In part 2 of this article, we went over albinism, a recessive genetic mutation which affects one type of pigment cells (melanophores, responsible for the dark pigment eumelanin). As you can easily guess, there are also mutations which affect the other two types of pigment cells: iridophores, which produce shiny white crystallized purines, and xanthophores, which produce yellow pteridines. In this section, we will focus on these two mutations, which are a bit more complex than albinism.
Melanism is a recessive mutation similar to albinism, but instead of affecting melanophores, the mutation acts on iridophores. All axolotls receive either the M or m allele from each parent, which means their genotype for the melanism trait is either:
M/M (homozygous dominant)
m/m (homozygous recessive)
Homozygous dominant and heterozygous axolotls develop normal iridophores, which means they are able to produce crystallized purines (the shiny white pigment). Homozygous recessive axolotls are called melanoids. Since they have no iridophores, they are unable to produce cystallized purines.
This mutation also has a spillover effect: the lack of iridophores triggers the conversion of some xanthophores into melanophores. This is why melanoid axolotls show more eumelanin (black) than any other color morph, and almost no pteridines (yellow). This gives them a grey appearance, which can border on blueish under the right wavelengths.
Due to the reduced number of pteridines, which are important to immune function, melanoid axolotl larvae have a slightly lower survival rate than wild-type or albino axolotls. This is why melanoid axolotls they tend to be a bit more expensive and slightly less common on the market than other color morphs.
As you can imagine, axanthicism acts on xanthophores, the pigment cells responsible for producing pteridines. But the name of the trait, which means “lack of xanthophores”, is actually misleading. As it turns out, axanthic axolotls do have a certain amount of xanthophores, but those xanthophores are unable to produce pteridines due to a genetic mutation, which is believed to have originated from a virus.
Even though they can’t produce pteridines, the mutant xanthophores are able to store some yellow pigments from the axolotl’s diet (chiefly riboflavin, also known as vitamin B2). This helps compensate a bit for the lack of pteridines, but since they are slowly accumulated over time, axanthic larvae still have a low survival rate compared to other color morphs. This, along with the strict import laws currently in place, explains why axanthic axolotls are nearly impossible to find on the Canadian market.
In addition to causing a complete lack of pteridines, the axanthic mutation prevents iridophores from differenciating during development. As a result, axanthic axolotls often look a lot like melanoids. One way to tell them apart is to look at them under a blueish light. The complete absence of yellow pigments at birth tends to give axanthic a purple hue, whereas melanoids are more of a blueish grey. The purple effect tends to fade over time due to the accumulation of other yellow pigments, but some axolotls (such as Sarah, below) do manage to retain it through adulthood.
To make matters more confusing, axolotls can be both axanthic and melanoid. If an axanthic axolotl is especially dark, chances are it is also melanoid, but there is no way to be certain unless the genotype of both parents is known. If an axanthic axolotl accumulates a lot of yellow pigment over the years, then it probably isn’t a melanoid, as melanism further reduces the overall number of xanthophores.
There are six known genetic traits that affect an axolotl’s pigmentation:
The Copper trait
The GFP trait
All six of these traits follow a Mendelian pattern of inheritance, which is good news, because it’s a very simple pattern to explain and understand. Trust me! Keep reading and you’ll be an expert on the topic in less than 5 minutes.
Mendelian inheritance: the Ikea metaphor
DNA is a pretty amazing thing: the complete set of instructions for the construction of one particular living organism. It’s often portrayed as one huge chain, but DNA is actually broken into individual segments called chromosomes. Think of each chromosome as one assembly instruction booklet, like the ones that come with Ikea furniture. Obviously it takes a lot of instructions to build a whole living being, so we need a whole pile of booklets.
The instructions inside the booklets also have to be fool-proof, because the ones reading them and performing the assembly are proteins, which pretty much work like mindless drones. This is fine, except that when the information in one booklet is messed up or missing, the proteins can’t pick up the phone and call Ikea for help.
Luckily, each instruction booklet comes in two copies: one that was obtained from the animal’s mother, and one from its father. So even if there is missing information in one of the booklets, the protein-drone just needs to look at the other copy. With any luck, the correct information will be there.
This is the basic principle behind Mendelian inheritance.
Let’s say I want to build a chair and I have two instruction booklets in my possession. Version 1 (which I got from my mom) shows detailed, step-by-step assembly instructions. Version 2 (which I got from my dad) has a bunch of mistakes in it, and it’s very confusing. If I follow version 1, I’ll end up with a chair. If I follow version 2, I might end up with some weird contemporary art sculpture that may or may not crumble when I sit on it. Obviously, I would rather follow version 1, right? I might call my dad up afterwards and tell him “Hey Dad, just so you know, the instructions you gave me made no sense! It’s okay though, I used a different set of instructions and I managed to build the chair in the end.”
But what if both of my parents had given me the faulty version 2? Since I’m not a mindless drone, chances are I would have gone “uhh, I don’t think this is right.” But if I were a mindless drone, I probably would take the fact that both sets of instructions are saying the same thing as a sign that the information is correct, and I would have built the weird contemporary art sculpture. And who knows, maybe the sculpture would have turned out even better than some boring old chair!
When I say that a particular genetic trait follows a pattern of Mendelian inheritance, what I mean is that the assembly instructions for that particular trait come in two different versions, and given the opportunity, the assembly protein-drone will always prefer one version over the other. The version that is always preferred is called the dominantallele. The one that’s used only if no other instructions are available is called the recessive allele.
Mendelian inheritance: the albinism trait
If a chromosome is like an instruction booklet, the section of the booklet that contains instructions for one particular trait is called a gene. Just like the booklet in our previous example, the albino gene comes in two versions: allele A and allele a. Dominant alleles are always represented by capital letters, whereas recessive alleles are always lowercase.
Just like humans, axolotls receive two versions of each chromosome — one from their mother and one from their father. Every axolotl either ends up with one of these pairs:
A/A (two identical copies of the dominant allele)
A/a (one copy of each allele)
a/a (two identical copies of the recessive allele)
Axolotls who end up with two copies of the dominant allele are said to be homozygous dominant. The ones with two copies of the recessive allele are called homozygous recessive. If they have one copy of each, we call them heterozygous (from homo = same, and hetero = different).
So what makes allele A the dominant version of the gene? It contains a set of instructions for the construction of melanophores, the pigment cells that produce the dark pigment eumelanin. In allele a, those instructions are either erroneous or missing due to a genetic mutation that randomly occured at some point during the evolution of the species. We call this mutation albinism.
Albinism works in a fairly straightforward manner: when an axolotl is homoyzgous for the recessive (mutant) allele a, it is unable to produce eumelanin (the brown/black pigment) because it simply does not have any melanophores. All other axolotls have melanophores and are able to produce eumelanin (with the possible exception of copper axolotls, which we will discuss later).
Even though albinism is a recessive mutation, it doesn’t mean that allele a is worse than allele A, or that albino axolotls are inferior in any way. Some mutations can yield positive results! Look at how cute these albino axolotls are:
Of the six mendelian traits that affect pigmentation, albinism is the most straightforward, because it only acts on one type of pigment cell. The other traits are slightly more complex, but the principle behind them is the same: as long the right sets of instructions are present, all pigment cells will be created and behave normally. But if they’re not, the assembly drones will follow whatever instructions they can find, and turn those functional chairs into pieces of art!
An axolotl’s coloring is the result of genetics, and to a lesser degree, environment and diet. Let’s go over the different color pigments involved, and you’ll understand what I mean.
The three natural color pigments are:
Eumelanin (brown, black)
Crystalized purines (iridescent white)
Pteridines (yellow, orange)
There is also a fourth pigment that is present in some transgenic axolotls:
Green fluorescent proteins (bright yellow, glowing neon green under a UV light)
We’ll get back to this one later — let’s focus on the three natural pigments first. These are naturally present in the majority of axolotls. Besides looking pretty and helping with camouflage, they also come with health benefits: eumelanin helps protect the skin against UV radiation, and pteridines play an important role in the axolotl’s immune system.
You can see all three pigments expressed in the picture below:
Axolotls that possess all three pigments are called wild-type. Even though they all have the same pigments, there can be a lot of variation in wild-type appearance. For instance, the axolotls shown above have a lot of yellow pteridines, which gives them an overall olive tint. They also have white spots on their tails. If I had taken the photo with the flash on, you would have seen that those white spots are shimmery, because they are made of crystallized purines.
The axolotl in the photo below is a much darker wild-type:
In this photo, we can see a lot of eumelanin. The other pigments are also present, but not very noticeable. You can see a little bit of crystallized purines in the eye ring and the tip of the gill stalks. Pteridines are almost completely invisible under the dark eumelanin.
Let me show you one more, very different wild-type look:
Isn’t this boy gorgeous? Here, eumelanin forms the base skin color, but the pteridines and crystallized purines being layered on top of each other create a gold flake effect.
In addition to the variety among wild-types, there are a lot of different color types, or “morphs”, besides wild-type. Over the course of their history, axolotls have undergone several genetic mutations which affect their pigmentation — some of which are natural, some of which are the result of human intervention.
Here are the six main genetic traits that affect axolotl pigmentation:
Albinism (affects eumelanin)
Melanism (affects crystallized purines)
Axanthicism (affects pteridines and crystallized purines)
Leucism (affects eumelanin, pteridines and crystallized purines)
We’ll talk more about these traits in the next section of the article. For, now I just want you to keep in mind that there are several genetic traits that can essentially switch pigment production on and off, or affect how pigments are distributed around the body.
Let’s take a closer look at what each pigment looks like individually.
Eumelanin is the pigment responible for shades of brown and black. It is produced by pigment cells called melanophores. To give you a better idea of what the pigment looks like on its own, here is what an axolotl looks like when it shows only eumelanin:
Fun fact: the amount of eumelanin produced by an axolotl depends on two things: genetics, and environment. Axolotls whose parents were especially dark tend to exhibit similarly dark features. Axolotls who grow up in dark environments also tend to exhibit darker features than ones kept in lighter environments.
The absence of eumelanin, due to an inability to produce melanophores, is called albinism. Here is what an axolotl looks like when you completely remove eumelanin, keeping only the other two pigments:
Pretty neat, right?
Crystallized purines are iridescent white pigments, which means they shimmer in a sort of rainbow effect. Combined with pteridines, they can also create a shiny golden color, as we’ve seen above. Crystallized purines are produced by pigment cells called iridophores. Here is what iridophores look like on their own:
The inability to produce iridophores is called melanism. Notice how the shiny white pigments are missing in the picture below:
Melanism is a little bit more complex than albinism. We’ll talk about it more in part 3 of this article.
Pteridines are responsible for yellow and orange coloration. They are produced by pigment cells called xantophores. This is what pteridines look like when you remove the other two pigments:
The inability to produce pteridines is called axanthicism. Axanthic axolotls are exceedingly rare, if not impossible to find in the Canadian pet trade. This is partly due to strict import laws, and partly due to the effect axanthicism has on axolotl health. Since pteridines play a role in immune function, axanthic axolotls have a lower survival rate than other axolotls.
In the absence of pteridines, axanthic axolotls take on a purple-grey look:
Do you notice some odd things about this picture? Axanthicism is a much more complex mutation than albinism and melanism. We’ll talk more about it when we get to the next section.
Green fluorescent proteins (GFP)
In the course of their use as animal research models [more on this soon!], some axolotls got a pretty cool addition to their genomes: the GFP trait. Originally found in a species of jellyfish, this trait causes nearly every cell in the axolotl’s body to produce a bright yellow protein which glows neon green under a UV light. Why is this cool? First, it’s been very helpful to researchers working on limb regeneration and organ transplants. Second, it looks very pretty! And third, the trait can be passed down from generation to generation. But my favorite thing about it is that, since the effect isn’t limited to pigment cells, it isn’t affected by leucism. You’ll see what I mean when we get to the next part!
Now that you have a good idea of what the individual pigments do, let’s take a look at the genetics behind them!
It’s not uncommon for axolotls to refuse food for a few days when they first arrive in a new home. Keep in mind, s/he is trying to adjust to a whole new environment, including a new owner, and possibly different food and feeding methods. Be patient! S/he will warm up to you once s/he realizes that there is nothing to be afraid of.
2. Warm water
Axolotls are subtropical, and do not handle summer temperatures well. Most axolotls suffer from heat stress and will refuse food as their water reaches 23°C or higher. Heat stress in axolotls can be deadly, particularly at 24°C or above. I will be posting an article on how to cool your aquarium [coming soon!], but in the meantime, feel free to email me for advice.
3. Ammonia issues
Ammonia makes axolotls queasy, so they may refuse food or even throw up. If you’re keeping your axolotl in a tank, make sure your filter is properly cycled. In a tub, remember to do a full water change every day!
4. Problems with the food
Axolotls may ignore or spit food out when it’s too big, too hard, or it just has a nasty taste. Try cutting overlarge food in half. You can use scissors to cut up large earthworms, or a pill cutter to cut overlage pellets. Choose a pellet that softens rapidly in water. Avoid worms that taste bitter, such as red wigglers (Eisenia fetida). To avoid spoilage, don’t buy larger quantities of dry food than your axolotl can consume in approximately one month, and try to reseal the package properly after use. Don’t allow frozen food to thaw and then re-freeze.
5. Aggressive tankmates
If your axolotl is moving away from food or staying hidden at feeding times, they may be afraid that moving towards the food will draw in their neighbor’s wrath — especially if they’ve gotten nipped by them before. The solution is to feed the more aggressive axolotl in a separate container. If you’re worried about nipping at other times, it’s best to rehome the aggressive axolotl to another tank entirely.
If your axolotl refuses to eat for several days in a row, they may have swallowed something that caused a blockage. I will be writing a separate article on the issue [coming soon!], but in the meantime, feel free to email me if you need help with this issue.
1. Make sure the pellet is small enough for your axolotl’s mouth.
2. Wait until they are hungry!
3. If they are used to feeding from tongs or fingers, try this method first.
4. Try dropping the pellets one by one just above their nose, so that they are tempted to snap.
5. It’s normal for your axolotl to hesitate at first, and maybe even spit the pellet out. Even if they don’t go for it right away, leave one or two pellets in the water overnight. A good quality pellet will entice them by smell, and will usually be gone by morning.
6. If your axolotl still won’t try the pellets, don’t feed them their usual food until the next day — you don’t want to create a “if I ignore the pellet I will get my favorite treat” association!
7. Don’t try introducing pellets several days in a row. You should alternate with normal feedings, to make sure that your axolotl stays healthy and that their refusal to eat is not due to a different stressor, such as water quality issues.
8. If your axolotl still won’t touch the pellets on your third try, and they have no trouble eating other foods… Use a better pellet!
Dwarfism is a genetic condition which causes a foreshortening of the chest area and a smaller than usual adult size. Limbs may also appear shorter than usual, although the axolotl’s fingers and toes keep a normal appearance. Dwarfism can lead to health issues and shortened lifespans, particularly in females, due to the large number of eggs they carry. Dwarf axolotls should never be allowed to breed, and may need to be housed separately to avoid getting picked on by larger adults.
A mini axolotl is one whose growth stops before reaching adult size, which can be the result of genetic issues (often due to inbreeding) or stunting due to poor husbandry. Minis may be normally proportioned, or have a somewhat smaller than average tail, with normal chest and limbs. Just like dwarves, minis may require separate housing, and it is preferable not to breed them.
Short toes syndrome
Axolotls with short toes syndrome look similar to dwarves, but they have short fingers and toes that give their hands and feet a padded appearance. Over time, they develop a pudgy appearance due to oedema, an accumulation of interstitial fluid within the body tissues, which causes bloating of the entire body (pictured above). Short toes syndrome is a very serious and irreversible condition which invariably leads to painful oedema, hemorrhages and organ failure. To prevent unnecessary suffering, axolotls affected by this condition should be euthanized as soon as the condition is detected.
Whether you’re a beginner or an experienced aquarist, here’s why you should buy the BIGGEST tank you can afford.
1. It’s less work!
Larger tanks require fewer water changes. Having a larger tank allows you to use more filtration, which keeps your water cleaner longer.
2. It’s more forgiving of your mistakes
Everything is more stable when you’re dealing with a larger body of water: the temperature doesn’t fluctuate as much, pH is more likely to stay constant, and nitrogenous waste has less of an impact when there’s a lot of water to begin with. These three factors (temperature, pH and nitrogenous waste concentration) also affect the overall toxicity of ammonia (article coming soon!). This means that smaller setups are more likely to swing rapidly between non-toxic and toxic conditions. Some species such as freshwater shrimp are especially sensitive to sudden environmental changes, which makes them challenging to keep in a small environment.
3. Your animals will appreciate it.
A larger enclosure gives you the opportunity to provide a more natural environment for your animal. They will certainly appreciate the freedom of movement and the mental stimulation that a more complex environment can afford. An animal who is comfortable in their enclosure will reward you by displaying more natural behavior.
4. It helps them fight off viruses!
Larger tanks provide a temperature gradient — the surface is warmer than the bottom of the tank. One side may also be warmer than the other, depending on light positioning (and heater positioning, if you’re keeping tropical species). Having a temperature gradient in your tank allows your animals to adjust their body temperature, and even to self-medicate! Fish and amphibians are poikilotherms, which means their body temperature is meant to vary along with their environment. It also means that their bodies are not able to trigger a fever when they are sick. Instead, they rely on what we call behavioral fever: a sick animal will gravitate to the hottest area of the tank, act sluggish for a while, and wait for the virus or bacterial infection to pass. Amphibians are also particular in the way that they gravitate to colder temperatures when recovering from illnesses and injuries. Some scientific studies suggest that axolotls’ impressive recovery abilities function best at near-hibernation temperatures.
Axolotls are carnivores, and insects make up the bulk of their diet in the wild. In the aquarium, they will accept a range of live, frozen and dried foods. Here are a list of recommended staples and treats. Scroll down for more info on each of these!
Soft, sinking carnivore pellet
Live nightcrawlers (Canadian earthworms)
Live red wigglers (compost worms)
Repashy Grub Pie
Live small fish (home-bred)
How to choose a pellet
I have tried a lot of the “axolotl pellets” on the market and I have to tell you, my critters were none too pleased. My personal recommendation is Northfin Jumbo Fish, which is a soft sinking pellet for carnivore fish. The reason I like it is that it has quality ingredients, is reasonably-priced, and I’ve never encountered an axolotl who didn’t like them.
If you want to try a different pellet, make sure it’s the sinking type, as axolotls have difficulty learning to look for their food at the water surface. Choose a pellet with a protein content around 40%, and which don’t list grains within the first three ingredients. It should be supplemented with vitamins and minerals, and the pellet should soften quickly without losing its shape or making the water cloudy.
Regardless of the brand you decide to go with, it’s a good idea to supplement your axolotl’s diet with the occasional live worm.
Axolotls love their nightcrawlers! I consider them a form as enrichment as well as a healthy, affordable food staple. Most axolotls will enthusiastically lunge at them as soon as they see them.
Where to find them: Nightcrawlers are the large Canadian earthworms sold as fishing bait throughout the country. If you want to use the ones you find in your backyard, make sure your neighbors aren’t using any herbicides or pesticides, as those could be toxic to your axolotl. If you’re in the area, you’re welcome to come by my shop to pick some up. I can also ship them when the weather permits. If you’d like to order some and they’re not listed in my shop, email me and I’ll see what I can do for you.
How to store them: Nightcrawlers need to be stored in a cool place, such as a basement or a wine cooler. If you transfer them to a plastic container with fresh soil and a couple of small ventilation holes, they will keep for several months. There is no need to feed them — just lightly mist the soil with water if it looks dry. If all of the worms are at the surface when you open the container, it’s a sign that they are either too hot or the soil is due to be changed.
How to feed them to your axolotl: I recommend using tongs, and swishing them in a bit of water first to dislodge any dirt and excess slime. You might want to cut the really big ones in half, too.
How much to feed: One nightcrawler every other day is enough. Alternatively, you could do half a nightcrawler every day.
Problems with fussy eaters? If your axolotl spits out his food, try offering it again once or twice — sometimes they just didn’t get a good enough grip the first time. If your axolotl is giving up on the worm after trying to wrestle it into submission for a while, try cutting the worm into smaller pieces. If your axolotl is immediately and repeatedly spitting the worm out, or turning away from it, see: why is my axolotl refusing to eat? [Coming soon!]
Red wigglers are compost worms, which means you can start your own culture at home if you have the patience for it. There’s a lot of trial and error involved, as certain foods cause them to develop a bitter taste which axolotls are quite fussy about.
Where to find them: Most of the big stores that sell camping and fishing supplies carry them as fish bait. You can also order them online through most of the year. I frequently have some in stock, as well. If they’re not listed in my shop, email me and I can probably order some in for you.
How to store them: These do well at room temperature. Make sure there’s some ventilation in their container. If you’d like to start your own culture, you’ll find plenty of vermicomposting guides online. Personally, I haven’t developed the knack for it, yet.
How to feed them to your axolotl: These survive longer than nightcrawlers in water, so you can just drop them in and wait for your axolotl to find them. I still prefer to use tongs, personally — it prevents the worms from sneaking under the decor, and makes it easier for the axolotl to grab. I also recommend swishing them in a bit of water first to dislodge any dirt and excess slime. Some axolotls are fussy about that.
How much to feed: It depends on the size, but I find that one per day is usually enough. Alternatively, you could do two every other day.
Problems with fussy eaters? Chances are your red wigglers taste bitter. Try a different kind of food, and if your axolotl accepts that one, take it as a sign that you need to modify your red wigglers’ diet.
What the heck is Grub Pie?
Repashy Grub Pie is ground bug powder that can essentially be turned into bug jello. Axolotls seem to really enjoy the smell (it’s quite stinky!)
Where to find it: You can buy it from some online shops. I frequently have it in stock.
How to store it: The gel keeps for up to two weeks in the fridge.
How to feed it to your axolotl: Axolotls like to gobble up their food in one bite, so you should start by cutting the gel into appropriate-sized pieces. I highly recommend using tongs to feed these to your axolotl — in my experience, axolotls don’t like to pick these up from the bottom of the tank. If they stay in the water for too long, the pieces start to fall apart and the water turns quite nasty.
How much to feed: Most adults will eat a piece that is roughly the size of half a gummy worm every day, or one whole gummy worm every other day. Juveniles who are still growing and females who are plump with eggs may want to eat a little extra.
Problems with fussy eaters? If you’re using the tong method, try hand-feeding. If that still doesn’t work, see: why is my axolotl refusing to eat? [Coming soon!]
Everyone loves bloodworms! They are the french fries of the aquatic world. They make a great treat, and are useful when trying to convince a sick or stressed axolotl to eat. They are high in fat and low in protein, so they should not be fed as a staple.
Where to find them: Your local fish store most likely carries them.
How to store them: Stick them in the freezer, and break off a little piece whenever you need it. They will thaw very quickly in the aquarium.
How much to feed: If you buy bloodworms in small amounts, chances are it will be pre-partitioned. If not, try to break off a piece that’s no larger than a quarter. Remember, it’s only meant to be a treat!
Problems with fussy eaters? If an axolotl is refusing bloodworms, something is definitely wrong. See: why is my axolotl refusing to eat? [Coming soon!]
Live small fish
“Feeder” fish sold at pet stores are best avoided, as they may harbor parasites or other pathogens. Fish that you breed yourself can be a healthy food source, so long as they are small enough that the bones won’t cause a blockage. Even so, I wouldn’t recommend feeding live fish as a staple. Axolotls are just not very good at catching them. Their natural hunting method is to dig through the mud with their noses to find bugs and invertebrates, or to camouflage themselves among plants and wait for prey to venture near their mouths. Trying to ambush fish this way can be a fun game for them, but you can easily see how they would starve if they had no other meal option!
If you do want to try raising fish to feed your axolotls, make sure you select a compatible species. You can find my recommendations here: Axolotl tankmates: fish edition.
Can you keep axolotls with fish? The answer, surprisingly, is yes — you just need to choose your fish carefully.
One thing to keep in mind when keeping fish with axolotls is that those long flowy gills can start to look like food to just about any fish who’s hungry enough. Make sure to keep your fish well-fed, and be ready to separate them if you notice that your axolotl’s gills are showing signs of damage.
My personal success stories! These peaceful fish enjoy cold, hard, neutral pH water. In addition, they are either too fast for axolotls to catch, too big to make an attractive meal, or they reproduce fast enough that the population should be able to maintain itself.
Swimming buffet These are fish who enjoy the same water parameters as your axolotls, but are likely to become dinner very fast. If you breed them in a separate tank, they could be an attractive option as a source of cheap live food.
Golden dwarf barb
Medaka (japanese ricefish)
Northern glowlight danio
Experienced fishkeepers only! These species could potentially be a good match, provided that you are able to maintain your water temperatures at a steady 20°C ±1°C. Do read the fish’s care requirements carefully before you make the plunge, as you may need to modify your tank setup or maintenance routine. Do keep an eye out for signs of stress in both species, and be ready to separate or adjust your setup as needed.
Blue moon danio
Dwarf spotted danio
Gold ring danio
Guppy (I know it’s typically considered a beginner fish, but trust me on this!)
While these fish can be kept at room temperature, they should not be kept at temperatures below 21°C for extended periods of time.
Black neon tetra
Black paradise fish
Black phantom tetra
Black ruby barb
Bleeding heart tetra
Brown spike-tailed paradise fish
Celestial pearl danio
Common hatchetfish (silver hatchetfish)
Crossband chocolate gourami
Crystal red tetra
Emerald dwarf rasbora
False spanner barb
False x-ray tetra
Fire bar danio
Flame red rasbora
Green line lizard tetra
Green neon tetra
Indian glass fish
Jelly bean tetra
Pookode lake barb
Red dwarf rasbora
Red phantom tetra
Red-tailed tinfoil barb
Siamese algae eater
Steindacher’s apisto (A138)
Striped flying barb
Three-striped apisto (A204)
Yellow phantom tetra
These bottom-dwelling fish would infringe on your axolotl’s turf, which could lead to stress and aggressive behaviors. This includes most loaches and catfish.
Chinese false gudgeon
Horse face loach
Mini dragon loach
Probably too aggressive
While these guys enjoy cold hard water, I’m not sure about their temperaments. Based on what I know of their close relatives, I would expect them to be too aggressive to be kept with axolotls.
Mekong tiger perch
New guinea tiger perch
Roundtail paradise fish
Given their precarious conservation status, it wouldn’t make sense to keep these fish in the same tank as a potential predator.
Siamese tiger perch
Don’t even think about it! These fish have a tendency to nip at flowy fins and gills, or have environmental needs that differ greatly from those of axolotls. This includes most bettas, cichlids, piranhas, pacus and sharks. I’m not including obligate brackish or saltwater fish, but it goes without saying that those would not be a good match either!