Date: 04 August 1999
From: myrvera@hotmail.com
To: shrimp@onelist.com
QUESTION:
Recently, I entered in the business of maturation labs. This is a new
trend in my country, Ecuador, basically for two reasons. One is the sudden absence (and consequently excessive price) of wild nauplii, and the other one is, of course, the white spot virus. As a result of these happenings, old maturation labs are getting back in the business and new ones are opening everywhere.
Here are a few questions that I strongly hope someone can give
me an idea about how to solve.
1.- Last night, from 8 "mothers", I got this morning two million eggs. This gives me a rate of 250,000 eggs per mother, which is good (at local standards). However, the fertility percentage is merely 43% in average, with 2 mothers giving me a rate as low as 5%! We tried selecting the best males, since we don't work with copulation, just with insemination. What causes this low fertility?
2.- From 600 mothers, I don't seem to harvest more than 15 every day for insemination. That is only a 2.5% per day, when the normal is 4-5% per day. The reason might be in the way I feed them, but I found discrepancies in people regarding what is the right combination of proteins, fatty acids, etc. that promote maturation.
3.- I've heard that the best way to attack the WSSV virus is at the early
stages of the nauplii with the proper care and washing. What would be the best methodology and what elements (formol, iode, etc.) should we use to accomplish a virus free nauplii?
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COMMENTS 1:
FERTILITY:
If your average % egg fertilization remains low then this could be due to problems related to water quality. Ask your neighbour if he has experienced the same recently. If he does, then the problem may come with the intake water and you can use a higher EDTA dosage in your spawning tanks to chelate heavy metals: try 15 ppm.
If your average is low only because of the poor performance of just a few spawners, then this has got to do with a high variability within your system. Find out why: The spawners? The technique you use for A.I.? ...
MATURATION FREQUENCY:
The frequencies that you have reported are low indeed. There can be many reasons for that, but if I assume that you are working under good conditions (or at least similar as elsewhere in Ecuador), then I would not be surprised if you are obtaining high mortalities among your spawner? There may be a disease problem... .
As you mentioned yourself, food is a crucial factor here and the
nutritional requirements are not quite known. However, most hatcheries do not encounter serious problems when feeding the typical diet consisting of frozen feeds: squid, bloodworm and enriched Artemia biomass. Some use small amounts of mussel, oyster, krill, and other fresh feed. Many hatcheries suplement with artificial diets: Breed(R) (INVE Aquaculture), Mad Mac(R) and Higashimaru(R) are locally available and I have heard good critics about them. There are other dry diets as well.
NAUPLII DISINFECTION:
We still recommend deIinfecting with iodine (1 ppm for 30 sec to 1 minute) and thorough washing of eggs and nauplii. Provide strong aeration during disinfection. Argentyne(R) is one of the products available on the market, and requires a 100 ppm concentration as it has 1% active product.
That would be 1 ml for every 10 liter of water. At least, that is what we
have been using routinely in our maturation lab.
The "official" recommendations with respect to WSSV are the following:
- collect eggs/nauplii
- wash for 1 to 2 min with seawater
- wash with 100 ppm formaline for 30 sec
- wash with 20 ppm iodine for 30 sec
- wash with seawater for 1 to 2 minutes
Roeland Wouters
Fundacion CENAIM-ESPOL
Casilla 0901 4519, Guayaquil, Ecuador
Tel. 593-4-916118/9, Fax. 593-4-916120
rwouters@cenaim.espol.edu.ec
cenaim@espol.edu.ec
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COMMENTS 2:
We put together a system some four years ago that is mostly closed when it has to be (biofiltration). This system has been in the +7%-12% per night spawning. The results were unanticipated since we sized the maturation modules based upon average spawning rates experienced in Ecuador. The other thing that did not make sense was that if hormones retained in the system was the cause for the better performance, why did not the biofiltration take care of this as well?
The system is in Central America and is 200 tons in four modules, each module with four maturation tanks. We extended this system concept to a broodstock growout facility as well for the option of biosecurity.
In practice, the closed system runs with a low exchange most of the
time (client philosophy) and at maximum during the rainy season.
During this time, we put on a salinity concentrator to maintain
constant salinity levels.
Leland Lai
Aquafauna Bio-Marine, Inc.
e-mail: lelandlai@aquafauna.com