Fish out of water
VulcanSpirit
Richard & Alison Brunstrom
Sun 14 Oct 2012 06:33
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The little animal below is a true fish, about
the size of a big newt, but a fish that spends most of its time out of water,
living in a muddy burrow and even climbing trees. He's a mudskipper of the genus
Periophthalamus, widely distributed around the world but mainly
associated with mangrove swamps, which is where I found these two in
Fiji:
 They can breathe air through their throat linings
just like a freshwater amphibian, and also have true gills - but when out of
water they seal the enlarged gill compartment (which is why they have cheek
pouches like a hamster)up with a bubble of air inside; the gill can then
continue to work provided that it remains moist. They are really comical to
watch, scooting round their ponds, jumping up onto branches and squabbling with
each other. They can zoom along on the surface of the water moving so fast that
they don't fall in, and can jump a surprising distance into the air by flicking
their tails. And they nearly have legs!
Here you can see the left pectoral fin folded flat
against the body, looking just like a normal fin (he's sitting on his pelvic
fins):
 But here is the same animal, with the fin folded,
looking and operating just like a leg:
 And here you can see how he sits on his pelvic
fins; these act as a grasper, and enable the whole body to be held clear of the
substrate - in this case a coconut:
 Mudskippers are very aggressive to each other,
constantly vying for the best lookout position and displaying to each other
using the dorsal fin like a signal flag - but rarely when there is a camera
watching. Here's the best I could do:
 While hopping frantically about they often raise
the hackles of other denizens of the swamp pools. Here is one over-enthusiastic
fish (bottom right) being warned off by a fiddler crab:
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