Q:

Like a fish in a puddle, what joy is there

For years I've been trying to find the source of a quote, but I've only been able to get so far. 
The quote is "Like a fish in a puddle, what joy is there."   
This seems to come from some verses titled, "Samantabhadra's Admonition to the Assembly".   
My research indicates that it's part of the evening service for Pure Land schools of Buddhism.   I've even found the Chinese for it. 
是日已過，
命亦隨減，
如少水魚，
斯有何樂；
大眾當勤精進，
如救頭然，
但念無常，
慎勿放逸。 
I can read and understand Japanese, but Chinese is only half a guess for me since I'm only using my understanding of Japanese to read it.   But, I'm having a hard time finding Japanese sources.   Most of my searches pull up Chinese sources. 
It seems it's from a sutra, but I don't which sutra it comes from.   I have figured out that it's not from the Flower Garland Sutra (Avatamsaka Sutra), nor is it from the Lotus Sutra. 
Could anyone help me out? 

A:

Absolutely.  Sn 4.15 Attadanda Sutta: 

"When embraced, the rod of violence breeds danger & fear:
  Look at people quarreling.  I will tell of how I experienced dismay. 
Seeing people floundering like fish in small puddles,
  competing with one another — as I saw this, fear came into me. 
  The world was entirely without substance. 
  All the directions were knocked out of line. 
  Wanting a haven for myself, I saw nothing that wasn't laid claim to.  
  Seeing nothing in the end but competition, I felt discontent. 
  And then I saw an arrow here, so very hard to see, embedded in the heart. 
  Overcome by this arrow you run in all directions. 
  But simply on pulling it out you don't run, you don't sink.   

In Pali this reads like a poem, 8 syllables per line.  Sometimes the authorship is attributed to the Buddha himself.  Apparently at one time the poem was a standard part of the ritual for new person joining the early Sangha. 
The line you're interested in says something like "I saw people crowding like the fish in shallow puddle, getting in each other's way, this really had scared me."