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I received the following message from Sadasivam Kaushik in response to a
posting on another list, and he agreed to let me post it to FISH-SCI as a
continuation of the earlier discussion on the nature of fish faeces.
Bill Silvert
----- Original Message -----
From: "Sadasivam Kaushik" <[log in to unmask]>
To: "William Silvert" <[log in to unmask]>
Sent: Thursday, October 31, 2002 8:51 AM
Subject: RE: Fish Faeces
Hallo
My own experience is that while shrimp emit feces with an external membrane,
most fish do not have any adhesive external membrane. However, as was
already pointed out by Bill, dietary binders do have an effect on fecal
cohesion and the trend these days for many land-based or recirc systems
(where the necessity and facility to remove fecal matter is much easier than
under cage culture conditions) is to try to obtain high fecal stability
through specific dietary binders.
As far as the metabolic or endogenous fecal nitrogen in fish (refecting
mucosal or other endogenous protein degradation), this is somewhere about
100 mg N /100 g dry matter intake (compared to more than 600 mg for instance
in pigs).
Hope this helps
Sachi
=======================================
Dr S.J. Kaushik
Director
Fish Nutrition Lab, INRA-IFREMER &
Unité de Recherches en Hydrobiologie, INRA
64310 Saint-Pée-sur-Nivelle
France
tel : +33 5 59 51 59 90; fax : +33 5 59 54 51 52
e_mail :[log in to unmask]; web : st-pee.inra.fr
=======================================
-----Message d'origine-----
Dr Jonathan Grey wrote:
Can anyone tell me whether fish (and of particular interest - perch)
form a 'membrane' around their faecal matter, and if so what is the
composition of such a membrane? Or is it just mucus from the intestinal
tract? I seem to recall when I was a kid that goldfish trailed strands
of the stuff around behind them as they circled the bowl and it seemed
to be packaged!
And Bill Silvert responded:
I would also like to see an authoritative answer to this. For salmon I have
heard some people say that the faeces are pellets that fall according to
Stoke's Law, while others have observed the faecal matter coming out in the
form of mucosoid strings. It makes a big difference if you are trying to
figure out where the faeces reach the bottom.
It may depend on the fish feed too. In any case, it would be nice to see
whether there is any kind of consensus about this.
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