Periophthalmus novemradiatus

Dwarf Indian Mudskipper

Classification

Gobiidae. Subfamily: Oxudercinae

Distribution

Found around the coastlines of India, Myanmar, Thailand, Malaysia, the Phillipines and parts of northern Indonesia.

Habitat

Occurs mainly in estuarine mangrove swamps, where it lives on and around mudflats at the water’s edge. Some populations live in highly tidal areas, where the flats are only exposed at low tide. The fish emerge to forage during these periods, retreating underwater to their burrows when the water level begins to rise.

Maximum Standard Length

P. novemradiatus is thought to be the smallest species in the genus. Although some sources suggest it can attain 4″ (10cm) in length, the largest specimen recorded to science measured only 2.6″ (6.4cm).

Aquarium SizeTop ↑

A 30″ x 12″ x 12″ (120cm x 30cm x 30cm) – 67.5 litre tank is just about acceptable for a trio of fish. The more floor space the better though. Aim for around 12″ x 12″ of territory space per fish as a bare minimum. If less space is available the fish will co-habit but frequent skirmishes are likely to occur.

Maintenance

The set-up must have exposed land areas. A bank or beach made of sand or mudflat mud is suggested but you could use partially submerged bogwood. It’s also essential that the atmosphere outside the water is very humid and has the same temperature as the water. A tightly-fitting lid is therefore a prerequisite, and will also prevent the fish from climbing out of the aquarium. If you want to grow plants use species that can tolerate brackish conditions such as Rhizophora (mangrove) sp. or perhaps Java fern (Microsorum pteropus). Plastic plants are also suitable.

The set-up should have an efficient filter as mudskippers are greedy, messy fish. Although the species has been recorded in both freshwater and full marine conditions in nature it is primarily a brackish animal. Marine salt should thus be added to the water until a specific gravity of around 1.005 is achieved. Any of the commercially produced marine salt “mixes” are ok to use.

Water Conditions

Temperature: A warmth-loving species. Aim for air and water temperatures in the range 77 – 86°F (25 – 30°C).

pH: 7.0 – 8.5. Mudskippers will not do well in acidic conditions. Consider the use of crushed coral or other calcareous material to buffer the water if necessary.

Hardness: 10 – 25°H

Diet

This species feeds chiefly on small crabs, insects and other invertebrates in the wild but proves surprisingly adaptable in captivity. It will accept live worms, crickets, flies, meal worms, beetles, small fish, crustaceans, frozen fare such as bloodworm or Artemia and even flake. However the feeding of dried food is not recommended as it can swell up in the animal’s stomach and cause bloating. A basic diet of frozen foods with regular live supplements is recommended.

Behaviour and CompatibilityTop ↑

It is territorial with conspecifics and should not be kept with very small fish as they may be eaten. In a well-designed set-up it can be kept with similarly-sized brackish species such as mollies, some Micropoecilia sp. and other gobies. A species tank is preferable in most cases though.

Sexual Dimorphism

Unconfirmed. Some specimens do appear significantly fuller-bellied at maturity and it’s possible that these are females. Certain individuals develop an extended first dorsal ray and this may be another indicator of sex.

Reproduction

As with other musdskippers, P. novemradiatus has not been bred in captivity, even in public aquaria. In nature the males dig deep, turreted shafts in the mud in which it is thought that mating and broodcare takes place. The natural environment of these fish is so complex it is near impossible to replicate, meaning that captive reproduction is unlikely in the forseeable future.

NotesTop ↑

Due to its highly amphibious nature this must be one of the most interesting, endearing species that can be kept in aquaria. Some specimens rarely enter deep water, preferring to sit in the shallows with the body submerged and eyes protruding above the surface. Others seem to favour resting completely exposed on rocks, sand or bogwood, returning to the water periodically to wet themselves. Subdominant individuals (those that are unable to secure a favourable territory) tend to attach themselves to the sides of the aquarium using their semi-fused pectoral fins.

The eyes are one of the features that give mudskippers such cutish charm. These are set high on the head, giving the animal 360° vision and a peculiar, froglike expression. You will often see the eyes being rolled back into their sockets or brushed with a pectoral fin in order to keep them moist. Movement oustide the tank is usually spotted very quickly, and the inquisitive fish will sometimes crowd to the front glass to see what is going on. They will also learn to recognise you quite quickly (especially if you are the only person feeding them) and can easily be trained to climb onto your hand to snatch morsels of food.

Mudskippers are highly territorial and if one infringes on anothers patch you may spot them “flagging” at each other. This is a display behaviour during which the individuals involved allow their attractively coloured dorsal fins to rise and fall rapidly, sometimes holding them extended for a few seconds. This serves as an initial warning and may be observed several times during a territorial encounter. If this proves an insufficient deterrent the dominant fish may resort to physical violence, leaping at the trespasser and attempting to bite it. Serious damage is rare and aside from the occasional nipped fin these battles are invariably entertaining rather than life threatening.

Mudskippers have developed several methods of locomotion that separate them from other fish. “Crutching” is used when on land and is so-called as the pectoral fins are rotated around their central axes, dragging the fish along. In “skipping” the tail is bent forwards and to the side, forming an efficient springboard. The tail can also be used like this to propel the animal across the water surface in a movement reminiscent of a skimmed stone. Unsuprisingly, these fish are also excellent jumpers.

Incredibly, scientific studies have shown that the gills of mudskippers are better suited to atmospheric than aquatic respiration in terms of physiology. When a mudskipper leaves the water it closes its opercula (gill flaps) and rapidly inflates the chamber behind the gills. This traps a reservoir of oxygen and water that is used for respiration while on land. The oxygen stored here can also be replenished by the fish rolling its eyes. In fact, almost 50% of terrestrial respiration in mudskippers occurs via specially adapted surfaces on the fins and body of the fish. A further adaptation allows the fish to breathe atmospheric air via highly vascularised membranes at the back of the throat and mouth.

This plethora of adaptations mean that mudskippers are actually very hardy and easier to maintain in captivity than many sources suggest, provided their basic needs are catered for. They are also incredibly entertaining, curious, intelligent and are highly recommended to those seeking an oddball species full of character.

With 15 member species currently recognised, Periophthalmus is the most populous of mudskipper genera. Most Periophthalmus look superficially similar, but the majority are almost never seen in the trade. P. novemradiatus is imported on occasion, and may be seen for sale with the alternative common names of Pearse’s or Dusky-gilled mudskipper. P. barbarus is the most commonly available species. Unlike most of its congeners P. novemradiatus does not have completely fused pectoral fins.