Dear all,
I need to estimate the gut fullness index in order to select which guts
might be included in the analysis and which not, since guts which are
less full would probably contain more thoroughly digested items. If I
can set a (arbitrary?) threshold to the index, I can assume that the
degree of digestion in "sufficiently full" stomachs is negligible. That
is, the gut contents are (frequencies, amount, bulk) representative of
the ingested items.
Therefore, I may be not interested whether the guts' weight is in
general heavier than the ingested food (incidentally, I am not using
weight, but the volume of the food items as a measure of bulk), as soon
as I can assume that the error made during such measurements is "much"
lower than the mean difference between the guts' and the gut contents'
weight.
Of course, another source of bias might be the variation of this
difference with size in the same fish species... e.g. in cases when the
gut is proportionally larger in larger animals.
An alternative would be to simply weigh the gut's content... but it
might be operationally more difficult than weighing the guts.
According to Berg (1979), it is defined as Ir ("indice de repletion" in
Hureau 1969) = ((wt of ingested food / wt of fish) x 100)%
1) since I am working on very small fishes (i.e. difficult to weigh),
could I use the guts' weight as a proxy of the weight of the ingested food?
Then FI = ((wt of dissected gut / wt of fish) x 100)%
2) Is it ok to use fishes fixed in 4% formalin? Wouldn't fixation affect
the weight of gut contents and fish tissues in a differential way? May I
simply ignore this potential effect?
Thank you for any comment, suggestion, criticisms, etc.
Best,
Gianluca
--
Gianluca Polgar Ph.D.
Senior lecturer
Institute of Biological Sciences
Institute of Ocean and Earth Sciences
Faculty of Science, University of Malaya
50603 Kuala Lumpur, Malaysia
Tel.: 017-6223549
Fax (ISB): 03-79674178
e-mail: [email protected]
www.themudskipper.org
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