It's a bit fishy lying in such a nervous way (5)
I believe the answer is:
shyly
'such a nervous way' is the definition.
I can't tell whether this definition defines the answer.
'it's a bit fishy lying in' is the wordplay.
'it's a bit' indicates the answer is hidden within the clue (the answer is formed by a bit of the clue).
'SHYLY' is hidden within 'fishy lying in'.
Can you help me to learn more?
(Other definitions for shyly that I've seen before include "In reserved way" , "In a timid manner" , "Nervously, timidly" .)