Creatively drawn Marine Fish

How to Choose Healthy Saltwater Fish

One of the most exciting parts of fish keeping is going down to your local aquarium store, browsing through their selection of fish, and picking out a few to take home with you. Or, if you buy marine fish online, getting your box from the delivery truck and unboxing your new pets. But unfortunately, many stores and holding facilities have problems in their systems. This may be parasites, contaminates, bacteria, aggressive fish, or even simple water parameter issues. It seems like every single beginner crashes their tank by introducing ich, velvet, or flukes within their first year of keeping saltwater aquariums, and it all stems from receiving fish in sub-par conditions and not fully quarantining them. As you advance further into this hobby, it is important to know what to watch out for in new arrivals. It’s much better to pass on a fish you have wanted for a long time than to impulsively purchase it, not quarantine, and wipe out your entire tank. Some of the fish most at risk for carrying diseases are considered “expert level” animals, so don’t let your guard down just because you have gotten lucky with beginner fish!

Signs of Stress
As we all know, stress in and of itself is enough to kill a fish. And, species that are known for being higher maintenance are much more fragile and are killed easier by stress. Signs may be subtle, so it’s important to watch your potential new fish carefully at the store. Darting through the tank, faded color, fast breathing, hiding in a corner or rock, or gasping near the surface are all signs of stress. These may also indicate illness. The biggest thing to watch for is his willingness to eat.

Before purchasing any fish, ask the store employee to feed it. If the fish has no interest in eating, it is not a good idea to buy him as the added stress of going into your tank will only add to the problem, and he will never start eating. Preferably, have them feed pellets unless you are interested in picky fish such as Anthias or Copperband Butterflies. If a fish is eating dry foods, it is a sign that he is acclimated to aquarium life and is settling in nicely. Feeding live foods to the tank will likely elicit a feeding response from every fish in it, and is not a great indicator for how the fish is doing. I have personally had fish come in from across the world and be willing to eat live brine an hour after being put in the tank, but still be extremely stressed and unwilling to eat any frozen or dry foods for a week. Fish caught with cyanide will also be extremely reluctant to eat.

Signs of Injury
While injuries heal, it is possible that they are extensive and causing a great deal of stress to the fish, so it is better to pick another animal in better shape. Nipped fins, scratched eyes, missing scales, and bite marks are all things to watch out for when picking new additions. Natural immune systems are also typically suppressed if the fish has injuries.

What If I Buy Marine Fish Online?
If you are in an area with no local fish stores, you may have no choice but to order saltwater livestock online. While this takes away your ability to observe the fish in person, it does not mean you are completely buying blind. If you purchase captive bred animals, it is much less likely that you will receive a fish with any type of disease. And, captive bred fish ship better, and usually exhibit way fewer signs of stress as opposed to their wild caught counterparts. Couple this with supporting sustainable aquarium practices, and a 0% chance your fish has been exposed to cyanide, and you are purchasing quality livestock! But, some fish haven’t been bred in captivity yet and that is okay too. Good, reputable online fish stores will guarantee that their fish arrive alive and disease free, so your investment is protected. And, good sources will also be willing to talk to you about the exact fish you are purchasing. This will tell you if you are buying from an honest, reputable source. Many places where you can buy marine fish online seem like they are in possession of what they sell, but are merely a drop ship company who acts as a hands-off middleman. That means, you pay them, they pay the fish wholesaler for a fish, and the wholesale facility ships the fish directly to you in a website labeled box. In this case, the company you paid never saw the animal and there is very little quality or health control, and you are buying completely blind. Reach out to the online store through phone, email, or social media and ask about the fish you are interested in. I have personally done this and been extremely happy with the results. Companies have been more than willing to email me pictures of the fish they had in stock, and a few even sent me videos of my fish eating to show that they were in good health before sending them out. Obviously, this isn’t needed for captive bred livestock who have lived their entire lives in captivity, but it is a very good idea for any wild caught specimens you are interested in.

Signs of Disease 
Obviously, we all know how to look for ich and velvet, any white spots on the fish means it stays at the store. Some diseases are more cryptic, so be willing to sit and watch the fish for a few minutes to see if you can pick up on any subtle hints. Cloudy or enlarged eye(s), faint red streaks or marks, enlarged or laboring gills, “slime” looking substances on clownfish, red or dark patches on chromis or butterflies, white or dark patches, erratic swimming, sunken belly or face, deterioration on fins, HLLE, wrasses unable to eat or close their mouths, cotton like growths, tiny tumors, or whitish coating over dull coloration are all signs of disease. If you see any of these, leave the fish at the store.

A Note About Quarantine
No matter what, you should always quarantine new fish. Even if the online retailer or local fish shop said they fully quarantine their fish, you should still do it at home as well. At a minimum, keep your new additions in a separate observation tank for two to four weeks. This will enable you to increase their feeding response, and settle in before going into the display and having to compete with others. Most disease will also present themselves during this time. Medicating their food with an antibiotic (preferably one for gram negative and one gram positive bacteria), anti-parasitic, and binder, and medicating the water column with Praziquantel and copper (not simultaneously) are standard quarantine procedures that will further ensure your fish are all as healthy as possible and greatly reduce the chances that stress or a new addition to the tank will cause mayhem. A few extra weeks of dealing with an extra tank for quarantine is a small price to pay for keeping your display tank healthy and safe.


Even though buying new fish is extremely exciting, it must be done responsibly and with care. Taking the time to observe your potential purchases and quarantining new arrivals are crucial steps in protecting your investment. Whether you buy marine fish online or in store, you can make sure you aren’t buying a stressed, injured, or diseased fish by knowing a few simple signs to look out for.

310 thoughts on “How to Choose Healthy Saltwater Fish”

  1. I have been fairly lucky with the fish I have taken home. But that luck will run out one day. Great read and makes me want to set up a quarantine tank.

    1. I have been in the hobby since the nineties and the quality of fish has definitely gone down. quarantining is always a good idea if you have the means to accomplish it.

    2. I love my 10 gallon quarantine tank with a hang on filter it has been going successful with water changes only before buying new fish and treatment has been great

  2. The value of quarantine cannot be overstated. Few vendors of live fish have the space and time to do an adequate job of holding the fish in low stress environments, let alone any extended quarantine or prophylactic process.

  3. I totally agree with quarantining, just not quarantining w/ “prophylactic” treatments that will end up stressing the fish.

  4. Always a good idea to do as much research as possible, realize that each fish has an individual personality, and make sure that it will fit in with your system. QT is CRITICAL….always! But, starting with a healthy appearing fish will give you a head start.

  5. If I’m just setting up my first tank, what’s the best way to setup a quartine tank? Or do I really just need to set up two tanks to begin with?

  6. I dont even have my tank running yet and already have the supplies to quarantine i have all the time to get my fish tank ready

    1. Bo Heath Kinsland

      Ive been looking into some fish from a local pet store and based off of this article, they are no where near healthy so i know where not to buy from now. Thanks!

  7. Qt is a big part of this hobby. If done correctly will leave almost 0 room for introduction of unwanted organisms.

  8. I always try to put fish on hold at fish stores. I feel if it makes it the 5 days on hold, it has a better chance of making it.

  9. Captive Bred is always an excellent way to go!! I hope those breeders are hard at work, bringing us some new species!! did a great job on the yellow tang

  10. Casey Whittington

    Love this post, I’ve often seen people get too excited over buying fish they are no ready for.. Post like this helps educate people, then it’s up to them to put the info to use because this is awesome information

  11. Its amazing the quality of fish at different local fish stores. One always gets great fish in but their system is loaded with Ich. I don’t know why they don’t treat it. I’ve purchased a few knowing this and have gone strait to tank transfer method.

  12. I’m sad how healthy fish can look in stores only to die at home. I’ve had some develop fun fingus shortly after and die.

  13. I have never thought about asking for the fish to be fed before I bought them. I’ve always checked out their scales and looked at their tank mates. If any was dead I normally steered clear of thank tank.

  14. Recently picked up some iched out clowns. Treating now. They seem healthy. Eating and doing clown stuff. What would constitute the “perfect” quarantine tank?

  15. Alejandro Rodriguez

    Always better to be safe than sorry especially when dealing with expensive aquarium fish. Always quarantine any new stock.

  16. i find that most mom and pop places near me have better prices but worse health. growing up they were always the best. but not anymore.

  17. Great info, although at the same time I feel like it should be common sense to avoid purchasing any animal that looks like it is in bad health. But then again, I know some people take being sympathetic way too far and never stop to consider what is actually best for the whether or not they can provide the most likely extremely special care it needs in order to recover.

  18. Patrick Stephens

    We personally run a 210g Quarantine Tank. QT for no less than 45 days while also using tank transfer method! Great info! Keep up the great work!!

  19. I usually try and go with captive bred and always make sure fish are eating before bringing them home. I usually only buy fish from 1 trusted lfs in my area

  20. I only buy fish from 1 trusted lfs in my area. Always make sure they’re eating and no signs of being sick. Try and buy captive bred whenever possible

  21. This is probably one of the most important information for fish keepers, you have to go to the fish store knowing what you are doing so you decrease the chance of loosing fish and money, this should be shared everywhere.

  22. Great article. I am cycling a tank now and beginning to set up a QT tank. I didn’t have one the first time around and totally regret it. I plan on doing things right this time!

  23. I’ve been lucky for the most part. My partner has no patience and wants to dump anything right into the display 🙁

  24. I always ask for them to feed the fish before j buy it. If it eats, it’s a good sign of a stress-free and healthy fish

  25. Since I hope to get my first saltwater tank ever soon (I had 9 Cichlid tanks ages ago) so this was very helpful. That has been a huge concern and why I didnt do salt in the oast.

  26. This is a really good read!! I only have one fish right now. I won’t go into detail how I got him, but he was missing an eye. Well he has been a part of our family for almost 3 years so he is just meant to be with us. I agree with everything said in how to pick the best fish especially for beginners!! Happy 2020 everyone!!

  27. Quarantine seems like such a pain, until you get a fish disease. I am guilty of not using a quarantine system for my fish or coral. I have been lucky with my fish, but would have been able to avoid vermatid snail and flatworms with my coral. A quarantine will be part of my bigger build before I start to cycle it.

  28. Great review and reinforcement of the importance of sustainable practices and protecting your animals through quarantine. Thank you!

  29. One on my LFS writes the date that they received the fish on the display tank. This is a good indication that the fish has been taking food.

  30. I unfortunately lost a six line wrasse to ich. Luckily I managed to treat my fish in the tank with metroplex before it was too late and managed to save my tank after a hefty water change! I definitely learned my lesson!

  31. Most people fear the extra care and time a QT will take, but it doesn’t have to be a full blown system like yours main display to take care of your new addition and protect your tank! QT for the win

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