AGGRESSION IN SEA BASS JUVENILES
From: Dave Cox dave@fishvet.co.uk
To: AQUA-L AQUA-L@killick.ifmt.nf.ca
Sent: June 13, 2000
QUESTION:
Does anyone have any experience of any techniques for reducing
aggression in juvenile sea bass?
I have heard of using different light wavelengths, green, as a
technique to reduce dorsal fin nipping in salmon.
Thanks in advance,
David Cox
Fish Vet group
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COMMENTS 1:
Although I have no direct experience in reducing aggression in sea bass, I have noticed that with other species (salmon and trout), the aggression is usually a result of cumulative stresses acting on the fish. The reduction of some of these stresses results in a marked decrease in the aggression. By its very nature, intensive aquaculture is going to impose a degree of stress on the fish, however there are other stressors such as water quality (oxygen, CO2 etc.) that we can do something about. In many systems I have worked with, simply adding oxygen to the water to maintain levels in the region of 85 - 95% in the tank, have caused an elimination of nipping and biting. We have also noticed that attention paid to light has an effect, not so much in the wavelengths, as we have not carried out any work in this, but with fading the lights up and down, rather than a sudden on/off, also causes a reduction in the overall stress level and the subsequent aggressive behaviour.
Bob Bawden Aqua Systems (UK)
Ltd Crossford Mill
Johnstone
Scotland, UK
Tel 01505 702217
Fax 01505 703155
e-mail bob@aquasystems.co.uk
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COMMENTS 2:
I have a friend (Joma S. deGuzman) who was commercially raising tropical groupers and sea bass in the Philippines up until 1995 or so. He got out of the business at that time because the estuary he was working in experienced a series of hypoxic events probably due to establishment of too many milkfish pens close by. He used floating (about 8 m³ each) net pens holding upwards of 4 fish/m³ or more for juveniles and was successful at growing fish to marketable size in less than a year. Early on (in the early to mid-80s) he used car tires with cut-out holes suspended into the net pens as 'hides' according to the prescription coming out of Malaysia (Teng, S.-K. and Chua,T.-E. 1979). Use of artificial hides to increase the stocking density and production of estuary grouper, Epinephelus salmoides Maxwell, reared in floating net cages. Aquaculture 16:219-232). But Joma abandoned the tires when he found that increasing the stocking density and using frequent (labour intensive) size grading of the fish worked to cut down on aggressive behaviour. This seems to fly in the face of a lot of conventional wisdom, but from what I could see he was pretty successful. He might have more info if you contact him directly "Joma deGuzman" joma@asiahrnet.net .
Michael A. Rice, PhD Professor & Chairman
Department of Fisheries, Animal & Veterinary Science
University of Rhode Island
Kingston, RI 02881 USA
tel. (401)874-2943 fax. (401)874-4017
e-mail. rice@uri.edu