Crossword Genius

Dump waste — head off fish and salamander (8)

Ross

I believe the answer is:

mudpuppy

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This could be a double definition.

'dump waste' is the first definition.
The definition suggests a singular noun which matches the answer.

'head off fish and salamander' is the second definition.
I can't tell whether this defines the answer.

Can you help me to learn more?

I've seen this clue in The Sunday Times and The Times.
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