Readers - look at this,even PB moderators are discussing fish order containation under the topic of Pond Construction - Building a Dam - Siphon Specifics.
When you buy large quanities of fish (all varieties) from hatcheries often they are not hand counted due to time constraints. They seperate the quantity by weight. One has to assume that no cross contamination has occurred at teh hatchery. I have been to several hatcheries where owners kids or relatives kids have been allowed to "play" in the hatchery tanks with dip nets. This is only one example of a possible source of cross contamination that could occur at the hatchery.
Another source of cross contamination at the hatchery level is when fish are pond raised. Any foreign fish in the pond can spawn and provide extra fish in the final seine hauls. Often these fish are not real closely hand sorted due to time constraints.
Some fish at hatcheries are raised in poly culture where two or more species are raised together to capitalize on increased production for a given water body.
I've watched hatchery workers hand sorting fish and they make mistakes either due to pure error or a fish in a sorting net accidently jumps at the right or wrong time and makes it into the wrong tank.
Lots of ways fish can contaminate your order.
