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In my fish tank I had three danios, but one of them died. They're schooling fish, so will that effect anything? If I need to get more to make them happy, how long would they be able to go with only the two of them?
There are also 3 guppies, 2 snails, and 5 ghost shrimp in the tank with them.
I have owned and worked with aquariums for well over 40 years, since I was around 12 or so. I have had all sorts of configurations and a large number of Danios and at given time. In fact, one of my current 55gal tanks has about 15 danios currently, mixed with various other fish.
Danios are a schooling fish, and I have always had better success with them in groups not less than 3. They will survive singly as well, but are always happier (subjective but viewable by their activity) in larger groups.
Any NEW Danios that you add to your tank will immediately join up with the others, thus protecting them from any other fish in the tank. That is the idea behind "schooling" in the first place. It defeats attackers by distracting them from any single fish as they all swirl around and the attacker gets lost as to which particular fish it was going to attack.
The key here though is to match, the TYPE of danio that you purchase to add to the tank, and if possible find ones that are very similar in size. No more than 1/4 inch less in length and no more than 1/4 inch longer in length. As I said though, the key is to match the type of Danio. Each fish store you visit may call different fish a Danio, and they are possibly sourced from different locations. Some are grown in huge ponds down in Florida, others are wild caught from various rivers in South America. The ones that are sourced from Florida are more likely what you currently have as they are generally cheaper in price. They are also already used to the various foods and/or chemicals that they will be exposed to in a local aquarium. Wild caught fish, may be brighter in color, their stripes may be more visible (if they are happy that is) but they also may not survive as long as they are used to the water that they were born in. Which is a wild river. Where the tank raised from Florida is raised in treated water, so they are more used to that sort.
Some Danios by trade name, are live bearing, others are egg layers, as I mentioned, the term Danio is used for a variety of fish. The live bearers are typically 3 to 4 inches in length, while the egg layers, when full grown seldom reach 3 inches and are more typically less than 2.5 inches in total length.
Anyway, my advice, add 2 or 3 more... likely no more than that depending on your tank size. Also be aware that Ghost Shrimp love, just absolutely love, baby fish as food.
