Raw treat prepared for amphibious rodent (5,3)
I believe the answer is:
water rat
'amphibious rodent' is the definition.
(I've seen this before)
'raw treat prepared' is the wordplay.
'prepared' indicates an anagram.
'raw'+'treat'='rawtreat'
'rawtreat' with letters rearranged gives 'WATER RAT'.
'for' acts as a link.
(Other definitions for water rat that I've seen before include "Small amphibious rodent" , "boatman" , "Swimming rodent" , "beastly thing" , "round little furry creature" .)