Selecting healthy fish

Introduction

Most of us especially new hobbyists don't use a quarantine tank for our new fish, this makes it especially important to make sure that only good healthy fish are purchased in the first place.
Even though at a glance it may seem that all fish look the same there are ways to spot good fish and ones that should be avoided.
I deliberately chose these photos because the first shows a fish, which is an absolute picture of health.

It is very alert and interacting with others and is obviously eating well. Its eyes are clear and they are free of any marks and blemishes.
All these things indicate good health. The second is so emaciated that there is an obvious problem. But this can't be diagnosed on the spot by an amateur fish keeper. It would be best not only to avoid this fish but all of it's tank mates too

What are the signs to look for when selecting a good fish?

A healthy fish should be actively swimming and not resting motionless on the bottom (unless that is its natural behaviour).
It should be swimming evenly and without any apparent effort. If the fish appears to have to make an effort to either sink lower in the water or if it struggles to break away from the surface then it is a sign that all is not well with the fish. But there are a few species which live in fast flowing water which have reduced swim bladders which allows them to hug the floor rather than be swept away.

A healthy fish should have all its fins erect and it eyes clear from any cloudiness.
Cloudy eyes and folded fins are a sure sign that the fish is suffering from an illness.
Reject any fish which is showing these signs so that you won't put your existing stock at risk.

They should be free of any deformities. It might be easy to feel sorry for a fish with deformities but the chances are that it won't be able to compete equally with other fish and it will lead a miserable life as a result. If the fish lived and managed to breed then the deformity could be passed on and leave you stuck with a problem because no shop will buy them.

Healthy fish should be alert and interacting with its surroundings. Fish with glazed eyes and which seem dazed could well be suffering from shock. Shock is a big killer and almost untreatable once the symptoms show. Fish in this condition rarely survive very long.

They should look to be reasonably well fed and not hollow bellied. Wasting is another sign of a diseased fish. It could be an indication of bacterial disease which could easily affect other fish or internal parasites which again may put your existing stock at risk.

They should be free from sores and blemishes. Sores and blemishes may be caused by nothing more than an abrasion which would quickly heal. But it might indicate the fish has been subjected to poor water quality and is suffering from nitrite toxicity which takes a long time to recover from and open sores mean the fish could act as an host to opportunistic infections which could then spread to other fish in the tank. Even if all these criteria are met the fish should still be rejected if any of the tank mates appear to be unhealthy. Bacterial and viral diseases are capable of spreading very quickly in an aquarium with so many potential hosts. So even if the fish that you want appears to be healthy, if it is in a tank with sick fish it may already be infected but the symptoms haven't started to show. Neon Tetra disease is a good example of this.

Are there any thing else which I should look for?

Poor quality fish are becoming much more of a problem now due to intensive breeding with little or no thought paid to the quality of the breeding stock.
Never buy a fish if other fish in the same tank look diseased in some way. Always reject any fish with any of the following.
Bent backs, missing gill covers etc. These are classic signs of inbreeding the entire batch of fish should be rejected even if they aren't showing any outward signs. The whole batch will be poor quality.

If the batch of fish has just arrived and is offered for sale immediately. This will cause some fish to die from the stress of it all.
If possible find a reputable retailer who quarantines his stock before it is offered for sale. And who is knowledgeable and helpful. Such dealers are worth sticking with even if they charge a little more.

If you do spot a known disease like Neon tetra disease which is highly contagious and untreatable. Is the net being used to catch the fish also being used for several different tanks, if it is then any fish which can fall victim to this disease and there are many, will stand a good chance of being infected with it. Which means that if you bought one of these fish you would lose most of your tetras and wouldn't be able to reintroduce any more for several months.

A final word

Don't expect to find a fish which would be a potential show winner sat in a fish shop. Fish shops are quite stressful places for fish, the tanks are relatively bare, over crowded and occasionally a large net drops in and chases the occupants around. Add to this the busy environment, kids tapping on the tank and the fact that some of the fish will have suddenly been placed there after a long journey in the dark having not been fed for a few days prior to the journey.
Would you be at your best if this happened to you?

Watch out for:

Is the same net used between tanks at your local fish store (L.F.S)?

Are there any dead fish in the tanks which have been there for a while?

Do you ever see the fish being fed at your LFS?

Are there obviously sick fish on sale?

Does your LFS allow the fish to recover for a few days before offering them for sale?

Check your LFS's advice on setting up a new tank and cycling it, this will tell you more about their attitude to fish than almost anything else.