Accurate measurement of fish produced is essential before the production or efficiency of hatcheries can be compared or evaluated correctly. Where large numbers of fish are liberated, a system of weighing offers an easy and accurate method. Precautions are necessary to assure accurate representative samples of the fish being counted. Large errors occur if seine samples from ponds are depended upon as average samples. Most accurate results are obtained when fish are seined into holding pens and 5‐ to 10‐pound samples of each 100‐pound load of fish are counted. Invisible losses occasioned by cannibalism, predators and unseen escapement often are unexpectedly high. Even when a very accurate record is maintained of all observed losses, the number of fish weighed out of the ponds is much less than hatchery records indicate. Conditioning of the fish before hauling is desirable when long truck hauls are necessary. This may be done by not feeding them for 24 to 36 hours. Losses occasioned by overloading or oxygen shortage may not occur until several days after planting. Such losses depend to a large degree on the physiological condition of the fish when they are removed from the hatchery.