Every time you seine fish you stress them. The OP would have to run ALL the fish through a grader to transfer smaller fish. (seine, remove fish from seine, grade inside a holding tank, return larger fish to the grow-out pond).
esshup (and others),
I was asking about much simpler process than that.
I was wondering if you partially seined after X days with no sorting, and moved over SOME BG presumably containing the bell curve of fish sizes at that age.
FishingRod, I think this has a lot of merit. The challenge, when the fish in grow out are spawned in-situ, will always be just how many are in there? This is important because it tells us what proportion we want to remove. In the beginning this is not an easy answer because the BG will not have reached a food limitation and will be growing at ad libitum consumption rates of growth. Once the BG have crashed the zooplankton and are dependent on feed for growth, then knowing the feed given and the rate of growth, one can estimate populations more reliably. To work, one must have evidence that the amount of food was limiting their growth below potential. When one observes this evidence, a decent estimate of population can be calculated.
If a particular size of fish and a particular number of fish are the goal. It would always be best to enumerate swim ups and stock specific quantities of swim up fry into pre-prepared nursery ponds. They don't say specifically, but I think this is standardization the paper was seeking. First stage of the process was stocking 311,000 fry to grow to 25mm. Second stage is growing 250,000 25mm fingerlings to 50 mm. It doesn't make alot of sense to me to move fish from the first stage to the second one. The population of fry stocked is only a little over what is stocked in the second stage. So, I take this to mean that second stage fish are survivors of first stage and grow-out in the same pond (80% survival).
So if one can control the number of the initial stocking of fry ... then your idea is a very valuable idea. Because the initial number is known, what number and when to remove predetermined numbers of fingerlings can be planned. This would allow one to grow 50,000 3" BG but also to stock up to 200,000 BG of smaller sizes. Keep in mind that 200,000 additional BG would be enough to feed ~238 LMB ad libitum for a year if they are consumed at 1% proportionate weights.
