My uncle, who owns a vineyard in South Africa, has been a keen collector of fish for as long as I can remember, and would often be seen walking around his numerous aquarium tanks with his trusty sidekick 'Rusty,' a Jack Russell.
Rusty particularly loved to torment the Oscar tank which was huge, and so were the fish, the biggest I have ever seen still to this day. He would run up and down the face of the tank barking and causing quite the commotion. One day, my uncle brought home some new Oscars and he decided that he was going to place them in the Oscar tank, and remove the big guys already living in there. I helped him transfer 6 of the Oscars to his cement water tank by the vineyards and was sure the fish would die. They did not and actually are even bigger now.
Rusty the Jack Russell, who would often go swimming in this cement tank on a daily basis, watched in awe as we dropped each fish in and stayed behind while we walked back to the homestead. All of a sudden there was this huge splash, a whole bunch of barking, followed by yelping and a very wet pet came flying through the front door and hid in the kitchen for almost three hours, shaking like a leaf. We never really found out what happened that day, but Rusty has never been swimming again, and if you just try to get him within six feet of that tank and he goes crazy!