Rover has complaint involving a fish (8)
I believe the answer is:
gadabout
'rover' is the definition.
(someone who roves or roams around)
'complaint involving a fish' is the wordplay.
'complaint' becomes 'gout' (gout is a kind of disease).
'involving' indicates putting letters inside.
'fish' becomes 'dab' (dab is a type of fish).
'a'+'dab'='adab'
'gout' placed around 'adab' is 'GADABOUT'.
'has' is the link.
(Other definitions for gadabout that I've seen before include "Restless seeker after amusement" , "restless sort" , "Person who wanders aimlessly in search of pleasure" , "Person who goes around aimlessly" , "Vagrant" .)