For those of us who are koi hobbyist, we have a great appreciation for the intelligence of our fish. Scientists, now studying more of the aquatic world and are researching the powers and intelligence of our finned friends. Another review of a study regarding the memory of fish. 
 
"It is popularly believed that fish have a memory span of only 30 seconds. Canadian scientists, however, have demonstrated that this is far from true -- in fact, fish can remember context and associations up to twelve days later."
 
https://www.sciencedaily.com/releases/2014/07/140701193253.htm