Home | Aquarium Livestock | Species Profile: Long Horn Cowfish

Species Profile: Long Horn Cowfish

Welcome back Melissa! Enjoy her profile on the Long Horn Cowfish, or Lactoria cornuta.
Cowfish are very cute curious fish. Who couldn’t love a bright yellow box shaped fish with whitish blue spots and little horns sticking out from its head and behind its caudle fin?? Cowfish are very friendly and have great personalities. They are generally peaceful and get along with other peaceful fish like chromis, anthias, and basslets. They may eat small inverts as well as graze on live rock, and pick at algae from time to time. In captivity, they usually accept brine shrimp, mysis shrimp, krill, as well as other frozen foods. They should be fed small portions several times a day. With frequent feedings water quality must be continual”Long Horn Cowfishly monitored. It is a good idea to only house one cow fish per aquarium since they are aggressive towards their own species. A single cowfish should have at least 100gal since adults can reach a max size of 18”. If cared for properly they can live in an aquarium for many years.
Cowfish, as well as other members in the box fish family, are able to produce an ostracitoxin which is found in the mucous secretions in their skin. However, the cowfish must be alive to to release this toxin. They only appear to excrete the toxin if they are stressed or feel threatened. Cleaner shrimp and fishes that feed on the slime coat of other fish should be avoided as tankmates because they may provoke the cow fish to release its toxin. If the toxin is released in a closed system the water will usually have a milky haze and the fish immediately start gasping. It would only take a matter of minutes to kill the cowfish as well as the rest of its tankmates. Inverts tend to withstand higher concentrations of the toxin than fish and are more likely to survive. If you suspect the toxin is in your tank, add fresh carbon immediately. If carbon is used and replaced regularly you may see little to no effects of the toxin.

Cowfish are a unique and interesting fish. They may not have soft cuddly fur but they are as close as you can get to an underwater puppy dog!


  1. avatar

    this is really cool. it helped me with my homework. thanks!
    ps-do you know how many species of cowfish there are

  2. avatar

    Glad we could help. There are at least 26 valid/recognized clownfish species, but there may be more out there!

  3. avatar

    hey, how are you.. I’ve been searchin for someone to help me with my cowfiah. it’s just past away and i’am worried that it has released it’s toxins. how do I know if it did?i don’t see anything wrong with my fish. i pulled the cowfiah out when i noticed it laying on the bottom of the sand bed and still breathing. he started 2 days ago appearing to get black spots. i think due to stress from my new purchased fish a clown tang that couldn’t stop swimming fast all over the place. so i assume that that is what caused the stress.. i hope you can help… thanks leroy

  4. avatar

    The toxin is pretty quick to wipe out a tank. If the other fish are still alive, chances are your tank is ok. May not hurt to do a small water change if you’re concerned, but the toxin is potent, and as stated you would have probably seen the other fish in the tank dropping off if it did release its toxin.

  5. avatar

    Is the Cowfish toxin dangerous to humans?

  6. avatar

    Hi Jennie, There isn’t a lot of information on the effects of this toxin on humans, and I’ve never heard of anyone becoming ill from external exposure. If I had to guess I would say it is probably only dangerous if ingested, or if somehow a person was exposed to the toxin in another more direct way. It is deadly to other fish and inverts in a closed environment (aquarium). The toxin isn’t always released when one of these fish is sick, threatened or dying, only in some cases…few, but it does happen from time to time. With proper precautions, I don’t believe that they are a danger to the aquarists that choose to keep them or to divers that may encounter them in the wild. That being said, I wouldn’t encourage anyone to handle or harass these fish to find out what the effects would be.

  7. avatar

    I had a long horn cowfish that lived 7 years. They have amazing personality almost puppy like. They are very very smart. Mine started doing all sorts of tricks to get my attention that I did not teach it. They seem to care more about whats going on outside the tank then in it. Sadly, my heart was broken when the little guy passed away.

    I ready many post about toxins nuking the tank but I have to say this never happened in my case. The stress level has to be very high, as in being attacked. My cowfish actually like cleaner shrimp and parked in that part of the tank regularly to get a cleaning. That is until I went out of town for 3 days and my fish sitter skipped a day without telling me. When I returned one cleaner shrimp was gone. After that, even with regular feeding he learned what tasted good and the other all ended up on the menu within weeks. Can’t eat the help. LOL

    Think twice if you decide to get one as a pet. They are easy to take care off but they go from the size of a sugar cube to 6″ in less than a year. They live up to 20 years in the wild. They keep growing even in a small tank. Defiantly on board with 100 gal min or larger after the first 6 months. They can grow up to 18″ in the wild, mine was over 1 foot in length.

    They also eat A LOT. The need to be fed about twice a day. Mostly protein like frozen Mysis and clams, but also some algae. Don’t use brine, they have no nutritional value after 24 hours of hatching so your fish will slowly starve to death. This is true also with feeding seahorses.

    What goes in, must come out. That means a lot of clean up. More importantly, that amount of bio load can really negatively affect the water quality.

    The tricky part is, these guys need slow moving water to hunt for food. Unlike other fish, cowfish have a specialized ability to hover in the water. They do not like high jets of water flow or reef tanks. But they do need clean water, so they need a high rate of turnover through the filters, but slow moving in the tank. Get the biggest protein skimmer you can afford.

    Think about this twice before you buy. They are a lot of fun and have lots of personalty but they are not just another fish, they have specialized needs and require a long term commitment like you would do for a cat or dog.

  8. avatar

    are they poisonous to humans?

  9. avatar

    The only danger would probably be if you were to ingest the toxin or water polluted by it. Careful maintenance, correct husbandry and proper handling should prevent any dangerous exposure.

  10. avatar

    this really helped me but do you know about how many offspring they produce

  11. avatar

    Hello Kelly, Cowfish really can’t be bred in captivity and I haven’t been able to locate any information on how many offspring they can produce at a time. The offspring are pelagic, meaning they are released into the water column rather than stuck to a hard surface like some other fish.

  12. avatar

    There is misinformation out there on other sites that seems to have gone viral but its not accurate, they live up to 20 years in the wild, not 2-8. They dont automatically release toxin when they die.

    I have personally owned two of them, one live past 7 years and died due to accidental tank issue, the other one lived 12.5 years. In both cases, the tanks were never “nuked” no other fish died. Not saying this can’t happen, just want to point out its not an absolute given. Both died peacefully, no predictors in the tank.

  13. avatar

    Hello, That is absolutely true. The fish must be alive to released the toxin as mentioned in this blog and it is usually only done under extreme stress.

  14. avatar

    How many feet is a long horn cowfish

  15. avatar

    Hello Maliha, Longhorn Cowfish can grow up to 18 inches, or about 1.5 feet, in length.

  16. avatar

    I have a 10 gallon tank and was wondering if this would be to small for a cow fish if I did not add any other fish to it?

  17. avatar

    Hello Nina, A 10-gallon tank would be too small for any cowfish or boxfish. One may be ok for awhile if purchased very small but all of them should have a much larger tank.

  18. avatar

    I Agree with Eileen. 10 gallon is way too small. Even if you get them the size of a sugar cube, they will grow to the size of several inches within 6 months. Moving them from tank to tank is very stressful on them, more then most fish. That is when they are at high risk of dying. If they get too stressed, they will release a poison in the same water they are in and it will also kill them. So your best bet is to get a good size tank. Typical recommendation is 50 gallon to start, 150 gallon for adults.

About marinebioblog

Read other posts by

Marinebioblog is the post name of That Fish Place - That Pet Place's aquatics and aquarium experts. Contact them through the links here or leave your comments below.