Fish with Caudates
By Abrahm Simons
A commonly asked question on the Caudata.org forums is "Can I keep fish with my axolotls/newts?" In general, the answer to this question is 'no'. This article will lay out the reasons to avoid mixing fish and aquatic amphibians, and what fish are exceptions to the rule.
Three basic reasons to avoid keeping fish with caudates
- Temperature
Most fish sold in pet stores are tropical, and their temperature requirements are incompatible with caudates. 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 74-82°F (23-28°C), and this does not overlap with a newt or axolotl's preferred temperature range, which has a maximum of 72°F (22°C) for most species. This means that if you keep tropical fish with newts/axolotls, 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 impairment of 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. If you care about breeding, your newts or axolotls will be less likely to breed if they are kept at a steady year-round temperature in order to accomodate fish. - Predation & Territory
All newts 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, the axolotl/newt will attempt to eat it. With some fish this is fine, but with others there are problems such as the cost of your fish or injury to the caudate caused by the fish's defenses, such as toxins or spines. Territorial newts may stress out and be stressed in return by fish that occupy their territory, leading to illness. Fish have been known to nip at an axolotl's gill, suck on the caudate's slime coat, or simply harass a newt for occupying its territory. - Contamination
Animals that are purchased from the pet store can be host to a 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 any established animal. Quarantine should be strict, with animals kept in separate locations and separate supplies and equipment used between tanks.
Specific fish
The information below delves into why certain fish make bad or good tankmates for newts or axolotls. Most fish make bad tankmates, but there are exceptions that deserve mention.
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Goldfish - Carassius auratus - Goldfish, being temperate animals, have an overlapping temperature range, but their eating habitats, large size, and waste production make them a poor choice. Goldfish grow to a total length of between 6-12" and are large chunky fish. With their impressive bulk, they create a 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 nipping on a large caudate or trying to eat a smaller one. There are incidents involving goldfish on the Species Mixing Disasters page. It should also be noted that goldfish are a poor feeder food as they are high in saturated fats. |
Photo by Jennifer Macke |
Sucker Fish, Pleco, Plecostomus - Family Loricariidae - 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" (46-61 cm) and is not really suitable for any but the largest aquariums. 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) have problems with temperature requirements and have dangerous defensive spines in the pectoral and dorsal fins. There are incidents involving plecos on the Species Mixing Disasters page. |
Photo by Stuart Halliday, Creative Commons | Cories - Corydoras spp. - They are tropical, bottom-dwelling fish preferring temperatures above 75°F (24°C), compete for territory and hides with newts, and are armed with defensive spikes in their dorsal and pectoral fins. Serious injury or death can result from an animal trying to eat a cory catfish. There are incidents involving cories on the Species Mixing Disasters page. |
Photo by Marrabbio2, Creative Commons | Otos - Otocinclus affinis - At 1-2" (2.5-5 cm), these small fish are especially dangerous. This fish can easily be eaten by an axolotl or large newt, and choke the caudate when it deploys its dorsal spikes. There are incidents involving otos on the Species Mixing Disasters page. |
| Chinese algae eaters - Gyrinocheilus aymonieri - When they mature, these fish are extremely territorial, aggressive, and do not eat algae. Avoid them at all cost! |
| Betta, Siamese fighting fish - Betta splendens - These fish, while beautiful, make especially bad tank mates for caudates. Betta fish do best at temperatures approaching 80°F (27°C). If they are kept below 75°F (24°C) for significant periods of time they will become listless, develop "the shimmies" or become increasingly susceptible to disease. These fish are well known for their territoriality which may cause problems with tankmates. There are incidents involving bettas on the Species Mixing Disasters page. |
Photo by jimmyroq, Creative Commons | Guppies - Poecilia reticulata - 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. |
Photo by sannse, Creative Commons | White Cloud Mountain Minnows - Tanichthys albonubes - These are quite likely the perfect fish if you must keep fish with your newt or 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 possibility. |
| Rosy red minnow, fathead minnow - Pimephales promelas - These North American fish are members of the same family as the White Cloud Mountain Minnow and have all the same benefits. |
Photo by Sean Murray, Creative Commons | Freshwater shrimp - Some freshwater shrimp do well at low temperatures and can be acceptable tankmates, as an alternative to fish. Your newt or axolotl will probably try to eat them, so be prepared for this possibility. Be sure to research the suitability of the particular species of shrimp, and follow the usual quarantine procedures before introducing them. |
Common reasons for wanting to keep newts or axolotls with fish
- "My tank has algae so I need an algae-eating fish." - Acquiring an algae-eating fish is an attempt to treat a symptom of an underlying problem. It will not be very effective. Algae grows in tanks due to excess nutrients, and this underlying cause must be treated first. Adding an algae-eating fish can make the problem worse, as the fish converts algae and other foods into other forms of waste, which becomes even more algae food. Some algae eaters don't actually eat algae, or may refuse to eat the type of algea you have. You can learn more about algae and how to combat it in Algae & Tank Critters.
- "Newts and axolotls live with fish in the wild." - This is often true, but there is no way to compare the tiny artificial habitats we provide with what animals experience in the wild. Even the largest aquariums we could provide are nothing in comparison to the sheer volume of water and territory that a 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 newt or axolotl looks lonely." - Caudates are not social animals. They don't feel lonely or have any need to be social. Caudates will usually be healthier kept in single-species enclosures, as there will be fewer sources of stress.
© 2009 Abrahm Simons; updated September 2023