Carnivorous walking FISH ‘are driven out of water by acidity, salt and carbon dioxide’ 

Northern snakeheads — carnivorous, walking fish that can survive on land for up to 20 hours — are driven out of water by acidity, salt and carbon dioxide, a study found.

This species of fish is the largest known to walk on land and, since its appearance in US waters, has eaten other fish and frogs, damaging local ecosystems.

Researchers had studied the reaction of the invasive fish when placed in different conditions of water, to see when the snakeheads would emerge into the air.

While the results do not explain why snakeheads voluntarily leave the water, they may help wildlife agencies better contain and eliminate the invasive pest. 

Northern snakeheads — carnivorous, walking fish that can survive on land for up to 20 hours — are driven out of water by acidity, salt and carbon dioxide, a study found

WHAT ARE NORTHERN SNAKEHEADS? 

Northern snakeheads are an amphibious and carnivorous fish.

They are native to Asia but were found to have invaded the US in 2002 when one was seen in a Maryland pond.

They have since spread to California, Florida, New York City, North Carolina, Philadelphia and Massachusetts.

Snakeheads eat various US native species, including fish, frogs and crayfish.

In some habitats, their presence can destroy the local food web. 

In moist conditions, they can survive on the land for up to 20 hours.

They can ‘walk’ by thrashing their fins, letting them to invade new waterways.

Biologist Noah Bressman of Wake Forest University in North Carolina and colleagues studied snakeheads from Maryland, where the fish are considered a threat to the area around Chesapeake Bay.

The fish — which ranged in size from 1–27 inches (2.5–68.6 centimetres) — were captured by the Maryland Department of Natural Resources in both tributaries off of the Potomac River and adjacent drainage ditches.

The experts lured the fish with electricity — passing a high-voltage current underwater between two electrodes can harmlessly force fish to move towards the positively-charged anode, where they can then be captured with nets.

Researchers subjected the fish to various poor water conditions — including high temperatures, salinities and acidities, as well as crowded, dark, polluted and stagnant waters. 

Mr Bressman and colleagues found that fish would tolerate all conditions except those of high salinities, high acidities and stagnant waters rich in carbon dioxide.

In these conditions, the fish would repeatedly emerge from the water temporarily — staying out of the water from between 2 seconds to 20 minutes — before returning.

This species of fish is the largest known to walk on land and, since its appearance in US waters, has eaten other fish and frogs, damaging local ecosystems

This species of fish is the largest known to walk on land and, since its appearance in US waters, has eaten other fish and frogs, damaging local ecosystems

It remains unclear how often snakeheads voluntarily leave the water and thrash their way across land to invade other waterways.

However, Mr Bressman said that the findings of the study may help natural resource agencies develop new approaches to containing and eliminating the invasive fish. 

In fact, wildlife resource officials in Georgia instructed anglers to kill the fish on sight earlier this month after a snakehead was found in a pond in Gwinett County.

Meanwhile, the Pennsylvania Fish and Boat Commission recently confirmed that a 28 inch (71 centimetre) snakehead was caught from Pittsburgh’s Monongahela River.

Wildlife resource officials in Georgia instructed anglers to kill the fish on sight earlier this month after a snakehead, pictured, was found in a pond in Gwinett County

Wildlife resource officials in Georgia instructed anglers to kill the fish on sight earlier this month after a snakehead, pictured, was found in a pond in Gwinett County 

Wildlife resource officials in Georgia instructed anglers to kill the fish on sight earlier this month after a snakehead, pictured, was found in a pond in Gwinett County

Wildlife resource officials in Georgia instructed anglers to kill the fish on sight earlier this month after a snakehead, pictured, was found in a pond in Gwinett County

Mr Bressman said that the findings of the study may help natural resource agencies develop new approaches to containing and eliminating the invasive fish

Mr Bressman said that the findings of the study may help natural resource agencies develop new approaches to containing and eliminating the invasive fish

Mr Bressman also noted that the amphibious fish move in a unique way — by making synchronised rowing movements with their pectoral fins while also wiggling their axial fins back and forth.

The team believe that it is these combined motions that enable the snakehead to traverse uneven surfaces like grass and soil.

‘Snakeheads move more quickly and erratically than once believed,’ said Mr Bressman. 

‘The fish we studied moved super quickly on rough surfaces such as grass, and we think they use their pectoral fins to push off these three-dimensional surfaces.’

While the results do not explain why snakeheads voluntarily leave the water, they may help wildlife agencies better contain and eliminate the invasive pest

While the results do not explain why snakeheads voluntarily leave the water, they may help wildlife agencies better contain and eliminate the invasive pest

Mr Bressman also noted that the amphibious fish move in a unique way — by making synchronised rowing movements with their pectoral fins while also wiggling their axial fins back and forth

Mr Bressman also noted that the amphibious fish move in a unique way — by making synchronised rowing movements with their pectoral fins while also wiggling their axial fins back and forth

‘When snakeheads were discovered on land, it caused a lot of fear because not much was known about them,’ Mr Bressman said. 

‘Sure, they can move fairly quickly on land, and they have sharp teeth. But you can easily outrun them, and they won’t hurt you, your children or your pets.’

‘But having a better understanding of how amphibious they are can help us better manage their population.’

With this study complete, Mr Bressman is now studying invasive walking flatfish in Florida.

The full findings of the study were published in the journal Integrative Organismal Biology.

Biologist Noah Bressman of Wake Forest University in North Carolina and colleagues studied snakeheads from Maryland, where the fish are considered a threat to the area around Chesapeake Bay

Biologist Noah Bressman of Wake Forest University in North Carolina and colleagues studied snakeheads from Maryland, where the fish are considered a threat to the area around Chesapeake Bay

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