Cryopreservation of sperm of an indigenous endangered fish species Nandus nandus (Hamilton, 1822) for ex-situ conservation

Use of Cryopreserved Sperm of Grass Carp (Ctenopharyngodon idella) for Seed Production at the Hatchery Level of Bangladesh-A Need for Development of Germplasm Repositories

Grass carp (Ctenopharyngodon idella), a freshwater nonnative fish species, is a potential aquaculture candidate in Bangladesh. The seed of the species is produced in the hatcheries by hypophysation, but the quality of seedstock of grass carp is deteriorated due to inbreeding, negative selection, and interspecific introgression among fishes. To increase the availability of quality seed and best genetic traits of grass carp, this study dealt with finding suitable conditions of sperm cryopreservation protocols and evaluated the effectiveness of cryopreserved sperm through breeding trials of C. idella. A broodstock population was developed from fingerlings imported from China by the Bangladesh Department of Fisheries. Sperm was collected from hormone-induced mature males, with an estimated concentration of 2.4 ± 0.3 × 1010 cells/mL and a pH of 8.3 ± 0.2. Sperm motility was evaluated in different concentrations of NaCl solution. The highest motility (96% ± 1%) and longest motility duration (22 ± 1 min) were achieved at 0.4% of NaCl (128 mOsmol/kg). The toxicity of DMSO and methanol at concentrations of 5%, 10%, and 15% was evaluated for 5-40 min using Alsever's solution and egg yolk citrate. The highest motility was achieved during 5 and 10 min of incubation with cryoprotectants at 5% and 10%. Alsever's solution with 10% DMSO at 1:9 dilution with sperm produced the highest equilibration motility (93% ± 2%) and when cooled at 10°C/min yielded the highest postthaw motility (85% ± 3%). Fertilization of 24% ± 3% to 51% ± 2% and hatching of 18% ± 2% to 41% ± 2% were achieved by using cryopreserved sperm in six selected private hatcheries. The fertilization rate for fresh sperm sourced from hatchery-reared males was 64% ± 5% to 85% ± 3%, and the hatching rate ranged from 53% ± 6% to 74% ± 5%. Thus, the cryopreservation protocol of C. idella sperm was found to be feasible for fry production at commercial hatcheries, but further research is needed to improve the fertilization and hatching rates.

Evaluate effects of the dilution medium and holding time on various motility parameters of delta smelt semen

Sperm preservation is an efficient technique used for the recovery, conservation, and management of some endangered fish species. The present study was conducted to explore how preservation time would affect sperm and spawning performance in the endangered delta smelt (Hypomesus transpacificus). Sperm were preserved with the modified Hanks balanced salt solution at 14.7-16.9 °C. The Kruskal-Wallis test of sperm parameters using OpenCASA plugin in ImageJ software showed that sperm (n = 33♂) had significantly higher velocity and motility within the first 5 s after activation than that of other time points, while sperm had the lowest velocity and motility after 3 min post activation (P < 0.001). The findings (n = 30♂) also showed fresh sperm had higher velocity and motility than preserved sperm, while the sperm preserved for over 24 h showed a significantly low performance (P < 0.001). The nonlinear mixed effects models of fertilization results (n = 14♂ × 70♀) indicated the fresh sperm and sperm preserved for 1 h had higher fertilization rates than other preservation times (P < 0.001). The hatching rate (n = 14♂ × 70♀) also showed the fresh sperm and sperm preserved for 3 min and 1 h had higher hatching rates than other preservation times (P < 0.001). Overall, the study showed the best sperm performance in delta smelt was found within the first 5 s post activation, and the best fertilization and hatching rates were found when the sperm were fresh and preserved for 1 h. The findings of this study provide information for the first time about how long the delta smelt's sperm are motile for quality analysis, and how the preservation time can affect sperm quality, fertility, and hatching of this species for future applications.

Development of a Sperm Cryopreservation Protocol for Critically Endangered Mohashol, Tor tor (Hamilton)

This study dealt with the development of a sperm cryopreservation protocol of Tor tor. Sperm was collected from hormone-induced males and the concentration and pH of sperm were estimated as 4.3 ± 0.1 × 10¹⁰ cells/mL and 8.6 ± 0.2, respectively. Activation of sperm motility was evaluated in different osmolalities of NaCl solution where motility of sperm decreased with increasing osmolality of extenders, and was completely inhibited at 319 mOsmol/kg. Similarly, the swimming duration of activated sperm was affected as the osmolality of the extender increased. The duration of initial motility of sperm was recorded as 8.4 ± 0.4 minutes at 48 mOsmol/kg, while the highest motility was recorded as 68.0 ± 7.2 minutes at 128 mOsmol/kg. To evaluate the toxicity of cryoprotectants, sperm was incubated with dimethyl sulfoxide (DMSO) and methanol at 5%, 10%, and 15% concentrations, respectively, for 5-45 minutes. Alsever's solution with 5% and 10% DMSO produced better motility during 5-10 minutes of incubation and 15% DMSO seemed toxic to sperm. For the cryopreservation of sperm, Alsever's solution, egg yolk citrate, and urea egg yolk were used as extenders with DMSO and methanol. Alsever's solution with 10% DMSO provided the highest equilibration (90.0% ± 3.5%) and post-thaw (80.0% ± 3.5%) motility followed by that of 87.0% ± 2.0% and 79.0% ± 1.9% with egg yolk citrate plus DMSO, and 82.0% ± 2.6% and 78.0% ± 2.0% with urea egg yolk plus DMSO, respectively. The sperm cryopreservation protocol developed through this study can be applied for long-term preservation of genetic materials of the critically endangered T. tor, and eventually, it will be an effective tool for protecting them from extinction.

Effect of melatonin supplementation to a cytoprotective medium on post-thawed Brycon orbignyanus sperm quality preserved during different freezing times

The aim of the present study is to verify the viability of frozen B. orbignyanus sperm cells after freezing with dilution media containing different concentrations of the melatonin and after different freezing times. Semen from 15 males was collected and pooled as five pools from three random animals. Oocytes (100) from three females were separately used for fertilization. There were three treatments: (C) Control Medium: 90% of extender Beltsville thawing solution (5% concentration) + 10% methylglycol (MG); (M1) Control Medium + 1 mM melatonin; and (M2) Control Medium + 2 mM melatonin. Sperm samples were diluted in media at a final proportion of 1:4 [125 μl sperm (25% V/V) + 337.5 μl BTS (65% V/V) + 37.5 μl MG (10% V/V)]. Melatonin was added at final solution. Three Dry shipper freezing times were used: T1 (15 min), T2 (12 h) and T3 (24 h). The samples were transferred, stored in a cryobank and thawed in a water bath at 60 °C for 5 s and evaluated concerning viability, morphology and fertilization rate. B. orbignyanus semen frozen in M2 presented the highest fertilization rate (8.40 ± 2.54%). The highest vitality (85.2 ± 2.8%), motility (64.63 ± 8.3%), motility duration (84.22 ± 11.4 s) and progressive motility (17.01 ± 1.2%) rates were maintained for M2. The highest number of altered cells was observed in C (57.4 ± 5.9%). Melatonin at 2 mmol L^-1 associated with the cryoprotectant methylglycol in cryopreservation could be used to improve a cryobank for endangered Brycon orbignyanus populations.

Studies of the cryopreservation condition of Gymnocypris przewalskii spermatozoa

The endemic naked carp (Gymnocypris przewalskii Kessler, 1876) plays an important role in the maintenance of the distinctive ecological system of Lake Qinghai at 3.2km altitude on the Qinghai-Tibet Plateau in China. This study aimed to develop a cryopreservation protocol for Gymnocypris przewalskii spermatozoa. Semen was collected from mature individuals during migration and frozen using the liquid nitrogen vapor method. The influence of different cryoprotectants and three extenders on the post-thaw quality of the sperm was analyzed. The highest sperm motility rate and longest motility time after cryopreservation were achieved by combining Ringer's solution with 15% ethylene glycol (P<0.05). The fertilization rate of this cryopreserved semen was 15.26±4.54%. This study thus provides a valuable method for the cryopreservation of the sperm of this important endangered fish species.

Development of sperm cryopreservation protocol of endangered spiny eel, Mastacembelus armatus (Lacepede 1800) for ex-situ conservation

The study was conducted to develop sperm cryopreservation protocol for the endangered spiny eel, Mastacembelus armatus as well as to use the cryopreserved sperm in breeding. Activation of sperm was evaluated by observing motility in different osmolalities of NaCl solution (48-319 mOsmol/kg) and found that sperm motility decreased with increasing osmolality of the NaCl solution and it was totally inhibited at 319 mOsmol/kg. The highest motility and swimming duration of sperm were observed as 14.5 ± 0.5 min and 4.75 ± 0.25 min at 128 mOsmol/kg and 67 mOsmol/kg, respectively. The concentration of sperm was found to be 1.75 × 10¹⁰ to 2.25 × 10¹⁰ cells/ml. Evaluation of toxicity of cryoprotectants of dimethyl sulfoxide (Me₂SO) and methanol to sperm was performed at 5, 10 and 15% concentrations during 5-30 min incubation period and found that cryoprotectants with 5 and 10% concentrations produced better motility up to 10 min incubation. In the selection of suitable diluent for cryopreservation of sperm, Alsever's solution with 10% Me₂SO performed best producing 91.67 ± 1.67% and 65 ± 2.89% equilibration and post-thaw motility, respectively. In breeding trials, sperm preserved with Alsever's solution plus Me₂SO produced more or less similar fertilization (82.25 ± 4.46%) and hatching (12 ± 0.65%) to those preserved with 0.9% NaCl solution plus Me₂SO as 79.88 ± 4.67% and 11 ± 0.46% fertilization and hatching respectively. Fresh sperm used as control produced 87.63 ± 3.6% and 14 ± 0.5% fertilization and hatching respectively. Both cryopreserved and fresh sperm-derived fry performed well but the control fry showed a significantly better (P < 0.05) growth. Fry derived from four diluents did not show any significant (P > 0.05) growth difference but Alsever's solution plus Me₂SO produced better results.