Fish gone astray in the fisherman's basket (6,3)
I believe the answer is:
conger eel
'fish' is the definition.
(conger eel is a kind of fish)
'gone astray in the fisherman's basket' is the wordplay.
'astray' is an anagram indicator.
'in the' indicates putting letters inside.
'fisherman's basket' becomes 'creel' (I've seen this before).
'gone' is an anagram of 'onge'.
'onge' going within 'creel' is 'CONGER-EEL'.
(Other definitions for conger eel that I've seen before include "long haul?" , "one is long in the water" , "Predatory fish" , "Predatory sea creature" , "Large slippery fish" .)