Optimization of the sperm:oocyte ratio and sperm economy in the artificial reproduction of Rhamdia quelen using fructose as a sperm motility modulator

Use of Powdered Milk in Semen Cryopreservation Protocols for Fish: A Systematic Review

This systematic review provides an overview of the history and current status of cryopreservation of fish sperm and a detailed evaluation of cryoprotocols using powdered milk. A literature search was performed in PubMed, Scopus, Web of Science, and SciELO databases. Twenty-nine articles were selected after excluding duplicate articles or articles that did not meet the eligibility criteria. Rhamdia quelen and Danio rerio were the most studied species. Slow freezing method, dry-shipper, freezing rate of -35.6°C/min, thawing in water bath (35.93°C ± 10°C), and 0.25 and 0.5 mL plastic straws were the main approaches evaluated. Methanol was the most used permeable cryoprotectant in combination with powdered milk, yielding the best results at 10% concentration. Motility rate was the main analysis performed after cryopreservation in virtually all studies, being subjectively evaluated by most authors. Powdered milk at 15% promoted the best results in the analyzed studies. For motility rate, the gains with the addition of powdered milk were observed in the orders Perciformes (Oreochromis mossambicus), Siluriformes (Pangasius pangasius, Pseudoplatystoma corruscans, and Pseudoplatystoma mataense), and Cypriniformes (Tor soro and Barbonymus gonionotus). For fertilization, gains were observed in the order Siluriformes (P. mataense) and Cypriniformes (T. soro). Sperm viability gains were observed in the orders Siluriformes (P. pangasius), Characiformes (Piaractus brachypomus), and Cypriniformes (B. gonionotus). The scientific evidence we present in this study may contribute and serve as a starting point for new and more refined studies to be developed in the field.

L-carnitine solution used on Rhamdia quelen thawed sperm activation boosts sperm movement, maintains larval quality, and permits to optimize the sperm use

The activation of cryopreserved sperm with solutions containing L-carnitine can improve sperm quality after thawing, owing to its involvement in several metabolic pathways. Sperm movement and viability for fertilization, hatching, and larval normality were assessed in Rhamdia quelen thawed sperm activated with L-carnitine solutions. Sperm from 24 males were cryopreserved in 0.25 mL straws. After thawing, the sperm movement was assessed by CASA (Computer-Assisted Sperm Analysis) in samples activated with distilled water containing 0.0 (control), 47.8, 96.2, 144.5, 192.3, and 240.7 mM L-carnitine, and another one with 79.9 mM D-fructose (control). Sperms from another 24 males were cryopreserved in an identical manner and used in the fertilization assays. Considering the sperm movement, fertilization assays were carried out using 0.0, 96.2, and 144.5 mM L-carnitine, and 79.9 mM D-fructose solutions. Greater motility and velocity were achieved with 144.5 mM L-carnitine at 28 and 18 s after activation, respectively. Linearity was not affected by time. The greater mean motility was provided by 144.5 mM as well as the greater mean velocity and linearity by 192.3 mM L-carnitine. Fertilization and hatching were not influenced; however, 144.5 mM L-carnitine and 79.9 mM D-fructose solutions produced more normal larvae. In summary, the L-carnitine solution increased sperm movement and maintained larval quality and production, similar to a conventional fructose activation solution.

Post-thaw dilution of Rhamdia quelen sperm improves the reproductive success

The aim was to evaluate the effect of a post-thaw dilution of Rhamdia quelen sperm in 1.1% NaCl (325 mOsm kg^-1; pH 7.6; 24 °C) solution on the quality and reproductive capacity. Sperm from eight males were cryopreservation in nitrogen vapor at - 170 °C for 18 h in 0.25 mL straws in a freezing medium containing 5% fructose, 5% Powdered milk, and 10% methanol. The samples were thawed and post-thaw diluted (1:20) in NaCl solution or not (control). The higher spermatozoa velocities were observed in the post-thaw diluted samples (curvilinear (VCL) - 69 ± 11 µm s^-1; average path (VAP) - 45 ± 8 µm s^-1; straight-line (VSL) - 43 ± 8 µm s^-1) compared to the control (VCL - 47 ± 10 µm s^-1; VAP - 31 ± 6 µm s^-1; VSL - 30 ± 6 µm s^-1). Greater straightness (STR), progression (PROG), and beat cross frequency (BCF) were observed in the post-thaw diluted samples (STR - 96 ± 7%; PROG - 666 ± 128 µm; BCF - 42 ± 2 Hz) than in control (STR - 95 ± 5%; PROG - 463 ± 92 µm; BCF - 40 ± 2 Hz). The strongly curled tail was the only morphology change that differ between the post-thaw diluted (5 ± 2%) and control (2 ± 1%). Membrane integrity, mitochondrial activity, and normal larvae rate were not different between treatments. Fertilization and hatching were higher in the post-thaw diluted sperm (93 ± 3%; 82 ± 9%) when compared to control samples (65 ± 13%; 55 ± 17%). Were used oocytes from one female, limiting these results. The post-thaw dilution improved the sperm kinetics and reproductive parameters. Thus, this methodology can be included in the sperm cryopreservation protocol for R. quelen.

Oxidative Stress and DNA Damage of Zebrafish Sperm at Different Stages of the Cryopreservation Process

Although gamete cryopreservation has facilitated advancement of reproduction research by allowing the storage of cells over prolonged periods of time, during freezing-thawing cycles, cells inevitably suffer from cryoinjuries. Here, we evaluate oxidative stress and DNA damage of zebrafish sperm at different stages of the cryopreservation process. It was generally observed that the freezing and thawing of the samples led to an increase in the generation of reactive oxygen species and the activity of the catalase enzyme and a reduction in the generation of sulfhydryl groups and superoxide dismutase activity. The alkaline comet assay demonstrated that DNA damage increased after equilibration time, with an even greater increase after freezing and thawing. The comet assay modified with the enzyme formamidopyrimidine glycosylase, and Endonuclease III demonstrated greater DNA damage than the standard comet assay, demonstrating a high degree of oxidation of purines and pyrimidines at all stages of cryopreservation. Our results show that the freeze and thaw processes cause greater oxidative stress and DNA damage than cryoprotectant toxicity during exposure at the equilibrium stage.

Determination of the ideal volume of activating solution and the optimal ratio of spermatozoa per oocyte for Prochilodus brevis fertilization

Prochilodus brevis is a rheophilic species with a threatened natural population that promotes studies aimed at optimizing reproduction in captivity. The correct quantity of inseminating dose and activating solution volume significantly improves fertilization rates, thereby increasing productivity in captivity. The objective of this study was to determine the proportion of sperm per oocyte and the ideal volume of activating solution to be used in the assisted fertilization of P. brevis. Gametes were collected and fertilization performed in two steps. In step 1, the ideal proportion of spermatozoa was determined based on the fertilization rate:oocyte by testing six doses of semen: D1 = 30 × 103, D2 = 150 × 103, D3 = 300 × 103, D4 = 3 × 106, D5 = 5 × 106, and D6 = 10 × 106. In step 2, the fertilization and hatching rates were evaluated using different volumes of activating solution (V1 - 25 ml, V2 - 50 ml, V3 - 75 ml,V4 - 100 ml, V5 - 125 ml, and V6 - 150 ml). A linear regression equation was estimated from steps 1 and 2. The Student-Newman-Keuls test was used to compare the means. In step 1, the percentage of fertilization increased linearly, reaching a plateau of 51.69%. In step 2, the best fertilization rates were obtained with an estimated ideal volume of 75.64 ml per 2 ml of oocytes. Therefore, the proportion of 928,410.29 sperm:oocyte, associated with the volume of 75.64 ml of water per 2 ml of oocytes, provided the maximum reproductive performance for P. brevis.

Effects on fertility of motile sperm to egg ratio with use of cryopreserved Rhamdia quelen semen at different post-activation times

The aim in the present study was to evaluate the effects of motile sperm:oocyte ratio and the use of thawed spermatozoa at different post-activation times in artificial reproduction of gray catfish (Rhamdia quelen). Cryopreserved sperm samples were evaluated for sperm motility and velocity using Computer Assisted Sperm Analysis (CASA). The sperm activation curves were generated using a non-linear statistical model and were used to assess the spermatozoa velocity after thawing. Thus, the oocytes were mixed with thawed sperm at a motile sperm:oocyte ratio of 70,000, 90,000, 110,000, 130,000, 150,000 and 170,000. The thawed sperm were used at 11, 16 and 30 s after spermatozoa activation. At these times, the sperm velocities corresponded to 52, 37 and 21 μm/s. The effects of experimental factors (spermatozoa:oocyte ratio and time after sperm activation) on oocyte fertilization, egg hatching, and percentage of normal larvae were evaluated. The response surface analysis indicated there was no interaction (P >  0.05) between the motile spermatozoa:oocyte ratio and time after sperm activation on fertilization, hatching or percentage of normal larvae. The time after sperm activation, however, affected (P <  0.05) in a directly proportional waythe oocyte fertilization and egg hatching rates. The time after sperm activation affected the sperm velocity and oocyte fertilization and egg hatching rates. Thus, the use of thawed sperm immediately after sperm activation or with the greatest sperm velocities (11s; 52 μm/s; 62.59% motility) at a relatively lesser motile sperm:oocyte ratio (70,000:1) allows for acceptable fertilization (48.68% for fertilization; 29.61% for hatching) in Rhamdia quelen.

Exposure of male tilapia (Oreochromis niloticus) to copper by intraperitoneal injection: DNA damage and larval impairment

The present work aimed to assess the genotoxic effects of intraperitoneally injected copper in males of O. niloticus, and to investigate its association with eventual changes in the quality of the gametes and in the generation of offspring abnormalities. Thus, to evaluate DNA damage, the alkaline comet assay was performed in sperm and blood; sperm parameters were analyzed to determine the quality of the gametes, and the incidence of morphological abnormalities of larvae, originated from eggs fertilized by males exposed to copper, was used as a measure of reproductive impairment. Male fish were exposed to three doses (1 mg/kg, 2 mg/kg, 4 mg/kg) of copper sulfate via intraperitoneal injection and observed after 96 h of exposure. We found that the quality of gametes was not affected by copper, as indicated by the lack of differences in sperm parameters between the exposed and the control groups. Nonetheless, copper induced an increase in sperm DNA damage at all tested doses. Taking into consideration the total number of abnormalities, larvae presented a higher proportion of morphological abnormalities at all the tested doses. Considering the morphological abnormalities separately, the 2 mg/kg and 4 mg/kg groups presented significantly higher frequencies of arrested development and spinal abnormalities than the control group. This work suggests that intraperitoneally injected copper is an inductor of DNA breakage in germ cells of O. niloticus males. Copper induces the formation of larval morphological abnormalities, causing reproductive impairment to this species. The fact that copper did not induce alterations on sperm parameters indicates that the parental genotoxic effects are inheritable to the offspring.