Hard sci-fi novel that begins with an entity cruising around space 'like a shark'?

Question

In a bookstore in the 1980s, I read the first pages of a hard science fiction novel that began with the memorable description of some creature or ship or intelligence that was like a shark swimming through space with the singular goal of turning anything it encountered into "shark shit".

For some reason I think it might have been by Frederik Pohl. Or maybe Harry Harrison or... I don't know.

Anyone know?

Edit: I just read the guide... I can't remember what it looked like but a few other details I can think of are that:

1) this thing was headed for our solar system, which would be Bad News for us...

2) I am almost sure that I put the book down because I hadn't read anything else by the author. Up to that point I am pretty sure that I'd only read Isaac Asimov, Arthur C. Clarke, Robert A. Heinlein, Frank Herbert, Larry Niven. So probably not by one of them... although I could be wrong.

Edit #2: I just tried a more thorough Google Books search than I have before and came across the passage from an old issue of Analog:

https://books.google.ca/books?id=y_JZAAAAMAAJ&q=%22shark+shit%22&dq=%22shark+shit%22&hl=en&sa=X&ved=0ahUKEwjN19-U8KziAhWJT98KHecADVY4FBDoAQgvMAI

was largely untranslatable, but you might think of it manifesting as a kind of giant space-going shark, a moving appetite, a vast, fast, terrible eating- machine which saw its purpose to be turning everything edible in the universe into shark shit.

...apparently by John Wood Campbell in Analog Science Fiction/science Fact - Volume 106 - Page 162

So maybe a short story... trying to figure out how to see more of it.

Answer 1

That's "The Mick of Time" by Spider Robinson, the last story in the collection Callahan's Secret. It was first published in the May 1986 issue of Analog, although it was by then edited by Stanley Schmidt, not John W Campbell. It's a short story not a novel, and it's not really hard SF, but it otherwise fits your description accurately.

The paragraph in question:

There was only one Master. We didn’t even know then just what a break that was. The telepathic aspect of the creature was largely untranslatable, but you might think of it manifesting as a kind of giant space-going shark, a moving appetite, a vast, fast, terrible eating-machine which saw its purpose to be turning everything edible in the universe into shark shit. Like a shark it was implacable, remorseless, unreachable. What made it much more terrible than any shark was that it was highly intelligent and very learned.