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.

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