I.M.O. is supported by the NIAAA (F32AA027135). W.G. is supported by R01DK090311, R01DK105198, R24OD017870, and the Claudia Adams Barr Program for Excellence in Cancer Research. W.G. is a Pew Scholar in Biomedical Sciences.

Zebrafish were raised and bred according to standard procedures. Experiments were approved by the Brigham and Women&#39;s Hospital&#39;s Institutional Animal Care and Use Committee (2016N000405). Adult zebrafish were fasted for 24 h prior to the start of the protocol. System water refers to the water in zebrafish housing tanks in the aquatic facility.
1. Preparation and anesthetization
<ol>
	<li>Prepare 0.016% Tricaine solution in system water. 
	CAUTION: Tricaine is an irritant if it comes in contact with the eyes, skin, or respiratory tract.</li>
	<li>Prepare a sponge to hold anesthetized zebrafish during the dissection protocol. Cut a full sponge into quarters. Using a razor blade, remove a thin wedge of sponge that runs parallel to the long axis of the sponge quarter.
	<ol>
		<li>The slit should be long enough to accommodate an adult fish (this will vary between different sizes of fish). For example, for an adult fish 35 mm in length, the length of the slit should be 20 mm. The head and body are snugly held in the sponge, but the tail runs past the edge of the sponge (Figure 1B).</li>
	</ol>
	</li>
	<li>Soak the sponge in 0.016% Tricaine solution.</li>
	<li>Place adult zebrafish (either male or female) in 625 mL of 0.016% Tricaine solution.</li>
	<li>Incubate for 6 min or until the fish is unresponsive to touch.</li>
	<li>Using forceps, carefully remove the fish from the Tricaine tank and place the fish ventral side up in the groove of the sponge (Figure 1A - B).</li>
	<li>Place the sponge under a dissecting microscope with top-down illumination.</li>
</ol>
2. Surgery
<ol>
	<li>Using fine forceps, pinch the skin and scales medially, just posterior to the heart (Figure 1B).</li>
	<li>Using spring-loaded scissors, make a cut under the forceps to create a hole in the body cavity (Figure 1C - D). Take care not to injure the heart or a major blood vessel, as this will result in increased mortality.</li>
	<li>Using spring-loaded scissors, make a 3-4 mm incision along the abdomen, processing posteriorly until the incision arrives at the pelvic fins (Figure 1D - E). By this point, the ventral lobe of the liver may be visible through the incision.</li>
	<li>Squeeze the sides of the sponge with one hand to force the visceral organs out of the body cavity. The ventral lobe of the liver will be visible on top of the intestine (Figures 1F,2A-B). The liver will appear as a pink or orange structure spread out over the golden-brown intestine. Animals designated as sham controls are recovered at this point.</li>
	<li>Squeeze the fine forceps so that the two tines are touching. While keeping pressure on the sponge, slide the tines of the fine forceps in between the liver and the intestine (Figure 1G). Take care to not puncture the intestine, as this will result in increased mortality.</li>
	<li>Slowly relax the pressure on the forceps so that the tines move away from one another (Figure 1H). This sliding action severs the numerous portal vein attachments between the ventral lobe and the intestine (Figure 2B), and is necessary to cleanly remove the ventral lobe. Repeat this process until all of the portal connections between the liver and intestine have been severed.</li>
	<li>Peel back the ventral lobe from the intestine using fine forceps and cut the ventral lobe free from the rest of the liver (Figure 1I).</li>
	<li>This procedure results in a one-third partial hepatectomy (Figure 1J).</li>
</ol>
3. Recovery
<ol>
	<li>Carefully remove the fish from the sponge and place it in a tank of system water.</li>
	<li>Pipette system water over the gills for a few minutes until the fish is swimming on its own (Figure 1K).</li>
	<li>Monitor fish for 2-4 hours before placing them back onto the system. Do not feed the fish for a full 24 h after the surgery.</li>
	<li>Monitor fish daily for the duration of the experiment.</li>
	<li>With time, the incision in the body wall will heal naturally without the need for sutures (Figure&#160;1L,2C).</li>
</ol>
4. Ventral lobe to intestine length analysis
<ol>
	<li>Euthanize all animals destined for analysis in ice water for 10 min until all opercular movements cease.</li>
	<li>Remove the fish from ice water and place it ventral side up in the groove of a sponge.</li>
	<li>Using spring-loaded scissors, make an incision in the ventral body wall at the anterior-posterior position of the heart. Then make two more incisions that run along the anterior-posterior axis from the first incision all the way to the pelvic fins. (Figure 2A).</li>
	<li>Peel back the skin and muscle to reveal the visceral organs (Figure 2A).</li>
	<li>Acquire bright-field and fluorescent images of the visceral organs using an epifluorescence microscope. This field of view will include the area where the ventral lobe was resected. Because animals are euthanized prior to analysis, this kind of analysis precludes long-term imaging of the same fish.</li>
</ol>
5. Liver to body weight ratio analysis
<ol>
	<li>Euthanize all animals destined for analysis in ice water for 10 min until all opercular movements cease.</li>
	<li>Place fish in a 50 mL conical tube.</li>
	<li>Add 25 mL of 4% paraformaldehyde in 1x PBS and 0.3% Tween to the tube. 
	CAUTION: Formaldehyde is toxic, and solutions containing formaldehyde should always be processed in a chemical hood.</li>
	<li>Nutate for 48 h at 4 &#176;C.</li>
	<li>Perform four 10 min washes in 1x PBS and 0.3% Tween.</li>
	<li>Retrieve fish with forceps, and blot dry on a paper towel.</li>
	<li>Record the weight of the entire fish.</li>
	<li>Using spring-loaded scissors, make an incision in the ventral body wall at the anterior-posterior position of the heart. Then, make two more incisions that run along the anterior-posterior axis from the first incision all the way to the pelvic fins. (Figure 2A).</li>
	<li>Peel back the skin and muscle to reveal the visceral organs (Figure 2A).</li>
	<li>Acquire bright-field images of the liver using an epifluorescence microscope.</li>
	<li>Dissect out the liver, placing the pieces of liver on a weighing boat.</li>
	<li>Record the weight of the liver.</li>
</ol>

<ol>
	<li>Michalopoulos, G. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Principles+of+liver+regeneration+and+growth+homeostasis.">Principles of liver regeneration and growth homeostasis.</a> Comprehensive Physiology. 3, 485-513 (2013).</li><li>Wang, S., Miller, S. R., Ober, E. A., Sadler, K. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Making+it+new+again:+insight+into+liver+development,+regeneration,+and+disease+from+zebrafish+research.">Making it new again: insight into liver development, regeneration, and disease from zebrafish research.</a> Current Topics in Developmental Biology. 124, (2017).</li><li>Michalopoulos, G. K., Bhushan, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liver+regeneration:+biological+and+pathological+mechanisms+and+implications.">Liver regeneration: biological and pathological mechanisms and implications.</a> Nature Reviews Gastroenterology and Hepatology. , (2020).</li><li>Gemberling, M., Bailey, T. J., Hyde, D. R., Poss, K. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+zebrafish+as+a+model+for+complex+tissue+regeneration.">The zebrafish as a model for complex tissue regeneration.</a> Trends in Genetics. 29, 611-620 (2013).</li><li>Sadler, K. C., Krahn, K. N., Gaur, N. A., Ukomadu, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liver+growth+in+the+embryo+and+during+liver+regeneration+in+zebrafish+requires+the+cell+cycle+regulator+uhrf1.">Liver growth in the embryo and during liver regeneration in zebrafish requires the cell cycle regulator uhrf1.</a> Proceedings of the National Academy of Sciences of the United States of America. 104, 1570-1575 (2007).</li><li>Goessling, W., 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=APC+mutant+zebrafish+uncover+a+changing+temporal+requirement+for+wnt+signaling+in+liver+development.">APC mutant zebrafish uncover a changing temporal requirement for wnt signaling in liver development.</a> Developmental Biology. 320, 161-174 (2008).</li><li>Dovey, 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=Topoisomerase+II+is+required+for+embryonic+development+and+liver+regeneration+in+zebrafish.">Topoisomerase II is required for embryonic development and liver regeneration in zebrafish.</a> Molecular and Cellular Biology. 29, 3746-3753 (2009).</li><li>Kan, N. G., Junghans, D., Belmonte, J. C. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Compensatory+growth+mechanisms+regulated+by+BMP+and+FGF+signaling+mediate+liver+regeneration+in+zebrafish+after+partial+hepatectomy.">Compensatory growth mechanisms regulated by BMP and FGF signaling mediate liver regeneration in zebrafish after partial hepatectomy.</a> The FASEB Journal. 23, 3516-3525 (2009).</li><li>Zhu, Z., Chen, J., Xiong, J. W., Peng, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Haploinsufficiency+of+Def+activates+p53-dependent+TGF&#946;+signalling+and+causes+scar+formation+after+partial+hepatectomy.">Haploinsufficiency of Def activates p53-dependent TGF&#946; signalling and causes scar formation after partial hepatectomy.</a> PLoS One. 9, (2014).</li><li>Feng, G., Long, Y., Peng, J., Li, Q., Cui, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transcriptomic+characterization+of+the+dorsal+lobes+after+hepatectomy+of+the+ventral+lobe+in+zebrafish.">Transcriptomic characterization of the dorsal lobes after hepatectomy of the ventral lobe in zebrafish.</a> BMC Genomics. 16, 979 (2015).</li><li>Michalopoulos, G. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liver+regeneration.">Liver regeneration.</a> Journal of Cellular Physiology. 213, 286-300 (2007).</li><li>Grisham, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Organizational+principles+of+the+liver.">Organizational principles of the liver.</a> The Liver: Biology and Pathobiology: Fifth Edition. , 1-15 (2009).</li></ol>

The authors declare that they have no competing financial interests.

The anatomical differences between zebrafish and mammalian models for liver regeneration present unique challenges to liver resection. The liver in zebrafish is in close proximity to the heart and the intestine; inadvertently damaging either organ results in increased mortality. The zebrafish liver is not encapsulated, making it more difficult to separate from the intestine. The liver receives nutrient-rich blood from the intestine through portal veins. In mammals, veins leaving the intestine converge on a primary portal...

Among the solid organs in humans, the liver is the only organ capable of regeneration1. This is critical, as the liver is an essential organ, responsible for key metabolic functions, energy storage, blood detoxification, secretion of plasma proteins, and bile production2. Hepatocytes lost due to toxic or inflammatory damage are replaced primarily via division of the remaining hepatocytes1. One classical experimental model for studying liver regeneration is partial hepatectomy, where individual lobes of the liver are removed, leaving the remaining lobes intact3. This procedure was initially developed in rats, in which approximately two-thirds of the liver mass is removed. After partial hepatectomy in mammals, compensatory regeneration occurs in the remaining lobes until the liver recovers its initial mass. Notably, the mammalian liver does not replace the missing lobes.
Zebrafish (Danio rerio) represent a tractable model for studying adult organ regeneration4. The zebrafish liver, while structurally different from the mammalian liver, is made up of the same cell types and serves the same function as in mammals2. It is composed of three lobes, with two dorsal lobes and a single ventral lobe that are flattened along the intestine. Partial hepatectomy has previously been performed in zebrafish, with conflicting accounts as to the precise mode of regeneration. Typically, a one-third partial hepatectomy is performed by removal of the entire ventral lobe. Initial reports indicated that after removal of the ventral lobe, it was fully regenerated within a week5,6,7, suggesting that in contrast to the mammalian liver, the zebrafish liver is capable of epimorphic regeneration. Subsequent studies demonstrated that removal of the ventral lobe resulted in compensatory regeneration in the dorsal lobes, rather than the regeneration of the missing ventral lobe, and ultimately the recovery of liver mass within a week8,9. Transcriptomic profiling of the dorsal lobes following resection of the ventral lobe revealed significant changes associated with compensatory regeneration10. Given that the mode of liver regeneration can vary with the extent of the injury8, we speculated that the discrepancies in results may be due to technical variation in the partial hepatectomy protocol between research groups.
This protocol describes a procedure for performing a one-third partial hepatectomy on adult zebrafish by removing the ventral lobe. This technique will be valuable for assessing mechanisms of liver regeneration.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>16% Paraformaldehyde Aqueous Solution, EM Grade</td>
			<td>Electron Microscopy Sciences</td>
			<td>15700</td>
			<td></td>
		</tr>
		<tr>
			<td>50 mL Falcon Centrifuge Tubes, Polypropylene, Sterile</td>
			<td>Corning</td>
			<td>352098</td>
			<td></td>
		</tr>
		<tr>
			<td>AS 82/220.R2 PLUS Analytical Balance</td>
			<td>Bay State Scale &#38; Systems, INC.</td>
			<td>WL-104-1051</td>
			<td></td>
		</tr>
		<tr>
			<td>Dumont #55 Forceps</td>
			<td>Fine Science Tools</td>
			<td>11295-51</td>
			<td></td>
		</tr>
		<tr>
			<td>EMS Kuehne Coverglass/Specimen Forceps</td>
			<td>Electron Microscopy Sciences</td>
			<td>72997-07</td>
			<td></td>
		</tr>
		<tr>
			<td>Epifluorescence microscope</td>
			<td>Zeiss</td>
			<td>Discovery.V8</td>
			<td></td>
		</tr>
		<tr>
			<td>Mastertop Cellulose Cleaning Scrub Sponge</td>
			<td>Amazon</td>
			<td>B07CBSM53Z</td>
			<td></td>
		</tr>
		<tr>
			<td>PBS10X Liquid Conc 4L</td>
			<td>EMD Millipore</td>
			<td>6505-4L</td>
			<td></td>
		</tr>
		<tr>
			<td>Super Fine Micro Scissors, 3 1/4&#34; straight</td>
			<td>Biomedical Research Instruments</td>
			<td>11-1020</td>
			<td></td>
		</tr>
		<tr>
			<td>Tricaine methanesulfonate</td>
			<td>Syndel</td>
			<td>TRIC-M-GR-0010</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween 20, Fisher BioReagents</td>
			<td>Fischer Scientific</td>
			<td>BP337-500</td>
			<td></td>
		</tr>
	</tbody>
</table>

partial hepatectomy in adult zebrafish

Liver failure is one of the leading causes of death worldwide, and mortality from chronic liver disease is rising sharply in the United States. Healthy livers are capable of regenerating from toxic damage, but in advanced liver disease, the natural ability of the liver to regenerate is impaired. Zebrafish have emerged as a powerful experimental system for studying regeneration. They are an ideal model for studying liver regeneration from partial hepatectomy, a procedure with direct clinical relevance in which part of the liver is surgically removed, leaving the rest intact. There is no standard protocol for partial hepatectomy; previous studies using this model have used slightly different protocols and reported disparate results. Described here is an efficient, reproducible protocol for performing a partial hepatectomy in adult zebrafish. We use this technique to demonstrate that zebrafish are capable of epimorphic regeneration of the resected lobe. This protocol can be used to further interrogate the mechanisms required for liver regeneration in zebrafish.

In order to examine the regenerative potential of the adult zebrafish liver, we performed partial hepatectomy (PHX) in adult zebrafish. In general, large adults (30-40 mm in length) were selected, ranging from 1.5-2.5 years old. Within individual experiments, animals were selected from the same tank, and were age- and size-matched. As an appropriate control, we utilized sham surgeries in which the animal was both anesthetized and received a large incision in the ventral body wall but was recovered without removing any ti...

Watch this Scientific Journal Video about Partial Hepatectomy in Adult Zebrafish at JoVE.com

Partial Hepatectomy in Adult Zebrafish

This protocol describes the procedure for removing the ventral lobe of the liver in adult zebrafish to enable the study of liver regeneration.

Liver failure is one of the leading causes of death worldwide, and mortality from chronic liver disease is rising sharply in the United States. Healthy ...

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3.8K Views.  Harvard Medical School. This protocol describes the procedure for removing the ventral lobe of the liver in adult zebrafish to enable the study of liver regeneration.

Video: Partial Hepatectomy in Adult Zebrafish

Transplantation of Whole Kidney Marrow in Adult Zebrafish

Hematopoietic stem cells (HSC) are a rare population of pluripotent cells that maintain all the differentiated blood lineages throughout the life of an organism. The functional definition of a HSC is a transplanted cell that has the ability to reconstitute all the blood lineages of an irradiated recipient long term. This designation was established by decades of seminal work in mammalian systems. Using hematopoietic cell transplantation (HCT) and reverse genetic manipulations in the mouse, the underlying regulatory factors of HSC biology are beginning to be unveiled, but are still largely under-explored. Recently, the zebrafish has emerged as a powerful genetic model to study vertebrate hematopoiesis. Establishing HCT in zebrafish will allow scientists to utilize the large-scale genetic and chemical screening methodologies available in zebrafish to reveal novel mechanisms underlying HSC regulation. In this article, we demonstrate a method to perform HCT in adult zebrafish. We show the dissection and preparation of zebrafish whole kidney marrow, the site of adult hematopoiesis in the zebrafish, and the introduction of these donor cells into the circulation of irradiated recipient fish via intracardiac injection. Additionally, we describe the post-transplant care of fish in an "ICU" to increase their long-term health. In general, gentle care of the fish before, during, and after the transplant is critical to increase the number of fish that will survive more than one month following the procedure, which is essential for assessment of long term (&lt;3 month) engraftment. The experimental data used to establish this protocol will be published elsewhere. The establishment of this protocol will allow for the merger of large-scale zebrafish genetics and transplant biology.

In this article, we demonstrate a method to perform HCT in adult zebrafish.

Hematopoietic stem cells (HSC) are a rare population of pluripotent cells that maintain all the differentiated blood lineages throughout the life of an ...

Retro-orbital Injection in Adult Zebrafish

Drug treatment of whole animals is an essential tool in any model system for pharmacological and chemical genetic studies. Intravenous (IV) injection is often the most effective and noninvasive form of delivery of an agent of interest. In the zebrafish (Danio rerio), IV injection of drugs has long been a challenge because of the small vessel diameter. This has also proved a significant hurdle for the injection of cells during hematopoeitic stem cell transplantation. Historically, injections into the bloodstream were done directly through the heart. However, this intra-cardiac procedure has a very high mortality rate as the heart is often punctured during injection leaving the fish prone to infection, massive blood loss or fatal organ damage. Drawing on our experience with the mouse, we have developed a new injection procedure in the zebrafish in which the injection site is behind the eye and into the retro-orbital venous sinus. This retro-orbital (RO) injection technique has been successfully employed in both the injection of drugs in the adult fish as well as transplantation of whole kidney marrow cells. RO injection has a much lower mortality rate than traditional intra-cardiac injection. Fish that are injected retro-orbitally tend to bleed less following injection and are at a much lower risk of injury to a major organ like the heart. Further, when performed properly, injected cells and/or drugs quickly enter the bloodstream allowing compounds to exert their effect on the whole fish and kidney cells to easily home to their niche. Thus, this new injection technique minimizes mortality while allowing efficient delivery of material into the bloodstream of adult fish. Here we exemplify this technique by retro-orbital injection of Tg(globin:GFP) cells into adult casper fish as well as injection of a red fluorescent dye (dextran, Texas Red ) into adult casper fish. We then visualize successful injections by whole animal fluorescence microscopy.

Here we show how to do retro-orbital injection in adult zebrafish.

Drug treatment of whole animals is an essential tool in any model system for pharmacological and chemical genetic studies. Intravenous (IV) injection is ...

Dissection of Organs from the Adult Zebrafish

Over the last 20 years, the zebrafish has become a powerful model organism for understanding vertebrate development and disease.  Although experimental analysis of the embryo and larva is extensive and the morphology has been well documented, descriptions of adult zebrafish anatomy and studies of development of the adult structures and organs, together with techniques for working with adults are lacking. The organs of the larva undergo significant changes in their overall structure, morphology, and anatomical location during the larval to adult transition.  Externally, the transparent larva develops its characteristic adult striped pigment pattern and paired pelvic fins, while internally, the organs undergo massive growth and remodeling.  In addition, the bipotential gonad primordium develops into either testis or ovary.  This protocol identifies many of the organs of the adult and demonstrates methods for dissection of the brain, gonads, gastrointestinal system, heart, and kidney of the adult zebrafish. The dissected organs can be used for in situ hybridization, immunohistochemistry, histology, RNA extraction, protein analysis, and other molecular techniques.  This protocol will assist in the broadening of studies in the zebrafish to include the remodeling of larval organs, the morphogenesis of organs specific to the adult and other investigations of the adult organ systems.

This protocol describes a procedure for identifying and dissecting organs from the adult zebrafish.

Over the last 20 years, the zebrafish has become a powerful model organism for understanding vertebrate development and disease.  Although experimental ...

Intraperitoneal Injection into Adult Zebrafish

A convenient method for chemically treating zebrafish is to introduce the reagent into the tank water, where it will be taken up by the fish. However, this method makes it difficult to know how much reagent is absorbed or taken up per fish. Some experimental questions, particularly those related to metabolic studies, may be better addressed by delivering a defined quantity to each fish, based on weight. Here we present a method for intraperitoneal (IP) injection into adult zebrafish. Injection is into the abdominal cavity, posterior to the pelvic girdle. This procedure is adapted from veterinary methods used for larger fish. It is safe, as we have observed zero mortality. Additionally, we have seen bleeding at the injection site in only 5 out of 127 injections, and in each of those cases the bleeding was brief, lasting several seconds, and the quantity of blood lost was small. Success with this procedure requires gentle handling of the fish through several steps including fasting, weighing, anesthetizing, injection, and recovery. Precautions are required to minimize stress throughout the procedure. Our precautions include using a small injection volume and a 35G needle. We use Cortland salt solution as the vehicle, which is osmotically balanced for freshwater fish. Aeration of the gills is maintained during the injection procedure by first bringing the fish into a surgical plane of anesthesia, which allows slow operculum movements, and second, by holding the fish in a trough within a water-saturated sponge during the injection itself. We demonstrate the utility of IP injection by injecting glucose and monitoring the rise in blood glucose level and its subsequent return to normal. As stress is known to increase blood glucose in teleost fish, we compare blood glucose levels in vehicle-injected and non-injected adults and show that the procedure does not cause a significant rise in blood glucose.

We demonstrate intraperitoneal injection into adult zebrafish. We use a 10 &mu;l NanoFil microsyringe controlled by a Micro4 controller and UltraMicroPump III. This demonstration includes the use of cold water as an anesthetic.

A convenient method for chemically treating zebrafish is to introduce the reagent into the tank water, where it will be taken up by the fish. However, ...

Dissection of the Adult Zebrafish Kidney

Researchers working in the burgeoning field of adult stem cell biology seek to understand the signals that regulate the behavior and function of stem cells during normal homeostasis and disease states. The understanding of adult stem cells has broad reaching implications for the future of regenerative medicine1. For example, better knowledge about adult stem cell biology can facilitate the design of therapeutic strategies in which organs are triggered to heal themselves or even the creation of methods for growing organs in vitro that can be transplanted into humans1. The zebrafish has become a powerful animal model for the study of vertebrate cell biology2. There has been extensive documentation and analysis of embryonic development in the zebrafish3. Only recently have scientists sought to document adult anatomy and surgical dissection techniques4, as there has been a progressive movement within the zebrafish community to broaden the applications of this research organism to adult studies. For example, there are expanding interests in using zebrafish to investigate the biology of adult stem cell populations and make sophisticated adult models of diseases such as cancer5. Historically, isolation of the zebrafish adult kidney has been instrumental for studying hematopoiesis, as the kidney is the anatomical location of blood cell production in fish6,7. The kidney is composed of nephron functional units found in arborized arrangements, surrounded by hematopoietic tissue that is dispersed throughout the intervening spaces. The hematopoietic component consists of hematopoietic stem cells (HSCs) and their progeny that inhabit the kidney until they terminally differentiate8. In addition, it is now appreciated that a group of renal stem/progenitor cells (RPCs) also inhabit the zebrafish kidney organ and enable both kidney regeneration and growth, as observed in other fish species9-11. In light of this new discovery, the zebrafish kidney is one organ that houses the location of two exciting opportunities for adult stem cell biology studies. It is clear that many outstanding questions could be well served with this experimental system. To encourage expansion of this field, it is beneficial to document detailed methods of visualizing and then isolating the adult zebrafish kidney organ. This protocol details our procedure for dissection of the adult kidney from both unfixed and fixed animals.
Dissection of the kidney organ can be used to isolate and characterize hematopoietic and renal stem cells and their offspring using established techniques such as histology, fluorescence activated cell sorting (FACS)11,12, expression profiling13,14, and transplantation11,15. 
We hope that dissemination of this protocol will provide researchers with the knowledge to implement broader use of zebrafish studies that ultimately can be translated for human application.

The zebrafish kidney is home to both renal and hematopoietic adult stem/progenitor cells, and represents an outstanding opportunity to study these cell types and their progeny in a vertebrate model organism. Here, we demonstrate a detailed dissection procedure that enables the researcher to identify and surgically remove the adult zebrafish kidney, which can be used for applications such as cell isolation, transplantation, and expression studies of kidney and/or blood cell populations.

Researchers working in the burgeoning field of adult stem cell biology seek to understand the signals that regulate the behavior and function of stem ...

Heart Dissection in Larval, Juvenile and Adult Zebrafish, Danio rerio

Zebrafish have become a beneficial and practical model organism for the study of embryonic heart development (see recent reviews1-6), however, work examining post-embryonic through adult cardiac development has been limited7-10. Examining the changing morphology of the maturing and aging heart are restricted by the lack of techniques available for staging and isolating juvenile and adult hearts. In order to analyze heart development over the fish's lifespan, we dissect zebrafish hearts at numerous stages and photograph them for further analysis11. The morphological features of the heart can easily be quantified and individual hearts can be further analyzed by a host of standard methods. Zebrafish grow at variable rates and maturation correlates better with fish size than age, thus, post-fixation, we photograph and measure fish length as a gauge of fish maturation. This protocol explains two distinct, size dependent dissection techniques for zebrafish, ranging from larvae 3.5mm standard length (SL) with hearts of 100&mu;m ventricle length (VL), to adults, with SL of 30mm and VL 1mm or larger. Larval and adult fish have quite distinct body and organ morphology. Larvae are not only significantly smaller, they have less pigment and each organ is visually very difficult to identify. For this reason, we use distinct dissection techniques.
We used pre-dissection fixation procedures, as we discovered that hearts dissected directly after euthanization have a more variable morphology, with very loose and balloon like atria compared with hearts removed following fixation. The fish fixed prior to dissection, retain in vivo morphology and chamber position (data not shown). In addition, for demonstration purposes, we take advantage of the heart (myocardial) specific GFP transgenic Tg(myl7:GFP)twu34 (12), which allows us to visualize the entire heart and is particularly useful at early stages in development when the cardiac morphology is less distinct from surrounding tissues. Dissection of the heart makes further analysis of the cell and molecular biology underlying heart development and maturation using in situ hybridization, immunohistochemistry, RNA extraction or other analytical methods easier in post-embryonic zebrafish. This protocol will provide a valuable technique for the study of cardiac development maturation and aging.

Heart Dissection in Larval, Juvenile and Adult Zebrafish, Danio rerio

A clear, standardized method for dissection and isolation of the zebrafish heart at multiple developmental stages are described. Annotation and quantification techniques are also discussed.

Zebrafish have become a beneficial and practical model organism for the study of embryonic heart development (see recent reviews1-6), however, work ...

In vivo Electroporation of Morpholinos into the Adult Zebrafish Retina

Many devastating inherited eye diseases result in progressive and irreversible blindness because humans cannot regenerate dying or diseased retinal neurons. In contrast, the adult zebrafish retina possesses the robust ability to spontaneously regenerate any neuronal class that is lost in a variety of different retinal damage models, including retinal puncture, chemical ablation, concentrated high temperature, and intense light treatment 1-8. Our lab extensively characterized regeneration of photoreceptors following constant intense light treatment and inner retinal neurons after intravitreal ouabain injection 2, 5, 9. In all cases, resident M&uuml;ller glia re-enter the cell cycle to produce neuronal progenitors, which continue to proliferate and migrate to the proper retinal layer, where they differentiate into the deficient neurons. 
	We characterized five different stages during regeneration of the light-damaged retina that were highlighted by specific cellular responses. We identified several differentially expressed genes at each stage of retinal regeneration by mRNA microarray analysis 10. Many of these genes are also critical for ocular development. To test the role of each candidate gene/protein during retinal regeneration, we needed to develop a method to conditionally limit the expression of a candidate protein only at times during regeneration of the adult retina. 
	Morpholino oligos are widely used to study loss of function of specific proteins during the development of zebrafish, Xenopus, chick, mouse, and tumors in human xenografts 11-14. These modified oligos basepair with complementary RNA sequence to either block the splicing or translation of the target RNA. Morpholinos are stable in the cell and can eliminate or "knockdown" protein expression for three to five days 12. 
	Here, we describe a method to efficiently knockdown target protein expression in the adult zebrafish retina. This method employs lissamine-tagged antisense morpholinos that are injected into the vitreous of the adult zebrafish eye. Using electrode forceps, the morpholino is then electroporated into all the cell types of the dorsal and central retina. Lissamine provides the charge on the morpholino for electroporation and can be visualized to assess the presence of the morpholino in the retinal cells. 
	Conditional knockdown in the retina can be used to examine the role of specific proteins at different times during regeneration. Additionally, this approach can be used to study the role of specific proteins in the undamaged retina, in such processes as visual transduction and visual processing in second order neurons.

In vivo Electroporation of Morpholinos into the Adult Zebrafish Retina

A method to conditionally knockdown a target protein&#x2019;s expression in the adult zebrafish retina is described, which involves intravitreally injecting antisense morpholinos and electroporating them into the retina. The resulting protein is knocked down for several days, which allows testing the protein&#x2019;s role in the regenerating or intact retina.

Many devastating inherited eye diseases result in progressive and irreversible blindness because humans cannot regenerate dying or diseased retinal ...

In vivo Electroporation of Morpholinos into the Regenerating Adult Zebrafish Tail Fin

Certain species of urodeles and teleost fish can regenerate their tissues. Zebrafish have become a widely used model to study the spontaneous regeneration of adult tissues, such as the heart1, retina2, spinal cord3, optic nerve4, sensory hair cells5, and fins6.
The zebrafish fin is a relatively simple appendage that is easily manipulated to study multiple stages in epimorphic regeneration. Classically, fin regeneration was characterized by three distinct stages: wound healing, blastema formation, and fin outgrowth. After amputating part of the fin, the surrounding epithelium proliferates and migrates over the wound. At 33 &deg;C, this process occurs within six hours post-amputation (hpa, Figure 1B)6,7. Next, underlying cells from different lineages (ex. bone, blood, glia, fibroblast) re-enter the cell cycle to form a proliferative blastema, while the overlying epidermis continues to proliferate (Figure 1D)8. Outgrowth occurs as cells proximal to the blastema re-differentiate into their respective lineages to form new tissue (Figure 1E)8. Depending on the level of the amputation, full regeneration is completed in a week to a month.
The expression of a large number of gene families, including wnt, hox, fgf, msx, retinoic acid, shh, notch, bmp, and activin-betaA genes, is up-regulated during specific stages of fin regeneration9-16. However, the roles of these genes and their encoded proteins during regeneration have been difficult to assess, unless a specific inhibitor for the protein exists13, a temperature-sensitive mutant exists or a transgenic animal (either overexpressing the wild-type protein or a dominant-negative protein) was generated7,12. We developed a reverse genetic technique to quickly and easily test the function of any gene during fin regeneration.
Morpholino oligonucleotides are widely used to study loss of specific proteins during zebrafish, Xenopus, chick, and mouse development17-19. Morpholinos basepair with a complementary RNA sequence to either block pre-mRNA splicing or mRNA translation. We describe a method to efficiently introduce fluorescein-tagged antisense morpholinos into regenerating zebrafish fins to knockdown expression of the target protein. The morpholino is micro-injected into each blastema of the regenerating zebrafish tail fin and electroporated into the surrounding cells. Fluorescein provides the charge to electroporate the morpholino and to visualize the morpholino in the fin tissue.
This protocol permits conditional protein knockdown to examine the role of specific proteins during regenerative fin outgrowth. In the Discussion, we describe how this approach can be adapted to study the role of specific proteins during wound healing or blastema formation, as well as a potential marker of cell migration during blastema formation.

In vivo Electroporation of Morpholinos into the Regenerating Adult Zebrafish Tail Fin

We describe a method to conditionally knockdown the expression of a target protein during adult zebrafish fin regeneration. This technique involves micro-injecting and electroporating antisense oligonucleotide morpholinos into fin tissue, which allows testing the protein&#x2019;s role in various stages of fin regeneration, including wound healing, blastema formation, and regenerative outgrowth.

Certain species of urodeles and teleost fish can regenerate their tissues. Zebrafish have become a widely used model to study the spontaneous regeneration ...

Blood Collection for Biochemical Analysis in Adult Zebrafish

The zebrafish has been used as an animal model for studies of several human diseases. It can serve as a powerful preclinical platform for studies of molecular events and therapeutic strategies as well as for evaluating the physiological mechanisms of some pathologies1. 
There are relatively few publications related to adult zebrafish physiology of organs and systems2, which may lead researchers to infer that the basic techniques needed to allow the exploration of zebrafish systems are lacking3. Hematologic biochemical values of zebrafish were first reported in 2003 by Murtha and colleagues4 who employed a blood collection technique first described by Jagadeeswaran and colleagues in 1999. Briefly, blood was collected via a micropipette tip through a lateral incision, approximately 0.3 cm in length, in the region of the dorsal aorta5. Because of the minute dimensions involved, this is a high-precision technique requiring a highly skilled practitioner. The same technique was used by the same group in another publication in that same year6. In 2010, Eames and colleagues assessed whole blood glucose levels in zebrafish7. They gained access to the blood by performing decapitations with scissors and then inserting a heparinized microcapillary collection tube into the pectoral articulation. They mention difficulties with hemolysis that were solved with an appropriate storage temperature based on the work Kilpatrick et al.8. When attempting to use Jagadeeswaran's technique in our laboratory, we found that it was difficult to make the incision in precisely the right place as not to allow a significant amount of blood to be lost before collection could be started. 
Recently, Gupta et al.9 described how to dissect adult zebrafish organs, Kinkle et al.10 described how to perform intraperitoneal injections, and Pugach et al.11 described how to perform retro-orbital injections. However, more work is needed to more fully explore basic techniques for research in zebrafish.
The small size of zebrafish presents challenges for researchers using it as an experimental model. Furthermore, given this smallness of scale, it is important that simple techniques are developed to enable researchers to explore the advantages of the zebrafish model.

This paper presents a technique for collection of blood from the dorsal aorta of Zebrafish. It also provides instructions for obtaining serum for use in biochemical analyses, such as tests for determining cholesterol and triglyceride levels.

The zebrafish has been used as an animal model for studies of several human diseases. It can serve as a powerful preclinical platform for studies of ...

Gavaging Adult Zebrafish

The zebrafish has become an important in vivo model in biomedical research. Effective methods must be developed and utilized to deliver compounds or agents in solutions for scientific research. Current methods for administering compounds orally to adult zebrafish are inaccurate due to variability in voluntary consumption by the fish. A gavage procedure was developed to deliver precise quantities of infectious agents to zebrafish for study in biomedical research. Adult zebrafish over 6 months of age were anesthetized with 150 mg/L of buffered MS-222 and gavaged with 5 &mu;l of solution using flexible catheter implantation tubing attached to a cut 22-G needle tip. The flexible tubing was lowered into the oral cavity of the zebrafish until the tip of the tubing extended past the gills (approximately 1 cm). The solution was then injected slowly into the intestinal tract. This method was effective 88% of the time, with fish recovering uneventfully. This procedure is also efficient as one person can gavage 20-30 fish in one hour. This method can be used to precisely administer agents for infectious diseases studies, or studies of other compounds in adult zebrafish.

The increasing use of zebrafish as an animal model requires the development of effective methods for the delivery of known quantities of compounds and solutions. The gavage procedure described below allows for the oral delivery of precise volumes of solution reliably, safely and efficiently to adult zebrafish.

The zebrafish has become an important in vivo model in biomedical research. Effective methods must be developed and utilized to deliver compounds or ...