It's difficult to hold when the top of the fishing tackle is missing (3)
I believe the answer is:
eel
'top of the fishing tackle is missing' is the definition.
I can't tell whether this definition defines the answer.
'it's difficult to hold when' is the wordplay.
'it's difficult' becomes 'el' (I can't justify this - if you can you should believe this answer much more).
'to hold' means one lot of letters goes inside another.
'when' becomes 'e' (I've seen this in other clues).
'el' placed around 'e' is 'EEL'.
'the' is the link.
Can you help me to learn more?
(Other definitions for eel that I've seen before include "Long thin fish" , "A sea snake" , "Slender fish" , "Teleost fish" , "Conger, e.g." .)