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Context:
... and he reacted at once, "Chen Shengshen? A great mathematician, wonderful! Every Tianjinese who has ears knows him! What a talent he is!"

The question is:

If what the speaker said in the quotation marks is just part of what he said at that time, could I remove the quotation marks? That is, can it be:

and he reacted at once -- Chen Shengshen? A great mathematician, wonderful! Every Tianjinese who has ears knows him! What a talent he is!

I fear that the usage of double dash is awkward. So could I use "colon" instead? That is:

and he reacted at once: Chen Shengshen? A great mathematician, wonderful! Every Tianjinese who has ears knows him! What a talent he is!
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You need the quotation marks if it is direct speech. The m-dash is not awkward, but it is not necessary either. A colon looks over-formal, however, to me. How about a period?-- that will work fine:

'... and he reacted at once. "Chen Shengshen? A great mathematician, wonderful! Every Tianjinese who has ears knows him! What a talent he is!" '
Comments  
Thank you.