Colourful swimmer turns crazy and egocentric (10)
I believe the answer is:
damselfish
'colourful swimmer' is the definition.
'damselfish' can be an answer for 'swimmer' (damselfish is a kind of aquatic vertebrate). I am not sure about the 'colourful' bit.
'turns crazy and egocentric' is the wordplay.
'turns' says the letters should be written in reverse.
'crazy' becomes 'mad' (synonyms).
'and' means one lot of letters go next to another.
'egocentric' becomes 'selfish' (I've seen this before).
'mad' in reverse letter order is 'dam'.
'dam'+'selfish'='DAMSELFISH'
Can you help me to learn more?
(Another definition for damselfish that I've seen is " Swimmer".)