can fish make other fish sick?

Yes!!! Without symptoms, I can't suggest what the disease might be, but there are several. Here is a pretty good set of guidelines for buying fish: http://fins.actwin.com/mirror/begin-stores.html I suggest buying from smaller specialty stores - I never had good luck with the large chain petstores.

Yes, if one fish is sick they will all get sick. The only disease I've ever seen take over a tank (and it happened when I introduced a new fish) was little white spots started to appear on him a couple days later. Then the other fish got it and died too.

Yes, I had 3 fish in a nice fish tank for years. Then one day we went to Walmart and saw a really cute fish. We bought the fish and brang it home and did everything you are supposed to do before putting in a new fish. We put the new fish in and not long after we put the fish in we noticed our fish acting really weird. They would rub themsevles along the bottom of the tank. Then they started to get a film on them. I called the pet store and told them what was wrong and they said it was Ick. They told us what to do and to buy this medication for the tank. Well it didn't work. Our fish didn't make it. We scrubbed our tank out and bought new fish and the Ick was still there. They all died. We got rid of our tank because it wont go away.

Yes if you have one sick fish it can infect your tank. If you suspect a new fish is sick i would separate the sick fish and treat both your full tank and the sick fish. ICH or ICK is a common disease that fish owners encounter. Your fish tend to develop specks. You can buy water treatments at any pet shop. Good luck!

Yes, this is why it is reccomended that you quarantine new fish for a week or so before added them into your main aquarium. If you don't have another tank you can even use a bucket or non-leaking tote container(as long as you are certain there have never been any chemicals in it). It will save you a lot of hassle.

Yes, they can pass on diseases to other fish. It is important that you buy your fish from a clean pet store. Example: ick - white spots on their scales. You need to treat the whole tank if you get this & they can die from this.

Yes its very easy for fish to catch disease from other fish.

Yes and yes. Absolutely!! Think about it. Could you get sick from another person? you should always look at fish before purchasing them a good book couldn't hurt you there are too many to list

Yes. It is best to hold your new fish in a quarantine tank [with it's own filtration system] for a week or two before introducing it to your main tank.

yes, very much so, that's why you should be very careful when buying new fish ideally you should have a quarantine tank where you could keep a new fish until you are sure that's it's healthy