So I recently moved my fish out from the basement to their summer home, 300 gallon horse trough lined with billboard vinyl, properly cycled and extra filtered til I get the plant beds going. Everything seemed fine overnight even with a thunder storm, H2O temps did go down to low 60's, rainy and overcast kept temps there. I felt fine heading off to work, when I came home though, totally tilapia lemmings, 13 were over the wall! I lost another couple the next day, but was able to revive a few by holding them over the pump outlet for several minutes. I fashioned a cover from plasticised wire fencing, and felt a little better about my husbandry for the moment. This morning I went to check, no casualties over night. Then as I walk away, jumpers again, and so enthusiastically some were getting through the wire mesh, so another day of running back every hour or so to check for escapees.
So, just me?
no, it is not just you. we have had to put plastic netting over our tanks too. we started with fine mesh netting, but they were jumping up and tearing that so we ended up with plastic/vinyl style netting.
All fish can jump and tank covers can be a real challenge. My second catfish death was from jumping and I lost tilapia out of tanks with even hard covers that they managed to bang open enough to get over the edge. And I've lost one small blue gill that jumped out of the tank a while back.
Netting that is tight and secure around the edge can make a good fish trampoline to bounce them back down but having some extra free board of tank above the water level as Sylvia says really does a lot to keep the fish in the tank.