Gold-spotted Mudskippers (Periophthalmus chrysospilos) waddling in the mudflat at Bako National Park, Sarawak. Photo by Chien Lee.

Fish On Land

Species: Mudskipper (Actinopterygii : Gobiiformes)

Known Range: Indo-Pacific, India, Africa

Size: (Adult) Up to 25 cm long

Interviewed: Khaironizam Md Zain, freshwater ecologist (khaironizam@usm.my)

(Photo: Gold-spotted Mudskippers (Periophthalmus chrysospilos) waddling in the mudflats at Bako National Park, Sarawak | Pic by Chien Lee)

WHAT IS an animal that walks on mud, breathes through its skin, and swims using fins? A mudskipper! While they are fish and classified in the fish family Gobiidae, mudskippers don’t quite look like one. 

Unlike almost every other fish, mudskippers spend much time out of the water. Through evolution, they have changed their bodies and behaviours to live on land as well as they do in water, says freshwater ecologist Khaironizam.

To start with, mudskippers walk, hop and skip on land. That is an adaptation to their peculiar living environment on the mudflats.

While fish commonly use pectoral fins – the first pair from the front – for balance in swimming, mudskippers use theirs for paddling and walking on the ground. 

That’s not all. The Giant Mudskipper (Periophthalmodon schlosseri) even uses its pelvic fins – the pair underneath – to cling onto plants during high tide, says Khaironizam.

Kharonizam explains how mudskippers use their fins in two ways to latch on to roots.

During low tide when the mudflats are exposed, mudskippers are one of the many animals that pop up to search for food and mates, as well as to defend their territories. 

As they spend most of their time on land during low tide, mudskippers have evolved to breathe through their skin, mouth and throat.

These are moist and lined with a network of fine capillaries under their skin. They help oxygen to diffuse into the blood and carbon dioxide out, says Khaironizam. 

Puffy cheeks

And if you look carefully at the sides of a mudskipper’s mouth, you would see large cavities. These let them expand their gill covers as large as possible to increase air diffusion.

Mudskippers gulp air into their cheeks to retain more oxygen when living on land.  

Mudskippers also eat on land despite feeding on small insects in the water during high tides.

Mudskippers emerge from their burrows to prey on small crustaceans like fiddler crabs when the tide goes low. They also graze on microscopic algae called diatoms on the mudflats. 

Good eyesight

While they see badly in water, mudskippers have good vision on land, which they use to hunt.

To keep their eyes moist when out of the water, they occasionally roll the eyes to the back, which makes them the only fish with eyelids that can blink! 

When mudskippers want to hide and lay eggs, they retreat into their burrows, to protect themselves from predators. The problem though, is that oxygen is scarce inside the muddy tunnels.

But mudskippers have a solution.

Oxygen carriers

Khaironizam shares that they would gulp air above ground, then carry the oxygen in their gills into the burrow where their eggs are and release it there.

Hence, mudskippers practise “breath-taking” parental care by transporting oxygen to their eggs. 

All the mudskippers’ hard work doesn’t help just themselves. When they dig burrows, they aerate the muddy soil, which helps mangrove roots absorb oxygen too, says Khaironizam. 

Keeping it clean

As such, mudskippers are also bioindicators that scientists can use to monitor the levels of pollutants in mangrove ecosystems.

And when they graze on the mud, they unintentionally pick up heavy metals through their gills, skin, to the muscle tissues, liver and digestion system – that helps clean up the soil.

Heavy metals from industrial processes accumulate in mudskippers, says Khaironizam.

[Edited by YH Law]

Lucy Wong (@lucy_cfc) is a Macaranga Sprouts journalist. We thank the supporters of the Sprouts initiative who made this story possible.

Further Reading

K. Sangur, et al. 2021. Mudskipper as an indicator species for lead, cadmium and cuprum heavy metal pollution in the mangrove, Ambon, Indonesia. Journal of Ecological Engineering, 22: 1–19.

Khaironizam M.Z. et al. 2000. Ikan Tembakul Unik dan Perbagai. Dewan Kosmik: 16-18.

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