Selecting Healthy & Appropriate Marine Fishes

This entire article is nothing more than my own personal opinion. But that opinion has developed during my 13 years of marine aquarium keeping as well as my 10 years of working full-time in the ornamental fish industry. I offer it not so much as a definitive statement, but as a guide to what I go through and what I look for when purchasing fishes, and as an aid to my fellow aquarists.

-Steven Pro

Research, Research, Research!


While I have attempted to thoroughly discuss the most common diseases of marine fishes in an effort to help fellow hobbyists save their aquatic pets once they have already been purchased (see the list of additional reading material at the end of this article), many problems with general fish health and anomalous losses can be averted by careful and critical selection of fishes at the time of their purchase. The first thing to do is to decide which fish are desired. I always advise clients to plan, with my advice and counsel of course, every fish they are going to add before adding the first fish. This prevents compatibility issues later and saves the trouble of removing one fish from a fully stocked display when it is later decided that another fish is more desirable. Many fish don't get along well with others of the same species or even with those of the same genus. Knowing this and planning accordingly saves trouble later.

Second, once a wish list of desired species is developed, further research is necessary. Will these fish get along? Even if the aquarist is aware that he may have only one surgeonfish, he may not realize that the planned yellow tang (Zebrasoma flavescens) won't get along well with a foxface (Siganus vulpinus), a raccoon butterflyfish (Chaetodon lunula) or most other fish with a grossly similar overall appearance.

Consider compatibility among intended tankmates prior to their purchase. The above two fish, for example, are best not combined. Photos courtesy of Greg Rothschild (left) and Tuan Pham (right).

Size - It is Even More Important than You Think:

After determining the compatibility of the planned tankmates, the full adult size of the desired fish should be determined. Purchase only fish that can be kept in the display currently owned. In many instances, an aquarist claims that he intends to purchase a bigger tank sometime in the near future and will be housing this larger animal in the relatively small display for only the next six months to two years. Unfortunately, though, life happens. People get laid-off. They get divorced and lose their house. Any number of reasons might derail their planned upgrade. And, because of this, the fish suffer from inadequate space and, in some cases, poor water quality as a result.

Know Some History:

  Three dead blue tangs and a fourth one struggling for life. This certainly does not instill a lot of confidence in purchasing fish out of this aquarium in particular or from this shop in general.

The next factor to examine is whether the selected fish has historically done well in captivity. Most hobbyists should realize that some fishes (and many other ornamental marine organisms) offered for sale do not fare well in captivity. Many have highly specialized diets that are currently impossible to replicate. Others hail from cool, temperate waters and do not survive long-term in a warm, tropical display. Careful research before their purchase helps to avoid these simple mistakes.

As more of an editorial comment, if we can't or won't police ourselves, eventually the government or some other entity will do it for us. The only reason we routinely see obligate coral polyp-eating butterflyfish, remoras, baby nurse sharks and other "dead fish - swimming" offered for sale to uninformed, new aquarists is to make a quick buck from an impulse purchase. This kind of shortsighted profit taking does not do the hobby or the industry at large any good. While it may appear that an endless stream of new "suckers" enters this hobby every day, imagine the money generated if most of these people were offered sound advice, good equipment and healthy livestock, thereby making for successful, long-term hobbyists. It is a shame that so many stores seem to operate instead on the P. T. Barnum "a sucker is born every minute" concept. And frankly, it is not a sound business model. Planning not to maintain clients, but instead to turn over nearly 100% of customers every year, is a difficult proposition to pull off. But, I digress.

Know Your Limitations:

Photo courtesy of Lisa Page.

I mentioned fishes whose diet cannot currently be replicated, but there are others that can be fed but which might be more challenging or consume more time than the aquarist wishes to invest. Careful research beforehand, as well as thorough and realistic introspection as to the level of skill in aquarium keeping and the amount of free time willing to be invested, can preempt these problems as well. For example, mandarinfish (photo left) are certainly not impossible to keep in captivity, but they are not for everyone. They require larger displays with noncompetitive tankmates and, preferably, a refugium to provide them with sufficient live food. Again, careful research before their purchase will help prevent needless livestock losses and make for a more conscientious hobbyist.


During this research period, pay particular attention to the diseases to which your potential tankmates may be prone. Certain fishes are typically plagued by certain pathogens. Surgeonfishes and puffers, for example, are routinely afflicted with Marine Ich/Cryptocaryon irritans. Puffers are also known to have problems with internal worm infestations (Jedlicki, pers. comm.). In my experience, Acanthurus species tangs frequently are stricken with both Marine Ich/Cryptocaryon irritans and Marine Velvet/Amyloodinium ocellatum. And, wild caught clownfish are often afflicted with Brooklynella hostilis. Knowing this prior to bringing the animal home helps during its initial examination at the local fish store as well as ensuring the aquarist is prepared by having the proper medications on hand for treatment in the event the fish becomes ill.

At first glance this Kole tang appears to be doing well. A closer inspection of this fish, however, reveals a Cryptocaryon infestation. Photo courtesy of Bill Chamberlain.

Additionally, it's important to research whether the fish poses any danger to the aquarist. While most aquarists are familiar with lionfish and stonefish envenomation, and some know about the dangerous spines of foxfaces/rabbitfishes and marine catfishes, there are other surprises as well. For example, I was recently surprised to discover that scats are venomous, and it's quite painful to be jabbed by their dorsal fin.

Click here for larger image Click here for larger image
Aquarists should pay attention to important details when examining potential livestock. Left: Some species, such as this Paracanthurus hepatus, are prone to HLLE (head and lateral line erosion). Right: This Chelmon rostratus suffers from a lesion on its tail fin. Photos courtesy of Mark Kingery.

Captive-bred, Tank-raised or Wild-caught:

One last thing to inquire about is whether or not the chosen animal is available captive-reared. Whenever possible, I encourage fellow hobbyists to buy a tank-raised specimen; they are generally far hardier and less disease-ridden than their wild-caught counterparts. Consequently, this translates into less work for the aquarist and makes for a better value for the money spent. And, it is arguably a more environmentally-friendly choice.

Evaluating the Specimen

Local Fish Store Versus Online or Catalog:

Once all of the research is complete, it is time to search for and evaluate the desired species. This is probably going to be one of the most controversial statements I make in this article, but I feel compelled to say it. I don't understand buying fish mail-order or online as a hobbyist. Frankly, I would not buy a pair of pants for myself without first looking at them in a store and trying them on, let alone purchase a live animal without evaluating it firsthand. How would you know if they are going to make your butt look big or not? Oh, wait a minute! I am supposed to be talking about fish.

That is not to say, though, that I am against online sales in all instances. There are certain things I would urge hobbyists to purchase online or mail-order: live rock, for instance. It does not make sense to pay a premium for something like that. Significant discounts, even with shipping prices factored in, can be had by buying online. Plus, the aquarist can obtain a fresher product with a higher likelihood of creature diversity. Other items, such as protein skimmers and lighting, are best purchased via the internet because of the potential savings, and also because of the range of choices available. How can anyone expect a small "Mom and Pop" local fish store to stock 175, 250 and 400-watt single-ended metal halide fixtures along with 150 and 250-watt double-ended options in 6,500 K, 10,000 K, 14,000 K and 20,000 K lamps for all those wattages and various manufacturers such as Ushio, Aqualine-Buschke, Iwasaki, XM, Hamilton, etc., not to mention the myriad of reflector and ballast options to be had? No store could possibly afford the expense of stocking all those variations. But, that is exactly what large warehouse vendors that sell through mail-order catalogs or via the internet do so well.

While I prefer to purchase fish locally after first being evaluated, I do not recommend purchasing fish from a store that practices poor husbandry or routinely stocks animals for impulse purchases that are historically known to fare poorly in captivity. I don't give my business to stores that prey upon the ignorant and uninformed, and I encourage others to do likewise. Vote with your dollars and reward the good local fish stores that are conscientious and run a clean shop.

Additionally, there are some areas of the country, unfortunately, that because of their small population or remote location cannot support a local fish store. As such, individuals living in these areas are relegated to purchasing online or mail-order exclusively. But, that is one of the beauties of the internet. It can fill those voids in retail markets and can also help consumers make good purchasing decisions. In these instances, buying decisions should not revolve exclusively around availability and price. Scour the internet looking for feedback on the vendor that is being considered. There is no shortage of people willing to volunteer their opinion online. Try to sift through those opinions to find legitimate praise or positive comment with regard to the quality of the animals received, packaging, shipping and customer service in general.

Collection Locale:

When evaluating a specimen, the first thing I want to determine is from where the animal hails. Collection locale is extremely important when selecting healthy livestock. Some places put more effort and money into collecting, holding and shipping livestock, and while that extra care comes at a premium in terms of its actual purchase price, it pays off in the livestocks' health and vigor. Some places that I am particularly fond of purchasing fish from include Hawaii, Fiji, the Red Sea and Australia. Also, don't simply take the word of the local fish store employee that the particular fish being looked at actually comes from where he says. Sometimes stores and their employees are simply misinformed regarding the correct collection locale, and in some instances I get the feeling that someone is trying to pull a fast one. Ask yourself, do the price, coloration and known geographic distribution coincide with the claimed collection locale? This takes a bit of research on the part of the hobbyist prior to walking into the store, but it is well worth it.

Knowing the fish's collection locale can also help an aquarist avoid fish that have been captured using cyanide. Unfortunately, cyanide is still a problem for marine ornamentals and the live food fish industry. But it is currently limited to a few places such as the Philippines, parts of Indonesia and I have recently heard of it spreading to Vietnam. On the other hand, I have never heard of any confirmed reports of fish coming from the Caribbean, Hawaii, Fiji, the Red Sea, Australia or the Sea of Cortez that are captured with cyanide, although I have heard of other drugs being used such as MS-222, clove oil, bleach and Quinaldine. But, I have not done enough research at this time to discuss how widespread they are or their potential negative impacts.

Another thing to look for in fishes potentially caught with cyanide is a dazed and confused appearance. The fish don't interact with others in the tank, nor do they react to your presence. A healthy fish should dart and hide when first approached, but should be curious enough to come back out to see what you are up to. Cyanide exposed fish typically remain motionless, staring off into space. They also tend to appear overly bright colored. I can best describe it as an aura, looking as if the holding tank is illuminated with a lot of actinic lighting when nothing more than standard full-spectrum lighting is actually in use.

General Appearance & Behavior:

As part of observing its general appearance, also examine the fish for spots, a dusty appearance, rapid breathing (anything greater than one respiration per second), red streaks, missing or damaged fins, cloudy or bulging eyes or anything else that is out of the ordinary. I won't buy damaged or obviously sick fish, and I would not recommend that others do it either. That is not to say, however, that a quick, cursory observation will allow aquarists to avoid all sick fish. Several diseases are difficult-to-impossible to detect from a brief observation because of the pathogen's life cycle or appearance. That is why quarantine is so critical. But, a careful observation helps minimize the outbreaks and damage done prior to the chosen treatment. This, in turn, helps to lessen subsequent losses.

Also, I pay particular attention to the mouth of long-snouted fishes like butterflyfish and certain surgeonfish. In some instances, these long-nosed fishes are damaged in transit when bounced around in shipping bags. This is evidenced by red streaks radiating out from the mouth or white "cottony" looking growths on their lips. If any of these signs is evident, I pass on that animal. To me, this is a double whammy. The infection must first be dealt with while the fish typically goes without eating. So, once the treatment is successful and the infection has cleared up, the aquarist is still left with a lean fish that needs additional "TLC" to regain its normal weight.

A challenging fish that has also been damaged in transit and lost most of its dorsal fin. This does not bode well for long-term success with keeping this specimen.

Next, I like to see if the animal is eating. I won't necessarily reject it if it won't eat the offered food, but it does factor into my decision if it will, or won't, feed. Secondly, what did it eat? Most any fish will consume live brine shrimp if offered, but they might not survive and grow to a full adult size on a diet of nothing but live Artemia. Fish that are feeding on pellet or flake food are a much better risk, in my opinion. Additionally, bear in mind that some fish probably won't make the transition to prepared foods in the short time they spend at the local fish store. Fish such as mandarins, or gulping predators such as lionfish and groupers, are typically going to require additional work to get them feeding on frozen or dry foods. But, that is simply par for the course with some fishes and something that was, hopefully, learned during the research prior their purchase.

The Goldilocks Analogy:

The last aspect of physical appearance to evaluate is size. While I have already mentioned researching the full adult size of the fish in question, its size at the time of purchase is also very important. Basically, I want a fish that is neither too big nor too small. I want one that's just the right size. I avoid all tiny, baby fishes - the ones typically seen that are under one-inch long. Of course this, like most any rule of thumb in this hobby, is simply a rough estimate. It obviously does not apply to small fishes like gobies, for example, that might not even grow to one-inch as adults, but hopefully you get the basic point, namely, avoid those that are exceptionally small. While these tiny offerings are awfully cute and tempting, there is a tremendously high mortality rate with these baby fishes. I have heard it theorized that baby fish are probably like human babies in that they need constant small feedings, which they don't get while navigating the chain of custody from the reefs to the final vendor. As such, they are probably half-starved to death by the time they are offered for sale. I definitely see the logic in that train of thought. While I don't know for sure if that is why they seem to perish more frequently, they still have a high rate of mortality, for whatever reason.

I also avoid very large specimens. These are the so-called "show" fishes offered for sale. For one, they are not a good value. Shipping large fishes is expensive because they need a box all to themselves and require a lot of water, i.e. weight, to go with it. Remember that much of the dealer's final costs associated with a fish, and therefore its purchase price, are the freight costs. Large bags of water drive up the price of shipping a fish from point A to B.

Also, it often takes a lot of work to get these large fishes to take prepared foods, assuming they ever do. Again, I have heard people theorize that these large fishes are too old and "set in their ways" to learn to eat prepared foods. To me, that sounds a little too anthropomorphic. But, I have seen a number of larger fishes refuse to eat for what seemed like a longer period of time than their smaller counterparts. It could simply be that these larger fishes, having searched day after day for food while looking downwards at the substrate for grazing material, have a hard time learning to look upwards for food dropping from the heavens.

Play the Waiting Game:

Once a specimen has been selected, one might wonder what is left to do besides taking it home. But remember that you are paying a premium from the local fish store because of its potential losses, along with other associated costs. Let that work to your advantage. Place a deposit on the fish you want, and let it sit for three to seven days before actually purchasing it. Morgan Lidster has spoken and written about something he calls "Post Traumatic Shipping Disorder." Additionally, Edward Noga has written about something he calls "Delayed Mortality Syndrome" (Noga, 2000). Both of these phrases characterize similar phenomenon. Basically, these terms mean a fish may die from any number of reasons related to shipping trauma; things such as temperature changes, lack of oxygen, depressed pH, salinity shock, etc. None of these stresses are readily apparent upon physical examination, though. So, by allowing the fish to acclimate for up to one week in the dealer's tank, I can be reasonably sure that the fish won't keel over at a later date from unexplained reasons when I bring it home.

Whenever I see a dead fish in a retail outlet, I automatically suspect the store. Some fish are going to die no matter what; losses are a part of working retail. But, leaving them in the tank for customers to see makes you wonder if other aspects of their husbandry get neglected as well. Not to mention it leaving me wondering why they died in the first place and why the store didn't catch the early symptoms and treat accordingly.

Again, like most rules regarding aquarium keeping, there are exceptions to this rule. In the case of fishes such as dragonettes, seahorses, pipefish and other frequent feeders, I take them home as soon as possible. Simply put, I trust the care I can provide for these challenging fishes more than that provided by any local fish store.


Hopefully, most will find this guide to be useful. I have tried to lay out in a systematic way the processes that I go through when purchasing a fish, even though I don't have a true checklist, either literal or mental. I do many things when evaluating a fish that are almost subconscious, honed from years of experience. In time, you too will learn and perform this sort of analysis without even thinking about it. In the meantime, use my advice as a guide to enjoying this hobby even more.

All photos copyright Steven Pro, except where otherwise noted.

If you have any questions about this article, please visit my author forum on Reef Central.


Noga, Edward. 2000. Fish Disease: Diagnosis and Treatment. Iowa State University Press, Ames, Iowa, pages 238-239.

Lidster, Morgan. Pers. comm.

Recommended Reading:'s Fish Category -

Fenner, Robert. 2001. The Conscientious Marine Aquarist. T.F.H. Publications, Neptune City, New Jersey.

Michael, Scott. 2001. Marine Fishes. T.F.H. Publications, Neptune City, New Jersey.

Pro, Steven. "Cyanide and Its Unfortunate Use in the Marine Ornamental Industry." Reefkeeping Online Magazine, Jan. 2006.

Pro, Steven. "An Ounce of Prevention is Worth a Pound of Cure: A Quarantine Tank for Everything." Reefkeeping Online Magazine, Oct. 2004.

Pro, Steven. "Marine Velvet/Amyloodinium ocellatum: A Discussion of this Disease and its Available Treatment Options." Reefkeeping Online Magazine, July 2004.

Pro, Steven. "Marine Ich/Cryptocaryon irritans: A Discussion of this Parasite and the Treatment Options Available, Part 2." Reefkeeping Online Magazine, Oct. 2003.

Pro, Steven. "Marine Ich/Cryptocaryon irritans: A Discussion of this Parasite and the Treatment Options Available, Part 1." Reefkeeping Online Magazine, Aug. 2003.

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Selecting Healthy & Appropriate Marine Fishes by Steven Pro -