Piranhas Dead How???

Well in one of my trips to Mexico i bought some piranhas from a pet store for 6 dollars each so i bought 2 .I put them in a jar with holes for oxygen and a battery powered air pump,so off I go to California,by the way I was traveling in car,We stopped at a rest area and got some rest and when i wake up my fish are dead.I don't know why they died,the air pump was on while I slept.
Anybody know why my fish died???

It could have been a couple of things in my opinion.

1. They could have gotten stressed out from being in a jar as opposed to a larger tank.
2. They were not healthy to begin with.
3. The temperature fluctuated too rapidly since they were in such a small body of water.
4. The air pump caused too much turbulence in the water and the fish had to expend a considerable amount of energy to fight the current--weakening and stressing them out.

...but here's my best guess:

5. The pH dropped real low, real fast. When you aerate "temporary water" for fish you're fixing one problem but causing another. Ammonia from fish waste harms fish by basically suffocating them, so aerating the water would increase the dissolved oxygen level, thus preventing ammonia toxicity from suffocating them as quickly. However, vigorous aeration of a body of unfiltered, uncycled water causes certain chemical reactions (sorry, don't remember what exactly they are) and causes the pH to drop rather quickly. pH shock can be fatal to fish.

Overall, I think it was likely a combination of a few of the above things. If you have to put fish in a jar again for any reason, you're best off either not aerating the water, or providing mild aeration along with frequent partial water changes to avoid the pH problem. It's hard to say exactly what happened without knowing all of the specifics, as well as observing the fish before and after death.

I didn't think you could legally bring piranha into California.

Nope you sure can not bring them in to California. However I agree it was a water quality issue that killed them.