Boxfish/cowfish best to start small or go for a bigger one?

[Flatearth]

I often see the yellow boxfish and the longhorn cowfish for sale at the LFS around me. They are either super small at like an inch long or bigger at about 2-2.5 inches sometimes a little bigger. Are the larger ones more likely to do well? I know in some species smaller specimens adept better to captivity, but other times smaller means more fragile.


Or is this the kind of fish where any healthy specimen is a good bet?

 

[A Young reefer]

it’s a subjective topic in my opinion. There are two faces to the coin for similar reasons you mentioned. A healthy specimen is always the best bet.

 

[ErikVR]

Sorry to just barge in here but I have an additional question on top of yours. Are these fish extremely hard to care for? Whenever I see pictures of lornhorn cow fish, they are tiny. I never see pictures of mature fish. From what I’ve read they can get to 20 inches long in the wild but all I see are 3 inch fish in home aquariums. Do they all die before they reach an adult stage?

 

[A Young reefer]

Sorry to just barge in here but I have an additional question on top of yours. Are these fish extremely hard to care for? Whenever I see pictures of lornhorn cow fish, they are tiny. I never see pictures of mature fish. From what I’ve read they can get to 20 inches long in the wild but all I see are 3 inch fish in home aquariums. Do they all die before they reach an adult stage?

In my experience they seem to be very prone to diseases. I think that not enough people are willing to take the risk of keeping them since if in case they die they would nuke the tank with toxins.

 

[livinlifeinBKK]

I've kept a couple Boxfish in the past... they're some of my absolute favorite fish! They're very personable like puffers and can interact with you which is really fun. As for your concerns regarding size, i wouldn't go for a baby because they're very fragile and they are very prone to ich and other parasites as well unfortunately.
Tbh, ime the toxins aren't a major concern as long as you take care to house them with peaceful tank mates where they won't be bullied. They're not strong swimmers and really are kind of defenseless which is why they have toxins in the first place.

 

[livinlifeinBKK]

Btw, if you can find a male Ostracion meleagris Boxfish and give it the care it requires, go for it...they do grow large though but they're absolutely gorgeous and really do have personalities of their own.
I see them fairly often here...their common name is the blue spotted Boxfish if I'm not mistaken (although only the males have this coloration. Females are brown with white spots.)

 

[Herbie's Reef]

Sorry to just barge in here but I have an additional question on top of yours. Are these fish extremely hard to care for? Whenever I see pictures of lornhorn cow fish, they are tiny. I never see pictures of mature fish. From what I’ve read they can get to 20 inches long in the wild but all I see are 3 inch fish in home aquariums. Do they all die before they reach an adult stage?

I believe that they also grow EXTREMELY slow. I think it can take a few years just for a couple inches of growth. Prestige Reef has one on YouTube and it seems that it has barely grown. Maybe there aren't any that have been in captivity for 20+ years for it to get to the behemoth size they grow into. Also they don't do too well adjusting to captive life so maybe nobody has kept one alive long enough.

 

[ISpeakForTheSeas]

I think that not enough people are willing to take the risk of keeping them since if in case they die they would nuke the tank with toxins.

Just to clarify here, boxfish/cowfish actually have to be alive (and stressed) to produce their toxins - they can't physically produce the toxins when they're dead.

No experience with keeping them myself, but, for boxfish specifically, these guys aren't toxic when they die, they're only toxic when alive and stressed (they have to be alive to produce the toxin, and they only produce it when stressed). The toxin they produce is a potent ichthyotoxin called Ostracitoxin or Pahutoxin (ichtythoxin meaning it's a toxin that primarily effects fish, though this toxin has been demonstrated to slowly affect a wide variety of inverts too). In small quantities, the effects may be mild as long as the toxin is promptly removed, but the effects of it on fish are irreversible (meaning the fish - if they heal from it at all - will recover over a long period of time, and they will only recover if the damage is mild and the toxin is no longer present in their environment).

When the toxin is present even at 5ppm in the water (the equivalent - if my math is right - of ~3.4ml of the toxin in a 180 gallon tank), 50% of the following species of fish died within the following times*:
Abudefduf abdominalis - 6 minutes
Acanthurus sandvicensis - 8.5 min
Kuhlia sandvicensis - 10 min
Mugil cephalus - 12.5 min
Mollienesia litpinna - 15 min
Bathygobius fuscus - 30 min

Given that the damage is irreversible and lethal even at relatively small doses (and that boxfish themselves aren't immune to the toxin, though they are more resistant to it than other fish), I'd guess it's probably not an overblown risk (though it is something you could likely try to prepare for by running carbon and having a water change and QT ready at all times).

That said, I don't know how fast these guys produce the toxin, but as long as the fish doesn't get too stressed, it should theoretically never produce enough toxin to cause an issue (though I'd constantly run carbon on the tank just to be safe).

* The study I pulled the data from:

Toxic Stress Secretions of the Boxfish Ostracion meleagris Shaw on JSTOR

Donald A. Thomson, Toxic Stress Secretions of the Boxfish Ostracion meleagris Shaw, Copeia, Vol. 1969, No. 2 (Jun. 3, 1969), pp. 335-352

www.jstor.org

For anyone scared by the numbers in the quote above:

I’ve kept various box fish over the years. The only time I’ve had issues with toxins were with boxfish I had just caught myself and placed in buckets on the boat.
That said, this is one of those fish that appear to do fairly well, but asking who has kept one longer than two years, not many hands in the air. The only ones I have had long term success with were temperate Australian species.

Jay

 

[Flatearth]

I have read everything I can get my hands on regarding these fish, and it seems these are the most poorly understood fish around. I will re-share all the info I have gathered since many seem to have questions regarding these. This is just from reading every forum post and video I could find as well as researching their natural habitat. The two species that interest me are the yellow boxfish and the longhorn cowfish although it seems most box/cowfish are similar so I imagine most info applies to them all.


First the tank nuke seems to be a myth. I didn't mention it in my original post because every topic regarding these fish seems to devolve into a discussion about the tank nuke. Someone probably added a boxfish then lost all their fish due to a tank crash, then read that these fish were toxic thus the myth was born. I can't find any first hand reports of this occurring.

There are some reports of boxfish that are being picked on making a toxin, but these fish don't seem to handle bullying well so the boxfish should never be in such an environment to begin with.


As for growth rates one of my LFS has had a yellow boxfish for sale nearly a year now(way over-priced so probably will never sell), and it has not grown at all in that time. The few I can find owned by youtubers also seem to grow slowly.


Their diet is also a point of misinformation. Searching "Longhorn cowfish diet" yields top results saying "mollusks and small fish". These slow clumsy animals could never catch small fish, and a closer look at their mouths(easy to see on large specimens) shows a rasping mouth very different from the mouth of an invertebrate eater. In reality it seems these fish need a lot of green in their diet similar to a tang, and I theorize the lack of greens is one of the major factors leading to this fish not living more than a year or two in some tanks.





The most common set-ups I have seen them in is a small reef tank where no greens are offered, or they are put in a large FOWLR with aggressive species that they can't handle which neither tank is suitable for them.


It seems they need a large peaceful tank where plenty of algae is offered to them, and according to those who have had them for years if these needs are met they aren't actually that difficult to keep. I will be giving them a go then reporting back in a few months with my progress.

 

[Herbie's Reef]

In my experience they seem to be very prone to diseases. I think that not enough people are willing to take the risk of keeping them since if in case they die they would nuke the tank with toxins.

Prestige Reef has a video talking about the toxins. Some people have had them die and no toxins were released.

I have read everything I can get my hands on regarding these fish, and it seems these are the most poorly understood fish around. I will re-share all the info I have gathered since many seem to have questions regarding these. This is just from reading every forum post and video I could find as well as researching their natural habitat. The two species that interest me are the yellow boxfish and the longhorn cowfish although it seems most box/cowfish are similar so I imagine most info applies to them all.


First the tank nuke seems to be a myth. I didn't mention it in my original post because every topic regarding these fish seems to devolve into a discussion about the tank nuke. Someone probably added a boxfish then lost all their fish due to a tank crash, then read that these fish were toxic thus the myth was born. I can't find any first hand reports of this occurring.

There are some reports of boxfish that are being picked on making a toxin, but these fish don't seem to handle bullying well so the boxfish should never be in such an environment to begin with.


As for growth rates one of my LFS has had a yellow boxfish for sale nearly a year now(way over-priced so probably will never sell), and it has not grown at all in that time. The few I can find owned by youtubers also seem to grow slowly.


Their diet is also a point of misinformation. Searching "Longhorn cowfish diet" yields top results saying "mollusks and small fish". These slow clumsy animals could never catch small fish, and a closer look at their mouths(easy to see on large specimens) shows a rasping mouth very different from the mouth of an invertebrate eater. In reality it seems these fish need a lot of green in their diet similar to a tang, and I theorize the lack of greens is one of the major factors leading to this fish not living more than a year or two in some tanks.





The most common set-ups I have seen them in is a small reef tank where no greens are offered, or they are put in a large FOWLR with aggressive species that they can't handle which neither tank is suitable for them.


It seems they need a large peaceful tank where plenty of algae is offered to them, and according to those who have had them for years if these needs are met they aren't actually that difficult to keep. I will be giving them a go then reporting back in a few months with my progress.

Wow very informative post. I plan on getting a yellow boxfish in the near future and have found it very hard to find much info at all on their care. Please do keep us informed on how things go with your boxfish quest.

 

[LadAShark]

I've kept a longhorn boxfish before it passed of old age. They really want to eat a lot. It readily took both algae/nori and shrimp/squid/octopus/clam. I had no trouble keeping it, probably because my reef runs somewhat high in nutrients, so there's always some algae or tiny invertebrates for them to eat. They do bite, by the way, quite painfully at that, but not out of aggression, their appetite is honestly just that crazy.