With similar personalities to puffers, Cowfish add amusement to the mix with their comical look and movements. Kind of looks like a jousting Kia!
Cowfish have a carapace or stiff outer body that their fins tail and mouth protrude. They start out life yellow with some shadowy hints of honeycomb shapes under the skin. As they age the honeycomb shapes develop a brown outline with a green to olive and orange center. The belly is plain and all ages have small blue spots all over the body. Their tail fin is long and looks really cool, and it starts out clear juveniles and stays clear yet develops blue and brown spots as adults. Both ages have horns on their forehead and under the tail fin. They have a downturned mouth to blow critters out of the sand and a small slit instead of gills. Their eyes are yellow to deep goldish brown or greenish. Cowfish can grow to 18” (46 cm) long, however, they typically grow to 15.7” (40 cm). They are mature at 10.6” (27 cm) long. They live 20 years in the wild and only 5 to 7 in captivity.
These fish are weak swimmers and are easily caught by hand, which makes them produce a grunting sound. It would be wise to avoid this to your pet since toxin can be released as well! Most people who have had Cowfish have not had toxin issues but they also have appropriate tank mates. Cowfish swim much like puffers with their undulating movements, however, they are not as agile or as fast as puffers. Some people think a boxfish and trunkfish are the same as a Cowfish; however, Cowfish bodies taper downward from the head to the tail and they have horns. Boxfish and trunkfish lack horns and their name alone indicates a boxy shape with no tapering.
Cowfish are considered difficult to are for and are best suited to expert aquarists or best left in the ocean. Among other things, they have been known to release a toxin called ostracitoxin when they are stressed out by loud sounds, bright lights and sudden movements. Special attention needs to be given to proper tank mates, proper water movement so your Cowfish isn’t getting blown around, and the huge tank that it needs. They can also be hard to feed when first captured, thus starving before they are adjusted. It is best to add them to the tank as the first fish and allow them to adjust before adding fish.
The ideal tank mates include mellow fish. Do not house with other Cowfish or puffers who would love to “taste” their horns and triggers are to inquisitive as well and tend to pester the Cowfish to the point of toxin release. Fast swimming fish also wig the Cowfish out so only slower moving peaceful fish are acceptable. Clownfish are perfect for example, and if you have a proper amount of live rock with amphipods and copepods, a Mandarin or Scooter Blenny. Reefs can harm them because of the stinging tentacles of many species. They do not have scales and can be harmed, simlar to seahorses. Also they will eat corals when hungry, which can be poisonous for them. Cleaner Shrimp will be allowed to clean the Cowfish as long as the cow has been fed well!
Minimum tank size is 250 gallons. Activated carbon is a must have just incase they release their toxin. This is very rare if kept with appropriate tank mates. Trying to remove the toxin after the fact usually doesn’t result in saving anything in the tank. Water movement should be good enough to keep water moving, but not so much that it blows your Cowfish around. Pumps like Sicce move a lot of water in a gentler way than Koralia type pumps.
For more Information on keeping this fish see:
Guide to a Happy, Healthy Marine Aquarium
- Kingdom: Animalia
- Phylum: Chordata
- Class: Actinopterygii
- Order: Tetraodontiformes
- Family: Ostraciidae
- Genus: Lactoria
- Species: cornuta
- Aquarist Experience Level: Expert
- Aquarium Hardiness: Difficult to Impossible
- Minimum Tank Size: 250 gal (946 L)
- Size of fish – inches: 18.0 inches (45.72 cm)
- Temperament: Peaceful
- Temperature: 72.0 to 82.0° F (22.2 to 27.8° C)
- Range ph: 8.1-8.4
- Diet Type: Omnivore
- My Aquarium – Enter your aquarium to see if this fish is compatible!
Habitat: Distribution / Background
The Cowfish, Lactoria cornuta, was first described by Linnaeus in 1758. This fish only has a few common names, which are descriptive and they are Cowfish, Long Horned Cowfish, Longhorn Cowfish, and Trunkfish. Trunkfish is incorrect because true trunkfish do not have any horns, and neither do boxfish for that matter. Cowfish are more angular in shape less “boxlike.” The genus Lactoria is latin for “concerned with milk,” however it would be quite distressing to the fish if you tried to milk it! The name is due to the two cow-like horns on their forehead, although they have some behind them as well. There are only 4 species in this genus, each having their own unique look.
The waters they are found in include mostly marine and occasionally brackish water. Their range in the Indo-Pacific is from the Red Sea and East Africa to the marquees and Tuamoto Islands then north to southern Japan and then south to Lord Howe Island. They are found in coastal habitats like calm bays, harbors and estuaries over sandy or muddy bottoms. Juveniles are found near river mouths, in brackish water where the tend to feed on more veggie material found there. Adults are constant foragers for meaty things, occasionally benthic weeds, however, data only shows inverts in their bellies. The depths that adults are found in range from 9.8 to 984 feet (3 – 30 m), and they feed on benthic invertebrates found in the mud or sand by blowing at the substrate to expose their meal. This can be foraminiferans, sponges and polychaete worms, mollusks, small crustaceans and tiny fish. As small juveniles, these would include amphipods and sea grass then as they grow larger prey will be eaten. Adults are found alone and juveniles are found in small groups among acropora. Predators include albacore, big eye tuna and other large fish.
Not having been evaluated, the Cowfish is not on the IUCN Red List for endangered species.
- Scientific Name: Lactoria cornuta
- Social Grouping: Varies – Juveniles in groups among acropora. Adult solitary.
- IUCN Red List: NE – Not Evaluated or not listed
Cowfish have a unique hard body called a carapace of fused plate-like hexagonal scales. This hard outer body is wider at the head but tapers down to the tail fin area. The carapace is covered in a “skin” of sorts and makes them susceptible to crypt. Their fins, protruding lips and tail stick out of holes of their stiff body. They have slits for breathing instead of conventional gills. The body color of the adult is green to olive and orange with blue spots and have dark tan to brown trimmed honeycomb shapes all over the body, excluding the belly. Their tail fin is very long and has blue and brown spotting. The mouth is pointed downward and their large protruding lips enable them to blow into sand or mud to expose inverts hiding in the sand or on other surfaces. The horns are typically a solid color, matching the body’s main color. Two of them are located on the forehead pointing forward and two of them are found below the tail fin pointing the opposite direction.
Juveniles are more yellow with a hint of the honeycomb shapes starting to show up like a shadow under the skin. Their tail fin is not as long as the adults and is more clearish, lacking the blue and brown spots. The little sugar cubed baby will grow to 6” within a year. Cowfish can grow to 18” (46 cm) long, however, they typically grow to 15.7” (40 cm). They are mature at 10.6” (27 cm) long. In the wild they live up to 20 years and only 5 to 7 in captivity. They do not stay alive in captivity long term.
- Size of fish – inches: 18.0 inches (45.72 cm) – Mature at 10.6” (27 cm)
- Lifespan: 20 years – Reports of having them 5 to 7 years in captivity (best left in the wild to live a full life).
Fish Keeping Difficulty
Cowfish are considered difficult and impossible to keep long term and should only be attempted by expert aquarists or in public aquariums. They only live 5 to 7 years in captivity in most aquarists tanks, but can live up to 20 in the wild. It would be like chopping our life span by 2/3rds! They are best left in the wild until there is more information about them. It can be hard to get them to start eating when first obtained and are very light sensitive and extremely shy. They should be the first fish added to the tank. Live gut loaded (enriched) brine shrimp and black worms can entice them to start feeding. Also provide small hermit crabs for them to hunt and offer frozen mysis shrimp and soak mysis in Selcon or Vibrance regularly. They are very touchy when it comes to tank mates. Any fish that are fin nippers, very active, competes for food or pester the Cowfish can freak them out enough to release toxin into the water or stress into a crypt breakout. If they do die, remove it as soon as you can before the body starts to rot, since that toxin can seep out. The tank size of 250 gallons alone is daunting for most and is needed, because, once again, limited swimming space can stress it out and they are BIG POOPERS! Consider a 16” fish in addition to the 2 projecting horns on the forehead and a person can surly understand the need for a rather large tank that can accommodate the Cowfish easily turning around even with live rock in the tank. Within that tank, water movement needs to be sufficient enough to keep the system healthy, yet not so hard as to blow the Cowfish around, which would also stress it out.
One more thing that needs to be pointed out. Young children who visit your home should be instructed to not bang on the tank or wave their arms about as they stand and watch. Kids will be amused by the Cowfish following their finger around. For the sake of your Cowfish, and the rest of your fish, do not allow unruly children near your tank!
- Aquarium Hardiness: Difficult to Impossible – Long term
- Aquarist Experience Level: Expert
Foods and Feeding
Cowfish are omnivores, leaning more towards the meaty end of things. Juveniles may be more of a veggie consumer since estuaries are perfect, teeming with sea grass and other greens that wont grow in full marine conditions. Feed them a variety of foods that match their bottom-dwelling invert menu. An aquarist who has successfully kept them for years suggests frozen mysis, supplemented with shell fish such as clams and sometimes algae. Feed with food soaked in Vibrance or Selcon on a regular basis. Add small hermit crabs and snails to supplement their diet. These crabs and snails should be relative to the size of the fish. Flake food may not have enough nutrition and occasionally pellets can be offered. They should be fed at least 3 times a day as adults, more as juveniles. Unlike the dangers associated with hand-feeding puffers, Cowfish are such slow movers and are so chill, and with careful attention, they can be hand fed!
- Diet Type: Omnivore – Juveniles eat more veggie material.
- Flake Food: No – Not nutritious enough
- Tablet / Pellet: Occasionally
- Live foods (fishes, shrimps, worms): Some of Diet – Supplement feedings with small hermit crabs and snails appropriate to size of Cowfish.
- Vegetable Food: Some of Diet – Juveniles need some veggie matter and more meaty as they age
- Meaty Food: Most of Diet – Adults eat primarily meaty foods
- Feeding Frequency: Several feedings per day – Adults at least 3 times a day, juveniles more often.
Cowfish do not do well when water quality is neglected.
Fish Only Tanks:
-Large Tanks 100 gallons and over, once water is aged and stable can be changed 10% bi-weekly to 20% monthly, depending on bioload.
-Large Tanks 100 gallons and over, once water is aged and stable can be changed 20% to 30% every 6 weeks depending on bioload.
For more information on maintaining a saltwater aquarium see: Saltwater Aquarium Basics: Maintenance. A reef tank will require specialized filtration and lighting equipment. Regular water changes done bi-weekly will help replace the trace elements that the fish and corals use up.
- Water Changes: Bi-weekly
Minimum tank size is 250 gallons. Provide live rock with caves and crevices for your Cowfish to hide in, keep in mind their size and horn length. As for substrate, only use sand due to their behavior in the wild. If seagrass of some kind can be added, that would be appreciated because they will like hiding in it, besides it can help with nitrates! Lighting should be subdued in the beginning and slowly increase over a reasonable period of time (not in just a week), to help them settle in. Your set up should already have small hermits and snails for them to munch on if they are not ready to eat prepared foods yet. Their temperature range is 72˚F to 82˚F and a normal pH of 8.1 to 8.4. Water movement from pumps that move water with out excessive linear movement are best. Sicce pumps fit the bill, moving a lot of water with out high pressue and they have a well protected intake area. They inhabit the bottom part of the tank most often in search of food but will venture into other levels of the tank as they become curious about their new home. Use a lid if they start to shoot water out of the tank at you, besides they have been known to jump.
- Minimum Tank Size: 250 gal (946 L)
- Suitable for Nano Tank: No
- Live Rock Requirement: Typical Plus Hiding Places – Make crevices and caves large enough for them to hide in.
- Substrate Type: Sand – Substrate besides sand are unnatural and can stress the Cowfish.
- Lighting Needs: Low – subdued lighting – Subdued when first introduced and slowly increase once they are acclimated.
- Temperature: 72.0 to 82.0° F (22.2 to 27.8° C)
- Breeding Temperature: – unknown
- Specific gravity: 1.023-1.025 SG
- Range ph: 8.1-8.4
- Brackish: No – Although found in brackish in the wild, they do not stay in it for long.
- Water Movement: Moderate – Weak in areas of feeding.
- Water Region: Bottom
Cowfish are peaceful, yet not to their own kind. Do not house them with other Cowfish.
These mega chill fish must be the first ones to inhabit the tank. They will need to get used to their new home and within 2 weeks they should start eating. It is after they are eating for a good while and are not skittish anymore that you can add the next fish. All peaceful, docile chill fish are acceptable, as long as they are not super fast swimmers (like the Bird Wrasse), pesky and nosey (like puffers or triggers), aggressive food competitors (large wrasses once again), or predatorial fish (groupers and large hawkfish), since that will just wig them out! Do not house sharks. Fish that they are fine with are smaller fairy and flasher wrasses, clownfish, basslets, etc. Basically any peaceful or semi-aggressive fish that will not bother it. Yellow Tangs and Blue Chromis are good, but avoid anything bigger or faster. Yes there are chill triggers, but they are fast movers. Eels should if they are chill like the Banded Snake Eel or the Zebra Moray Eel from Hawaii.
Do not house with stinging corals because of their lack of scales, similar to seahorses can cause them to be badly injured. If they are hungry, at times they will sample corals which can make them sick or kill them. They are best kept in a fish only system with a section of sea grasses which can make for a cool aqua-scape.
One successful aquarist states Cowfish can be kept with Cleaner Shrimp as long as they are well fed. Miss a meal, the shrimp becomes it! They will eat snails, hermit crabs, sponges, polychaete worms, mollusks, small crustaceans (amphipods) and tiny fish. Starfish tentacles will be chewed on. Any sedentary worms like christmas worms and tube worms will be slurped up with joy.
This is another fish that needs a compatibility with humans paragraph. Observations and experiences from those who have owned Cowfish for many years state that they are very intelligent. They are more curious about what is going on outside their watery home than inside. To get your attention, like puffers and triggers, they can shoot water out of the tank at you when you walk by, so make sure there isn’t anything that can be ruined by water nearby. Some suggest a cover if that starts to happen. Unlike other fish, they have feeling on the sides of their “skin” covered body similar to humans. They can even hear sounds outside of the tank with an inner ear! To get your attention they can make sounds or grunts or flare their tail fin to get your attention. They do need attention from their owner for them to be happy. Small humans need to be taught to not hit the tank, tap the tank or wave their hands around in front of the tank. Teach them respect for other living things.
- Venomous: No – Poisonous to eat.
- Temperament: Peaceful
- Compatible with:
- Same species – conspecifics: No
- Peaceful fish (gobies, dartfish, assessors, fairy wrasses): Safe
- Semi-Aggressive (anthias, clownfish, dwarf angels): Safe
- Large Semi-Aggressive (tangs, large angels, large wrasses): Monitor – Easy going tangs and peaceful larger angels are okay. No large wrasses
- Large Aggressive, Predatory (lionfish, groupers, soapfish): Threat
- Anemones: Threat – Will harm the Cowfish if they run into it.
- Mushroom Anemones – Corallimorphs: Threat – Will harm the Cowfish if they run into it or eat it.
- LPS corals: Threat – Will harm the Cowfish if they run into it or eat it.
- SPS corals: Monitor – May be poisonous to cowfish if they eat it.
- Gorgonians, Sea Fans: Unknown
- Leather Corals: Threat – May be poisonous to cowfish if they eat it.
- Soft Corals (xenias, tree corals): Monitor – May eat if not well fed
- Star Polyps, Organ Pipe Coral: Monitor – May eat if not well fed
- Zoanthids – Button Polyps, Sea Mats: Threat – May be poisonous to cowfish if they eat it.
- Sponges, Tunicates: Threat
- Shrimps, Crabs, Snails: Monitor – May not eat cleaner shrimp if well fed.
- Starfish: Threat
- Feather Dusters, Bristle Worms, Flatworms: Threat
- Clams, Scallops, Oysters: Threat
- Copepods, Amphipods, Mini Brittle Stars: Monitor
Sex: Sexual differences
Breeding / Reproduction
The male and female will display in a paired courtship just before sunset and spawn in open water. The eggs and larvae are pelagic, or free floating.
They have not been reported to spawn in captivity.
- Ease of Breeding: Unknown
These fish are also susceptible to crypt and are often called, crypt magnets. Hypo salinity is best. Copper will kill them as it will all scaleless fish and eels. Slowly bring their quarantine tank down to 1.009 or 1.010, taking 5 to 7 days, and use a refractometer for exact readings. Keep them at 1.009 or 1.010 for 4 to 6 weeks and make sure the pH doesn’t drop below 8.1 during this time. Monitor ammonia and do appropriate water changes as needed. After that time, take 9 to 10 days to bring the salinity back to 1.023. If you rush either direction, they can stress and die. Treat them in the same tank since moving them can stress them and kill them.
Usually available on line for $40.00 (USD) for a 2” to 3” juvenile. (May, 2015)
500 + ESSENTIAL-TO-KNOW AQUARIUM SPECIES
By Scott W. Michael
Copyright © 2001 by T.F.H. Publications, Inc.
by Bob Goemans
© 2012 Bob Goemans. All rights reserved
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Longhorn Cowfishes, Lactoria cornuta
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