Looking on the internet deeply has found these results:

The fish sang. is the most popular phrase on the web.

The fishes sang. 10 results on the web	The fish sang. 154 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
It doesn't look like this phrase is very popular! The search could not find any examples on the internet.	The man who was penetant? It is not good to strike against God. Hast thou heard what the fish sang, As he floundered among the stalks? Nature is stronger than ... Feb 14, 2010 ... The fish sang out his heart, his longing, and his hopes, but the moon just sat in the sky, aloof. Even with the squirrel lifting him up as high as ... and the fish sang in the sea; and God looked on the whole wide world and then said, “I am pleased!” Oh, the people dance, oh, the people dance, and the stars ... ... on an oval plaque, was a newer product than the one pictured and therefore functioned! The head turned, the fish sang, and there was no sound distortion.

The fishes sang.

10 results on the web

The fish sang.

154 results on the web

More popular!

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

The man who was penetant? It is not good to strike against God. Hast thou heard what the fish sang, As he floundered among the stalks? Nature is stronger than ...
Feb 14, 2010 ... The fish sang out his heart, his longing, and his hopes, but the moon just sat in the sky, aloof. Even with the squirrel lifting him up as high as ...
and the fish sang in the sea; and God looked on the whole wide world and then said, “I am pleased!” Oh, the people dance, oh, the people dance, and the stars ...
... on an oval plaque, was a newer product than the one pictured and therefore functioned! The head turned, the fish sang, and there was no sound distortion.