Murky vs Medivh
Murky can lane against Medivah easily. Medivah does have some damage but is more a support hero. With Medivah's portals and shield do not expect to be able to kill him. Just focus on the minion wave.
Fish Tank does nothing for Medivah. Typically you will be focusing on other squishies. One trick you can use is to throw a puffer fish on her portal. Depending on Medivah's talents enemy heroes will get bonuses for using the portal.