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Just as on land, the ocean is filled with a diverse community of fish that make up various food chains. While some fish are further down the food chain and only eat aquatic plants, others need a much meatier diet. Let’s get to know some of the ocean’s predators.
Herbivore, Omnivore & Carnivore Fish – Differences
When it comes to fish, their diets can be extremely varied. Depending on whether they are plant eaters, meat eaters, or a bit of both, they can be broken down into three categories.
An herbivore is an animal that only eats a plant-based diet. Where fish are concerned, this includes a range of plants, algae, and even fruits. In the marine pet business, you will sometimes see herbivorous fish eating live food, but this isn’t a good idea as it’s not part of their diet, and they’re not adapted to handle this type of food.
There are lots of species of herbivorous fish but they only make up around 5% of all fish species. These include various species of surgeonfish, grass carp, and the parrot fish.
In coral reefs, herbivorous fish are incredibly important as they help to maintain a balance between the microalgae and the coral. They’ll spend most of their time foraging for food around the reef, but they can also be found in bodies of freshwater.
Main Characteristics of Herbivore Fish
The digestive system of fish herbivores differs from that of a carnivorous species. For starters, these fish have much longer digestive tracts that are easily able to break down plant matter. What’s more, these fish do not have stomachs where food can be stored. However, this does mean that, when the fish finds food, it must eat large quantities before moving on to look for more; they’re constant grazers.
Herbivorous fish’s teeth are vastly different from meat eaters. Instead of sharp teeth, they have flat ones which are designed to grind up the fibrous foods that they eat. In some species, there will be a beak that allows the fish to remove algae from rocks and other surfaces.
Fish that are omnivores are among some of the most abundant; it seems that fish need a balanced diet between protein and plant-based foods. In fact, while you might think meat eaters would grow bigger and stronger, the largest fish in the world, the whale shark, is actually an omnivore.
Omnivorous fish eat both animal and plant-based meals and include species such as the freshwater angelfish, the goldfish, the catfish, and the koi carp.
Main Characteristics of Omnivore Fish
Just like the herbivore cousins, omnivorous fish have specially adapted bodies to cope with their diets. However, it has been noted that these species have traits of both herbivores and carnivores when it comes to their physiology.
Unlike herbivorous fish, omnivores do have a stomach for storing food. However, this is typically smaller than that of a carnivore, although omnivores whose diet consists of more meat do tend to have slightly longer stomachs.
Moreover, these fish species have sharper teeth than their herbivorous relatives which are designed for tearing through meat.
Carnivores are animals, in this case, fish, that exclusively eat meat. Many carnivore fish are opportunistic hunters and will wait for prey to pass by before ambushing it, although others will actively hunt.
These fish can be found in both fresh and saltwater environments and will usually prey on anything that is smaller than they are. There are some species, such as the great white shark, that are feared by humans but while they may bite, they don’t prey on humans.
Other species of carnivorous fish include the arowana, piranha, and the mud perch.
Main Characteristics of Carnivore Fish
In order to be able to catch, eat, and digest meat, carnivore fish need to have specific traits. This includes having sharp teeth that are able to tear through meat as well as strong jaws that allow the fish to take good hold of its prey.
Carnivorous fish don’t chew their food, so there’s no need for flat, grinding teeth. However, since the food is swallowed whole, there’s a need for a larger stomach to store their meals before digestion. The digestive tract of these fish is much shorter, so this doesn’t allow them to take any nutrients from plant matter, even though they may ingest it from time to time.
What do Carnivorous Fish Eat?
Since carnivorous fish are mainly meat eaters, their diet usually consists of smaller fish. However, they are opportunistic and since there is an abundance of life in the ocean, there’s a lot more on the menu.
These fish will often prey on things like squid, seals, penguins, whales, and anything else that’s available to them. This is especially the case with fish like the white shark that isn’t at all a fussy eater.
Tuna are carnivorous fish, and there have even been reports of some larger specimens chowing down on dolphins.
Some freshwater species such as Siamese fighter fish and oscars will also eat insects. In some cases, they’re also known to eat plants but this would put them into the omnivore category.
Importance of Predatory Fish in Marine Ecosystems
There always needs to be a balance and the same is true of an aquatic environment. Without predatory fish, the numbers of prey species would skyrocket, creating massive imbalance in the ecosystem. It might be easy to assume that large numbers are a good thing as it ensures the survival of the species, but in reality, it could deplete marine resources, meaning there isn’t enough to go around.
The activity and abundance of top predators such as pike play an important role in what’s going on further down the chain. For example, where there are substantial levels of pike, this keeps minnows in check which in turn ensures a good community of plankton that are able to maintain healthy algae levels.
What’s more, studies have shown that fish provide far more nutrients to the ecosystem than other species that are right at the bottom of the food chain. Without them, ecosystems just wouldn’t be as healthy.
Additionally, predatory fish help to keep good biodiversity within the ecosystem. If that wasn’t enough, their importance is extended because they will often leave behind parts of a carcass that will attract other species, further growing the diversity of the local community.
Types of Carnivorous Fish
Carnivorous fish are the second most abundant type of fish in our waters, so it’ll come as no surprise that there are lots of species. Here, I’ll provide you with some information on some of the most well-known and interesting ones.
1. Northern Pike (Esox lucius)
The Northern pike is an abundant freshwater species that lives in everything from ponds to lakes and even rivers. They’re native to North America and Eurasia and can live up to 12 years in the wild.
Their diet consists of varieties of fish and crustaceans as well as small mammals, amphibians, and even birds.
In any environment that they inhabit, pikes are the top predators, and are known for their ability to remain still while waiting for prey. When their target is close, they’ll move quickly in ambush, catching the prey sideways in the mouth. Those sharp teeth quickly immobilize anything the fish catches.
2. Piranhas (Family: Serrasalmidae)
There are several species of piranha, including the black, red-bellied, and redeye piranhas. These fish have a reputation for stripping the meat from the bones and are often depicted in cartoons doing just as much.
But what is the reality? Well, these fish do have razor-sharp teeth, but they’re typically scavengers, and some even feed on plants.
These ancient fish can be found across South America, and there’s a story, told by Teddy Roosevelt, that a school once devoured an entire cow carcass! This isn’t that hard to believe when you consider that some species, like the red-bellied piranha, hunt in groups of up to 100 and can grow to 20 inches (50 cm). While this does mean that feeding frenzies can happen, it’s not very common.
3. Great Barracuda (Sphyraena barracuda)
Great barracudas are common in any warm ocean and are found all over the world. The only place they’ve not been spotted is in the eastern Pacific. These large fish can grow up to 3.3 feet (1 meter) and have a distinct lower jaw that protrudes past the upper jaw.
In terms of diet, the great barracuda preys on a variety of smaller fish species, including gobies, herrings, anchovies, and many others. One of the reasons they’re such pros at hunting is their long, thin bodies which make them less visible to their prey.
What’s very interesting is that these fish will often seem to protect schools of fish. But what they’re really doing is waiting until they’re hungry so they’ve got a meal right where they want it; cunning!
4. Paiche (Arapaima gigas)
Found in the Amazon River basin, the paiche is a species of air-breathing fish that can regularly be seen coming to the surface.
They’re pretty big fish that can grow up to 6.6 feet (2 meters) and may get as heavy as 440 lbs (200 kg). They don’t waste any time when it comes to hunting and can simply open their vacuum-like mouths to suck in prey when they want a meal.
Paiche usually feed on other fish but when they come up to the surface, it’s not uncommon for them to eat terrestrial animals or birds should they have the opportunity.
5. Goliath Tigerfish (Hydrocynus goliath)
The goliath tigerfish has an appearance that looks as though it’s come out of a nightmare, with dagger-like teeth on constant display. And these teeth aren’t just for show; they’re so sharp that they can cut prey in half with just one bite.
What’s more, the goliath tigerfish isn’t a small creature. Some individuals can get as large as 4.9 feet (1.5 meters).
They’ll lie in wait for their prey to approach, at which point they’ll ambush it with great speed. And they’re not fussy; they’ll eat all types of fish, including other goliath tigerfish!
6. Moray Eels (Gymnothorax spp.)
There are more than 80 species of moray eel, including the green moray and the giant moray. In any case, they’re considered to be one of the most dangerous fish in the world, especially to their prey with those super sharp teeth. While they don’t usually go for humans, they will if they’re disturbed or feel threatened.
When catching prey, moray eels not only have sharp teeth but incredibly powerful jaws that take a stronghold of their victim. They also have pharyngeal jaws that help to move the prey to the back of the throat.
7. Alligator Gar (Atractosteus spatula)
It’s thought that the alligator gar has been on earth for at least 100 million years, according to fossil records. This is the largest species of gar and is found across much of North America, most notably in the Ohio River, the Mississippi River, and the Gulf of Mexico.
Alligator gars are not fussy about their prey and will feed on smaller fish, turtles, and even ducks. They might look slow while they’re sitting and waiting, but when prey comes near, they show surprising speed, albeit in short bursts.
8. Wels Catfish (Silurus glanis)
The wels catfish is native to Europe and is found in the Caspian, Baltic, and Black Seas. However, it has been introduced to other areas of Europe since it is one of the most prized sport fish on the continent.
Wels catfish have several rows of small teeth in their wide mouths, and being a bottom-dweller, usually preys on things like crustaceans, small fish, worms, and insects. However, it’s not uncommon for larger individuals to have a more varied diet that can include frogs and even small mammals.
They are opportunistic creatures that usually hunt at night.
9. Payara (Hydrolycus scomberoides)
Payara fish are relatively cute for a carnivore and have large eyes that take over most of the face. However, there’s also a mouthful of small, but razor sharp teeth, which is why it’s sometimes called the vampire fish.
These fish mainly feed on smaller fish but may also eat worms and other live bait in the wild. However, when kept in an aquarium, it’s not uncommon for pet owners to give them frozen whole foods. Although this isn’t something that is done without some serious weaning.
10. Great White Shark (Carcharodon carcharias)
I couldn’t write a list of carnivorous fish without including the biggest and most feared, the great white shark. These large predators can grow up to 16 feet (4.9 meters), although the biggest ever recorded was well over 19 feet (5.8 meters) and weigh almost 4500 lbs (2041 kg)!
Great white sharks will typically feed on rays and small fish when they are young. However, as their dietary needs change in adulthood, they’ll start preying on things like big fish, seals, dolphins, and even seabirds where they are available.
They usually position themselves below their prey and swim quickly upwards, grabbing it in their strong jaws that are filled with 300 serrated teeth. While they are known to attack humans, this is usually a case of mistaken identity, and after biting, they’ll normally retreat.
While these are incredibly adept predators, great white sharks are also endangered. It’s thought that there are as few as 3,500 left in the wild.
11. Barramundi (Lates calcarifer)
The barramundi is found in abundance across the western Pacific and Indian ocean. It’s sometimes called the Asian seabass or the giant sea perch and is a long fish with an extended upper jaw.
The main part of the adult barramundi’s diet consists of bony fish. This accounts for around 80% of what they eat but they’ll also feed on macrocrustaceans which is part of their diet from day one.
They’re opportunistic hunters that have large mouths which they use to suck in their prey and swallow them whole!
12. Monkfish (Lophius spp.)
The prize for the strangest-looking carnivorous fish goes to the monkfish. But while they’re very unusual looking, monkfish are brilliant predators and will use their illicium on the head to lure prey right toward them.
These fish, sometimes called anglerfish, are found in the Mediterranean Sea and the North Atlantic. While they start off feeding on invertebrates, once they reach adulthood, the monkfish will begin targeting larger fish like the blue whiting and may even prey on lobsters.
Living at depths of up to 3280 feet (1000 meters), there’s still a lot to learn about these fish. However, since many have been found with empty stomachs, it’s thought that they don’t feed regularly.
13. Tuna (Thunnus spp.)
Tuna are large ocean-dwelling fish that are commercially fished around the world for their meat. However, they’re also adept hunters that will prey on a variety of shellfish, squid, and fish.
There are seven species of tuna, including the yellowfin, bluefin, and bigeye tuna. The Atlantic bluefin is the largest and may grow to almost 7 feet (2.1 meters) in length and can live for more than half a century!
These fish might be large, but their streamlined bodies enable them to travel at lightning speed which makes it super easy for them to catch their prey. In some cases, tuna have been recorded moving at up to 47 miles per hour (76 kilometers per hour)!
14. Lionfish (Pterois spp.)
The lionfish is another of the most dangerous fish in the world, and not just because they are predatory, but they’re also toxic. They sting with their toxic spines, and while the venom is not fatal to humans, it can cause some unpleasant symptoms.
In terms of hunting, lionfish use their large fins to trap prey which they’ll then snap up and swallow whole. They’ll feed on invertebrates and crustaceans as well as small fish and it’s not unheard of for them to display cannibalistic behavior.
15. Arowana (Osteoglossum spp.)
The arowana is a long, sleek fish with a large lower jaw and teeth that bite up against the roof of the mouth. They even have one super sharp tooth on the inside of the lower mouth known as a bony tongue. This is something of a primitive trait, but then these are prehistoric fish that are thought to have been around for more than 100 million years.
Arowana is found in South America and can grow up to more than 3.3 feet (1 meter). They’re common in the Amazon and, being facultative air breathers, they’re often seen feeding at the surface where they’ll prey on everything from fish and crabs to snakes, insects, and even birds.
They have perfectly placed mouths for catching prey and will usually lie in wait, jumping out of the water when they’re ready to nab their target.
16. Walleye (Sander vitreus)
The walleye is a freshwater species related to the pike. For most of the day, they’ll hang out in the deeper parts of rivers and lakes, only moving to shallower areas at night.
Walleyes begin their lives feeding on plankton, but as they reach adulthood, their needs change, and so does their diet. At this stage of life, these nocturnal hunters will prey on fish, crayfish, snails, insects, and even small mammals.
17. Swordfish (Xiphias gladius)
The swordfish is one of the most curious looking marine species with its long snout, which is commonly referred to as a sword. But these aren’t there just to add aesthetic value to the fish; they use them by swinging them side to side to stun their prey.
Swordfish are large animals that are found mainly in tropical and temperate waters. Their main diet is made up from several species, including various fish, squid, octopus, and sometimes, shellfish, although these aren’t on the menu as often.
Not only do they use their swords to help them catch a meal, but swordfish are also incredibly fast, swimming up to 50 miles per hour (80 kilometers per hour), which makes them among some of the most agile hunters in the ocean.
18. Giant Trevally (Caranx ignobilis)
The giant trevally is a huge fish that can get up to almost 6.6 feet (2 meters) and weigh more than 176 lbs (80 kg). They’re found in tropical regions within the Indian and Pacific Oceans and are usually found at around 262 feet (80 meters), although they will come closer to the surface when hunting or breeding.
Where diet is concerned, the giant trevally patrols reefs for a suitable meal which could be anything from smaller fish to crustaceans or squid. They typically hunt first thing in the morning or at dusk and are incredibly strong swimmers when in pursuit of their prey. They’re not afraid to bite and can be very aggressive when they have their sights set on a target.