Hello, everyone. I hope you're doing well. And of course, Arnie does too.

Now, today's video,

I'll be going through five of the worst invasive fish species around the world.

And for those of you who don't know,

an invasive species is any plant or animal which has

been introduced into an ecosystem where it doesn't belong.

And in most cases,

this can completely ruin an ecosystem or in some of the worst cases,

it can lead to some native species becoming extinct.

And our first invasive fish was originally native to Mexico and

the Southern United States and it is the mosquito fish.

Now, this fish is native to Central and North America.

They've been introduced into many countries around the

world and they were introduced to control a problem

that's been plaguing humans for thousands of years because

as you can probably tell from its name,

the mosquito fish is very good at eating mosquitoes

and mosquito larvae and mosquitoes aren't just an annoying pest

as they're known to transmit malaria and malaria is one

of the worst infectious diseases that has ever existed.

And it's still very present today. As 409,000 people were killed by malaria

in 2019 and 411,000 in the previous year.

So many countries,

fish were imported as a last resort and to be fair to the mosquito fish,

they are quite good at their job.

As in the places where they were introduced,

they did reduce the spread of malaria and it worked so well in one Russian town

that they even created a monument to honor the fish as it saved so many lives.

And as the maximum length of this fish is around seven centimeters,

you wouldn't think that it would have that much impact on a new ecosystem.

But the mosquito fish doesn't only limit itself to eating mosquitoes as

they're also known to eat zooplankton beetles, mayflies, mites, and other inverts

spirits which leaves little food for the native species.

And the mosquito fish is also a very hardy species as they can

survive in almost stagnant waters with a very low dissolved oxygen content.

And these areas are normally free of predators,

meaning that the mosquito fish can breed without

being predator on and they really can breed at a fast rate.

As mosquito fish are livebearers and within 16 to 28 days of mating,

a female can give birth to around 60 young.

And after this, the males will reach sexual maturity within 43 to 62 days.

So, if left unchecked,

their numbers can soon become out of control.

And as they feed on prey items that are right at the bottom of the food chain.

It affects everything else above it.

So, it's not just native fish that suffer even amphibians,

small mammals and waterfowl.

And they are still a problem invasive species in many countries around the world.

As they've been placed on the world's 100 most invasive species lists.

And as this problem has become so large, whether you like it or not,

mosquito fish will be an invasive species for many years to come.

And our next fish was originally native to Europe, North Africa, and Western Asia.

And it is the brown trout.

Now, it might surprise many of you that the brown trout is a problem invasive species.

As many people see the brown trout as a positive fish to have in an ecosystem.

As they're a popular food fish and they're also very popular with fishermen.

But today, the brown trout has been introduced into many countries far away from its natural range.

As it now has a very large presence in the southern hemisphere,

being found in the cooler parts of Australia, New Zealand, and even South America.

But brown trout can have a massive impact in an ecosystem where they don't belong.

As they mainly feed on aquatic and terrestrial invertebrates as well,

the smaller fish and as the species can reach maximum size of around 80 centimeters,

this can be a wide range of fish.

If the brown trout is introduced into an ecosystem with other large predators,

their numbers can be kept in check.

But in places such as New Zealand,

they can become a real problem as they've been known to outcompete the native New Zealand Galaxy.

It's causing their numbers to drastically decline.

And although the brown trout is widespread throughout the U.S. today,

that wasn't always the case.

As the first introduction of brown trout into

a U.S. ecosystem happened in 1883 where brown trout

introduced and raised in a few hatcheries in Long Island.

And by 1900, 38 states and two territories had received stocks

of brown trout which were eventually released into the ecosystem.

And as there's such a streamlined, highly adapted predator,

I don't think they'll be going anywhere anytime soon.

But our next invasive fish is the walking catfish and the walking

catfish is native to Southeast Asia, and it got its name for

its ability to move from one water source to the other as

it wriggles and rolls along the ground almost like it is walking.

And to be able to do this without suffocating is an air-breathing catfish.

So, it can spend a surprisingly long amount of time out of water.

And in its natural habitat is an

omnivorous opportunistic feeder, feeding on smaller fish,

mollusks and other invertebrates as well as detritus and aquatic weeds.

And the walking catfish is a very popular fish when it comes to aquaculture,

they can survive in very poor water conditions

and they reproduce and grow very quickly.

And it turns out in the 1960's,

the U.S. wanted a part of the market.

As aquaculture farmers in Florida imported the fish.

And within 10 years, the fish had spread to

20 counties in the state.

The farmers surely weren't ready for their walking abilities,

meaning that the catfish could easily move from one water source to the other.

And today, the walking catfish can be found in southern Florida, and as

far west as California and as far north as Massachusetts.

Luckily, in the U.S.,

there are a few large predators that can take out the walking catfish such as wading,

birds like herons and egrets, predatory fish like bass, and of course alligators.

But despite this, the walking catfish still has a large presence in the area.

And even though it doesn't seem to threaten that many new species,

it does still cause millions of dollars of damage.

As they're known to venture into fish farms to feed on all the fish and eggs.

And this has led to many fish

farmers putting up fences to stop the walking catfish strolling in.

So even though they're not an overly dangerous threat, they are a very costly one.

But our next species is the northern snakehead.

Now, this predatory fish species originates from China, Russia, and Korea.

And like most other snakeheads,

they are tough hardy and at the top of the

food chain and not only is it a great predator?

But it's a very adaptable fish as just like the walking cat,

they are able to breathe atmospheric oxygen,

meaning that they can live in very poor water quality.

And it's thought that this species was originally introduced into many

other countries for both food and for the aquarium trade.

But some of these specimens either escaped

or deliberately released into freshwater ecosystems.

And as northern snakeheads are known to feed

on a wide range of foods including insects,

small amphibians and other fish,

they can have a huge impact in an ecosystem where they don't belong.

As not only do they out-compete native predators,

but they can also take out threatened or endangered species.

And part of the

and why there's such a problem is because they make great

parents as not only did the adult fish create a nest,

but they also guard the young viciously from other predators.

And this ensures that a lot of the fry make it to adulthood.

Though, in some countries around Europe,

you can still find many species of snakehead available in aquarium stores.

And this is because the northern snakehead

is different to most other snakehead species.

As in their native range,

they can be found in waters with near-freezing temperatures.

So even in places where snakeheads are legal,

the northern snakehead is not.

One of the worst infected areas for the snakehead invasion,

is the USA and unfortunately,

one native species has taken the brunt of the anger.

As the snakehead looks very similar to the bowfin.

And this has led to the native bowfin being

killed by many people thinking that they were snakeheads.

So, because of their hardiness and the fact that they're great parents,

they are very hard pests to get rid of.

Our next species is one that I'm sure many of you will be very familiar with.

And it is the Common Pleco.

Now, the common Pleco native range is South America,

where it's quite widespread throughout many countries.

But today, they're found in many other tropical regions around the globe.

And this was almost completely created by the aquarium trade because

as I'm sure many of you know,

these fish are normally sold very small, and they grow very large.

As they're thought to reach a maximum size around 50 centimeters or 20 inches,

which means they outgrow most aquariums.

And if you're faced with the problem of a fish that's growing too big for its tank,

you can either do the responsible thing and try and rehome it or you

can do the lazy thing and try and release it into your nearest river.

And if you do choose the second option,

it can have disastrous consequences on the ecosystem.

Pleco's are known as armored catfish as they have

tough, rigid scales along their body.

And this means that they're a very difficult prey item for many predators.

And although Pleco aren't predatory fish,

they can still threaten native fish species as they're

famous for feeding on algae and other microfoods.

But this means that there's less food to go around for the native algae-eating fish.

But of course, the pleco is limited because it needs warmer water.

So, it's not going to be invasive in the colder parts of the world.

In places such as Florida,

they have become a real problem as they've been

known to annoy manatees like raising the algae which grow

on their body and they don't just rasp away the

algae also take out parts of the manatee skin.

And as there are not many predators that go after Pleco's

in Florida, they have become a real problem,

but they only alligators really limiting their numbers.

So, if this goes to show us anything,

it's that you really shouldn't release your aquarium fish into the wild.

But that's about it for this video.

If you have any other suggestions for problem invasive species

and let me know down in the comments below and I might make a part two.

But thank you for watching. I hope you enjoyed.

If you liked it, please leave a like, and subscribe if you want to

see more videos like these and until next time, goodbye.