Fish, holding shortened rod in biannual event (8)
I believe the answer is:
solstice
'biannual event' is the definition.
'fish holding shortened rod' is the wordplay.
'fish' becomes 'sole' (I've seen this before**).
'holding' indicates putting letters inside.
'shortened' means to remove the last letter.
'rod' becomes 'stick' (I've seen this before).
'stick' with its last letter removed is 'stic'.
'sole' going around 'stic' is 'SOLSTICE'.
'in' is the link.
(Other definitions for solstice that I've seen before include "Shortest or longest day of the year" , "When night and day are most unequal" , "Midsummer or midwinter point" , "When the sun is farthest from the celestial equator" , "Midsummer or midwinter day" .)