Box & Cowfish - What You Need to Know

DarthChaos

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So, let talk about the adorable yet largely misunderstood Cowfish & Boxfish.

Before I begin, let me say that I’m NOT an expert, I’m not a marine biologist and everything I’m sharing is based on very real personal experience. I’m going to group these two fish (Cow & Boxfish) together, as I find their care is very similar. I am aware that there are many types of Boxfish (I’ll touch on that shortly) – but for the sake of this “guide”, we’ll call it, we are going to speak in general terms.

Currently, I have a Longhorn Cowfish (named Taco) – who’s been with me for just over 2 years. With Taco, is a Striped Female Boxfish (named Pickles), who I’ve had for almost a year. I am in the process of adding a baby Yellow Boxfish to the mix shortly.

CARE:
There is a lot of misconceptions out there about these very popular fish. I see them a lot for sale and people read different things and a lot of the things you can find online, just aren’t true.

These fish are in fact, very good swimmers. As they get older, they learn the flow patterns of your tank and will love to play in the stronger currents. Flow wise, no different that any other fish requirements – don’t pin them to the glass and you’ll be fine.

Tank size, varies. Ideally, like any marine fish, you wants as big as you can get. Marine fish grow. That being said, Cowfish do tend to grow faster than boxfish. A cowfish may be fine to start in a under 100g tank, but within a few years; that tank will not be enough room for it. My cowfish – in 2 years, has probably grown 10x his starting size, at least! Boxfish on the other hand, appear to grow slower. Mine is not much bigger than she started, a year ago. I know others who’s Boxfish are barely doubled their size in years.

Live rock is important (for obvious reasons) – live sand, as Cowfish love to blow away sand and look for critters, is a plus. Early on, you want to keep an eye on your cowfish. I have heard of cases where the cowfish gets its horns stuck in the rockwork. As the fish learns the tank, I find this becomes less of an issue.

It's been my experience that Boxfish care in general stays the same, regardless of color/type. So, don't stress anything of you get a baby Black Boxfish or a adult Yellow Boxfish.

DIET:
What don’t they eat? Cowfish & Boxfish, once they are settled are absolute gluttons for food. Both of mine eat anything that hits the water – including Nori. Nori I think is one thing a lot of people over look for these types of fish, but it’s great for their digestion.

That being said, my very first Yellow Boxfish, didn’t eat for months. It lived on pods, scouring the rocks 24/7 – till one day it finally tried some mysis and it was all over. After that, no issues getting it to eat everything and anything that was fed.

To date – I have never seen either my Cow or Boxfish both any corals or inverts. I have seen 1 or 2 case where my cowfish would taste or try a freshly bailed hammer coral skeleton, but that’s it. My tank is quite stocked with LPS & SPS. As always though, we never know what fish are going to do in a reef tank – so, take this with a grain of salt.

Again, I do feed quite heavy myself and my fish are well fed, probably a big reason they aren’t interested in corals. No need.

TANK MATES:
So you bought a Boxfish, what can you keep with it? For the most part your options are wide open. Tangs, Wrasse, Anthias, Butterfly and so on. Any ‘reef fish’ should be fine.

One of the most important fish to NOT stock – is a CLEANER WRASSE. Cleaner Wrasse survive, for the most part, on picking and cleaning other fish. This if fine for most fish – but Cow/Box fish don’t necessarily like to be cleaned often. The bigger issue is the cleaner wrasse is going to be faster – so, what happens is it tend to harass and chase; just trying to clean, these fish and leads to unnecessary stress.

Clean up crew, falls in line with tank mates. Keep reef safe stuff and you shouldn’t have an issue. I have a wide array of snails, crabs, cucumber and starfish and neither of my fish have even given them a second look.

TANK “NUKES”:
Ok, lets talk about “Pahutoxin”.
Pahutoxin is released by Cow/Box fish when they come under tremendous stress. It is a defense mechanism – nothing more. Contrary to popular belief, a DEAD fish, will not release it’s toxin. I have lost boxfish in the tank and never had a nuke.

From what I have read and researched – the toxin is located in the red blood cells and works by the blood cells being ruptured. Eye witness accounts say it’s like a white cloud that comes off the fish – and you MUST act quickly! The toxin does damage by attacking the red blood cells of predator (or whatever the fish is trying to escape). That all being said, in a closed aquarium – these fish are not immune to the toxin and indeed die themselves. At the end of the day, the fish must be alive. A dead boxfish, cannot excrete it’s toxin.

The best way to know if this has happened is there will be a soap-like mucus foam on the top of your aquarium water and your skimmer will be going haywire.
In all my years (which isn’t many, let’s be honest) – I’ve never heard of a legitimate in tank nuking. They are extremely rare. In most cases, the fish is more likely to nuke itself in the bag shipped to you – then it is in a properly stocked aquarium.

This bring us back to the Cleaner Wrasse. These fish shouldn’t be housed in a stressful situation, so imagine being relentlessly harassed by a wrasse, trying to clean you? Doesn’t sounds like fun does it.

It’s all about mitigating the risks. The risk is always going to be there, but in reefing, there’s more likely bigger things to worry about.

FINAL THOUGHTS
Cow/Boxfish are amazing fish. I’ve yet to find a fish with a better personality. They learn to beg for food (I’ll let you find out that one on your own) – will follow you around the tank and in general, are unique additions to a reef tank.

My experience has been quite positive. I’ve found them to be hardy fish and acclimate to reef life quite easily. They are rarely bothered or both other fish. They are active, playful and tend to be a conversation piece for people that see them in your tank.

If you find yourself curious and have the right tank size and time for these fish, you will be rewarded with an amazing animal. I hope I touched on the major points. As with any fish - you'll find maybe some of my points vary from individual experiences, it happens. This post is more of a generalized guide - a starting point.

Attached is a picture of Taco and Pickles (you’ll see Pickles below Taco…lol). Don’t think Id own a reef tank, without keeping one of these super fun fish!

20230222_173320.jpg
 

Kayvon

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Thanks for the awesome write up. I’ve never considered one of these. Maybe a box fish is in my future
 

ISpeakForTheSeas

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I also haven't heard of any confirmed "nukes" by these fish; as you said, the risk is there, but given a decent environment, the risk seems to be quite low. Also, glad to see someone pointing out that the fish needs to be alive to produce the toxin!

Just to add a bit more info on the toxin and some food for thought on the risk:
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:
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
 

Debramb

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So, let talk about the adorable yet largely misunderstood Cowfish & Boxfish.

Before I begin, let me say that I’m NOT an expert, I’m not a marine biologist and everything I’m sharing is based on very real personal experience. I’m going to group these two fish (Cow & Boxfish) together, as I find their care is very similar. I am aware that there are many types of Boxfish (I’ll touch on that shortly) – but for the sake of this “guide”, we’ll call it, we are going to speak in general terms.

Currently, I have a Longhorn Cowfish (named Taco) – who’s been with me for just over 2 years. With Taco, is a Striped Female Boxfish (named Pickles), who I’ve had for almost a year. I am in the process of adding a baby Yellow Boxfish to the mix shortly.

CARE:
There is a lot of misconceptions out there about these very popular fish. I see them a lot for sale and people read different things and a lot of the things you can find online, just aren’t true.

These fish are in fact, very good swimmers. As they get older, they learn the flow patterns of your tank and will love to play in the stronger currents. Flow wise, no different that any other fish requirements – don’t pin them to the glass and you’ll be fine.

Tank size, varies. Ideally, like any marine fish, you wants as big as you can get. Marine fish grow. That being said, Cowfish do tend to grow faster than boxfish. A cowfish may be fine to start in a under 100g tank, but within a few years; that tank will not be enough room for it. My cowfish – in 2 years, has probably grown 10x his starting size, at least! Boxfish on the other hand, appear to grow slower. Mine is not much bigger than she started, a year ago. I know others who’s Boxfish are barely doubled their size in years.

Live rock is important (for obvious reasons) – live sand, as Cowfish love to blow away sand and look for critters, is a plus. Early on, you want to keep an eye on your cowfish. I have heard of cases where the cowfish gets its horns stuck in the rockwork. As the fish learns the tank, I find this becomes less of an issue.

It's been my experience that Boxfish care in general stays the same, regardless of color/type. So, don't stress anything of you get a baby Black Boxfish or a adult Yellow Boxfish.

DIET:
What don’t they eat? Cowfish & Boxfish, once they are settled are absolute gluttons for food. Both of mine eat anything that hits the water – including Nori. Nori I think is one thing a lot of people over look for these types of fish, but it’s great for their digestion.

That being said, my very first Yellow Boxfish, didn’t eat for months. It lived on pods, scouring the rocks 24/7 – till one day it finally tried some mysis and it was all over. After that, no issues getting it to eat everything and anything that was fed.

To date – I have never seen either my Cow or Boxfish both any corals or inverts. I have seen 1 or 2 case where my cowfish would taste or try a freshly bailed hammer coral skeleton, but that’s it. My tank is quite stocked with LPS & SPS. As always though, we never know what fish are going to do in a reef tank – so, take this with a grain of salt.

Again, I do feed quite heavy myself and my fish are well fed, probably a big reason they aren’t interested in corals. No need.

TANK MATES:
So you bought a Boxfish, what can you keep with it? For the most part your options are wide open. Tangs, Wrasse, Anthias, Butterfly and so on. Any ‘reef fish’ should be fine.

One of the most important fish to NOT stock – is a CLEANER WRASSE. Cleaner Wrasse survive, for the most part, on picking and cleaning other fish. This if fine for most fish – but Cow/Box fish don’t necessarily like to be cleaned often. The bigger issue is the cleaner wrasse is going to be faster – so, what happens is it tend to harass and chase; just trying to clean, these fish and leads to unnecessary stress.

Clean up crew, falls in line with tank mates. Keep reef safe stuff and you shouldn’t have an issue. I have a wide array of snails, crabs, cucumber and starfish and neither of my fish have even given them a second look.

TANK “NUKES”:
Ok, lets talk about “Pahutoxin”.
Pahutoxin is released by Cow/Box fish when they come under tremendous stress. It is a defense mechanism – nothing more. Contrary to popular belief, a DEAD fish, will not release it’s toxin. I have lost boxfish in the tank and never had a nuke.

From what I have read and researched – the toxin is located in the red blood cells and works by the blood cells being ruptured. Eye witness accounts say it’s like a white cloud that comes off the fish – and you MUST act quickly! The toxin does damage by attacking the red blood cells of predator (or whatever the fish is trying to escape). That all being said, in a closed aquarium – these fish are not immune to the toxin and indeed die themselves. At the end of the day, the fish must be alive. A dead boxfish, cannot excrete it’s toxin.

The best way to know if this has happened is there will be a soap-like mucus foam on the top of your aquarium water and your skimmer will be going haywire.
In all my years (which isn’t many, let’s be honest) – I’ve never heard of a legitimate in tank nuking. They are extremely rare. In most cases, the fish is more likely to nuke itself in the bag shipped to you – then it is in a properly stocked aquarium.

This bring us back to the Cleaner Wrasse. These fish shouldn’t be housed in a stressful situation, so imagine being relentlessly harassed by a wrasse, trying to clean you? Doesn’t sounds like fun does it.

It’s all about mitigating the risks. The risk is always going to be there, but in reefing, there’s more likely bigger things to worry about.

FINAL THOUGHTS
Cow/Boxfish are amazing fish. I’ve yet to find a fish with a better personality. They learn to beg for food (I’ll let you find out that one on your own) – will follow you around the tank and in general, are unique additions to a reef tank.

My experience has been quite positive. I’ve found them to be hardy fish and acclimate to reef life quite easily. They are rarely bothered or both other fish. They are active, playful and tend to be a conversation piece for people that see them in your tank.

If you find yourself curious and have the right tank size and time for these fish, you will be rewarded with an amazing animal. I hope I touched on the major points. As with any fish - you'll find maybe some of my points vary from individual experiences, it happens. This post is more of a generalized guide - a starting point.

Attached is a picture of Taco and Pickles (you’ll see Pickles below Taco…lol). Don’t think Id own a reef tank, without keeping one of these super fun fish!

20230222_173320.jpg
Great Post! Love your pics, Anyone else love Magnum PI just for the photobombing Puffer fish behind Ricks bar? This season, NBC still kept the tank but I think it’s a smaller Puffer, last one was growing big, loved watching!
 

danieyella

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Great writeup, I got a cowfish and absolutely LOVED him, but unfortunately I don't think he was getting enough to eat. I've since upped my pod population and am starting a culture of them next week. I found your writeup because I was debating between another cow or a box. Maybe I'll go with both eventually.
 

ReeferHD

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Great post, I've been keeping boxfish since i impulse bought one as a reefing noob. unfortunately that first one i had jump out cause i didn't have a lid :( Your experience with them is very similar to mine, I've had amazing results with them and they have become my favorite fish, almost everything I've read about them has been false and it gives them a really bad reputation. thank you for sharing this info!

These are my cowfish.
Longhorn & Scrawled
(Lactoria Cornuta & Acanthostracion quadricornis)
84576D68-2AC1-49BB-A0F9-DA114EDC770C.jpeg

Humpback (tetrosomus gibbosus)
213AEBC7-A79A-4BB3-A58F-1EFCCA61CA52.jpeg
 
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laughing tang

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Very interesting thread, I love box/cowfish and it's been my dream to one day keep them. I see you all have several types together, that is OK? And also, if at full size (I know, if you ever get that far), what size aquarium would you be looking at?
 

kamkam1999

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i have never successfully keep cowfish longer than 3 months. every time they will eat pellets really quick but after 1-3months they will suddenly stop eating and dead after few days.

i am wondering, is No3 Po4 kill them?(No3~50 ppm)
 

Daniel@R2R

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