Abrahm
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A commonly asked question on these forums is "Can I keep fish with my axolotls/newts?" In general the answer to this question is no and this article is planned to lay out the reasons to avoid mixing fish and axolotls/newts and what fish are exceptions to the rule.
In general - Fish and newts are best kept separately mainly due to differences in temperature preference, predation/territory and contamination issues.
Specific Fish - I'll use this space to delve into why certain fish make bad or good tank mates for newts/axolotls. Most fish make bad tank mates but there are occasional stand outs that deserve mention.
Common Reasons People for Keeping Axolotls/newts with Fish
In general - Fish and newts are best kept separately mainly due to differences in temperature preference, predation/territory and contamination issues.
- Most fish sold in pet stores are tropical. These fish only thrive and reach their true life expectancy if they are kept within an appropriate temperature range. For most pet store fish that is between 76-82F (24-28C) and does not overlap with a newt's preferred temperature range which has a general maximum of 70F (21C). This means that if you keep tropical fish with newts one of the two will be at an inappropriate temperature. While this may not be immediately fatal it will cause a great deal of stress to the animal that is kept at the wrong temperature. Stress can cause physical symptoms which include hurting the immune system. An animal with a depressed immune system does not fight off infections well and is more susceptible to new diseases. Over the long term animals kept in a high stress environment are more likely to die from disease or other problems.
- All newt and axolotls are predators and some newts such as Pachytriton and Paramesotriton are quite territorial. It is quite likely that if the fish being housed with the newt/axolotl is small enough an attempt will be made to eat it. With some fish this is fine but with others there are many problems such as the cost of your fish or more important to your newt defenses such as toxins and spines. Territorial newts may stress out and be stressed in return by fish that occupy their territory leading to both becoming ill. The reverse can be said of many fish; many of which can nip at an axolotl's gill, eat the caudate's slime coat or simply harass the newt for occupying its territory.
- Animals that are purchased from the pet store can be host to any number of diseases. Due to the close quarters of fish and amphibians during wholesale, shipping and the pet store it is very common for these animals to be ill and stressed. There are many diseases that can jump from fish to amphibians and not all the fish you buy will be showing symptoms of their disease. Illnesses such as ich (Ichthyophthirius multifiliis) can hide in the gill rakers of fish and be completely invisible. Animals acquired from pet stores should be quarantined before being introduced to an established animal. Quarantine should be strict with animals kept in separate locations and no supplies used in both tanks.
Specific Fish - I'll use this space to delve into why certain fish make bad or good tank mates for newts/axolotls. Most fish make bad tank mates but there are occasional stand outs that deserve mention.
- Goldfish - Goldfish should not be housed with newts/axolotls. They have an overlapping temperature range, goldfish being temperate animals, but the eating habitats, large size and waste production of this fish makes them a poor choice. Goldfish grow to a total length of between 6-12" and are large globular fish. With their impressive bulk they create an utterly massive amount of waste which makes keeping these fish with any other animal a difficult proposition. Goldfish are omnivorous and will try to eat just about anything which could include sucking on a too large caudate or trying to eat a smaller one. It should also be noted that goldfish are a poor feeder food and are high in saturated fats.
- Sucker Fish, Pleco, Plecostomus - These fish generally belong to the family Loriicaridae or armored catfish. These are bulky fish with an armored look to them complete with strong and dangerous defensive spikes on the pectoral and dorsal fins. The common petstore pleco is a behemoth of a fish that generally tops out at 18-24" (46-61cm) and is not really suitable for any but the largest aquariums. Keeping them in smaller tanks will stunt their growth (and be harmful to their health) but even so these large algae eaters produce a lot of waste. It is best to think of these animals as being similar to a cow in that they eat a lot of algae/grass and produce a lot of poop. Smaller members of this family (Ancistrus or bushy nosed plecos and Otocinclus affinis as two examples) have problems with temperature requirements and extremely dangerous defensive spines in the pectoral and dorsal fins. The Otocinclus is especially dangerous at 1-2" (2.5-5cm) in that it can easily be eaten by an axolotl or large newt and choke the newt when it deploys its dorsal spikes. Chinese algae eaters should also be mentioned even though they are not plecos. These fish are extremely territorial, aggressive and do not eat algae. Avoid them at all cost!
- White Cloud Mountain Minnows - These are quite likely the perfect fish if you must keep fish with your newt/axolotl. They are small, devoid of defensive spines and do well in cool water. These small fish may be eaten by your axolotl so be prepared for this eventuality.
- Guppies - Wild type guppies tend to be a very hardy and prolific fish while their fancy cousins are usually very finicky. Wild type guppies can survive at the upper reaches of a newt's/axolotl's temperature range and provide a healthy snack. Guppies are livebearers so if you have a male and a female expect to see fry (babies) on occasion.
- Rosy red minnow or fathead minnow - Pimephales promelas This North American fish is a member of the same family as the White Cloud Mountain Minnow and has all the same benefits.
Common Reasons People for Keeping Axolotls/newts with Fish
- My tanks has algae and now I need an algae eating fish! - Acquiring an algae eating fish is trying to treat a symptom of an underlying problem. It will not be effective. Algae grows in tanks due to excess nutrients, whether that is light or biomaterial, and this underlying cause must be treated first. Acquiring an algae eating fish, some of which do not truly eat algae, can make the problem worse as the fish converts algae and other foods into even more waste which becomes even more algae food. You can learn more about algae and how to combat it here.
- Newts and Axolotls live with fish in the wild. - This is absolutely true but there is no way to compare the tiny artificial habitats we provide with what a caudate experiences in the wild. Even the largest aquariums we could provide are nothing in comparison the to the sheer volume of water and territory that natural habitat provides. There is no way for fish or newts to escape any stressful situation in an artificial habitat leading to increased risk of disease and death.
- My caudate looks sad/lonely. - Caudates are not social animals. They don't feel lonely or any need to be social. Caudates will usually be healthier kept in single species enclosures as there will be less sources of stress.
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