Selecting and stocking fish for a saltwater aquarium is one of the most common problems people create for themselves in this hobby. There are many traps that we let ourselves fall into that are very easy to avoid. Hopefully, this will help you avoid all of them.
Selecting saltwater fish is a VERY in-depth topic that no article or video can cover 100%. There are lots of variables including you and your experience, tank size, tank style (reef, you think it’s fish-only but it’s really going to become reef in two months, actually fish-only, predatory, etc.), feeding abilities (types and schedule), coral selection, your risk tolerance, your budget, your beliefs on wild-caught versus captive-bred, and all sorts of other factors.
This article is not going to answer everything. This article should help you avoid the biggest, most common mistakes and get you started on a good foundation to help you avoid mistakes in the future. This is to help you not become one of the vast majority of customers that come in that created problems for themselves just by the fish they added to their tank. Saltwater and reefs can be challenging enough, don’t let something you actually have so much control over set you up for challenges or even failure.
You need to research fish before you buy them. You need to limit yourself to fish that actually have a reasonable chance of thriving in your tank no matter how tempting other fish may be. You need to know that no matter what question you ask, you will find the answer you want, but that doesn’t mean it’s the right answer. If you ask if two fish can go together or if a certain fish can go with corals, you really need to pay attention to the people saying no and figure out why. The people saying yes may have just lucked out and not had problems in their case, that doesn’t mean their experience is typical or even close to likely for you.
For specific questions beyond the scope of this article, ask on a forum about your tank. Let multiple people with more experience weigh in and pay attention most to the answer you don’t want to hear, otherwise there’s no point in even asking.
Captive-Bred vs. Wild-Caught
Unfortunately, the vast majority of saltwater fish are still wild-caught. Except for clownfish, even the species that can be bred in captivity aren’t bred in enough volume to supply the demand, so even with those species, the vast majority are wild-caught.
Wild-Caught fish are much more likely to not start eating well, to have internal parasites or other pathogens, and be stressed by being in captivity in general. You need to know this before you take animals that were thriving in the wild, subject them to the stresses of capture and being moved from wholesaler to retailer (half of them die before they even get into someone’s tank), and then put in your tank where they may or may not even have a good chance of thriving.
Ask your local fish shop about captive-bred fish. This will let you know what the shop carries that’s captive-bred, and lets them know there is interest out there if they bring in more captive-bred versions (which usually cost a lot more).
Buy captive-bred as much as possible.
Suppliers That Aquarium Stores Buy From
This is an often overlooked aspect of buying fish, but it will make a huge difference for you in the end. Where your store buys their fish from can have a massive impact on how well those fish settle into captivity. Note, I am not talking about the store itself (although that can also make a huge difference), I’m talking about which suppliers the stores are buying from. Almost all saltwater fish are wild-caught. This means that as little as a week ago, they were in the wild. Be aware that about half of saltwater fish are STILL captured with cyanide.
A little background here will help you understand the differences between suppliers. Some care more about quality than price. They will pay higher prices to the local people who actually dive and hand-net fish. The better suppliers will also hold fish for a period of time to make sure they are settling in well, others just rush to get them into their customers’ hands (your local shop) as fast as possible so that any deaths don’t occur while the fish are still in their possession. So whereas one supplier rushes the fish from questionable capturing methods to the U.S. where they are re-bagged and immediately shipped out to the retailer, other suppliers pay more for better capture methods and then hold the fish in the U.S. for at least a week to make sure the fish has the best chance of actually making it for both the retailer and the final customer (you).
Generally, nicer stores that are better managed will appreciate the difference in quality and are more likely to buy from better suppliers. However, some stores that could use an update and some cleaning can still appreciate the difference in quality, so it’s always good to ask. However, some stores are worried most about price, so they buy from the cheaper suppliers who don’t pay extra for better quality.
From your point of view, the only difference you may see may be the price. When a fish runs 50% more than the same fish at the same size at the shop across town, you can almost guarantee the more expensive fish is from a much better supplier, which costs the store more, which means it costs you more. This is usually a significant price difference, but your success rates will be much higher with these more expensive fish, so you won’t be replacing them. The difference can be half of your fish dying before you get one of each species to settle in well and only 10% of your fish dying and needing to be replaced. That’s a big difference.
And remember, these fish were in the wild very recently. Then the aquarium trade scooped them up, sent them around the world, half the fish died during that process, and now you want to stare at them in a glass box. It’s not fair to them for you to cheap out and create demand for mistreated fish that don’t even live. Do whatever you can to make sure your fish live.
What Order to Add Fish
The order you add fish will make a huge difference in how well they all settle in. In general, it is best to add fish from least aggressive to most aggressive. This allows more timid fish to settle in well before more boisterous fish are added. Unfortunately, this means that the clownfish that was one of the main reasons you wanted a reef tank should be the last fish to go in since they are usually the most aggressive fish in a reef tank. The most peaceful and passive fish that are best to go in first are fish such as firefish, chromis, royal gramma, small blennies such as tailspot blennies, small gobies such as clown gobies, cardinals, and more. Tangs are large and even if they aren’t usually actively territorial with new fish (even though some will be, such as yellow tangs), it’s still best to add them later so the smaller fish have the best chance of not being stressed by them. Tangs are large and active and that alone can cause a stressed response in smaller, more timid fish.
Almost all clownfish are captive bred now and one of the hardiest fish you will ever own. This would make them an ideal candidate for the first fish to go in, however, they are also the most aggressive fish that most tanks will ever have. This means they should actually go in last.
In addition, if you want to have an anemone with your clownfish, anemones generally shouldn’t be added until the tank has been running for at least six months, and the anemone needs time to settle in (and usually needs to grow as well). Although getting clownfish to host in an anemone can sometimes be a challenge, an eager clownfish can harass a new anemone to death, especially if the anemone is still small.
For more information on clownfish, check out the Clownfish article.
Damsels are horribly aggressive and can be nothing short of a nightmare. Even the best ones such as azure and Talbot’s can easily be too aggressive for anything else in the tank. Sometimes, they will accept fish that were in the tank before they were added and will only be a problem to fish added after them, but even if this were always the case, it still wouldn’t help, especially since damsels are usually put in first because they are so hardy. Many are fine for a long time then suddenly turn and start killing their tankmates. Do not buy damsels unless you have some sort of predator tank with very large fish that will definitely not be intimidated by damsels (hint, this is almost never the case).
Believe me, if there were reliable exceptions, I’d love to recommend them. They are active, can have amazing colors, and are incredibly hardy, but they aren’t worth it. Every time you find someone who has one without issues, you will find five other people who had problems with that same type. Even the one that’s fine, is only fine so far. That same person may be singing a very different tune a year from now. Don’t risk it. As soon as they kill their first fish, you will regret ever adding them.
Banggai cardinals are beautiful, peaceful, relatively small, schooling, not overly active, and frequently captive-bred. All these traits make them excellent fish for almost any reef tank. However, they are extremely threatened in the wild and THIS HOBBY is the main cause. They have a very limited range and are exceptionally easy to catch. This has led to humans having a massive impact on their wild populations, much moreso than other fish in the hobby. So you think, “Okay, I’ll make sure to buy captive bred ones then, I’m happy to do that.” Well, that doesn’t help as much as you think. If 100 people want Banggai cardinals and there are only 40 captive-bred ones available and you buy from those 40, will other people not buy them at all? No. 100 Banggai cardinals will still be sold. 60 still come from the wild. It doesn’t matter that YOUR TWO came from the captive-bred group, there are still 60 coming from the wild. The only way to not contribute to their going extinct in the wild is to not buy them at all unless you will definitely be breeding them and the ones you buy will contribute to a net positive impact within the hobby. DON’T BUY BANGGAI CARDINALS.
As an alternative, go with pajama cardinals. They are just as hardy but do not have the threats to their wild populations.
Green chromis have great color, they school, and stay relatively small. However, they are VERY susceptible to an infection that almost all seem to get. It can start as a white blotch on their side and may have some red to it as well. If ANY fish in the entire system has this, don’t buy any of them because they will all die. It’s best to get long-term captive green chromis to avoid this. Yes, they may cost 2-3x as much or more, but it’s worth it since they will actually live.
Certain fish are worth having even if you don’t particularly like them for their looks.
Tangs can make a big difference in keeping algae under control. The best are the bristletooths such as tomini and kole (my preference is definitely the yellow eye kole tang). If your tank is large enough for one, I highly recommend including a kole tang.
Yellow coris wrasses help eat pests that can harm corals. Six line wrasses will too (although they can be fairly aggressive sometimes) as well as melanarus wrasses (although they get larger than the yellow coris). Another great thing about yellow coris wrasses is their bright lemon yellow color. Yellow tangs are popular for their color, but kole tangs are better at algae control and a lot less likely to be aggressive. The yellow coris wrasse lets you have that same bright yellow without having a yellow tang.
Matted filefish eat aiptasia, but occasionally they go after corals (at least once they’ve eaten all the aiptasia). Try Aiptasia-X first, but if you can’t get the aiptasia under control, then try a matted filefish. Just keep a close eye on it and your corals.
Lawnmower blennies are also great at helping with algae, especially in smaller tanks where a kole tang wouldn’t thrive.
Diamond gobies are great at keeping the sandbed nice and clean.
Don’t just toss all these fish into your tank, do the proper research regarding minimum tank size, compatibility with other fish you may want to include, etc. But do consider all of these if you can fit them. You will probably enjoy them and their helpful habits can make a big difference.
Stick to reef-safe fish only. Fish that are only sometimes reef-safe aren’t reef-safe. This includes flame angels, coral beauties, and many others. The fish that are only sometimes reef-safe vary from individual to individual. So one flame angel may not touch anything, another will only nip at SPS or clams, another will only nibble on zoanthids, and another will nip at everything. The same goes for coral beauties, other dwarf angels, and any other fish that is not always reef-safe. This is why any day of the week you can ask this question and people will say “They’re fine, I’ve had one in my mixed reef for 10 years and he’s never touched anything.” But you will also find at least as many people who have had problems with them. Don’t risk it. It isn’t worth having to tear your tank apart after losing hundreds of dollars in corals to catch one problem fish that you should have known before you even added it that it was probably not going to work out. Stick to truly reef-safe fish.
Cover Your Tank
Many people keep open-top tanks and this is a good way to lose fish. Many fish are jumpers, and many others will jump if startled. Some won’t even make it a single night in an open-top tank. The usual reason for open-top tanks is to let the light in. That’s fine, but you can do that with a mesh top. My tanks have glass tops and I have no issue getting enough light into the tank (if you do, you probably have barely enough light to begin with and need to consider a light upgrade, not an open-top). At the very least, use a mesh top. Remember, these fish were in the wild and happy there, half died during capture and transport, then you went and crammed them into your glass box for decoration. The least you can do is make sure something as simple as an open-top doesn’t kill them.
Below is a list of my favorite saltwater fish. They tend to be relatively hardy, peaceful, they all get along with each other, and each is my top choice for that type of fish (tang, blenny, clownfish, etc.). None are usually rare or hard to find, but availability can always vary. They are what you are likely to find in regular stock at most stores, so you shouldn’t have to special order most of them (although, requesting them can help since the shop will know you definitely want them and when). They are also in the general order I would add them.
- Royal Gramma
- Tailspot Blenny
- Pajama Cardinal
- Green Chromis
- Lawnmower Blenny
- Green Clown Goby
- Yellow Coris Wrasse
- Diamond Goby
- Kole Tang
- Pair of Clownfish (ocellaris or percula)
Obviously, these won’t all fit in every tank, but this would be my starting point. I would consider a 75-gallon tank to be minimum to have all of these. I prefer slightly heavier stocking, it makes feeding a lot easier. This would max out a 75, but assuming enough rock, good filtration, and a good feeding schedule, it will work very well.
Some people have very different ideas of what is minimum for a tang, so don’t be surprised if you find recommendations, often presented as laws, that no tang should be in anything smaller than a 125 (or larger, depending on who you talk to). I had a kole tang in a 75 and it was very active and happy, so I’m comfortable recommending them for a 75 or larger.
Picking Out Fish at the Store
When you go to the store to actually pick fish to take home, in addition to asking about captive-bred as described above, you want to take your time. Don’t just buy the first one that looks okay, take your time. Watch how it acts in the tank. You want one that is active (at least for its species), is alert, holds its fins erect, and eats.
Take a good look at it and make sure there are no marks, blemishes, white patches, etc. Make sure it’s not breathing heavily. Ideally, it shouldn’t have any bite marks on the fins. If it has one or two that don’t look infected, it will probably be okay, especially if it’s acting normally.
Ask them to feed it for you. If a shop doesn’t want to feed the fish for you, don’t buy them. That’s a huge red flag. It’s not unusual for customers to ask to see saltwater fish eat, so if a store doesn’t want to accommodate this, there’s a reason and you shouldn’t buy from them. When fed, the fish should actively go over to the food as soon as it realizes it’s in the tank. Make sure it actually eats the food. Sometimes, fish will actively go after the food, but spit it out instead of actually eating it. Sometimes these fish come around and actually eat, but sometimes they just slowly go downhill and eventually die. You want them excited to take one bite, then the next, then the next. It’s okay if they’re only going after one food in particular, that’s good enough for a fish that hasn’t been in captivity for that long.
For more information about feeding saltwater fish, please read the article on Feeding Saltwater Fish.