Fish found regularly in Trent area (5)
I believe the answer is:
tetra
'fish' is the definition.
(tetra is a kind of fish)
'regularly in trent area' is the wordplay.
'regularly in' means one should take alternating letters.
'trent'+'area'='trentarea'
The alternate letters of 'trentarea' are 'TETRA'.
'found' acts as a link.
(Other definitions for tetra that I've seen before include "Bright tropical fish" , "Denoting four (prefix)" , "starter for four" , "Swimmer" , "Small tropical fish" .)