Paracheirodon innesi or Neon Tetra
Neons are absolutely intolorable to bad water conditions, they like heavily planted, safe havens.
They dont enjoy being chased around by larger fish
they get along well in large groups to feel secure, around 4-7 is fine, the more the marrier IMO
if a single one of them is diseased, its demise is imianent due to their social behaviors,
what I have noticed is when a single neon gets sick or diseased or even 'not normal' the rest of the group will single him/her out, cutting off ties to the rest of the group, this is even more stressfull for the fish in question and will most likely die in a shorter period of time.
they are also very intolorabe to medications, salt and most other additives
they enjoy smaller frozen or live foods on occasion and take to frozen brine shrimp and daphnia readily, they love daphia
when neons are first introduced into a tank they will huddle together, but as time passes and they feal more comfortable they will shoal loosly or not at all,
they will however always chase each other trying to figure out who the leader should be (the pecking order)
they are a good indicator of water conditions, as their brilliant red stripe will fade (other then when first turning the lights on), when water parameters start to deteriate
if you notice a neon that looks isolated and is avoided by the rest of the group, after close observation Quarentine of the fish should be taken, as there is probably something wrong with him.
having a test kit is a must have in the fish keeping hobby, its right up there with heaters and filters. I recommend the test tube variation becasue of its accuracy and cost.
good luck
Matt