We just made ceviche with ahi tuna, lots of lime juice, avocado, onion, cilantro and jalapeño. It's wonderful. Unfortunately we made too much. Now, I've never made it before and want to know about how long I should keep it in the fridge, if at all?  Note: this is not super high quality sashimi grade fish. Nor is it the freshest fish in the world. 
The acidic ingredients in the ceviche dressing will not significantly preserve or extend the quality of the tuna, but it will continue to break down the connective tissues in the fish and gradually ruin the texture.  You will also run the risk of contamination just as if you'd kept the unprepared raw fish in your fridge.  This is especially a concern if your fish wasn't very fresh (i.e. purchased the same day) to begin with.  I would keep this for no more than 48 hours at absolute maximum, depending on your tolerance for the change in texture.  Pour off as much of the marinade as possible and keep the ceviche tightly sealed.  When serving again, you can add fresh lime juice to adjust the flavor.  If you detect any fishy odor whatsoever at any time, discard immediately. 