Threadfin Fish Description And Care Tips


Last updated on September 9th, 2022 at 08:09 am

Threadfin is a type of fish that can be found in the Atlantic Ocean. They are quite unique, not only for their appearance but also because they have thread-like fins which give them their name. Threadfins are an important food source for many larger fish and humans alike, which is why they are often caught by fishermen trying to make a living off of this abundant resource.

The threadfin is a fish that can be found in the Indo-Pacific region. It is not typically very large, but it does have some interesting features. The threadfin’s dorsal fin has three lobes and its anal fin has two lobes. This gives the fish both good agility in the water as well as stability when resting on the bottom of the ocean floor.

The threadfin is a beautiful fish that makes an active addition to the right tank. If your aquarium has enough room and other peaceful, docile inhabitants, then this could be the perfect choice of pet for you!

Origin and description


The threadfin is a fish that can be found in the waters of Southeast Asia and Australia.

While most people have never heard of this type of fish, it has been highly important to certain cultures for thousands of years. For example, aboriginal Australians used them as food and also made nets with their scales so they could catch more threadfin. The threadfin is also a popular food source for many other cultures in the area as well.

The scientific name of this type of fish is Polynemidae, which means “many-filament fin” and refers to its large dorsal and anal fins that can grow up to two feet (61 cm) long on the adult. These fins are also what allow the threadfin to feel a vibration, which is important for hunting because they have no external ears.

Threadfins are deep-bodied and compressed, which allows them to be more streamlined so that they can move through the water quickly with little effort. Their bodies range from dark grey/brown on the back and sides to a pale yellow on the belly and can also be speckled with black spots.

They have large eyes that are located near the top of their head, which helps hunt above them in shallower water where prey tends to hide because it allows them to see better up-close without having very good vision through binoculars as humans do.

The threadfin has a large mouth with small teeth that they use to eat invertebrates like shrimp and crayfish, but also some larger fish prey when available. They are opportunistic feeders, meaning they will eat pretty much anything in front of them if it is the right size for their mouths!

Amphilophus Citrinellus (Midas Cichlid)

Since this type of fish likes to eat invertebrates, they are often found in shallow bays and mangrove swamps where the water is clear so their prey can be easily seen.

Species profile


Threadfins are an iconic species in the Gulf of Mexico. They may be caught by sport anglers, commercial fishers, and subsistence fishermen alike. Threadfin populations have declined alarmingly over the past four decades however, it is estimated that there used to be 330 million threadfins covering more than 20 square miles on their spawning grounds. Nowadays they are listed as a species of concern in the Gulf of Mexico where their numbers have dropped to just 57 million.

The threadfin is a member of the Polydactylus genus and has been given multiple names by anglers including dollarfish, freshwater gar fish, long-jawed john, least mullet, red-finned triggerfish, and the Mississippi threadfin.

The common name is derived from their long dorsal fin which extends forward almost to its head – in comparison with other members of this family, it is still quite small, however. The body has been described as “fusiform” which means they are “spindle-shaped” and this is strikingly different from other Polydactylus species. This shape allows them to maneuver through the water easily, perfect for chasing after their prey.

The threadfin’s head has a small terminal mouth with no protrusions. Their eyes are relatively large – about one-third of the size of their head. This is in stark contrast to other Polydactylus species where the eye-to-head ratio is much smaller.

Color and appearance

Threadfin fish has a silver body with black spots and stripes on the dorsal, anal, pectoral fins. They are similar to sunfish or crappies which also have dusky bars that run across both sides of their bodies just behind the gills. However, there are many differences between these two species as well. The threadfin’s body is more elongated than the sunfish.

Threadfin has a long dorsal fin that starts at their mouth and runs nearly all the way to the anal fins base, whereas the Sunfish has short-based dorsal fins which are usually contained in one or two spines. Threadfins also have large eyes for deep water fish and largemouth.

Range and habitat

Threadfin fish belong to the family Polynemidae and are widely distributed throughout tropical waters in Asia, Africa, and Australia.

They live in freshwater habitats such as rivers, streams, canals, or tidal creeks where their prey consists of invertebrates including insects, snails, and crustaceans which they catch from the water bottom.



Threadfin fish are often confused with the similar-looking but unrelated common carp. The threadfins have a maximum length of about 12 inches whereas the Common Carp is much larger at 40-50inches in size.

Tank size

The threadfin fish are a hardy species and can adapt to most water conditions. However, they prefer warmer temperatures between 78-82 degrees Fahrenheit, which is the temperature range that is suitable for their natural habitat. They should have an aquarium that is at least 20 gallons with plenty of live plants along with driftwood or bogwood (for substrate).

Heros severus (Banded Cichlid)

Since threadfin fish are not as aggressive as some other species, they can be kept with other peaceful community fishes. It is best to avoid smaller and slow-moving species such as the neon tetra since their small size makes them easy prey for threadfins.

Life cycle

Threadfin is native to tropical waters around the world. They grow quickly and become sexually mature at one year old, usually living for only two years. After spawning in shallow water, they make their way back out to sea where they spend five or six months migrating over great distances before returning again to spawn on reefs near coastlines. Despite being an inshore fish, threadfin is found in oceanic islands right through to the coast. Spotting a threadfin is pretty hard as they are nocturnal and spend the day hiding in cracks or caves.

Their size varies depending on location, with fish found around Australia reaching maximum lengths of 60 to 70 cm. However, specimens caught throughout their migration can reach up to three meters long! Threadfins feed at night, feeding mainly on crustaceans, mollusks, and urchins. They have a very unusual method of feeding where the fish will slowly rise up off the reef in order to expose their mouths above the substrate that they then suck sediment from.

Their color patterns vary with each location but are usually brownish-grey on top fading to a silvery-white on the stomach.

As a fish, threadfin can be very hard to find and catch, but if you do manage to get your hands on one, it is definitely worth cooking up! Threadfins have firm white flesh that flakes easily when cooked making them perfect for grilling or frying.

Are they aggressive or peaceful?

Threadfin is extremely peaceful. They will often simply swim away if someone is trying to catch them or touch them!

Threadfin care


Threadfins are extremely hardy fish and have even survived days out of water during collection. They can be kept in either fresh or saltwater, though they need plenty of space to swim around as mature adults.

Threadfin diet

A good diet is a key to keeping your threadfin healthy and happy so make sure that their food contains plenty of protein which they will need in order to grow big and strong. They are carnivores, eating small invertebrates including insect larvae, crustaceans, mollusks, urchins, brine shrimp, or daphnia as well as any smaller fish in the tank.

Tiger Loach Fish "Syncrossus Hymenophysa"

Feed them small meals several times a day to keep their metabolism high so that they are always hungry and eager for more food.

Tank mates

Threadfin is generally a peaceful fish and can be kept in a community aquarium with other non-aggressive creatures or species of similar size and temperament..

As they grow, threadfin becomes increasingly territorial so it’s best to keep them in an aquarium by themselves or with smaller species of fish.

They do well when paired up with their own kind but would also make good additions to larger tanks containing several different types of small fish.

What else should I consider?

Threadfin is a very pretty fish that would make a stunning addition to the right aquarium. They can be quite shy at first but will soon grow more confident and begin darting about, showing off their beautiful colors so they need room to swim around without feeling threatened or stressed because this could cause them to harm in the long run.

Water conditions

In order to thrive, threadfin needs water that is clean and well-oxygenated.

They also benefit from a few live plants in their tank as it provides refuge for smaller fish when the threadfin gets too big.

We recommend using an aquarium heater in cold climates to maintain a temperature of between 65°F – 73°F and using a hydrometer to test the hardness and pH levels of your water.

These fish are known for their agility so you should provide them with plenty of space to swim around as well as some sturdy plants, rocks or driftwood in order to create natural barriers that prevent other fish from entering its territory.


The female threadfin lays thousands of eggs and the male will guard them until they hatch. After hatching, both parents continue to care for their young by providing protection and food such as infusoria or baby brine shrimp.

When it is time to breed, you should only introduce a single pair into your tank because more than that can cause a fight to break out. Once mating is complete, the male threadfin will begin to prepare an area for the eggs and then fertilize them once they are laid by his mate.

The female threadfin should be removed at this point because her presence can interfere with the incubation of the eggs which usually lasts around two days after being laid.

The eggs should hatch within a few days and once they do, you can feed them some baby brine shrimp or similar foods. After another week the fry will be large enough to eat bloodworms or similar food items for more advanced fish.

Threadfin is not an easy species of fish to breed, but with patience and research, you can help them reproduce in your aquarium.

Heros notatus (Spotted Severum)

What do they look like?


Threadfin is large fish that gets their name from the long dorsal fin found on their backs which resembles a feather or thread. Their mouths are small and generally upturned, making it easy for them to catch prey around rocks and other obstacles in their environments. They vary in color, depending on the species but most are gold or silver with large black spots along their backs.

When they are fully grown, threadfin can reach lengths of up to three feet, so you should plan accordingly when preparing an aquarium for them – they’re not a fish that fits into all tanks!


Threadfin can live for up to ten years when cared for properly.

Parasites and diseases

Threadfin is generally hardy fish that do not often succumb to the disease. However, they can become infected with internal parasites if they eat food containing them, or if other threadfins in the tank have the parasite and release it into the water via their waste. If you notice your fish has a large bulge on its stomach or is swimming erratically or close to the surface of the water, it may have a parasitic infection and should be treated as soon as possible.


Threadfin fish are not particularly preyed upon by other large fish, so they can be housed with larger varieties if you have enough space in your aquarium. However, keep small or slow-moving bottom feeders away from this active predator as it will eat them.

Does it make good pets?

Threadfin is a great fish for beginners and can be a wonderful addition to the right aquarium. They get on well with other peaceful, docile tank mates and look fabulous when they swim around your tank. If you have enough space in your aquarium and want an active predator that will add movement to your tank while being easy to care for, then this fish may be for you.

Conclusion – What do I need to know?

It’s important to research threadfin before deciding whether you want them in your aquarium so that you understand their needs and requirements fully before purchasing one of these beautiful fish. When kept in a healthy environment with plenty of space, they are easy to care for and make a great addition to the right tank.