Greetings,
For the past few months we've seen small fish jumping in our pond of Rainbow Trout, we knew that none of our rainbows should be that small and wondered if they might be breeding. However, yesterday my father found a large white sucker floating dead in the pond. The pond is totally isolated from other water systems. It's fed from an underground spring, and the water exits through a screened 5' vertical drop pipe into a ditch.
Two questions.. Any idea how the suckers could have gotten there? And, will there be any effect on our Trout by having them there?

How confident are you that the pond is totally isolated? When it rains extremely hard water levels can get very high and fish are capable of moving both up and down water systems. That is the most likely way they got in there...

White suckers will not compete with rainbow for most food sources. If it's just a pond with no inflowing stream, what suckers are in there will most likely not reproduce as they require flowing water with a gravel bottom. If they do reproduce, white sucker are excellent forage. Their biggest issue is they reach large sizes, in excess of 18". So... They can get so large, so fast that they cannot be preyed on and can become too abundant. With just rainbow trout as a predator, this could become an issue... IF they are naturally reproducing.

LR,

The chance of buying/stocking trout, with any stray fish breeds in the batch, seems extremely remote. Everybody I know who raises trout from eggs, to fingerlings, to stocking size, does so in very controlled conditions that would make it very difficult for intruder fish into the batch.

Quite a few of us believe that fish only get into new bodies of water through flooding or human intervention -- except possibly under some very extreme circumstances. The chance of birds or animals transferring eggs, fry, etc., from one body of water to another is pretty slim.

I can only think of a few ways of getting suckers into your pond. Have you or friends used "minnows" as bait? Or, worse yet, have you or friends ever dumped a bucket of "minnows" into, or near the pond?

As for competition, I doubt you will see any significant effects from the suckers, unless they somehow become very seriously huge, or overpopulated, and they start to really disturb the turbidity of the water. When I regularly fished for trout "up nort" I often caught way many more redhorse and white suckers than trout. Yet, the trout I caught were usually pretty healthy and fat. I suspect the trout were eating a lot of sucker fingerlings.

Regards,
Ken

We all live downstream from somebody and "somebody" often seems to help us stock our ponds.

Yes angling friends using live bait could be a likely source of suckers. Guests thought dumping the bait bucket would help feed the trout.

Thanks for all the help guys... still a bit of a mystery. I'm very sure about the isolation factor of the pond, and very few people in this area fish with minnows (in fact, I've never actually 'seen' anyone fish with minnows anywhere in our river system, although I won't say that it doesn't happen). The nearest stream with a sucker population is a couple of miles away.
I agree that the chance of a bird dropping a fish into the pond is very slim.
Perhaps someone has dropped a pail of minnows in...seems weird to me, but no other explanation seems to fit.
Thanks too for the good news regarding interactions between these species. I guess I'll just see where this goes from here.