Pet dying stupidly fast

Sometimes my pet appears to get almost one shotted by a mob, I noticed this a few times whilst levelling but figured the mobs were just hitting hard however at 85 I took my newly acquired shale spider back to vash'jir for some leather farming whilst waiting for dungeon queues and poor old fluffy got taken down in about a second by a level 81 fish. This made me a little suspicious since he can cope fine with 7 or so crabs on him! 

So anyone else noticed this or is it just me? Might be an extension of the famous pet health bug but I've been making sure my pet is at full health and with mend pet ticking before I send him in and it doesn't appear to make any difference:(