EVEN fish can end up fighting over land. These land-dwelling great blue spotted mudskippers are facing off on the mudflats of Kyushu Island, Japan, their gaping mouths and raised dorsal fins a sign of aggression.
Mudskippers are highly territorial, with some species building mud walls to keep out trespassers. Walls also trap a pool of water in the fish鈥檚 territory, encouraging the growth of single-celled algae called diatoms, the main food for this species, Boleophthalmus pectinirostris.
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If a mudskipper infringes on a neighbour鈥檚 territory, a fight may ensue. The 20-centimetre-long fish can leap 50 centimetres in the air during combat, or in mating displays, by propelling themselves with their pectoral fins.
As mudskippers have adapted to spend 90 per cent of their lives out of water, it is tempting to see them as a snapshot of our evolutionary past, when our ancestors first flapped onto land. They seem to have easily overcome many of the challenges for fish living on land. They move around using their fins, lay eggs in water-filled burrows and breathe through their gills and skin (although they have to keep their bodies moist).
This transition isn鈥檛 as difficult as it might seem, however: amphibious behaviour is reported in 33 families of fish, and many may have evolved independently. The earliest tetrapods, which gave rise to amphibians, reptiles, birds and mammals, were more closely related to lungfish, which gulp air to help them survive in water with little dissolved oxygen.
