COUNTING pl
From: Steve Costomiris steve11@eudoramail.com
To: shrimp@yahoogroups.com
Sent: 22 May 2002
QUESTION:
When PL are being dispersed or acquired, how is the
quantity estimated generally?
Steve Costomiris
Los Angeles
e-mail:
steve11@eudoramail.com
***************
COMMENTS 1 :
If it is wild seed, you first determine what
percentage is really the species you want. Then you check the condition of
the larvae. For both you set percentage points that you will deduct from the
total count to follow.
Stir the water with the animals well by hand. Than
take 3-5 samples with a 200 ml
beaker (some say 500 ml is better) at different depth in the tank, holding
the beaker open-end down when immerging,
until the "test-depth" is reached, then turn to let water
and animals flow in.
Pour out the contents of the beaker and count the animals as they pass the
sprout of your beaker.
Jot down the numbers and divide the total by the numbers of samples you have
counted. This is your average amount of animals in that tank (roughly)
referred to the volume of your beaker used.
Now set this into relation to the total volume of the tank and you can come
up with a fairly nice number.
If it is hatchery stock, you can normally rely on what those people
tell you they have sent. Better anyhow to check on arrival because of
mortality in transport.
Or buy an electronic counting device that’ll cost you.
If you are buying off-the-shore wild larvae I strongly recommend carrying a
Stereoscope.
The results however are exelent. We are now working on getting the
resolution down to PL 1 or even Nauplii. This is an in-house project and not
intented for sale. If you are interested in information about the
companies supplying the basic stuff please contact me off-list.
Burkhard
e-mail: mantenec1@t-online.de
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COMMENTS 2:
There are at least two companies with opto electronic units capable of counting 10 mg pl's. The Vakki unit is distributed by Sterner and manufactured in Norway. The unit has changed names at least once, but at one time was called the 2500 and then the Biomass unit. It may be expensive (relative to counting by hand), but it is fast and gives information about the size of the individual animals and can give you complete distribution information. If you "train" the unit to recognize body weight vs body length relationships, it even gives you weight distributions. It can be coupled to any 2" pipe and is capable of externally controlling a solenoid to stop or redirect flow. Just set 10,000 and it will stop when it gets there. We have borrowed a unit and found it to be better than 97% accurate with pl12 animals. We transfer one gram animals from the nursery, the accuracy of the unit at this average size is excellent with 99% accuracy on count, along with length and weight dispersity measurements. I'm aware of at least two shrimp farms that use them routinely.
Rod McNeil
e-mail: mcneilrj@digisys.net