After a trip to Edinburgh I'm now on 5 species:
Spectacled bear [Chester]
European brown bear [Whipsnade]
Sri Lankan sloth bear [Whipsnade]
Sun bear [Edinburgh]
Giant panda [Edinburgh - and my first ever

]
Even if I can't get the 8, this challenge has encouraged me to visit Edinburgh much sooner than I thought I would and to see the species I've wanted to see from childhood, so thank you Shorts for giving me the motivation to do Edinburgh as a day trip, and thank you RZSS for giving me all three species that I've constantly wanted to see from childhood [Koala, polar bear and giant panda].
Now, if they can just add walrus, beluga and manatee to the collection