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

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Now, today's video,

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

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And for those of you who don't know,

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an invasive species is any plant or animal which has

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

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And in most cases,

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

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it can lead to some native species becoming extinct.

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And our first invasive fish was originally native to Mexico and

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the Southern United States and it is the mosquito fish.

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

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They've been introduced into many countries around the

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world and they were introduced to control a problem

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that's been plaguing humans for thousands of years because

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as you can probably tell from its name,

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the mosquito fish is very good at eating mosquitoes

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

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

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of the worst infectious diseases that has ever existed.

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

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in 2019 and 411,000 in the previous year.

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So many countries,

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

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they are quite good at their job.

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As in the places where they were introduced,

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

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

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

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

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

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

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spirits which leaves little food for the native species.

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

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

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And these areas are normally free of predators,

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meaning that the mosquito fish can breed without

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

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

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a female can give birth to around 60 young.

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

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So, if left unchecked,

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their numbers can soon become out of control.

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

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It affects everything else above it.

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

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small mammals and waterfowl.

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

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

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

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

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

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And it is the brown trout.

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

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

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

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

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

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

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

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

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

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this can be a wide range of fish.

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

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their numbers can be kept in check.

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But in places such as New Zealand,

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

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It's causing their numbers to drastically decline.

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

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that wasn't always the case.

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As the first introduction of brown trout into

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

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introduced and raised in a few hatcheries in Long Island.

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

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of brown trout which were eventually released into the ecosystem.

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

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

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

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

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

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

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

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

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And in its natural habitat is an

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omnivorous opportunistic feeder, feeding on smaller fish,

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

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

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they can survive in very poor water conditions

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and they reproduce and grow very quickly.

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And it turns out in the 1960's,

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

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As aquaculture farmers in Florida imported the fish.

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And within 10 years, the fish had spread to

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20 counties in the state.

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

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

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

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far west as California and as far north as Massachusetts.

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Luckily, in the U.S.,

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

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

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

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

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it does still cause millions of dollars of damage. 

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

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And this has led to many fish

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

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

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But our next species is the northern snakehead.

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

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And like most other snakeheads,

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they are tough hardy and at the top of the

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food chain and not only is it a great predator?

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

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they are able to breathe atmospheric oxygen,

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meaning that they can live in very poor water quality.

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

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other countries for both food and for the aquarium trade.

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But some of these specimens either escaped

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or deliberately released into freshwater ecosystems.

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And as northern snakeheads are known to feed

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on a wide range of foods including insects,

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small amphibians and other fish,

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

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As not only do they out-compete native predators,

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but they can also take out threatened or endangered species.

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And part of the

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

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

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but they also guard the young viciously from other predators.

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

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Though, in some countries around Europe,

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

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And this is because the northern snakehead

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is different to most other snakehead species.

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As in their native range,

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

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So even in places where snakeheads are legal,

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the northern snakehead is not. 

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One of the worst infected areas for the snakehead invasion,

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is the USA and unfortunately,

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one native species has taken the brunt of the anger.

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As the snakehead looks very similar to the bowfin.

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And this has led to the native bowfin being

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killed by many people thinking that they were snakeheads.

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

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they are very hard pests to get rid of. 

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

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And it is the Common Pleco.

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Now, the common Pleco native range is South America,

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where it's quite widespread throughout many countries.

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

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And this was almost completely created by the aquarium trade because 

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as I'm sure many of you know,

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

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

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which means they outgrow most aquariums.

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

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

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

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And if you do choose the second option,

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it can have disastrous consequences on the ecosystem.

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Pleco's are known as armored catfish as they have

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tough, rigid scales along their body.

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

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And although Pleco aren't predatory fish,

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they can still threaten native fish species as they're

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famous for feeding on algae and other microfoods.

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

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

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

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In places such as Florida,

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they have become a real problem as they've been

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known to annoy manatees like raising the algae which grow

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

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algae also take out parts of the manatee skin.

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

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in Florida, they have become a real problem,

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but they only alligators really limiting their numbers.

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So, if this goes to show us anything,

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

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But that's about it for this video. 

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If you have any other suggestions for problem invasive species

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

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But thank you for watching. I hope you enjoyed.

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

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