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Aquatic and Semi-Aquatic Amphibians
Amphibians of various types are commonly sold in aquarium shops, but on the whole they don't make good companions for tropical fish. As we'll see in this article, frogs, toads, newts and salamanders are best treated as subjects for their own aquarium or vivarium.
But this doesn't mean amphibians are difficult to keep! Indeed, compared to reptiles such as snakes, turtles and lizards, amphibians are surprisingly undemanding. For a start they don't need a UV-B basking lamp and many do perfectly well at room temperature, so that's two expenses removed from the equation right from the start. They also tend to be smaller and less fussy about their diet, which makes them much easier animals to maintain than most reptiles.
Aquatic, semi-aquatic and terrestrial systems compared
Fully-aquatic amphibians can be kept in aquaria similar to those used for keeping fish, but note that only in exceptional situations should fish and amphibians be kept together in the same tank. For a variety of reasons it is almost always better to keep amphibians in their own aquarium. In terms of aquarium set-up, you'll need a filter for certain, and a submersible heater if the amphibian in question is a tropical species. Amphibians are easily burned so the heater should be protected with a heater guard if possible (this isn't an issue if the heater goes outside the tank, as with the Hydor ETH units). Choose a robust, easily maintained filter because amphibians can pollute the tank heavily and consequently filters tend to become clogged quite quickly. In most cases, a good quality internal canister filter would be ideal. African Clawed Frogs, Dwarf Frogs, Axolotls and Rubber Eels are all examples of fully-aquatic amphibians.
Semi-aquatic amphibians are those species that spend time a lot of time in the water but will also go onto the land for extended periods as well. At its simplest, housing these amphibians will be similar to housing fully-aquatic amphibians except that the water level will be lower, typically no more than about 15-20 cm, with dry land above the waterline created using rocks, bogwood and piles of gravel and/or sand. Various wood, plastic and ceramic items are available in pet stores to divide the tank up in a similar way, so that shelves, terraces and other above-the-waterline areas could be created. Live or plastic plants can be further used to decorate the tank, with many aquarium plants (such as Anubias and Amazon Swords) doing exceptionally well if planted with their roots underwater but their leaves left to grow above the waterline. Heat may be provided either by using a standard aquarium heater or an undertank heating mat. The humidity of the air in the tank is important as well, so this set-up will need a hood that traps the warm, damp air inside the vivarium. Fire-Bellied Toads and Tiger Salamanders are classic examples of semi-aquatic amphibians.
Terrestrial amphibians spend only short periods of time underwater. They can be housed in purpose-made vivaria designed for their needs, but a standard aquarium can be used as well, albeit with a few modifications. The key things are that an undertank heater is used to warm the tank, while a hood is used to keep the warm, damp air inside. Furthermore, rather than the gravel or sand, the substrate will be either moss or coconut fibre (coir). Moss is prettier, but coir is much cheaper and a "greener" product. These factors are important because the substrate will collect all the wastes produced by the amphibians, so needs to be replaced every few days. A shallow pool of water should be provided so the amphibians can drink and bathe, but take care to ensure the amphibians can't drown by using a container with nice sloping sides. Houseplants like Philodendron are often used in vivaria of this type, but these will of course need bright light to grow. Alternatively, there are all sorts of plastic plants and vines sold in pet stores that work just as well. Among the most widely traded terrestrial amphibians are Tree Frogs and Pac-Man Frogs.
Axolotls, Ambystoma mexicanum
Axolotls are very unusual amphibians that retain their juvenile ("tadpole") form into adult life. Even as adults they have external gills like the tadpoles of other amphibians and are fully aquatic. Wild-type Axolotls are greyish in colour, but a pale pinkish-white form is widely traded. Axolotls get quite large, up to 30 cm including the tail, though most specimens are somewhat smaller. Given their size, these are amphibians for relatively large set-ups. A pair can be kept in systems 150 litres upwards, but do be aware than Axolotls are snappy and will fight if they feel cramped, particularly the males. Male and female Axolotls look similar, but if the cloaca ("vent") is examined, that of the male will appear much more swollen in appearance. Females also tend to be more robust in build than the males. Maintenance is straightforward. Apart from a good-sized tank, they need excellent water quality which can be provided through heavy-duty filtration, such as an external canister filter, but heating is generally not required as Axolotls thrive at normal room temperatures around 15-18 degrees C. They dislike strong light, so the ideal tank will use subdued lighting and plastic plants. Feeding is unproblematic as Axolotls are very opportunistic. They enjoy earthworms and river shrimps, but will also take fresh meaty foods like tilapia fillet and the occasional prawn. While they should never be handled (their skin and bones are easily damaged) Axolotls can be hand-fed using steel forceps or chopsticks to present items of food. Overfeeding can be a problem, and the usual approach is to feed Axolotls every other day to avoid fouling the water.
Fire-Bellied Toads, Bombina spp.
There are several species of Bombina species sold under the Fire-Bellied Toad name, but the most commonly traded one is the Oriental Fire-Bellied Toad, Bombina orientalis. As its name suggests this species comes from East Asia where it is spread across Russia, China and Korea. It is green and black on the upper surface and orangey-red and black underneath. Maximum body length is about 6 cm, with females being noticeably more rounded than the males. Bombina orientalis is an undemanding species well suited to a semi-aquatic system with good, clean water and a few dry land areas where it clamber about from time to time. Water temperature should be around 20-22 degrees C for most of the year, but slightly cooler conditions, around 18 degrees C, is helpful in winter, especially if you want them to breed. Bombina orientalis likes to float at the surface of the water under the lights, so the use of floating plants is recommended. Feeding isn't too difficult, but mostly happens on land rather than underwater, with live foods like cricket, mealworms and small earthworms being the most readily accepted prey items. Bombina orientalis is active and gregarious, and a group of 4-6 specimens could easily be maintained in a 90 litre aquarium.
African Dwarf Frogs Hymenochirus spp.
Several species of Hymenochirus are traded in aquarium shops, including Hymenochirus boettgeri and Hymenochirus curtipes They are fully aquatic frogs that get to body lengths of 3-4 cm, so are well suited to well-planted tanks from 25 litres upwards. Although sometimes kept successfully with very small fish (dwarf rasboras for example) they are best kept on their own in small groups. They also mix well with shrimps, providing the aquarist with a mix of interesting livestock. Hymenochirus are tropical animals and need to be maintained at around 25 degrees C. They are not difficult to feed, but their small size means they often lose out when kept with fish. Kept on their own they will happily consume frozen foods like bloodworms and brine shrimp as well as suitable pellet foods.
Paddle-Tail Newt, Pachytriton labiatus
This Chinese newt is fully aquatic and naturally inhabits fast-flowing streams. It gets to about 15 cm or so in length and needs an aquarium no less than 150 litres in size equipped with a good, strong filter that provides clean, oxygen-rich water. A pair could be maintained in a tank this size, with males being similar to females except that males (in breeding condition at least) have a white blotch on their tails that the females lack. Males are very aggressive though, so two males should not be kept in the same tank! These newts are active but slow-moving, and like to clamber through smooth, waterworn cobbles and bogwood, just as they would in the wild. Hollow ornaments and caves provide welcome shelter. They dislike high temperatures, and a heater is not normally required as they do best at room temperatures between about 15-18 degrees C. Direct sunlight must be avoided as overheating the tank will quickly stress them. Feeding is not difficult, with foods such as earthworms, tilapia fillet and frozen bloodworms being readily taken.
Rubber Eel or Sicilian Worm, Typhlonectes natans
This is a member of limbless amphibians called caecilians (pronounced "say-see-lee-ans"). While most of them spend their lives burrowing through soil and leaf-litter, this species is fully aquatic. Because it gets to around 40 cm in length it needs a large aquarium, 150 litres or more. It looks particularly good in planted aquaria, and enjoys climbing through vegetation close to the surface, such as floating plants. On the other hand, like all caecilians they enjoy burrowing, so the sediment should be smooth silica sand (such as pool filter sand) rather than gravel. Typhlonectes natans is not a demanding species and does well in both hard and soft water. It is a tropical species though and should be maintained at around 25 degrees C. Typhlonectes natans are predators and eat live and fresh foods such as bloodworms, mealworms, earthworms, tilapia fillet, lancefish and prawns. They will eat very small fish, but may be combined with peaceful fish too large to be swallowed, such as Swordtails. Take care with catfish and loaches though, partly because they'll compete for the same food, but also because the defensive spines of catfish and loaches present a choking hazard should the caecilian attempt to swallow them.
African Clawed Frog, Xenopus laevis
These large frogs come from South Africa where they live in shallow ponds and lakes. They are fully aquatic and have been kept as lab animals for decades. They are fairly popular pets as well, and besides the standard brown form, a golden form is available as well. Xenopus laevis reaches a body length of over 10 cm but despite its size it is remarkably undemanding. Pairs may be maintained in tanks from around 90 litres upwards, and adults show little evidence of aggression outside of breeding. They are strong, active animals that enjoy tanks with plenty of floating plants and good water quality. Maintenance isn't hard, but they are heavy polluters so robust filtration and frequent water changes are essential. They eat all sorts of meaty foods, with earthworms being particularly popular but frozen foods like krill and bloodworms being taken as well. Settled specimens will take good quality pellets as well. Xenopus laevis is a subtropical species that should be maintained at 18-22 degrees C. It enjoys light and will bask at the surface given the opportunity.
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