Fish carnivores include some of the largest and toothiest fish in the hobby. But there are just as many species that eat other things. What kind of fish do you have? Are fish herbivores or omnivores in your tank?
Are Fish Carnivores?
Some fish are carnivores, but not all. Fish cover the entire range of eating behaviors. So let’s first discuss how fish eat. Before focusing on carnivorous fish and their needs.
Omnivorous, Carnivorous and Herbivorous: Three Ways of Eating
How fish eat is organized into three different behaviors: omnivory, carnivory, and herbivory. Carnivores are fish that eat other animals. We tend to think of meat eating fish as those who must eat other fish. Or maybe even frogs, birds, and other animals.
But carnivorous fish also includes tetras and betta fish, which eat insect larvae, worms, and fish fry. That sounds funny to us, but only because we’re used to seeing the term carnivore used on lions or wolves. When frogs are as carnivorous as any lion.
That said, I’ll be focusing on “traditional” carnivores in this article. The toothier fish that eat larger prey, rather than micro predators like betta fish.
Carnivorous fish have sharp teeth for shearing into flesh and killing prey. They tend to be fast moving, active fish that chase down prey.
Others are ambush hunters that use camouflage to sneak up on unsuspecting prey. Ambush hunters may not have large teeth; they often suck their victims up with bucket like mouths.
Herbivorous Freshwater Fish
Herbivores are fish that focus on eating plant matter. Freshwater herbivores have different teeth and digestive systems from carnivores. Their teeth tend to be flat, scoop-like, or grinding, depending on the species.
The digestive system of a herbivore is longer and more complex than that of a carnivore. Plant matter is lower in calories and nutrient density than meat. It also has a lot of fiber, slowing down absorption even more.
The extra length of the gut ensures it will extract as much nutrition as possible. That’s why you see land herbivores like cows and horses spending so much time eating.
There are a number of herbivorous freshwater fish in the aquarium trade. Some of the most common include tinfoil barbs, silver dollars, mollies, algae eaters, mbuna, and tilapia cichlids.
Fish that are Omnivores
Last we have omnivores; fish that eat both plant and animal matter. Omnivorous fish are popular because they are the easiest fish to feed. Omnivore fish species include danios, goldfish, and guppies. They are as happy with brine shrimp as they are with green algae.
Tying it all together, omnivory, carnivory, and herbivory fall under the umbrella term of heterotrophy. Heterotrophs are organisms that have to consume living or dead organisms for survival. All fish are heterotrophic, as are all animals.
The other category is autotrophs; organisms that make their own food. Plants, algae, and several kinds of micro organisms fall under this category.
Types of Carnivorous Aquarium Fish
Fish carnivores are often dramatic in appearance and very large. If I had to pick one as the most impressive, the goliath tigerfish (Hydrocynus goliath) would get my vote. Tigerfish are African freshwater predators that grow 4 to 5 feet long.
Their teeth are as long as nails; perfect for grabbing hold of other fish. But they are also known to snatch birds flying too close to the water. They also bite humans swimming or wading in the Congo River. Goliath tigerfish are apex predators; only Nile crocodiles eat them.
Goliath tigerfish are too big for most aquariums. But smaller members of the genus Hydrocynus show up in stores sometimes.
Piranhas have teeth that are almost as impressive. They are also easier to find and care for than tigerfish. Piranhas can be dangerous in the wild but aren’t much of a threat in a home aquarium.
Cichlids are even easier to find and several are fish carnivores. Oscar fish are ravenous eaters that aren’t too aggressive and grow up to 15 inches long. But even they are dwarfed by two of the largest carnivorous cichlids: the peacock bass and umbee cichlid.
Both species will reach 24 to 30 inches long as an adult. Umbees are also infamous for killing anything you keep with them. You’ll need a 150+ gallon tank to keep either cichlid.
Other carnivorous aquarium fish include freshwater stingrays, arowanas, datnoids and African butterfly fish. Sharks are also fish carnivores. But even the smallest saltwater sharks are too large for any but the biggest of fish tanks.
Building a Carnivorous Fish Diet
Feeding carnivorous fish is not so simple. You can’t find cheap ground beef and toss it into the aquarium. Carnivores need a varied diet, and the type of meat matters a lot to overall health.
Terrestrial animal flesh (beef, pork, chicken, etc) should always be off the menu for predatory fish. It is too high in fat, tougher to chew, and bad for fish digestion. Stick to seafood.
White fish, fatty red fish like salmon, shrimp, mussels, squid, and octopus are all excellent. Insects, insect larvae, snails, and worms are all digestible and nutritious.
Most carnivore fish appreciate you slicing seafood up into smaller pieces and removing any shells. But there are some exceptions.
Puffer fish and triggerfish need hard shelled prey like clams, snails, and crabs offered with shells intact. These fish have teeth that grow continuously through life. Without shells to chew on their teeth will become overgrown. Requiring surgical filing or clipping to correct.
Most fish carnivores will also accept prepared foods if trained onto them. Carnivore fish food is sold at most pet stores.
It should have high quality animal protein sources like fish meal, ground krill, and other items. If the first two ingredients on the label aren’t animal based, search for a different brand.
Carnivores and Feeder Fish
Feeder fish are easy to find anywhere in the world. Feeder goldfish, rosy red minnows…You even have feeder guppies for little carnivores like Asian needlefish. Ghost shrimp are also sold in the feeder department for invertebrate eaters.
I recommend using feeder fish with caution. Choose your source with care because feeders are excellent vectors for parasites and diseases.
They come covered in aquarium fish ich, body fungus, fin rot, and other infections. If you keep feeding your pets sick fish it’s just a matter of time until your prized animals also get sick.
Feeder fish also get fed poor quality food, lowering their nutritional content. If you are able to substitute fresh or frozen seafood, I’d recommend it. Some predatory fish won’t eat dead prey, however. Feeders might be your sole option.
In that case, try raising your own live food. Feeder goldfish would be difficult without a pond but guppies are easy to breed.
Carnivorous Fish and Water Quality
One difficulty in keeping meat-eating fish is that they create a lot of ammonia. Both as waste as well as through messy eating.
Fish carnivores release food particles when they chew. A cloud of diffuse meat bits is released into the water. Which is food for bacteria, making the water smell bad and raising nitrogenous waste levels.
You will need a heavy duty filter for a predatory fish tank. Massive canister filters like the Fluval FX6 contain enough space for ammonia-absorbing zeolite resin. Alongside the usual suite of mechanical, chemical, and biological filter media.
You may need to do more water changes than usual as well. Ammonia levels need to be kept low or undetectable. Several carnivores tend to be sensitive to it, including stingrays.
Conclusion
Fish carnivores have different care needs from herbivore fish and omnivore fish. They make the most ammonia due to their protein-rich diet. And you need to be selective in the kinds of meat that you offer. That said, few pets are as fun to feed as meat eating fish.
FAQs
Crayfish are omnivores, which is a big reason why they are raised as food. They eat anything organic, including plants, worms, dead fish, and even other crayfish.
Shellfish are planktivores; they filter the surrounding water and eat suspended micro organisms. Infusoria, phytoplankton, and zooplankton are all a part of their diet.
