Available data are rather scant as to other
possible contamination sources, the magnitude
of contamination expressed as volume fraction,
and the importance of sample volume on
its composition. Furthermore, no direct comparison
between CT and CVP seems to have
been published. Although CT most probably
leads to greater contamination than CVP, it is of
interest to know to what extent, since CT may
be preferred when small fish are sampled.
It is now established that teleosts possess
a secondary circulatory system connected to
the primary circulatory system at both arterial
and venous poles. In the rainbow trout, Uncorhynchus
mykiss, the volume of the secondary
circulatory system is approximately I .5-fold
that of the primary circulatory system (see
review by Steffensen and Lomholt, 1992).
According to the descriptions of Harder (1975)
and Satchel1 (1992), secondary blood from the
caudal peduncle is drained by cutaneous and
deep veins which communicate cranially with
several sinuses. Consideration of the contribution
of secondary blood to the sample thus
appears to be of importance.
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