Date: 27 October 1998
From: Bradley.Crear@dpiwe.tas.gov.au
To: AQUA-L@killick.ifmt.nf.ca
QUESTION:
Has anyone out there encountered problems with sudden increases in
mortality in rotifer cultures that were previously OK?
During the pre-boosting and post-boosting wash procedures (including a 5 minute freshwater wash) I am experiencing higher than usual mortality. We normally expect low mortality due to mechanical damage during wash, around 10-15%. After the wash the majority of rotifers is left to settle with no aeration, sink and attach to the bottom of the container; a proportion of these are obviously dead. The remaining rotifers from the initial harvest that are still swimming (10-20%) are very slow moving and sluggish.
Species - Brachionus plicatilis - type L
Culture method:
- semi-continuous
- fed compressed bakers yeast at the rate of 0.6 grams of yeast / 1 million rotifers
- regular input of Tetraselmis suecica
- regular water exchange
- salinity range of 22 - 26 ppt.
- temp. 21 degrees
- culture density is maintained at 350 rotifers / ml approx., with
densities reaching 500 + / ml between maintenance routines.
The cultures seem healthy and the high productivity at present would
indicate that this is the case. There is some degree of ciliate
contamination.
Even though the cultures are very productive, I suspect the rotifers are
weak for some reason and can not cope with the stress of the rinsing
procedures. Has anyone else encountered this problem and if so can they shed some light on the problem and possible causes?
Tasmanian Aquaculture & Fisheries Institute, Taroona.
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COMMENTS 1:
Take care with the ratio of yeast, could be so much for a 500 rot/ml density. I remember that I used a maximum of 0.04 mg/L day of yeast, and a minimum of 0.02 mg/l day (actually I am not sure if it was mg or gr) for a starter density between 80 to 100 rot/ml. If I use more yeast, then always I had problems in raising rotifers, and therefore bad production. I tested this in batch, semicontinuous and recirculating systems; vessels of 500 L, without any algae added.
Other information provided by you is quite similar to my personal data.
Which kind or ciliate do you have? I found if you have more than 3000 ciliates/mL, it causes some problems in the production of rotifers, but over 5000 cil/mL always my cultures were going down.
My regular maximum density of rotifer using bread yeast was 300 rot/ml in batch system, 500 rot/ml in semicontinuous system and 700 rot/ml in recirculating systems.
German E. Merino
Aquacultural Engineer
Department of Biological and Agricultural Engineering
University of California, Davis
Davis, CA 95616, USA
email: gemerino@ucdavis.edu
Phone-USA: (530) 752-0821
Fax-USA: (530) 752-2640
---------
Departamento de Acuacultura
Universidad Catolica del Norte
P.O. Box 117, Coquimbo, CHILE
email: gmerino@nevados.cecun.ucn.cl
Telefono: (56-51) 209765
Fax: (56-51) 209759
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COMMENTS 2:
We have several research project underway using an artificial diet called RotiMac. This has been able to replace most all
microalgae, maintain good reproduction, balanced female/male ratios, and multiple egg production per female.
Consistent production of the rotifer population may be related to the consistency of nutrient package which for most is microalgae cultures.
Leland Lai
Aquafauna Bio-Marine, Inc.
AQUAFAUNA.BIO-MARINE@postoffice.worldnet.att.net
***************
COMMENTS 3:
There are in literature backwash systems described for Japanese
researchers, and recently was presented in 'Aquaculture and water fish
culture, shellfish culture and water usage' abstracts of a meeting held in France at the beginning of this month. This last one was presented by P. Sorgeloos from Belgium, you sure had been heard something about his work, mainly in Artemia.
You could put inside the reactor culture a mesh between 50 to 80 um with big screen area, so the rotifers and neonats could be maintained inside the vessels, and the debris, including protozoa are removed continuously, then put several microscreen systems (say 10, 5 and 1
um), then some foam fractionator, then UV systems, then a biofilter and that all. If you feel comfortable with the procedures for design this closed culture system, then go ahead!
> We also have problem with ciliates as Uronema and Euplotis. Especially, when fed with Tetraselmis chui and baker's yeast (0.5-1g/one million rotifers) at 28 C, 25ppt salinity. And if we can provide microalgae, the rotifer activity always is in good condition, but bad when continuously fed with only yeast or Culture Selco.
I believe that the problems are those ciliates, the same that I had in my
systems. Sometimes I also find some vorticellas (also dangerous).
Independent of the type of feeding, if you have Uronema and Euplotes they both could screw up all your culture, dependent of the concentrations. Usually the rotifers look healthy, but suddenly you see them with a lot of this Euplotes riding over them, that interferes with the swimming of the rotifers, and that is a signal of problems. I guess that you see two kinds of Euplotes, a little one and a big one (size like a rotifer egg). This last one does not cause problems, and it is a good idea to keep together in culture, but the little one is dangerous. Actually I am not sure if these protozoa are the main problem or something related with them, because I also found huge quantities of bacteria (Vibrio) when the little Euplotes was present in culture, but I do not find the same when the big one was present.
German E. Merino <gemerino@ucdavis.edu>