Skippers on mud September 13, 2015, Sunday Mary Margaret
Mudskippers are fish that are more at home on land than in the water.
IS that a fish or a lizard?
At low tide mangrove mudflats appeal to few, but mudskippers, which are more at home on land than in the water, rule as they hunt, nest, slide and fight over their muddy territories.
Visitors to Bako or Kuching Wetlands national parks in Kuching are likely to see these rulers of the mudflats.
These fish, which are members of the Gobiidae family, are sometimes mistaken for snakes or reptiles. Gobiidae, Gobies, are small mostly tropical and subtropical fish found in coastal waters, which include over 2,000 species.
Mudskippers are uniquely adapted to the harsh inter-tidal area that links the land and sea. The area can be dry or wet depending on the rise and fall of the sea. The saltiness of the poorly-aerated water varies with the tides. Mudskippers thrive in this varied and challenging habitat as well as are tolerant to poisons including cyanide.
Bulging periscope-like eyes on the top of their heads allow the fish to see in a complete circle.
Their mouths face downward enabling the fish to graze the muddy surface for algae, insects and invertebrates, but they can keep a sharp eye out for predators while feeding.
Mudskippers can see colour when they look through the top of their eyes and in black and white when looking down.
These land-loving fish have developed three ways of breathing. Like scuba divers who take air with them, mudskippers take water with them on land as they store water in their enlarged gill sacks. The gills of most fish collapse when they are out water, but mudskippers keep theirs fluffed up by rotating their eyes.
Mudskippers are also able to breathe through their wet skin, so despite being comfortable out of water, they still need water.
The third method for oxygen exchange is through membranes at the back of their mouths.
Mudskippers skip, leap and climb across muddy surfaces due to specially-adapted fins. They skip by pushing their bodies sideways and then spring forward, but their tails drag. Although this sounds like an awkward way to walk, they are fast.
Species of mudskippers that can climb have specially adapted pelvic fins that act like suckers. The front pectoral fins are used like arms and the mudskippers use them to drag themselves up roots and rocks.
Mudskippers, unlike many other vertebrates that inhabit the mudflats, raise their young in this perilous zone.
Male mudskippers excavate tunnels that can reach 1.2 metres deep with an entrance up to one metre in diameter, which is surrounded by a low wall. The tunnel is also likely to be flooded even in low tide.
Females lay eggs in the egg chamber that loops up like a ‘J’ at the end of the tunnel.
Male mudskippers guard the tunnel and care for the eggs. Most species fan their eggs to ensure that there is sufficient oxygen, but mudskippers bring in mouthfuls of fresh air into the egg chamber, which has almost no supply of oxygen.
Mudskipper eggs are able to develop in air but must be submerged to hatch. The larvae emerge in about one week, quite often during high tide when the nest is inundated.
Atsushi Ishimatsu and his team published an in-depth study on the brooding techniques of the Japanese Mudskipper (Periophthalmus modestus) in The ‘Journal of Experimental Biology’ in 2007.
Ishimatsu and his team believe that the larvae must escape the burrow quickly due to low oxygen supplies, but other writers suggest that the burrows give protection to the larvae. Burrows offer protection to the eggs from predators, high tide, changes in currents and temperatures.
Mudskippers are tightly woven into complex mangrove food webs. They prey on insects, while other invertebrate predators higher up on the food chain, for example egrets and snakes, prey on them.
Four genera — Boleophthalmus, Periophthalmus, Periophthalmodon and Scartelaos — are chiefly found in the coastal waters of tropical Asia with a few species in Africa.
Katherine Atak in ‘The Fishes of Kuching Rivers’ published by Natural History Publications in 2006 identified three species of mudskippers in the coastal rivers around Kuching.
Serpent Mudskipper (Parapocryptes serperaster) has a long body and small head. It is light brown with four dots along either side. It feeds on algae and dead plant materials. Generally it is located in areas where freshwater mixes with salt water.
One of the largest at 27 centimetres is the Giant Mudskipper (Periophthalmodon schlosseri), which is also known as Tamakul or Tembakul. It is found in mangroves and tidal zones of rivers. Large eyes protrude from its blunt face. It is dark brown with light brown and numerous pale blue spots along its side. The lung cavity of this species is 16 per cent of its body volume. This species is eaten in some places such as Taiwan.
During high tide, the Giant Mudskipper remains near the surface of the water clinging to roots, rocks or other surfaces. At low tide these carnivorous mudskippers hunt invertebrates, other fish and even mudskippers. When threatened, they move quickly and dive either into the water or burrows.
The Blue-finned Mudskipper (Boleophtalmus boddarti) or Layar has a large head and mouth. Its entire body is brown with blue speckles, but its belly is a lighter shade.
It gets its name from its first dorsal fin, which when extended has five long blue streamers. At high tide it retreats to its burrow and lies hidden in pockets of air. Territorial battles lead to the looser retreating to its burrow.
Mudskippers are not endangered but like other plants and animals of the intertidal zone, their numbers are affected by pollution and loss of habitat due to land reclamation.
Mudskippers skip, leap and climb across muddy surfaces with their specially-adapted fins.