Monday, 22 August 2016

New series: Indian Dwarf Mudskipper

Indian Dwarf Mudskipper
After a long break, I have decided to restart this blog with an updated series on the aquarium at Bristol Zoo. There has been a major rebuild of the large tanks and other changes in the displays, but I will start with a new display of one of the oddest fish in the sea, the Indian Dwarf Mudskipper Periophthalmus novemradiatus.

 There are over 30 species of mudskippers around the world, almost all of them in south east Asia, but some species are found in east Africa and one species is found in west Africa. Mudskippers are actually a highly specialised group of gobies, familiar from rockpools around the world. Gobies tend to be very small fish, and spend a lot of time in concealed holes or burrows depending on the species. The typical habitat for mudskippers is mangrove swamps and mudflats, and where they are found they are often very numerous and are a major prey item for fish eating birds such as kingfishers. The largest species can be up to 30cm, but the species on show at Bristol is one of the smallest at under 7cm.

West African Mudskippers
The unique lifestyle of mudskippers is completely attuned to the changing tides, and the lack of protection on the exposed mudflats. They compensate for this by constructing burrows into the mud which they maintain at low tide and conceal themselves in when the tide rises. When the tide goes down they emerge to feed on small crustaceans, other small prey items, and in some species algae growing on the surface of the mud. When the tide comes in the burrows provide safety, but at the cost of a serious problem with respiration. The mud the burrows are in is highly anoxic and full of poisonous hydrogen sulphide, and oxygen levels in the burrows drop to the point of suffocation very quickly.

The mudskippers cope with this by use of their ability to absorb oxygen from atmospheric air. While the tide is out they take mouthfuls of fresh air deep into the flooded burrows to create an air pocket deep in the mud, and when the tide comes in they can continue to breathe air even when deep underwater.

Reproduction in mudskippers involves care of the eggs in the burrow, but of course eggs are if anything even more vulnerable to the toxic environment of the burrow water than the adults. Mudskippers solve the problem by laying their eggs out of water in a special egg chamber extension to the burrow. In the species studied so far, it is the male that constructs and guards the breeding burrow and keeps the egg chamber full of air when the eggs are developing. When the eggs are due to hatch, he floods the burrow to cause the eggs to hatch and the larvae make their way to the entrance, entering the plankton on the rising tide.

While mudskippers are quite widely kept in both public aquaria and by private aquarists, up to now there has been no successful breeding. This is the result of their highly specialised behaviour, but there are more aquarists attempting to replicate their environment in dedicated tanks, and I have found at least one record of larvae being produced, though not yet reared to metamorphosis.

For a video of the breeding burrow see this Youtube video of a breeding male:

Next time, I will begin a survey of the inhabitants of the new large marine tank in the Aquarium, now home to a very interesting range of species.

Images from wikipedia

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