As you didn't actually see the specific fish that were being stocked, there's not any realistic way to know anything for certain.

I would just do your best to observe as many of the fish, in pond, as you can, and then make any adjustments you feel necessary as time goes on.

In future stockings, you can be more hands-on to ensure you're getting what you want.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."