium (CPA + extender), loaded into cryovials (2.0 mL) and frozen. The cryopreserved sperm was thawed at 30 °C for 90-120 s and their quality was evaluated. Among the experimented factors, sperm diluted in cryomedium (0.3 M glucose + 10% EG) and frozen at 4 cm above the LN surface registered significantly (P < 0.05) highest post-thaw motility (73 ± 2%) and (71 ± 1%) viability. Fast-rate freezing has resulted in lower (about 30%) post-thaw motility and viability of sperm. The storage days (7, 30 and 180) did not have a significant effect on post-thaw sperm quality. Overall results show that using the factors optimized through this study, high-quality sperm can be obtained after cryopreservation.

Effect of egg yolk of free-range chicken and methanol as a cryoprotective agent for the sperm preservation of cyprinid fish, Neolissochilus soroides (Valenciennes, 1842)

The objective of this study was to determine the optimum concentration of egg yolk of free-range chicken as a cryoprotective agent on cyprinid fish, Neolissochilus soroides sperm after 48 h frozen. One level of methanol (10%) combined with six levels of egg yolk solution (0%, 5%, 10%, 15%, 20% and 25%) were tested. Fish Ringer's solution was used as an extender. The diluted sperm was equilibrated for 10 min at 5 °C, then kept at -10 °C temperature for 48 h. Sperm was thawed for 1 min at 40 °C. Spermatozoa viability, abnormality, and fertilization rates were analysed afterwards. The one-way ANOVA showed that the combination methanol with several concentrations of egg yolk solution had a significant effect on spermatozoa viability, abnormality, and fertilization rates (P < 0.05) by improving semen character. The study revealed that the 5% egg yolk solution combined with 10% methanol resulted in the highest rates of viability (82.13 ± 1.75%) and fertility rates (92.96 ± 1.94%), with the lowest abnormality (25.25 ± 2.22%). A 5% egg yolk solution was identified as the best cryoprotective agent for N. soroides spermatozoa preservation at -10 °C for 48 h.

The Anesthetic Effects of Clove Oil and MS-222 on Far Eastern Catfish, Silurus asotus

The objective of this study is to evaluate the anesthetic effects of clove oil and tricaine methanesulfonate (MS-222) on the Far Eastern catfish, Silurus asotus, by measuring the times to anesthesia and recovery. Each anesthetic effect of clove oil and MS-222 was tested in two groups of fish with different body sizes: a group of small fish (mean body length: 15.5±1.58 cm, mean body weight: 50.1±5.91 g, n=20) and a group of large fish (mean body length: 31.5±4.19 cm, mean body weight: 302.1±15.22 g, n=20). The anesthetics were used at concentrations of 200, 300, 400, 500, and 600 ppm. The results showed significant relationships between the concentration of the anesthetic and the body size of the fish. Each of these variables showed statistical significance (p<0.05). The time to anesthesia decreased linearly with increasing concentration in the large fish for both clove oil and MS-222 (p<0.05). Based on an optimal anesthetic time of approximately 1 min, the preferred concentrations of the anesthetics were 500 ppm for clove oil and 600 ppm for MS-222. Both the anesthetic time and the recovery time were shorter for the small fish than for the large fish (p<0.05). Our study showed that the smaller-sized Far Eastern catfish was more easily anesthetized and recovered more rapidly from anesthesia than the larger-sized fish.