We thank David Martasian, Diedre Heyser, Amy Parkhurst, Craig Foote, and Mandy Ng for valuable contributions to the Jeffery laboratory A. mexicanus culture facility. The research in the Jeffery laboratory is currently supported by NIH grant EY024941.

This procedure has been approved by Institutional Animal Care guidelines of the University of Maryland, College Park (Currently IACUC 469 #R-NOV-18-59; Project 1241065-1).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61708/61708fig1.jpg" /> 
Figure 1. Calendars during a breeding week and a non-breeding week. <a href="https://www.jove.com/files/ftp_upload/61708/61708fig1large.jpg" target="_blank">Please click here to view a la...

<ol>
	<li>Jeffery, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cavefish+as+a+model+system+in+evolutionary+developmental+biology.">Cavefish as a model system in evolutionary developmental biology.</a> Developmental Biology. 231, 1-12 (2001).</li><li>Jeffery, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Emerging+model+systems+in+evo-devo:+cavefish+and+mechanisms+of+microevolution.">Emerging model systems in evo-devo: cavefish and mechanisms of microevolution.</a> Evolution &amp; Development. 10, 265-272 (2008).</li><li>Jeffery, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evolution+and+development+in+the+cavefish+Astyanax.">Evolution and development in the cavefish Astyanax.</a> Current Topics in Developmental Biology. 86, 191-221 (2009).</li><li>Protas, M. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetic+analysis+of+cavefish+reveals+molecular+convergence+in+the+evolution+of+albinism.">Genetic analysis of cavefish reveals molecular convergence in the evolution of albinism.</a> Nature Genetics. 38, 107-111 (2006).</li><li>Protas, M., Conrad, M., Gross, J. B., Tabin, C. J., Borowsky, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regressive+evolution+in+the+Mexican+cave+tetra,+Astyanax+mexicanus.">Regressive evolution in the Mexican cave tetra, Astyanax mexicanus.</a> Current Biology. 17, 452-454 (2007).</li><li>O'Quin, K. E., Yoshizawa, M., Doshi, P., Jeffery, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+genetic+analysis+of+retinal+degeneration+in+the+blind+cavefish.">Quantitative genetic analysis of retinal degeneration in the blind cavefish.</a> PLoS ONE. 8 (2), 57281 (2013).</li><li>Yoshizawa, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Distinct+genetic+architecture+underlies+the+emergence+of+sleep+loss+and+prey-seeking+behavior+in+the+Mexican+cavefish.">Distinct genetic architecture underlies the emergence of sleep loss and prey-seeking behavior in the Mexican cavefish.</a> BMC Biology. 13, 15 (2015).</li><li>Elliot, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Astyanax+caves+of+Mexico.+Cavefishes+of+Tamaulipas,+San+Luis+Potosi,+and+Guerrero.">The Astyanax caves of Mexico. Cavefishes of Tamaulipas, San Luis Potosi, and Guerrero.</a> Association for Mexican Cave Studies Bulletin. 26, 1 (2018).</li><li>Luo, S., Wu, B., Xiong, X., Wang, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+total+hardness+and+calcium:magnesium+ratio+of+water+during+early+stages+of+rare+minnows+(Gobiocypris+rarus).">Effects of total hardness and calcium:magnesium ratio of water during early stages of rare minnows (Gobiocypris rarus).</a> Comparative Medicine. 66, 181-187 (2016).</li><li>Balasch, J. C., Tort, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Netting+the+stress+responses+in+fish.">Netting the stress responses in fish.</a> Frontiers in Endocrinology. 10, 62 (2019).</li><li>Borowsky, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Determining the sex of adult Astyanax mexicanus. , (2008).</li><li>Paschos, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Circadian+clocks,+feeding+time,+and+metabolic+homeostasis.">Circadian clocks, feeding time, and metabolic homeostasis.</a> Frontiers in Pharmacology. 6, 112 (2015).</li><li>Scheiermann, C., Kunisaki, Y., Frenette, P. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Circadian+control+of+the+immune+system.">Circadian control of the immune system.</a> Nature Reviews Immunology. 13, 190-198 (2013).</li><li>Williams, M. B., Watts, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Current+basis+and+future+directions+of+zebrafish+nutrigenomics.">Current basis and future directions of zebrafish nutrigenomics.</a> Genes &amp; Nutrition. 14, 34 (2009).</li><li>Harper, C., Wolf, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Morphologic+effects+of+the+stress+response+in+fish.">Morphologic effects of the stress response in fish.</a> ILAR Journal. 50, 387-396 (2009).</li><li>Neubauer, P., Andersen, K. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermal+performance+in+fish+is+explained+by+an+interplay+between+physiology,+behavior+and+ecology.">Thermal performance in fish is explained by an interplay between physiology, behavior and ecology.</a> Conservation Physiology. 7 (1), 025 (2019).</li><li>Hinaux, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Developmental+staging+table+for+Astyanax+mexicanus.">Developmental staging table for Astyanax mexicanus.</a> Zebrafish. 8 (4), (2011).</li><li>Borowsky, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> In vitro fertilization of Astyanax mexicanus. , (2008).</li><li>Simon, V., Hyacinthe, C., R&#233;taux, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Breeding+behavior+in+the+blind+Mexican+cavefish+and+its+river-dwelling+conspecific.">Breeding behavior in the blind Mexican cavefish and its river-dwelling conspecific.</a> PLoS One. 14 (2), 0212591 (2019).</li><li>Harvey, B. J., Carolsfield, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Induced+Breeding+in+Tropical+Fish+Culture.">Induced Breeding in Tropical Fish Culture.</a> International Development Research Centre. , (1993).</li><li>Ma, L., Parkhurst, A., Jeffery, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+a+lens+survival+pathway+including+sox2+and+aA-crystallin+in+the+evolution+of+cavefish+eye+degeneration.">The role of a lens survival pathway including sox2 and aA-crystallin in the evolution of cavefish eye degeneration.</a> EvoDevo. 5, 28 (2014).</li><li>Krishnan, J., Rohner, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cavefish+and+the+basis+for+eye+loss.">Cavefish and the basis for eye loss.</a> Philosophical Transactions of the Royal Society B: Biological Sciences. 5 (372), 20150487 (2017).</li><li>Biland&#382;ija, H., Abraham, L., Ma, L., Renner, K., Jeffery, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Behavioral+changes+controlled+by+catecholaminergic+systems+explain+recurrent+loss+of+pigmentation+in+cavefish.">Behavioral changes controlled by catecholaminergic systems explain recurrent loss of pigmentation in cavefish.</a> Proceedings of the Royal Society. 285, (2018).</li><li>Ma, L., Jeffery, W. R., Essner, J. J., Kowalko, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genome+editing+using+TALENs+in+blind+Mexican+cavefish.">Genome editing using TALENs in blind Mexican cavefish.</a> PLoS ONE. 1093, 0119370 (2015).</li><li>Klaassen, H., Wang, Y., Adamski, K., Rohner, N., Kowalko, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CRISPR+mutagenesis+confirms+the+role+of+oca2+in+melanin+pigmentation+in+Astyanax+mexicanus.">CRISPR mutagenesis confirms the role of oca2 in melanin pigmentation in Astyanax mexicanus.</a> Developmental Biology. 441, 313-318 (2018).</li></ol>

Astyanax mexicanus is a novel biological model that spawns frequently and can be bred easily in the laboratory1,2. Because we are interested in the developmental mechanisms that underlie evolutionary changes in A. mexicanus cave fish, the production and use of embryos is vital to our research goals. The primary purpose of maintaining an adult stock of fish is the production of embryos and young fry for use in developmental experiments and for re...

The teleost Astyanax mexicanus has an eyed surface-dwelling (surface fish) form and many different blind cave-dwelling (cave fish) forms1,2. Cave fish have evolved in perpetual darkness and under food limitations, resulting in the appearance of novel constructive and regressive traits3. The constructive traits include increases in taste buds and jaw size, sensory organs of the lateral line, and fat reserves. The regressive traits include the loss or reduction of melanin pigmentation, eyes, and behaviors, such as sleep, schooling, and aggression. An attribute of the Astyanax system is complete fertility between the two forms, allowing the use of quantitative trait loci (QTL) mapping to determine the genomic region(s) associated with constructive and regressive evolution4,5,6,7. A. mexicanus offers an advantageous system to study development because it can be induced to spawn frequently in the laboratory. The embryos of A. mexicanus are translucent, slightly larger than those of zebrafish, produced in large quantities, and develop into sexually mature adults in approximately 8-12 months. Their period of maximal spawning capacity is about 5 years. This protocol describes the workflow needed in an A. mexicanus culture facility during a typical breeding week and includes the details of fish system maintenance and the temperature control regime for maximal spawning.
A. mexicanus is a tropical fish that lives in rivers originating in limestone plateaus (surface fish) and in pools in limestone caves (cave fish)8. Limestone dissolves to produce hard water, and A. mexicanus thrives in hard water. Fish adapted to hard water conditions can tolerate a range of salty conditions, but generally breed in specific ones9. Induction of spawning behavior is accomplished by a combination of factors. Because fish are cold-blooded and rely on their environment to maintain homeostasis, their metabolism is sensitive to environmental changes and they react more quickly to stressors10. A. mexicanus should be cultured in aquatic systems under carefully regulated conditions of water flow, pH, conductivity, osmotic pressure, lighting, and water temperatures.
In the Jeffery laboratory, fish are maintained in two running water systems: (1) a &#8220;baby system&#8221; for young adult fish prior to sexual maturity and (2) an adult (or main) system for sexually mature, breeding adults. The &#8220;baby system&#8221; consists of 8 L and 15 L tanks supplied with running water. The &#8220;baby system&#8221; is seeded by fry and young metamorphosized juveniles grown from larvae in smaller (1-10 L) tanks, in which water is exchanged weekly. Larvae, fry, and juveniles are extremely food dependent and must be fed live food (brine shrimp) once a day to ensure a high rate of survival. Young juveniles from the &#8220;baby system&#8221; are placed into the adult system after about 1-1.5 years. At first, they are fed pulverized tetra flakes, and after further growth they are transferred to the regular adult feeding regime. Sexual maturity can be assessed by abdominal volume in females, and methods for determining sex have been described11. In the adult system, water is exchanged automatically in 42 L tanks 3 times per 24-hour period. The adult system is monitored daily by visual inspection and automatic temperature, pH, and conductivity readings from probes. The optimal pH is around 7.4 and can range between 6.8-7.5, the base temperature of the system is 72/73 &#176;F, and the ideal conductivity ranges between 600-800 mS. Automatic readings are displayed on a controller screen, and visual checks of water pressure are read at flow meters distributed throughout the system. Independent checks on water quality are made weekly by testing temperature and measuring water quality parameters for pH, ammonia, and nitrate using a colorimetric test. Ammonia and nitrate levels are kept at or close to zero by adding beneficial bacteria (e.g., Nutafin Cycle) to the system. Room lighting is controlled by a timer adjusted to 14-hour light and 10-hour dark periods. In addition to the overall water quality parameters mentioned above, the following considerations need special attention during a breeding week.
The first consideration is photoperiod, as fish (even cave fish in the laboratory) depend on light cycles to set their circadian clock. Circadian rhythms can affect everything from breeding and feeding to immune system health12,13 and must be consistent for maximum health benefits. Fish are maintained in a running-water system on a 14-hour light and 10-hour dark photoperiod. The surface fish generally begin spawning an hour after the system has been darkened, and light introduced during this period can interfere with and terminate spawning. The spawning of blind cave fish is less disturbed by light. Compared to surface fish spawning, cave fish spawning is delayed, usually beginning four to five hours after the system has been darkened.
The second consideration is nutrition. Adult fish are normally fed a diet of tetra flakes once a day. Prior to spawning, fish are fed a protein-rich diet supplemented with extra amounts of tetra flakes and other food: egg yolk flakes and occasionally living California blackworms (Lumbriculus variegatus) to compensate for protein loss due to egg production during the previous spawning cycle. During the breeding week, fish are fed twice per day, once in the morning and again in the afternoon/evening. Fish feeding only once a day but with a single very large portion of food should be avoided, as this can cause malnutrition14.
The third consideration is space. The space requirements are based on the average body mass of an adult as well as behavioral considerations, such as whether the fish have schooling behavior or aggressive behavior. Over or under-crowding tanks can lead to heightened aggression and constant stress, making fish vulnerable to injury from their tank mates and reluctant to participate in spawning15. We typically house 10-20 fish per 42 L tank.
The fourth consideration is temperature. As mentioned above, fish are cold-blooded animals and rely on the environment to maintain body temperature. Because temperature has a direct effect on metabolic processes, changes in temperature can trigger behavioral alterations in fish16. This breeding program consists of two-week cycles in temperature: the first week introduces a temperature spike to 78 &#176;F, and the next week maintains a static temperature of 72 &#176;F. During the first (breeding) week, plastic-edged breeding nets are placed at the bottom of the tanks each evening. The breeding nets serve as a barrier between the fish in the tanks and the spawned eggs, which would otherwise be consumed. The temperature is raised by 2 &#176;F per day to a maximum of 78 &#176;F by mid-week, and spawning is induced according to the light cycle in the first 2-3 evenings of this week. The temperature is then lowered by 2 &#176;F increments to 72 &#176;F during the remaining days of the week, and base temperature is maintained until the beginning of the next breeding week. Breeding is usually stimulated no more than twice a month to allow the fish time to recover.
Overall, this method allows for the spawning of large&#160;quantities of the highest quality embryos over a longer period of time.

<table border="0" cellpadding="0" cellspacing="0" style="width:874px;" width="875">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Blackworms</td>
			<td style="width:299px;">Eastern Aquatics, Lancaster, PA</td>
			<td style="width:161px;">None</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Breeding Nets</td>
			<td style="width:299px;">Custom made</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Brine shrimp eggs</td>
			<td style="width:299px;">AquaCave Lake Forest, IL.</td>
			<td style="width:161px;">None</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Colorimetric test kit</td>
			<td style="width:299px;">Petco</td>
			<td style="width:161px;">SKU:11916</td>
			<td>API Freshwater pH Test Kit</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Egg yolk flakes</td>
			<td style="width:299px;">Pentair, Minneapolis, MN</td>
			<td style="width:161px;">None</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Fingerbowls</td>
			<td style="width:299px;">Carolina Biological Supply</td>
			<td align="right" style="width:161px;">741004</td>
			<td>Culture dishes, 4.5 in, 250 mL</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Hand held nets</td>
			<td style="width:299px;">Any Pet Store</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Incubator for embryos</td>
			<td style="width:299px;">Fisher Scientific</td>
			<td style="width:161px;">51-029-321HPM</td>
			<td>405 L</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Instant Ocean sea salts</td>
			<td style="width:299px;">Spectrum Brands, Blacksburg, VA</td>
			<td style="width:161px;">None</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Methylene Blue</td>
			<td style="width:299px;">Sigma-Aldrich, St. Louis, MO</td>
			<td style="width:161px;">M9140</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Pasteur Pipettes</td>
			<td style="width:299px;">Fisher Scientific</td>
			<td style="width:161px;">13-678-20</td>
			<td>5.75 in.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Net soaking solution</td>
			<td style="width:299px;">Any Pet Store</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Nutrafin Cycle</td>
			<td style="width:299px;">Amazon</td>
			<td style="width:161px;">None</td>
			<td>Bacterial boost</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Refrigerator for live feed</td>
			<td style="width:299px;">Any source</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Stereomicroscope</td>
			<td style="width:299px;">Any source</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Thermometer</td>
			<td style="width:299px;">Any source</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Tetra Tropical Crisps</td>
			<td style="width:299px;">Spectrum Brands, Blacksburg, VA</td>
			<td style="width:161px;">None</td>
			<td></td>
		</tr>
	</tbody>
</table>

incremental temperature changes for maximal breeding and spawning in astyanax mexicanus

The Mexican tetra, Astyanax mexicanus, is an emerging model system for studies in development and evolution. The existence of eyed surface (surface fish) and blind cave (cave fish) morphs in this species presents an opportunity to interrogate the mechanisms underlying morphological and behavioral evolution. Cave fish have evolved novel constructive and regressive traits. The constructive changes include increases in taste buds and jaws, lateral line sensory organs, and body fat. The regressive changes include loss or reduction of eyes. melanin pigmentation, schooling behavior, aggression, and sleep. To experimentally interrogate these changes, it is crucial to obtain large numbers of spawned embryos. Since the original A. mexicanus surface fish and cave fish were collected in Texas and Mexico in the 1990s, their descendants have been routinely stimulated to breed and spawn large numbers of embryos bimonthly in the Jeffery laboratory. Although breeding is controlled by food abundance and quality, light-dark cycles, and temperature, we have found that incremental temperature changes play a key role in stimulating maximal spawning. The gradual increase of temperature from 72 &#176;F to 78 &#176;F in the first three days of a breeding week provides two-three consecutive spawning days with maximal numbers of high-quality embryos, which is then followed by a gradual decrease of temperature from 78 &#176;F to 72 &#176;F during the last three days of the spawning week. The procedures shown in this video outline the workflow before and during a laboratory breeding week for incremental temperature stimulated spawning.

We generally breed and spawn the descendants of surface fish originally collected at Nacimiento del Rio Choy in San Luis Potosi, Mexico (Rio Choy surface fish) and San Solomon Springs in Balmorhea State Park, Texas (Texas surface fish) and cave fish derived from Cueva de El Pach&#243;n (Pach&#243;n cave fish) in Tamaulipas, Mexico, and Cueva de los Sabinos (Los Sabinos cave fish) and Sotano de la Tinaja (Tinaja cave fish) in San Luis Potosi, Mexico. &#160;
Throughout a breeding week, data is c...

Watch this Scientific Journal Video about Incremental Temperature Changes for Maximal Breeding and Spawning in Astyanax mexicanus at JoVE.com

Incremental Temperature Changes for Maximal Breeding and Spawning in Astyanax mexicanus

This article outlines the basic laboratory conditions and protocols for an incremental temperature regime to stimulate maximal spawning in the Mexican tetra Astyanax mexicanus, which is an emerging model for developmental and evolutionary studies.

Incremental Temperature Changes for Maximal Breeding and Spawning in Astyanax mexicanus

The Mexican tetra, Astyanax mexicanus, is an emerging model system for studies in development and evolution. The existence of eyed surface (surface fish) ...

So as the Astyanax mexicanas is a small fish. It is indigenous to Northeastern Mexico and Southern Texas. The important thing about it is it exists in two forms.One form is a surface dwelling fish that has large eyes and pigmentation, and the other form is a cave-dwelling fish that has lost its eyes and lost its pigmentation. They're still capable of spawning, of hybridizing with each other, so they can be used in a forward genetic analysis to study genetics and development. Also have large embryos that are transparent, and they can be used to study comparative developmental biology.So they've been used for many years now as a system to understand the evolution of development. Several days before the spawning is desired, we begin to feed the fish better. We also increase the temperature incrementally such that within the time we want them to spawn, they will then undergo about two or three days of excessive spawning, producing large numbers of fertilized embryos that develop well and through the larval stages to adults.After feeding the fish at 10:00 a.m. with a pinch of Tetra flakes, check the incubator that will be used to house finger bowls of developing embryos and change the water if necessary. Check the water level in all of the reservoirs and add system water to any reservoirs that are running low.Then set the incubator to 23 degrees Celsius At least 30 minutes after the first feeding, feed the fish in the breeding tanks with a pinch of egg yolk flakes, enough black worm clusters to allow each fish in the tank to consume about five to 10 worms or both. At least one hour after the second feeding, scrub the breeding tanks as necessary and carefully set up breeding nets without interfering with the tank air supply. The next morning, remove the breeding nets from the bottoms of the adult system tanks between 9:00 and 10:00 a.m.and use the hose attached to the to gently rinse the embryos into a handheld net. Invert the net into a finger bowl of clean system water and transfer about 100 embryos per finger bowl into 200 milliliters of clean system water supplemented with 0.00003%methylene blue. Stage the embryos under a light microscope to estimate the time of fertilization according to the A-mexicanas developmental timetable.After staging, place the finger bowls into an incubator for five to seven days and feed the cultures with living brine shrimp. For every tank that dropped embryos, record the date and tank number and record the number and quality of embryos dropped. Record the average time of spawn according to staging table and record the temperature of the system at the time when the fish spawned.Monitor the finger bowls of embryos throughout the day, using a pasture pipette to remove any dead or deformed embryos and debris, such as uneaten food or feces, and changing the blue water as necessary. At 1:00 p.m. feed the fish in the breeding tanks as demonstrated and set the water temperature to 24 degrees Celsius.Then remove any excess food and debris from the tanks and scrub the tanks before resetting the nets. On Wednesday and Thursday, repeat the embryo collection and evaluation as demonstrated for Tuesday. Feed the fish and set the water to the appropriate temperature.Check the embryos in the incubator and replace the finger bowl water with fresh methylene blue treated system water. Then clean the breeding tanks as needed and reset the nets. On Friday, after feeding the fish, set the water temperature to 23 degrees Celsius and check the embryos in the incubator.On Saturday and Sunday, feed the fish. In this figure, the breeding data from July 2017 through March 2020 for the Rio Choy and Texas Surface Fish and the Los Sabinos, Tinaha, and Pachon cavefish are shown. The data were analyzed by breeding week and the average number of embryos collected per day during a single breeding week.The data indicates that breeding was continuous throughout the year in Rio Choy and Texas Surface fish and in Pachon cavefish. The quantity and quality of most Rio Choy surface fish was between low and high, while the quantity and quality of most Texas surface fish and Pachon cavefish was between low and medium. The occurrence of spawning was not continuous in Tinaja or Los Sabinos cave fish, with spawning being low or non-existent during the late summer to autumn in these fish.Although the lowest levels of spawning were recorded for Los Sabinos cave fish, the quality of embryos was the best. Overall, this surface fish exhibited a better spawning quantity and quality than cavefish. Using this system, we can spawn hundreds, actually thousands of eggs bi-monthly, and these eggs are then used, these embryos are then used for many different purposes.

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JoVE Journal

Developmental Biology

3.9K visualizações.  University of Maryland. Assim como o Astyanax mexicanas é um peixe pequeno. É nativa do nordeste do México e sul do Texas. O importante é que ele existe de duas formas.Uma forma é um peixe que habita a superfície que tem olhos grandes e pigmentação, e a outra forma é um peixe que habita cavernas que perdeu os olhos e perdeu sua pigmentação. Eles ainda são capazes de desovar, de hibridizar uns com os outros, para que possam ser usados em uma análise genética avançada para estudar genética e des...