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Mudskippers
Mudskippers are gobies that have become adapted to an amphibious lifestyle. They are common on tidal mudflats throughout tropical Africa, Asia and Australasia where they crawl about out of water feeding on small animals, particularly flies and small crabs, as well as algae. A number of mudskippers of the genus Periophthalmus are quite regularly traded, though other species may be seen occasionally as well.
Genus Periophthalmus
This is the group of mudskippers most commonly traded. A single species is found on the West African coastline of the Atlantic; the others are from the Indo-Pacfic region between East Africa and Australasia.
All Periophthalmus species are territorial and aggressive, though the degree of aggression varies. The biggest species are often so aggressive they cannot be maintained in groups under home aquarium conditions, and are best kept alone. Male Periophthalmus barbarus in particular have a well-earned reputation for being extremely aggressive and intolerant of tankmates, as well as surprisingly predatory towards small fish and crabs. On the plus side, these big mudskippers are intelligent and easily tamed, making them fun pets in the truest sense of the word.
Several species are traded, though often without their scientific names, making selection difficult. Provenance is a useful clue though, the West African mudskipper being the only species that invariably needs to be kept alone. The smaller and less aggressive South and Southeast Asian species are generally readily maintained in multi-speciment settings, particularly if somewhat overcrowded to prevent any one male from becoming dominant. If you decide to take this approach and overstock the vivarium, great care will need to be taken with regard to issues such as water quality and general hygiene. Because the filter cannot clean the sand above the waterline, compensate for this by regularly cleaning up the tank, removing uneaten food and fish wastes.
- Periophthalmus barbarus is commonly traded as the West African mudskipper and is one of the larger mudskipers and also one of the most commonly traded. It is mature at 25 cm (10 inches) and is the only mudskipper in the Atlantic Ocean, being found along the coast of West Africa. It feeds primarily on small arthropods but will also take small fish. The name Periophthalmus papilio has been used for this species in some aquarium books. It is an extremely aggressive species, and the males in particular almost invariably need to be kept alone once mature. Periophthalmus barbarus can be recognised not just by its large size but also by its two navy blue dorsal fins both edged with electric blue bands.
- The species traded as the Indian dwarf mudskipper is Periophthalmus novemradiatus is a small (~5 cm/2 inches) species that works particularly well in aquaria because its territorial demands are easily met. This small species has yellowy dorsal fins with red and white spots. Both finds are edged with black bands but the front dorsal fin also has a large orange blotch.
- Silver-barred mudskippers, Periophthalmus argentilineatus, are larger (~20 cm/8 inches) and consequently less easily accommodated, but isn’t nearly as aggressive as Periophthalmus barbarus. They can be recognised by the silvery vertical stripes along the flanks. The dorsal fins are brown with silvery spots, edged with thick black and narrow white bands.
Periophthalmodon species
- Periophthalmodon septemradiatus is a mudskipper species with blue dorsal fins and consequently often confused with Periophthalmus barbarus by the trade. It is a Southeast Asian species though, so simply checking whether the species offered for sale comes from Africa or Asia should clear up any confusion. In addition while both species have blue dorsal fins, the dorsal fins of Periophthalmodon septemradiatus are blue with yellow and white spots. The body also has a distinctive metallic sheen. Maximum size is about 10 cm.
Boleophthalmus species
- The less terrestrial Boleophthalmus boddarti and its congeners get to about 20 cm (8 inches) and are rather more goby-like shape. Their eyes are located in a more normal position and they lack the bright coloured dorsal fins of Periophthalmus. Members of this genus feed on smaller food items than Periophthalmus, primarily algae, and do not do well in most aquaria. All species in this genus are best avoided.
Water chemistry
Mudskippers are famous for their ability to leave the water and climb out and feed on mudflats and mangrove roots, but they do need to go into the water periodically. One common mistake is to keep them in freshwater: they cannot live for long under such conditions!
The precise salinity is not important and most species will do well in brackish water with a specific gravity between 1.005 to 1.015. While variations in salinity do them no harm and would in fact be encountered in the wild, big changes in salinity can stress (or even kill) biological filter bacteria, so are best avoided.
Social behaviour and tankmates
Mudskippers are best kept in single species groups: big species will bully smaller ones, and even similarly sized species may exhibit different levels of territoriality and aggression. Males are much more aggressive than females, and the males of larger species, particularly Periophthalmus barbarus, are so aggressive they invariably end up being kept alone. Unfortunately for the aquarist, sexing mudskippers is difficult even with adults, and impossible with juveniles.
In terms of tankmates, mixing crabs with mudskippers is possible but risky. Some crabs will view mudskippers as potential food, while larger mudskippers certainly do feed on small crabs in the wild. The best crabs are fiddler crabs (Uca spp) rather than the more widely sold things like red-claw crabs (Perisesarma spp).
Mudskippers view fish of similar or larger size with suspicion, and will avoid going into water where there are large, active species that the mudskippers assume are predators. But small fish can be added, with livebearers and gobies being the most obvious choices. Do bear in mind that large mudskippers will try and eat small fish, and livebearer fry in particular are very vulnerable. You also have the problem that the amount of water in a mudskipper tank is very small, around one-quarter of the total capacity of the aquarium. So choose fish that will do well in relatively small, shallow bodies of water.
A mudskipper aquarium
Mudskippers are essentially hardy fish, and the main problems for the aquarist are creating a tank with enough land for them to explore and also to stop them from escaping. The first problem is solved by choosing a tank big enough that you can incorporate one (or more) sandbanks made from a coral sand/silica sand mix shored up with smooth stones, coral rubble, slates and bogwood. Mudskippers like to dig, and in part they feed by sifting sand; consequently they do not appreciate being kept in tanks with gravel substrates. To stop them from escaping make sure the hood is tightly fitted and block any potential escape routes with plastic mesh or even filter wool. A cover glass (usually made from thin plastic these days) is extremely useful for this. Mudskipper tanks do need some ventilation though, so take care not to completely seal the aquarium!
Filtration is easily provided using any suitable filter. Because the quantity of water in the tank will be relatively small, even something like an internal canister filter could easily be adequate. As with any other fish water quality should be good, and you should aim to replace 25-50% of the water each week. Mudskippers come from tidal habitats so would naturally encounter strong water currents. While not essential in captivity, if you can provide a decent current and/or a bit of extra aeration, so much the better.
Heating is more of a problem because mudskippers like to clamber over solid objects and can easily be scaled by standard aquarium heaters. Either choose a heater that fits inside the filter; use a standard heater protected with a plastic guard; or use an undertank heating mat of the type used to keep reptile and amphibian enclosures warm.
Diet generally does not pose a problem because the commonly traded species are adaptable omnivores, with the exception of the primarily herbivorous Boleophthalmus species best avoided by aquarists anyway. For the Periophtalmus species that do well in captivity, a mixed diet containing a certain amount of flake along with frozen bloodworms, live brine shrimps and chopped seafood will work well. Occasional offerings of small live insects will be welcomed, but avoid anything they wouldn’t normally encounter in their mangrove habitats because these may cause digestive problems. Small flies, particularly fruit flies, as well as small moths usually work well, but don’t use things like mealworms or crickets.
The image below shows a simple mudskipper aquarium (click on the image for a larger version).
