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Have a Cow; the Longhorn Cowfish,
Lactoria cornuta

Bob Fenner

As an aquarist as well as dive-travel adventurer I have some subjects as favorite species that I look to encounter underwater as well as captivity. The cowfish, Lactoria cornuta is definitely among these. It’s a great fish at any size, from pipsqueak to a foot or more. Longhorn cowfish are cute-as-Dicken denizens of both worlds.





Longhorn cowfish are also known as hovercraft fish due to the way they move about; akin to a helicopter. Here is a three inch juvenile in captivity.


            Cowfishes period; family Ostraciidae, are faves, although many get too big and they have a dire downside if disturbed: ostracitoxin compounds they produce that can have a quick and deadly effect on other fishes, even in large systems. So, what to do? Either excludes them or read and heed here regarding keeping yours happy. I choose the latter.

            Another name for the longhorn cowfish is “hovercraft fish”; an allusion to how this species buzzes about helicopter-wise (“ostraciiform swimming”), waving its fins in their small openings from the hard body casement, investigating its reef world, discovering and consuming food items.

Cowfish Basics:

            Cowfishes are part of the boxfish or trunkfish family, Ostraciidae (Greek: “ostracum”, meaning “shell”); they’re the puffers that don’t puff up! Their bodies are encased in hard body armor with small openings for their fin insertions, mouth, eyes and gills. This is a great strategy for avoiding predation, except that it makes them quite slow and clumsy in maneuvering. Some species, like the cowfish of this article, have further body armament, a pair of prominent spines in their “foreheads” and another duo trailing back off their rea anal area.

            Boxfishes are found worldwide on shallow reefs of the Pacific, Atlantic and Indian Oceans. Lactoria cornuta itself occurs in the western Pacific and through-out the warm waters and subtropical reefs of the Indian Ocean, including east Africa’s coast and the Red Se to depths of about 165 feet.

            Though caught and traded as small specimens only, due to the real rate-limiting costs of shipping, the longhorn cowfish grows to 18 inches in the wild, and this is “fisheries length” (not counting the actual tail/caudal fin). Yes, this is a largish, messy fish that needs room and good circulation and system filtration.

            Although L. cornuta is by far the most popular boxfish in aquarium use, many other choices exist- larger and smaller, and much colder water.

            Lactoria cornuta can vocalize, producing grunting noises by stretching muscles along the gas bladder. This is much the same as you rubbing your fingers over an inflated balloon. These noises can be heard underwater and even through aquarium system walls. Cowfishes produce vocalizations in relation to pleasure or aggravation.

Compatibility Concerns:

            Compatibility is an important issue for two reasons: 1) To ensure you are able to get food to your cowfish and 2) To discount the likelihood of over-upsetting this fish, causing it to release ostracitoxin, which is toxic to fishes (ichthyotoxic). To be sure, the probability of such poisoning is actually quite small. Most of the few events I’ve encountered have involved the cowfish dying- getting stuck on a pump intake, otherwise gone undiscovered dead and dissolving. Take care when netting this species and do not dump their shipping water into your system. Avoid housing this species with overly aggressive tankmates.




To keep a longhorn cowfish happy and prevent it from releasing its fish-killing toxin, keep only one longhorn cowfish to a tank, and be sure that its tankmates are friendly toward it; providing easy access to food.


            Fish I’d be ware of placing with boxfishes include moray eels, large angelfishes, triggerfishes and some largish puffers and wrasses. I’ve even encountered bigger basses and groupers that bossed them about to all-s detriment.

            Reciprocally, cowfishes will sample to completely chomp most all crustaceans, mollusks, sponges, worms and some echinoderms if they’re available and the Ostraciid is hungry or just curious. Most all fish of size are safe from their sharp, snipping beaks, as long as they’re healthy. Stinging-celled life (corals, anemones, etc.) is usually left alone; in fact, juveniles of this species are often encountered and collected in their association with Acropora corals.

            Adult cowfish are solitary and territorial and should only be kept one to a tank.

No Tank is Too Big:

            Big, bigger, biggest- get the largest tank you can afford and fit in your available space. Though not apparently very energetic, these are massive, messy fishes that really go through a bunch of food. They are almost always in motion; and they’re not great at making turns; so large spaces, including width, make it easier for them to move about without colliding into their tank or objects in the aquarium. Due to their copious meaty foods and after effects, much blowing of water into the sand, overall feeding and wastes produced, your system needs plenty of circulation and biofiltration, along with regular (weekly) partial water changes and gravel vacuuming to discount the eventual loss of water quality. As long as water movement is diffuse, i.e., non-unidirectional, it really can’t be too vigorous. The current need not come from an outside pump; simple powerheads and/or submersible recirculating pumps will serve well.

Feeding Notes:

            Lactoria is an omnivore that eats various free-living invertebrates and fish in the wild; along with a considerable amount of Foraminiferans, worms of many sorts, mollusks etc. that they blow the sand away from, while ingesting a good deal of substrate.

            Lactoria in captivity almost all learn to accept commercial meaty foods or frozen/defrosted mixed seafood for human consumption. Best practice is to feed all your other fishes on one side of the system, and utilize feeding tongs or stick to offer your cowfish food at the other end.

Watch Out for Too Much Stress and Injury:

Here is a good example of a stressed, damaged cowfish, with its “horns” on either end broken and petecchial bleeding evident in the distal part of its caudal/tail fin.


Cowfishes and boxfishes are very tough and are generally about the last to show signs of environmental or pathogenic disease. However they can contract the usual parasites, e.g. Crypt and Velvet, Cryptocaryon irritans and Amyloodinium ocellatum respectively; and like all puffers, are sensitive to copper treatments. I encourage you to look into Quinine compounds if/when you find yourself in a situation that calls for direct treatment.

With unknown bumps or blobs on their skin or fins, I’d take a wait-and-see approach, as often these are manifestations of physical trauma (run-ins with something in the environment) or stress. Check your system and be patient; and they will often heal in time of their own accord.

If your cowfish goes on a feeding strike or seems to be sitting about a good deal of the time, don’t panic! These apparent “time outs” are quite common and almost never are cause for concern. These fish can literally go without food for weeks, and lay about for even longer, only to spontaneously snap out of their funk. Moving and isolating them in small volumes is counterproductive.

More Cowfish! Reproduction:

            There are no known identifiable (sexual dimorphism) or color (dichromatism) differences between the sexes in this species. Not bred/reared in captivity as yet; in the wild pairs are formed near sunset, just ahead of spawning, and the eggs and young are pelagic.


            Cowfishes, including L. cornuta, aren’t difficult to keep, with the proviso of keeping them “happy” so they don’t release ostracotoxins. This happy requirement is easily met by providing plenty of uncrowded room- hundreds of gallons ultimately- and training yours on meaty foods in a way that prevents their tankmates from stealing it all. For reward, you’ll have a true “aqua dog” for many years as an ever-interesting, comical pet.

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