The Classroom Aquarium

Pets are a common fixture in many elementary classrooms all around the country. I still remember walking into my 2^nd grade teacher’s room and brimming with joy that she had a fish tank. And I’m not alone in that delight. Many researchers have found that classroom pets have a positive impact on students. Pets increase students’ positive attitude towards school and can actually make them want to come to school (Anderson & Olsen). They have been found to improve the emotional well-being of students and contribute to humane education (Daly & Suggs). Contrary to popular belief, one study showed pets did not distract from the teacher (Kortschal & Ortbauer).  And of all the possible choices for classroom pets, fish are the most common (Rud & Beck).

Freshwater aquarium (Neale Monks)

This is with good reason. Fish are relatively easy to care for. They don’t need to be fed daily, so they can easily be left over the weekend or a short break. During the summer, they can be taken home or just cared for on a weekly basis. There are also a wide variety of species that can be very easily acquired. It is also possible to keep fishes that are native to your location to give students a view of wildlife they don’t normally see.

Aquariums also have a well-established relaxing effect. Watching aquariums is known to reduce heart rate and blood pressure (Cracknell et al). And if I remember school correctly, tests certainly can generate some elevated heart rates! My mother is a middle school teacher and if there is one thing teachers need, it’s reduced stress levels. So in this way, the fish tank will help the teacher as much as the students. 

Lessons with an Aquarium

Aquariums can be very useful teaching tools. Students can examine how a fish tank attempts to reproduce a native habitat. How the light emulates the sun; how the filter gives the fish clean water like a stream; how the pump oxygenates the water like a waterfall. If native species are available students can observe their natural habitat and try to recreate it. Fish don’t have to be the only inhabitants in an aquarium. Plants can be added to further simulate a natural environment. Plants can also be used to introduce students to the idea of nutrient cycling.

Trout Unlimited volunteer helping with tank maintenance on the class's Trout in the Classroom project. Trout in the Classroom is a program started by the nonprofit Trout Unlimited which seeks to preserve freshwater streams and rivers around the USA. Students raise fish from eggs and release them at the end of the year. (Julia Ross, Troutfest.org)

Water chemistry and pollution are other lesson that can be taught with fish tank. Many pet stores carry small freshwater testing kits simple enough for middle school students. They can measure, record, and graph the temperature, pH, and nitrate levels in their fish tank. These water quality readings can be compared to local a river or pond. Teachers can actually let the fish tank get dirty to show students what happens to fish in polluted environments.

The nitrogen cycle is very important to success with an aquarium, and although it isn’t the same nitrogen cycle that happens in the air, it can be used to introduce students to the concept. Fish tanks can also help illustrate the water cycle from cloud to ocean. Students can even measure how much water evaporates from the tank on a weekly basis.

Math and science are very tightly linked, so an aquarium can also help with math lessons! Students can calculate the volume and surface area of the fish tank and convert those measurements from metric to standard units. From the volume, you can have them calculate the weight of the aquarium (hint hint, water weights 8.34 lb/gallon). These fun examples bring math out of the textbook and into real world.

Help Setting up a Tank

Right about now, you may be thinking, this sounds great but where do I start? Thankfully fish tanks aren’t difficult to set up and maintain, but they will require a bit of effort on your part initially. The first thing you will want to read and research is the freshwater nitrogen cycle. This is the article I wrote on it. Many many resources exist online to help you in starting a fish tank, and I encourage you to check out the other fish blogs I recommend for additional resources. My friend Mari at Aquariadise has some wonderful articles to help new fishkeepers such as types of filters & choosinga substrate. The National Science Teachers Association also has guidelines for keeping live animals in the classroom which I highly recommend reading.

Suggestions to a New Fishkeeper

If native fish are at all an option, I highly recommend them. In the eastern USA we have many stunningly beautiful fish right in our own backyard. You can read more about them in my article: The Beauty in Your Backyard.

 If native fish aren’t an option, then the next best suggestions I can make are small tetra like the glowlight (Hemigrammus erythrozonus) and X-ray tetra (Pristella maxillaris). Small barbs like cherry barbs (Puntius titteya) and gold barbs (Barbodes semifasciolatus) also make great classroom fish. Zebra danio/glo-fish (Danio rerio) are a staple and great, hardy fish. All of these species need to be in groups larger than 10 because they are shoaling species, meaning they survive best when in groups. They all need a tank larger than a 10 gallon, too. You can read more about these species in my article: Best and Worst Beginner Fish.

A few of the glowlight tetra in my personal tank. They are rather hardy and don't mind me leaving them for a weekend. 

For tank size, I recommend starting with a 20 or 30 gallon tank. It seems counter-intuitive but small tanks are actually harder to keep. Larger volumes of water mean there is more of a buffer in case something goes wrong. Larger tanks also mean you’ll be able to keep more fish which are always delightful to students.  

I highly recommend plants in an aquarium. They create a soothing natural environment and open new doors for educational opportunities in addition to helping keep it clean. To successfully grow plants you will need a plant-specific light. An aquarium kit should come with a hood and light, but that light isn’t going to be tailored to plants. You will need to get a 6500k full spectrum daylight bulb. Many pet stores also sell these, but hardware stores will have them if your pet store doesn’t. They only need to be replaced once a year to keep your plants growing green and beautiful. Some plant species that are a good, hardy beginner species are anubias, java fern, amazon sword, and duckweed. Pet stores often have these common plants for sale.

Help with Funding

Aquariums (like all pets) require money, but fortunately for you, there is a nonprofit organization that gives grants for teachers interested in getting a classroom pet. Pets in the Classroom allows teachers to submit proposals for grants to assist with setting up and maintaining classroom pets. Their website also contains lesson plan and habitat ideas for many species of pets. I highly encourage you to check it out. If regulations and demographics allow, you can ask for a small donation from your students to help fund your classroom pet experience.

Works Referenced

Anderson, K.L. and M.R. Olson. 2006. The value of a dog in a classroom of children with severe emotional disorders. Anthrozoös 19(1): 35-49.

Aquatic WILD: K-12 Curriculum & Activity Guide. 2013. Revised ed. Council for Environmental Education, Houston.

Cracknell D., M. P. White, S. Pahl, et al. 2015. Marine Biota and Psychological Well-Being: A Preliminary Examination of Dose-Response Effects in an Aquarium Setting. Environment and Behavior. DOI: 10.1177/0013916515597512

Daly, B. and S. Suggs. 2010. Teachers’ experiences with humane education and animals in the elementary classroom: implications for empathy development. Journal of Moral Education 39(1): 101-112.

Kortschal, K. and B. Ortbauer. 2003. Behavioral effects of the presence of a dog in a classroom. Anthrozoös 16 (2): 147-159.

“Responsible Use of Live Animals and Dissection in the Science Classroom.” National Teachers Science Association. www.nsta.org/. Updated: March 2008. Retrieved: 24 Nov 2015.

Rotman, E. 2008. Hatching Stewardship. Outdoor California (March-April): 33-35.

Rud, A.G. and A.M. Beck. 2003. Companion animals in Indiana elementary schools. Anthrozoos 16 (3):241-251.

Rutherford, B. 28 March 2015. Tanks in Classrooms: Setting Up an Educational Aquarium. Reef to Rainforest Media. Retrieved: 24 Nov 2015.

“Trout in the Classroom.” Trout Unlimited. www.troutintheclassroom.org/. Updated: Nov 2015. Accessed: 24 Nov 2015.

Freshwater Aquarium Nitrogen Cycle

Welcome to the most important article I or anyone can ever write about fishkeeping: the aquarium nitrogen cycle. Contrary to what you may hear at a pet store, it is not just filling your aquarium and running the filter for a week.

What Is It?

The nitrogen cycle is how we maintain a healthy environment, and it surprisingly relies completely on bacteria. These microorganisms change the toxic waste of our fish into a relatively harmless substance, thereby allowing us to keep fish in contained areas. In the wild, the fish waste is diluted by the humongous volumes of water. 

The cycle begins with fish. They produce ammonia as a byproduct of their metabolism. The problem is ammonia is toxic to them (and us for that matter). Luckily a genus of bacteria called Nitrosomonas exists. These bacteria take ammonia and convert it into nitrite to generate energy for themselves (much like plants use photosynthesis to generate energy from the sun). However, nitrite is still toxic to fish. That’s where second genera of bacteria called Nitrobacter and Nitrospira come in. They convert the toxic nitrite into nitrate which takes much higher levels to reach toxicity. However, nitrate is still toxic to fish and will need to be removed from the aquarium by its caretaker. This is one reason we perform periodic water changes on our aquaria.

Aquarium nitrogen cycle schematic. (public domain)

Nitrobacter and Nitrosomonas also have requirements just like our fish. They live on surfaces in your aquarium although a small amount can be found floating in the water. They operate best between the pH’s of 6.0 and 9.0 and need water above 50F. They also require highly oxygenated water, so they are most commonly found in the filter. For this reason, it is important to never wash your filter media in chlorinated water. 

When plants are added to an aquarium, they use up nitrogen in all three of the forms (ammonia, nitrite, and nitrate). If enough fast-growing plants are present, there may be very little ammonia that makes it to the filter. However, even with a planted aquarium, I recommend having some type of filter where these important bacteria can grow. Plants can be finicky and stop growing for odd reasons, and when that happens an ammonia spike can be deadly to fish and invertebrates. Having plants does not negate the necessity of the nitrogen cycle in your freshwater aquarium.

How to Establish a Cycle

Cycling an aquarium takes weeks to a month because the colonies of bacteria replicate slowly. Nitrosomonas need a source of ammonia to produce nitrite before Nitrobacter can begin to grow.  The only way to know when it is complete and what stage you are in is to test for ammonia, nitrite, and nitrate. First you will see an ammonia spike, followed by a nitrite spike, and then nitrates. You should test your water daily and record your results to chart your progress. A few different methods of getting ammonia into your aquarium and starting the cycle are detailed below.

Chart of expected ammonia and nitrite spikes while recycling a tank. (theaquariumwiki.com)

Live Fish

This is the most common and oldest method. Simply throw the fish in and hope for the best. The bacterial colonies will build up over time, but while you are waiting your fish will be subject to ammonia poisoning and nitrite poisoning in the weeks it takes the Nitrosomonas and Nitrobacter colonies to establish themselves. This is how many ignorant aquarists (including myself) originally establish a cycle, however it is not the most humane. Other alternatives should be explored first. 

Fish Food

In addition to living fish producing ammonia, decaying food will also produce ammonia and can be used to start a cycle. You can use fish food or raw seafood. However, this method isn’t without risks as rotting food will attract other bacteria and fungi. If you are using this method, you need to do a large (70% or more) water change before you add fish and invertebrates. 

Pure Ammonia

You can find this sold as a cleaning agent in many stores. Just make sure you check the label because the ones with surfactants will not work. Add the ammonia to your tank water until you get a concentration of 3ppm (any higher and it will inhibit the Nitrosomonas). When the ammonia concentrations drops to zero and you see nitrites, add more again. Keep doing this until adding ammonia produces nitrates. You will have to keep dosing the tank until you add fish to sustain the colonies. Before you add fish, do a water change to reduce the nitrate levels to below 40ppm. 

Seeded Filter

If you have a friend or store you trust, you can ask for some of their filter media to add to your filter. Because these bacterial colonies are most commonly found attached to filter media, you will instantly establish a cycle. You can add fish the day you add in the media. If you have multiple tanks you can borrow media from one tank to cycle another. Since I cycled my first aquarium, I have used this method exclusively to cycle my tanks. 

Bacteria in a Bottle

Nitrosomonas and Nitrobacter can be bought from pet stores and online. A few select products are believed to work quite well. Dr. Tim’s One and Only and Tetra Safestart are two that are claimed to work wonderfully. By adding these products you can cycle your tank instantly and add fish that day. You can also use these products in conjunction with any other method to increase your chance of success. I have not personally used these products at the time of writing, however I have heard amazing reviews from others. I do have plans to try these products myself one day.

Cycling an aquarium is the single most important thing you can do for the health of your fish. It is time and effort, but it is worth every minute for the headaches it will save you. The best medicine is clean water, and that is just what a cycle gives you.

Works Referenced

“Ammonia & the Nitrogen Cycle: Important Steps for YourAquarium.” Drs Foster and Smith. www.drsfostersmith.com. Updated: 18 October 2015. Retrieved: 18 October 2015.

“Aquarium Nitrogen Cycle.” Fishlore. www.fishlore.com. Updated: 30 September 2015. Retrieved: 18 October 2015. 

DeLong, D.P. and T.M. Losordo. 2012. "How to Start a Biofilter." Southern Regional Aquaculture Center. Retrieved: 18 October 2015. 

“Fishless Cycling.” Algone. www.algone.com. Updated: 15 March 2012. Retrieved: 18 October 2015. 

“’Fishless’ Cycling.” The Skeptical Aquarist. www.skepticalaquarist.com. Updated: 21 March 2011. Retrieved: 18 October 2015. 

Helm, Ben. 2014. “Controlling Ammonia in a Fish Aquarium.” www.fishchannel.com. Retrieved: 18 October 2015.

 Losordo, T.M., M.P. Masser, and J. Rakocy. 1998. "Recirculating Aquaculture Tank Production Systems: an overview of critical considerations." Southern Regional Aquaculture Center. Retrieved: 18 October 2015. 

Monks, Neale. 2011. “FishlessAquarium Cycling Method.” www.fishchannel.com. Retrieved18 October 2015. 

“Nitrifying BacteriaMixtures Work.” Dr. Tim’s  Aquatics. www.drtimsaquatics.com. Updated: 8 September 2015. Retrieved 18 October 2015.

Fish in their Natural Habitats

I like my aquariums to replicate the natural homes of fish as much as possible. There is no better way to get an idea of the streams and rivers our tropical fish come from than to visit those streams. But for those of us like myself that don't have the money to do something like that, we can use videos as an alternative. Freshwater enthusiast and Venezuelan native Ivan Mikolji makes those journeys for us and shows us the wonderful natural aquariums that are home to our beautiful aquarium fish.

Divided Betta Tanks

The easiest way to keep multiple bettas!

Everyone knows that bettas need clean, warm water. Personally I don’t like to keep bettas in anything smaller than a 5 gal (19 L) because they are harder to maintain a cycle or proper temperature in. Most people have two to four bettas, and cleaning that many 5 gal (19 L) tanks can take a while. This is why the divided tank is my favorite way to keep bettas.

The Basic Setup

The idea is to separate the bettas by a solid divider. Some people use plastic mesh, and some will use solid glass or plexiglass with tiny holes drilled for water movement. The intention is to physically separate the fish so they cannot touch each other. But the two fish can still see each other.

Left without any visual barriers, they will flare uncontrollably which is stressful to them. This can lead to fin-biting or wasting away. Some fish will refuse to eat and attempt to fight the other fish until they die. This is counter-productive. So you have to obscure their view of each other by placing numerous tall decorations along both sides of the divider. Some people use fake plants; some people use décor like castles and other trinkets. I prefer to use live plants. What is important is that these decorations make it easy for one betta to get out of sight of the other. 

Newly set up divided 10 gallon tank (Pixiefarts @ Flickr)

Other decorations in the tank such as caves should be angled away from the divider to give the bettas more refuge from each other. As always a tank stuffed with decorations and live plants seems to be the best habitat for a betta. In this situation it also gives the bettas ample space to avoid looking at each other.

Most any size tank above 5 gallons (19 L) can be easily divided. The kinds of tanks you want to stay away from dividing are the tall tanks like hexigons. A tall and long tank like a 40 gal (150 L) breeder could be divided, but you would need to provide the bettas ample resting places close to the top. That is a tall tank for a fish with heavy fins. The most commonly divided tanks are 10 gal (38 L), 15 gal (56 L), 15 gal (56 L) long, 20 gal (75 L), and 20 gal (75 L) long.

Variations

There are a couple of variations on this idea, but they all have the basic concept. Some people add multiple dividers to a long tank such as a 20 gal (75 L) long. In a tank like this you could have between three and four (depending on preference) dividers. But you have to take special care to provide the betta in the middle with more than average hiding spaces because he will think he’s being attacked from both sides.

Divided 20 long (Jadesong520 @ photobucket)

Some people take this a step further and create betta barracks. The methods to do this vary greatly from placing a lot of dividers in a tank to having glass custom cut and siliconed into place, but the outcome is the same. There are usually 4+ compartments in the front for bettas and a single large compartment behind the bettas to facilitate water flow, allow for a heater, and a filter. This method is preferred by breeders because it allows you to house hundreds of bettas in a pretty compact area using multiple barracks and industrial shelving racks.

Betta barracks for 10 bettas (LittleBettaFish @ Bettafish.com)

My personal favorite dividing method is the double divider. Instead of just one divider in the tank, I use two to create three compartments, but only two compartments house fish. The middle one houses the heater and filter and a few plants. The additional divider makes it more difficult for the bettas to see each other and also offers a buffer zone in case of a jumper. Bettas are known to jump, and they do jump the divider from time to time. This HAS happened to me before while I was on vacation, but because of this middle buffer zone the bettas did not tear each other apart. They were there for hours until they were discovered. If not for this middle section, I could have come home to one or two dead bettas.

My personal divided betta tank.

View from the side. Note how opaque the divider is.

Problems

No setup is perfect and when you put two bettas in a tank together (even with a divider) you still have the potential for problems. As I was just talking about with my tank, jumping is a serious issue. Just last week a friend of mine who also has divided tanks lost one of her bettas when the other jumped the divider and beat him to death. The double divider is one way to help prevent that. The other thing you can do is make a jump guard. Because I made my dividers from craft mesh, which is bought in sets of multiple sheets, I had some left over. I cut the leftover mesh to make a jump guard. It’s just a piece of mesh that rests on top of the divider and hangs out over the edges about 3 inches (7 cm). If a betta jumps at the divider, he or she will just hit the mesh.

Jump guard made with craft mesh.

Another issue is the spread of waterborne diseases like ich, fungus, and columnaris. If one fish gets sick you have to treat the whole tank for it because the other betta (or bettas) have been exposed. Most disease can be prevented by having a good quarantine regimen.

Sometimes you will just get males or females that just can’t handle living in a divided tank. Even with lots of plants along the divider they will fin-bite or pace all day, trying to get away. Generally the bettas that are more relaxed tend to do better in divided tanks. Having two very aggressive bettas in a divided tank can be a problem. This is a specialized setup; it isn’t for every betta.

As I have said before this is my favorite way to keep bettas. You get double the fish for the same amount of maintenance. My betta tank gets one 30% water change weekly and takes the least time of all of my tanks. I highly recommend this type of setup to anyone. I leave you with a video of my divided betta tank. The two males do not notice each other at all.

Is my fish a girl or a boy?

How to determine the sex of your fish

Most people like to name their fish and want to have a name that fits the fish’s gender. Other people want to try breeding and need to know if they have males and females. Sexing fish can be a tricky thing, but there are some species and families of fish that are relatively easy. Before we get into those, I’ll talk about some general trends in sexing fish.

Females are rounder

Of course this only works with mature animals, but for the most part the female will have slightly thicker bodies. This is because the eggs that females carry take up more space than sperm. The females also need larger fat reserves to produce the eggs.

Males are smaller and more colorful

Just as in birds, males are the more colorful of the genders. Males compete with other males by showing off their vibrant colors. The most colorful male gets to mate. They are also slightly smaller than the females.

Sexing popular fish

Goldfish (Carassius auratus auratus)

These fish can actually be a little tricky as they have no obvious differences when the fish are not breeding, but there are two things you can look for when they breed: breeding stars and the shape of the vent.

Breeding stars or breeding tubercules will only appear on the males. They appear on the gill plate and pectoral fins. These are a sign of virility, and a study performed on a relative of the goldfish found a correlation between the number of breeding stars and how healthy a male fish is. These stars help a female fish decide who she wants to mate with.

Breeding stars on pectoral fin and gill cover (goldy fk @ flickr)

The next thing to look for is the shape of the vent (this is also called the cloaca and is the opening near the anal fin). The vent of the male will be slightly larger and concave (meaning it curves inward). The vent of the female will be smaller and protrude slightly. The pictures below better illustrate this.

Circled male vent (mikroll @ TheGAB)

Circled female vent (mikroll @ TheGAB.org)

I find using the vent method to be a little difficult as my goldfish usually like to have their heads facing towards me begging for food. I prefer to use the breeding star method because they are more visible in my experience.

Betta fish (Betta splendens)

These small, popular tropical fish are a little easier than goldfish to sex because some of it can be done out of the breeding season. There are two main ways to sex bettas: fin length and the presence of an ovipositor.

If you see a long-finned betta it is a male. There have been cases where females have longer than normal fins, but they aren’t nearly as long as the typical halfmoon spread seen below.

These extremely long fins indicate a male(Aquariumloto @ Flickr)

Sexing bettas gets a little trickier when you are dealing with plakat (or short-finned) bettas because the male and female fins are the same length. Now you have to look for the ovipositor on the female. The ovipositor is a small white tube protruding from the vent of the female; in breeding she uses this to position eggs. It will appear as a small white dot behind the ventral fins. The lack of such indicates a male.

Arrow points to ovipositor (Stuart Halliday)

Angelfish (Pterophyllum spp)

Another extremely popular aquarium fish, but much harder than bettas or goldfish to sex. They have no discernible differences when they are not spawning, and when they are spawning you have to look very closely to see the only difference:  the males will have a thinner breeding tube which is visible in the vent of the fish. Both males and females have breeding tubes, so the key is to look for the smaller one.

Female angelfish breeding tube (koiangelfish.com)

Male angelfish breeding tube (koiangelfish.com)

Neon tetra (Paracheirodon innesi)

Like angelfish, neon tetra are difficult to sex. The only difference will be in size. The females will be slightly larger and fatter especially when they are ready to breed. Males may show slightly better color, but these differences are so minute that they will likely go unnoticed.

Livebearers (Poecilidae)

These are fish like guppies, platies, swordtails, and mollies. The males and females are very easy to tell apart. There is a large size difference with some females being almost one and a half times the size of the males. The males will have long, flowing fins and are very colorful. Males also possess a modified anal fin called a gonopodium; this is used to transfer sperm to the females. Below you can see two illustrations showing the differences between male and female guppies

General female livebearer characteristics (jabraguppyroom.blogspot.com)

General male livebearer characteristics (jabraguppyroom.blogspot.com)

Cory catfish (Corydoras spp)

Another popular but difficult fish to sex, cories have no highly visible differences between the genders. Females will tend to be the larger ones and look much chubbier when they are breeding, but for the most part males and females look exactly alike.

Bristlenose pleco (Ancistrus spp)

These small plecos are surprisingly easy to sex. Both males and females will have the bristly nose, but the number and size of the bristles will be much greater in the males. This is especially true when the fish are in breeding condition. Scientists believe that males evolved the bristles to mimic young fish because females are more likely to mate with a male who is already caring for eggs.

Male bristlenose with month old offspring (goldy fk @ Flickr)

Oscar (Astronotus ocellatus)

Probably the most popular of the cichlids next to angelfish, but even more difficult to sex. Among wild populations the males show more color than females, but this isn’t reliable with the captive-bred fish that show up in stores nowadays because they have been bred for color.

Cherry barb (Puntius titteya)

This is a species that is easy to sex based on the general trends in fish genders. The males are smaller and have more red color and the females are larger and will be more brown in color. This holds true with wild-caught and naturally bred cherry barbs. There are some that have been specifically bred to make the red even brighter; these are much more difficult to gender. 

Female cherry barb on left, male on right (aquapage.cz)

Gourami

They aren’t as easy to sex as livebearers, but they are pretty easy if you know what to look for. If it’s not a captive-bred variant, the males will be a brighter color especially when breeding. If they are a color variant you have to look for a few other things. For the Trichogaster gourami (this is dwarf, honey, thicklips, and banded) look at the end of the dorsal fin; males will have a pointed dorsal, and females will have a rounded dorsal. These pictures below illustrate this as it can be hard to pick out if you’ve never seen it.

Male honey gourami (CK Yeo @ Flickr)

Female honey gourami (CK Yeo @ Flickr)

For the Trichopodus gourami (opaline, three-spot, blue, gold, pearl, and moonlight) you also look at the dorsal fin. The males will have a longer dorsal fin. Males of the pearl and moonlight species will show more red color than the females.

Pearl gourami. Male above, female below (seriouslyfish.com)

With some of our aquarium fish it can be very easy to tell the males from the females, but others can give you a lot of trouble. Some like oscars and angelfish can even give breeders trouble in determining gender. If you wish to breed any of these fish, I highly suggest you do a lot of research and read personal experiences. While breeding can be fun and rewarding, it can also be costly and heartbreaking when done incorrectly.

Works referenced

Christie F. 2006. Sexing Bettas: The Ovipositor. nippyfish.net. Retrieved: 31 Jan 2013

How to tell Male and Female Guppy Apart. Jabraguppyroom.blogspot.com. Updated: 29 July 2011. Retrieved: 1 Feb 2013.

Kortet R., J. Taskinen, A. Vainikka, and H. Ylonen. 2004. Breeding Tubercles, Papillomatosis and Dominance Behavior of Male Roach (Rutilus rutilus) During the Spawning Period. Ethology 110:591-601.

Seriously Fish

Sexing Angelfish. Koiangelfish.com. Updated: 2013. Retrieved: 1 Feb 2013. 

Sexing Goldfish. Bristol-aquarists.org.uk. Updated: 26 October 2012. Retrieved: 31 Jan 2013

Sexing Goldfish. theGAB.org. Updated: 16 Aug 2009. Retrieved: 31 Jan 2013