This work has been funded by the Norwegian University of Life Sciences and the U.S. Fulbright program. The authors would like to thank Anthony Peltier and Lourdes Carreon G Tan at NMBU for fish facility maintenance and Guillaume Gourmelin from the ISC LPGP at INRAE (France) for providing fish and lab space to further test these methods.

All experimentation and animal handling were conducted in accordance with the recommendations on the experimental animal welfare at Norwegian University of Life Sciences (NMBU). The experiments were performed using adult (6-9-month-old) male Japanese medaka (Hd-rR strain) raised at NMBU (&#197;s, Norway). The methods were also briefly tested in 9-month-old male Japanese medaka (CAB strain) raised at the National Research Institute for Agriculture, Food, and the Environment (INRAE, Rennes, France).
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The authors have nothing to disclose.

Osmolality is an important factor in the activation of fish sperm36,37. Generally, sperm are immotile in the testes and become motile in media that is hyperosmotic relative to seminal fluid for marine fishes, and hypo-osmotic relative to seminal fluid for freshwater fishes37. Similar to blood, seminal plasma in freshwater fishes is typically lower than that of marine fishes (about 300 mOsmol/kg compared to 400 mOsmol/kg)2...

Japanese medaka is a small, egg-laying freshwater teleost fish native to East Asia. Medaka has become an excellent vertebrate model system for ecotoxicology, developmental genetics, genomics, and evolutionary biology and physiology studies1,2. Similar to the popular zebrafish, they are relatively easy to breed and highly resistant to many common fish diseases1,2. There are several advantages of using medaka as a model, including a short generation time, transparent embryos1,2, and a sequenced genome3. Unlike zebrafish, medaka has a sex-determining gene4&#160;as well as a high temperature (from 4-40 &#176;C)&#160;and salinity (euryhaline species) tolerance5. Also, many genetic and anatomical tools, as well as protocols6,7,8,9,10,11,12, have been developed in medaka to facilitate the study of its biology.
Reproduction is an essential physiological function as it allows a species to perpetuate. Vertebrate reproduction requires a myriad of precisely orchestrated events, including the production of oocytes in females and the production of sperm in males. Sperm are unique cells, produced through the complex process of spermatogenesis, in which there are a number of checkpoints in place to guarantee delivery of a high-quality product13. Gamete quality has become a focus in aquaculture and fish population studies due to its impact on fertilization success and larval survival. Sperm quality is, therefore, an important indicator of male fertility in vertebrates.
Three useful factors for assessing fish sperm quality are motility, progressivity, and longevity. Percent motility and progressive motility are common indicators of sperm quality as progressive motion is necessary for and correlates strongly with fertilization success14,15. Duration of movement is also an important indicator in fish as sperm remain fully motile for less than 2 min in most teleost species and the trajectory of sperm is generally less linear than in mammals15. However, many studies assessing sperm motility in the past relied on subjective or semi-quantitative methods of analyzing sperm15,16. For instance, sperm motility in medaka has been estimated in the past visually under a microscope17. It has also been estimated by recording sperm movement and using imaging software to merge frames and measure swimming path and velocity18,19,20. Such approaches often lack robustness, providing different results according to the person performing the analysis15,21.
Computer-assisted sperm analysis (CASA) was initially developed for mammals. CASA is a fast quantitative method to assess sperm quality by recording and measuring velocity and trajectory in an automated manner15. In fishes, it has been used in different species to monitor the effects of several water pollutants on sperm quality, for identifying interesting progenitors to improve broodstock, to improve the efficiency of cryopreservation and storage, and to optimize conditions for fertilization15. Therefore, it is a powerful tool for reliably assessing sperm quality in different vertebrate species. However, due to the important diversity in reproductive strategies between fishes, the sperm of teleost fish differs from that of mammals and from one fish species to another. Teleost fish, which primarily fertilize eggs externally by releasing gametes into water, have highly concentrated sperm that are relatively simple in structure with no acrosome, unlike mammals, which fertilize internally and therefore do not have to compensate for dilution in water, but do have to withstand more viscous fluids14. Additionally, sperm from most fish move rapidly but are fully motile for less than 2 min after activation, although there are several exceptions15,22. Because motility can decrease rapidly in most fish, extreme care should be taken with the timing of analysis after activation when determining a sperm analysis protocol for fish.
Reproduction is one of the fields in biology in which teleosts and medaka have been extensively used as model organisms. Indeed, medaka males show interesting reproductive and social behaviors, such as mate guarding23,24. In addition, several transgenic lines exist to study the neuroendocrine control of reproduction in this species25,26,27. Sperm sampling, a procedure that is relatively simple in larger fish, can be more complicated in small model fish as they produce less sperm and are more delicate. For this reason, most studies involving sperm sampling in medaka extract milt (fish semen) by crushing dissected testes17,28,29,30. A few studies also use a modified abdominal massage to express the milt directly into activating medium18,19,20; however, with this method it is difficult to visualize the amount and color of milt extracted. In zebrafish, abdominal massage is commonly used to express milt, which is immediately collected in a capillary tube31,32,33. This method enables estimation of the volume of milt, as well as observation of ejaculate color, which is a quick and simple indicator of sperm quality32,33. Therefore, a clear and well described protocol for sperm collection and analysis is lacking for medaka.
This article therefore describes two methods of sperm collection in the small model fish Japanese medaka: testes dissection and abdominal massage with capillary tubes. It demonstrates that both approaches are feasible for medaka and shows that abdominal massage can be performed a repeated number of times as the fish quickly recovers from the procedure. It also describes a protocol for computer-assisted sperm analysis in medaka to reliably measure several important indicators of medaka sperm quality (motility, progressivity, longevity, and relative sperm concentration). These procedures, specified for this useful small teleost model, will greatly enhance understanding of the environmental, physiological, and genetic factors influencing fertility in vertebrate males.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1.5 mL tubes</td>
			<td>Axygen</td>
			<td>MCT-150-C</td>
			<td>Any standard brand can be used</td>
		</tr>
		<tr>
			<td>10 &#181;L disposable calibrated glass micropipette and aspirator tube assembly</td>
			<td>Drummond</td>
			<td>2-000-010</td>
			<td></td>
		</tr>
		<tr>
			<td>10x objective with phase contrast</td>
			<td>Nikon</td>
			<td>MRP90100</td>
			<td></td>
		</tr>
		<tr>
			<td>2 mL tubes</td>
			<td>Axygen</td>
			<td>MCT-200-c-s</td>
			<td>Any standard brand can be used</td>
		</tr>
		<tr>
			<td>Blunt forceps</td>
			<td>Fine Science Tools</td>
			<td>11000-12</td>
			<td></td>
		</tr>
		<tr>
			<td>Blunt smooth forceps</td>
			<td>Millipore</td>
			<td>XX6200006P</td>
			<td></td>
		</tr>
		<tr>
			<td>Disposable 20 micron counting chamber slide</td>
			<td>Microptic</td>
			<td>20.2.25&#160;</td>
			<td>Leja 2 chamber slides</td>
		</tr>
		<tr>
			<td>Dissecting microscope</td>
			<td>Olympus</td>
			<td>SZX7</td>
			<td>Any standard brand can be used</td>
		</tr>
		<tr>
			<td>Fine forceps</td>
			<td>Fine Science Tools</td>
			<td>11253-20</td>
			<td></td>
		</tr>
		<tr>
			<td>HBSS</td>
			<td>Sigmaaldrich</td>
			<td>H8264-1L</td>
			<td></td>
		</tr>
		<tr>
			<td>Holding sponge</td>
			<td>self-made</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Inverted microscope</td>
			<td>Nikon</td>
			<td>Eclipse Ts2R</td>
			<td></td>
		</tr>
		<tr>
			<td>SCA Evolution</td>
			<td>Microptic</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Small dissecting scissors</td>
			<td>Fine Science Tools</td>
			<td>14090-09</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Chloride (NaCl)</td>
			<td>Sigmaaldrich</td>
			<td>S9888</td>
			<td></td>
		</tr>
		<tr>
			<td>Tabletop vortex</td>
			<td>Labnet</td>
			<td>C1301B</td>
			<td></td>
		</tr>
		<tr>
			<td>Tricaine</td>
			<td>Sigmaaldrich</td>
			<td>A5040</td>
			<td></td>
		</tr>
	</tbody>
</table>

sperm collection and computer-assisted sperm analysis in the teleost model japanese medaka (oryzias latipes)

Japanese medaka (Oryzias latipes) is a teleost fish and&#160;an emerging vertebrate model for ecotoxicology, developmental, genetics, and physiology research. Medaka is also used extensively to investigate vertebrate reproduction, which is an essential biological function as it allows a species to perpetuate. Sperm quality is an important indicator of male fertility and, thus, reproduction success. Techniques for extracting sperm and sperm analysis are well documented for many species, including teleost fish. Collecting sperm is relatively simple in larger fish but can be more complicated in small model fish as they produce less sperm and are more delicate. This article, therefore, describes two methods of sperm collection in the small model fish, Japanese medaka: testes dissection and abdominal massage. This paper demonstrates that both approaches are feasible for medaka and shows that abdominal massage can be performed a repeated number of times as the fish quickly recover from the procedure. This article also describes a protocol for computer-assisted sperm analysis in medaka to objectively assess several important indicators of medaka sperm quality (motility, progressivity, duration of motility, relative concentration). These procedures, specified for this useful small teleost model, will greatly enhance understanding of the environmental, physiological, and genetic factors influencing fertility in vertebrate males.

Type of data obtained 
Sperm motility analysis from the SCA Evolution software provides data on motility (percentage of motile and immotile sperm), as well as progressivity (percentage of progressive and non-progressive sperm), and velocity (percentage of rapid, medium, and slow-moving sperm). It also combines progressivity and velocity (rapid progressive, medium progressive, non-progressive). These labels are based on measurements (Figure 3A) and calculations (<strong ...

Watch this Scientific Journal Video about Sperm Collection and Computer-Assisted Sperm Analysis in the Teleost Model Japanese Medaka Oryzias latipes at JoVE.com

Sperm Collection and Computer-Assisted Sperm Analysis in the Teleost Model Japanese Medaka Oryzias latipes

This article describes two quick and efficient methods for collecting sperm from the small model fish medaka (Oryzias latipes), as well as a protocol for reliably assessing sperm quality using computer-assisted sperm analysis (CASA).

Sperm Collection and Computer-Assisted Sperm Analysis in the Teleost Model Japanese Medaka (Oryzias latipes)

Japanese medaka (Oryzias latipes) is a teleost fish and&#160;an emerging vertebrate model for ecotoxicology, developmental, genetics, and physiology ...

This technique enables the sampling of milt from a small model fish, Japanese Madaka, and the investigation of its quality in a consistent manner. Specifically sperm collection by abdominal massage allows repeated sampling on the same fish as this approach is not invasive. Furthermore, this technique can be applied for Madaka sperm cryo preservation.Sperm quality is an essential indicator of fertilization success, and therefore an important parameter to analyze in ecological and whole productive physiology studies. To begin, prepare a soft holding sponge, by cutting it to fit smugly in a Petri dish. Cut a straight line in the middle of the sponge, that is long enough to hold the fish on its ventral side up.After anesthetizing the fish, dry the abdomen of the fish by gently wiping it with a paper towel. Place the fish in the trough of the damp holding sponge with the ventral side up, so its gills are exposed to the anesthetic solution in the sponge. If the area around the cloaca is wet, gently dry the underside of the abdomen with a disposable tissue wipe.Under a dissecting microscope, place the micro pipette with an attached aspirator tube against the cloaca of the fish. Now massage the abdomen of the fish by gently squeezing with a blunt end smooth forceps in a rostral to caudal motion. For recovery of the fish, release it from the sponge into the previously prepared recovery water before returning the fish to the aquarium system.Transfer the collected milt into a tube containing preheated activating solution and pipette solution up and down several times using the aspirator tube assembly. Homogenize the diluted sperm gently by flicking the tubes before analysis. After euthanizing the fish dry it as demonstrated previously and place the fish under a dissecting microscope with its left lateral side facing up.Using small dissecting scissors, cut a flap dorsally from the cloaca and then across the ribs to the gills to expose the internal organs. Locate the testes and cut the attachment at both ends with fine forceps. Remove the testes and transfer them to a prepared tube containing pre-heated activating solution.Use the forceps to crush the testes several times against the side of the tube to release the sperm, which can be visualized by the slightly cloudy appearance of the solution. To begin the analysis, open the sperm analysis software and select the motility module. Set the configurations in the software for all parameters.Place a pre-warmed disposable 20 micrometer counting chamber slide under the microscope on a heated stage, set to 27 degrees Celsius. Pipette the sample into the chamber on the slide until it fills, but without overfilling. Carefully wipe away excess samples from the entrance of the chamber to prevent drift movement of cells in the solution.Select analyze to look at the sample under the microscope. Ensure the microscope is focused and select analyze again to record the sperm in the field. Move the slide to a new area of the sample in the frame and repeat the procedure for three to five different fields of view, avoiding air bubbles, cell masses, or artifacts.To view the results, select results, and double click on a field to visualize the individual field or to manually check for any mislabeled or untracked spermatozoa. If necessary, right click on individual spermatozoa to relabel the motility. In the present study, computer assisted sperm analysis was used to record various velocity and movement parameters.The calculated values include the straightness index, linearity index, and wobble. The osmolarity of the activation solutions impacted the motility of the sperm from testees dissection. The sperm were immotile in aquarium water, but motile in HBSS with high and low osmolarity.However, motility is significantly reduced at 36 milli osmol per kilogram, compared to higher osmolality solutions. Motility was also affected by the sperm collection method, wherein the sperm are significantly more motile in the testis dissection method compared to abdominal massage. Also, a higher percentage of the cells were progressive and more cells were either medium or rapid moving.The percentage motility and progressivity are significantly higher in the sperm stored at four degrees Celsius or on ice, compared to 27 degrees Celsius storage. The environmental and housing conditions also slightly impacted sperm motility. No significant difference in sperm motility was seen in the sperm collected after and before spawning.Males housed without females for a month showed high motility, but the difference was insignificant. For sperm collection by abdominal massage, training is needed to learn the proper forceps pressure and movement and to avoid feced contamination. This technique will be very useful to investigate for instance, the effects of diverse pollutants on male fertility in ecotoxicologial studies, where Medaka is a commonly used model.

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Research

JoVE Journal

Biology

3.7K visualizações.  Norwegian University of Life Sciences. Esta técnica permite a amostragem de milt de um pequeno modelo de peixe, o japonês Madaka, e a investigação de sua qualidade de maneira consistente. Especificamente, a coleta de espermatozoides por massagem abdominal permite a amostragem repetida no mesmo peixe, pois essa abordagem não é invasiva. Além disso, esta técnica pode ser aplicada para a preservação do crio de esperma de Madaka.A qualidade dos espermatozoides é um indicador essencial do sucesso da fertilização e, ...