Shellfish found in broken toys by European river (6)
I believe the answer is:
oyster
'shellfish' is the definition.
(oyster is a kind of shellfish)
'broken toys by european river' is the wordplay.
'broken' indicates an anagram.
'by' is a charade indicator (letters next to each other).
'european' becomes 'e' (abbreviation e.g. EU).
'river' becomes 'r'.
'toys' anagrammed gives 'oyst'.
'oyst'+'e'+'r'='OYSTER'
'found in' acts as a link.
(Other definitions for oyster that I've seen before include "Pearl creator" , "Native -- seafood" , "Content of stew" , "Bivalve that may nurture a pearl" , "person unwilling to communicate" .)