About Jay

  • Jay Hemdal

    Jay F. Hemdal is curator of fishes at a large U.S. zoo / aquarium and is actively involved in the AZA (Association of Zoos and Aquariums). He is the author of numerous magazine articles and books for aquarists. Read more...

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January 17, 2009


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Melinda Joakimson

I'd just like to thank you for this article. Too often, the fishkeeper runs into all sorts of 'police'. While I am the first to inform those who intend to keep their Red-Tailed Cats in a 55 that it just isn't possible (and maybe I have become that which we fear!!), I highly dislike when individuals inform me that a 125 is 'too small' for 9 silver dollars, who are all doing fine, and reproducing, etc. The responsible aquarist changes setups when he or she sees need, and there are always 'leftover' tanks from previous tenants who have moved up. There is no reason that tank cannot be used to allow a specimen to grow, and then that specimen can move up, just as the others have. The issue here is responsibility. Can you keep a Hippo Tang in a 75? Sure, but just keep an eye on the specimen -- if it shows signs of distress, start looking to put together a larger environment. Too many 'police' assume aquarists are being irresponsible, when, in fact, there is no reason to start with a gigantic aquarium if the aquarist is willing to do whatever the particular fish needs in the future. Water quality and fish behavior will always dictate need for a new setup. Again, thanks.

scott yager

previously posted on reef central:

Jay-----I have just become a fan of your work and ideas---and I'll will be reading more---thank you


The example in your article of the Pacific blue---you did mention that when it got to big for your tank you would not have a problem finding a home for it.
That brings back the question of "when" and actually how you decide it is too big for your tank.
I am sure I will be facing that delima in that I have a pacific blue and a sailfin---for almost three years now--and they are at the 5 inch point. Upgrading my tank to a 220gal is now longer an option due to our economic sitution.
There are four tangs in my tank--yellow, powder blue , pacific and sailfin---they are very healthy and get along well with each other.

Jay Hemdal

Hi Scott,

Thanks for your kind words of support. I fully understand that some of the ideas I present in my writings are not "mainstream", and some have evidently bordered on "unpopular" with some of the "Tang Police". I also realize that not every idea I present will eventually stand up to closer scrutiny - but I do hope that people think about what I write, try to keep a more open mind about such things, and then perhaps actively question certain "truths" that have become entrenched in the aquarium hobby.

In regards to your question about how to tell if a certain fish has exceeded a comfortable aquarium size - sorry, but I can't answer that(yet!). I often struggle with that same question myself. It is rare to have a fish outright DIE from being kept in too small of an aquarium. I have seen a few examples - a snakehead that hit the end of its aquarium, broke the glass and died when the tank drained - it was obviously kept in too small of a tank. Pangasius catfish that rub their snouts on the tank wall each time they turn around would be another example. Harder to determine is the fish, like yours, that have grown gradually larger in an aquarium - when do they need to be moved out? My lame answer is: move them before they suffer any adverse health effects....



Hey Jay,

I also work at a large public aquaria and when frequenting some of the popular message boards I see minimum recommendations for surgeon-fishes being a 6 ft tank. Everyone says that this is what the so called "experts" say. Now I do agree with them when they say that the larger tang species need bigger quarters to do well, but I think the 6 ft minimum may be a little extreme for the smaller species of surgeons (koles, scopas, yellows). Just curious about your thoughts on this.

Jay Hemdal


No - I don't agree that all surgeonfish require a six foot tank - especically the smaller Ctenochaetus.

I worked out a preliminary formula for anticipating swimming space needs in an article I did last year for Practical Fishkeeping. I can't recount it all here, but basically, you add the longest open water dimensions of the tank (length and width) and then calculate the maximum adult size of the fish (as per my other blog entry). Dividing that number into the dimensions gives a ratio. Tangs, being open water swimmers, require a minimum ratio of around 1:6 - with 1:8 being better. (The whale sharks at Georgia would be around 1:6 when full grown). A six inch tang in a relatively open six foot tank (with open water length + width of perhaps five foot by 16 inches would give a ratio of 1:12, much more than is really needed to keep the fish HEALTHY. The problem is that the "tang police" say that in a smaller tank, the fish wouldn't be HAPPY. Hard to measure that though....




Your formula looks interesting. I agree with you that hippos are not the most active swimmers out there. In our 400,000 gallon display they seem to be lazily swimming in one area of the exhibit, with a few "sleeping" on the coral rubble. Even the yellow tangs which share the exhibit seem to be only concentrated in one area of the tank. It is the larger tangs (Unicorns, nasos, and vlamingis) which utilize the entire exhibit. Im curious as to how they came up with this six foot rule of thumb. Again the larger species of surgeons probably require larger aquariums which are not feasible for the average hobbyist. Again im not advocating keeping surgeons in nano aquariums, and the bigger the tank the better, but the smaller species (koles, smaller zebrasomas) can be kept perfectly healthy in smaller/average sized aquariums (say 75 gallons).

Jay Hemdal

So - if you have read this far, the topic must be of particular interest to you. Here is the outcome of my being arrested by the "Tang Police" one more time, two years after my first run-in with them. This time they brought in moderators to delete my posts and defend the "police action". Ultimately, it resulted in my having so many "infractions" that I was just one away from being banned for life, so I left that particular message board for good - and its convoluted and angry culture.
Stay tuned for MORE developments!


Jay! I Just wanted to say THANKS for your participation on that particular message board and trying to bring some semblance of rational thought into the conversation on tank sizes. I'm sorry to see you go. I tend to prefer smaller fish, so I don't really have a dog in that fight except I hate seeing "requirements" placed on people that are based on little more than opinion.

Jay Hemdal


Thanks for the words of support. After I got sort of "edged out" of Reef Central by a couple of the admins, I started spending more time as a moderator on the fish section of reefs.org (but that board isn't very active).
If you haven't seen it yet, here is an interesting link:


I have no idea where that came from though......

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