9338

• UCREFRP Catalog Number: 9338
• Author: Schler, P. J.
• Title: Colorado Pikeminnow Culture Manual.
• USFW Year: 2001.
• USFW - Doc Type: FY92-37,
• Copyright Material: NO

bubble action does not move the eggs.

DISINFECTION

All eggs were disinfected in 100 ppm Wescodyne (1.0-1.6% iodine) for 10 minutes at a pH
of 7.8. Eggs were completely rinsed after treatment.

MEASUREMENTS AND ENUMERATIONS

Gravimetric Method
Use standard procedures as with any species.

Volumetric Method
Use standard procedures as with any species.

Mechanical-J ensorter
A commercial fly counter (Jensorter FCI, Jensorter Inc., Bend, Oregon) designed for counting
walleye and yellow perch fry was experimented with at the FRH for adaptation to counting
pikeminnow eggs and fly. Eggs and fly were placed in a water-filled hopper and graVity-fed through
eight tubes which directed them past eight individual photoelectric cells where each egg or fry was
counted. A total count was displayed on a digital readout. A flow of fresh water was supplied to the
hopper to keep the water level and flow constant. After passing through the counter, eggs and fry
were collected in a container below the counter.

The counter is extremely sensitive and counts any small particle ( ie: air bubbles, egg
membranes, and sand particles) that can pass from the hopper thru a small hole to the photoelectric
cell. Adjusting the photoelectric cells to just count pikeminnow eggs was very time-consuming and
involved a lot of handling of eggs (each cell is adjusted individually for sensitivity). Even though the
eggs were submerged in water, they stuck to the side of the hopper and required constant probing
to force them through the eye to be counted. This can cause damage to the eggs. Hand counts of
eggs were within 1.2 percent of counts by the Jensorter.

Comparisons made between hand counts and the Jensorter showed a difference of7.6 percent
for swim-up fry and 3.7 percent for 21-day-old fry. In most trials, the sorter 'had the higher count.
This was attributed to the extreme sensitivity of the machine and, in all likelihood, counting things .
like' air bubbles. The system worked very well when there was a high density of fry in the hopper.
As the numbers became less in the hopper, it was more difficult and time-consuming to get the
remaining few through the system.

Due to damaging and detrimental effects on eggs and swim-up fry, it is recommended using
this kind of counter only with fry that were 21 days or older.

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