I'm confused, you are buying probably thousands or 10s of thousands of minnows and EVERY fish is checked for an ovarian parasite? How in the world can they say something like that? it is a chemical test in the water in the bag? Do they filet open every 100th fish?
Someone help me here!
Nothing is ever 100%.
It's likely that they spot check with a highly sensitive test.
The sensitivity and specificity of the test is determined and then sample size and frequency are tuned to give a certain level of confidence in the result. This is my experience with livestock testing e.g. brucellosis surveillance for cattle.
E.g. "APHIS conducts surveillance on animals at slaughter by testing their blood for presence of Brucella antibodies. Around two million animals are tested annually. Surveillance is more than sufficient to detect one affected herd out of 100,000 herds at a confidence level of 95%."
https://www.aphis.usda.gov/aphis/ourfocu...sis-eradication
