1 NOVEMBER 1999
Date: 21 Sep 1999
From: Kostas Yannakopoulos <kyannako@otenet.gr>
To: AQUA-L@killick.ifmt.nf.ca
QUESTION:
I am particularly interested in what causes the absence of the swim bladder or the loss of it (if that can happen) during early juvenile stages. My specific problem has to do with stocks of sea bream (juveniles) that are found to have a high percentage of fish with no swim bladder, when samples from the same stocks taken during their larval development had showed considerable lower percentages of no bladder fish.
Kostas Yannakopoulos
Evia, Greece
mailto:kyannako@otenet.gr
ICQ : 181940
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COMMENTS 1:
This was a common problem with sea bass in the early 80's and it has to do with filling of the swim bladder in the larval stage. The effects become visible at a much later stage when you get so called "hockey stick fish". The problem has been solved in the late 80's by Portuguese scientists. They filtered the top layer of the larval rearing tanks to get rid of the oil film
Gertjan de Graaf
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COMMENTS 2 :
Non-inflation of the swimbladder was a persistent problem in intensive
culture of the freshwater larvae Stizostedion vitreum (common name walleye or pickerel in N. America) resulting in very high mortality. These larvae have a finite biological window in which to initiate swim bladder filling (5-10 d post hatch at 16-18C), after which time the pneumatic duct closes. It seems that the problems relating to non-inflation are linked to the oil layer from commercial feeds that rise to the water surface. This oil layer restricts the ability of the larvae to effectively ingest air bubbles to initiate swimbladder inflation. Dr R. Summerfelt (Iowa State University) and others have successfully overcome this problem by installing a water jet on the tanks that acts to break the oil layer, thus providing access to the water surface. We have used this system effectively in our culture tanks and observed very high percentages of gas bladder inflation.
For details on the subject, there is a Walleye Culture Manual available
that is quite comprehensive- it is available through the North Central
Regional Aquaculture Center and is published through Iowa State University Extension Distribution at (515) 294-5247.
Grant Vandenberg
Dépt des science animales
Pavillon Paul-Comtois
Université Laval
Ste-Foy, QC, G1K 7P4
Canada
Tel: 418.656.2131 poste 4043
Fax: 418.656.3766
Home: 418.878.4998
E-mail : Grant.Vandenberg@san.ulaval.ca
E-mail (home) : gjl3@globetrotter.net