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

(12.4%) than the entire lot average (6.3%). If true, this indicates that
they were most likely dumped too early to be sufficiently trained to feed.
It is interesting to note that use of the fry sorter necessitated
a delay in the first cleaning of the rearing tanks. The delay was for up
to four days from the time of initial dumping. Initial observation indi-
cated the postponement had a positive effect on fry survival. This hypothe-
sis was further tested by deliberately delaying the first cleaning by three
to four days in all three production lots. Mortality over the test period
was then compared to historical averages for the two species over the past
five or six years (Table 1).
The results were somewhat dramatic; in the case of the brown trout,
mortality in the test lot was 29% lower than a 6-year average. For the fall
rainbows, test lot mortality in one case was 28% lower than a 5-year average.

Table 1. Mortalities

Lot # Run # Sorter Mort. First Cleaning Mort. %Mort. - 1st Inventory
20-82 1
2 280 350 -0.4 (overrun)
3
4 240 240 -2.9
Control N.A. 260 -8.7
21-82 1 65
2 210 72 2.6
3 145
4 105 42 6.0
Control N.A. 100 0.7
22-82 1
2 270 200 12.4
3
4 110 150 7.2
Control N.A. 90 6.3
20-82
Whole
Lot 184 (per tank) -3.1 (overrun)
21-82
Whole 58 (per tank) 1.8
22-82
Whole 210 (per tank) 9.1
Rbw.
Avg. 141 (per tank) 2.5 (N=5 )
Brown
Avg. 105 (per tank) 12.8 (N=6 )
83