8097

• UCREFRP Catalog Number: 8097
• Author: American Fisheries Society.
• Title: Proceedings of the 18th Annual Meeting, Colorado - Wyoming Chapter, American Fisheries Society.
• USFW Year: 1983.
• USFW - Doc Type: March 2-3, 1983.
• Copyright Material: NO

that a light source suspended over the sorter would improve its efficiency,
a bare 300-watt bulb was suspended from an old scale stand. This was used
in part on all lots tested.
Three large production lots of fish were tested, in part, using the
sorter. Lots 20-82 and 21-82 were fall-spawn rainbow, containing 303,000 and
283,000 fish, respectively. Lot 22-82, containing 375,000 brown trout, was
the third lot tested. It is customary that lots of swimup fry at Clark's
Fork are trained first to feed in hatching baskets, and then when sufficient-
ly trained, they are stocked into the hatchery rearing troughs at a rate of
approximately 50,000 fish per tank. For this experiment three rearing tanks
were marked and set aside within each lot. Two of these tanks eventually
contained fry which had been introduced to the sorter; the third was a
control.
Initially the fish in each experimental tank were divided into two
sub-groups. This avoided overcrowding the sorter and allowed the testing
of four dumping dates within each lot of fish. The fry were placed in the
sorter and left to their own devices for a minimum of 24 hours (rainbows)
to 48 hours (some sub-groups of brown trout). Rainbows were dumped at
days 5, 6, 7, and 8 from initial feeding date, and browns at days 10,
11, 12, and 13. Testing of the sorter began on December 25th of 1982, and
the experiment was concluded in February, 1983, when all three test lots had
been inventoried for the first time.

RESULTS

The first test group, lot 20-82 fall rainbow, was sorted as outlined,
except that overhead lighting was not used. Lot 21-82 fall rainbows were
exposed to the additional lighting. Daily observations indicated there
was no apparent advantage to use of the light.
Initially the light was used on the brown trout too, but it became
rather obvious that it had a negative effect. For example the brown trout
fry were repelled strongly by the light, but rather than swim out of the
sorter they merely crowded into the deepest portion. After 24 hours, most of
the brown trout fry remained in the sorter. Much better results were obtained
1) by eliminating the additional lighting, and 2) by allowing 48 hours in
the sorter before further handling. When this was done, the sorter's per-
formance was comparable to that experienced with the two rainbow groups.
After each group of fry was introduced to the sorter and the appropriate
waiting period passed, cripples and mortalities were counted and removed by
hand with a picking bulb. Any fish remaining in the sorter were then dumped
into the tank with their brethren. On one occasion for each lot of fish,
those individuals remaining in the sorter were placed in a hatching bask~t
and observed for one week. No evidence of inferiority was noticed in any
case, and these individuals were dumped into their respective tanks.
Daily and cumulative mortalities were recorded for each test group,
each control, and for each entire lot. A comparison of these data failed to
show any conclusive differences (Table 1). However, the first test lot of
brown trout, dumped on days 10 and 11, appears to have a larger mortality

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