DEFORMITIES IN SHRIMP LARVAE
From: "Aedrian Ortiz" <aedrianortiz@hotmail.com>
To: shrimp@egroups.com
Date: 16 Nov 2000
QUESTION:
I am working in the maturity department in a hatchery in Mexico and I am
having some problems with my nauplii production. My water quality is
very poor but I am working on that, the problem I have is that the N2 that
I am producing have a lot of deformities in the zoeas and do not want to
eat when they change into zoea I.
I am using 10 ppm of EDTA in the reservoir.
Aedrian Ortiz
****************
COMMENTS 1:
I can't help with the deformity problem but I can help with "Zoea
Syndrome" issue. My company produces a strain of Tetraselmis
microalgae that is very effective in stimulating the feeding of marine
organisms. It works equally well with shrimp, rotifers, copepods, fish,
corals, bivalve shellfish, and other filter feeders. The algae
contain amino acids that give animals "the munchies". It
is currently being used by many of the shrimp hatcheries in Ecuador.
In a test at one of the hatcheries we saw a tank that was suffering from
zoea syndrome start feeding and fill their gut in less than 1/2 hour after
the Tetraselmis was introduced. The survival rate afterwards was >
85%.
If you are interested you can find more information on our website at
www.instant-algae.com.
Randy Reed
E-mail : aquamail@seafarm.com
***************
COMMENTS 2 :
There are a number of problems that can cause deformities in shrimp
larvae. Apparently you suspect a heavy metal problem, and are therefore
treating with a fairly high concentration of EDTA (10 ppm).
High EDTA concentrations can be toxic to shrimp larvae, although at 10 ppm
I doubt that is your problem. Still, you might cut back to 5 ppm just to
see if that has any impact. I routinely use 7 ppm of EDTA in my
system.
You haven't mentioned what other water treatment procedures you are
using. If you are chlorinating, residual chlorine can be toxic to shrimp
nauplii. Chlorine can react with proteins in the water to form toxic
chemicals called chloramines. Also, sodium thiosulfate, which
is used to neutralize residual chlorine, is known to cause deformities in
shrimp larvae. I think chlorine is a useful water treatment for
hatchery water when used cautiously. Avoid treaments of more than 3
ppm and be sure to allow the chlorine time to dissipate naturally.
I sometimes will use a tiny amount of thiosulfate (about 0.25 ppm) to
neutralize any residual chlorine after I have given the water 24 hours for
the chlorine to dissipate.
Another potential cause of deformities in the nauplii is broodstock
with Vibrio infections. If it is determined that your broodstock are
infected, you can treat them with a medicated feed for 7-10 days.
It is important to determine before attempting such a treatment what
antibiotic the bacteria infecting the broodstock is sensitive to.
Nauplii produced during the treatment period and for one week after the
treatment should be discarded. Rotating in new broodstock is an
alternative to antibiotic treatment. But the bacterial infection is
probably due to poor water quality in the maturation tanks. Make
sure your staff is doing a good job of removing uneaten feed. If you
are recycling the water in the maturation system, a foam fractionater will
help keep dissolved organics to a minimum, and a good UV sterilizer
will help reduce bacterial loads.
Peter Van Wyk
Aquaculture Division
Harbor Branch Oceanographic Institution
5600 Highway U.S. 1 North
Ft. Pierce, FL 34946
Tel: 561-465-2400 x353 Fax:561-466-6590
E-mail: vanwyk@hboi.edu
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