Fish around island proving source of energy (7)
I believe the answer is:
biomass
'proving source of energy' is the definition.
I can't judge whether this definition defines the answer.
'fish around island' is the wordplay.
'fish' becomes 'bass' (bass is a kind of fish).
'around' indicates putting letters inside.
'island' becomes 'IOM' (abbreviation for Isle of Man).
'bass' going around 'iom' is 'BIOMASS'.
Can you help me to learn more?
(Other definitions for biomass that I've seen before include "source of 8 [RENEWABLE ENERGY]" , "Organic source of energy" , "Measure of living organisms" .)