Voucher specimens, I would guess.
If you find a specimen that's larger than what's generally known, pickle it,
record collecting data, and send it off to either a taxonomic expert in that
particular taxa, or to the closest natural history museum that houses a fish
collection. Include a note that mentions that this specimen exceeds the
largest known size.
If you don't want to pickle the fish, pose the fish above a ruler and take a
photograph. This may not be as reliable as a voucher specimen, but
should indicate if a species exceeds a certain size.
It's not that the Peterson Field Guide -- or any other "Fishes of..." book -- is
wrong. It's just that it was written using the best available data. Science is
self-correcting. So don't be afraid to correct!
Chris Scharpf
Baltimore
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