1. Introduction
The induction of triploidy in salmonid fish has become a valuable tool in the Tasmanian aquaculture industry. In Canada, the production of triploid salmonids has
been proposed to address concerns regarding the environmental impact of domestic Ž
. Ž
. escapees Benfey, 1999 . All-female triploid Atlantic salmon
Salmo salar remain
sexually immature, subsequently energy investment in somatic growth is not hindered by Ž
. metabolic costs of sexual maturation Benfey, 1999 . As a result, somatic growth
continues in triploids and flesh quality is maintained over the period when diploid fish are sexually maturing and undergoing associated reduction in flesh quality. In Tasmania,
all-female triploid Atlantic salmon are routinely used to extend the annual harvest period
Ž .
and thereby improve commercial returns Jungawalla, 1991 . In order to accommodate the extra genetic material, triploid fish are composed of a
smaller number of larger cells, though outwardly the fish cannot be distinguished from natural diploids. Several researchers have called attention to the theoretical problem of
Ž .
carrying out basic metabolic processes in enlarged cells reviewed by Benfey, 1999 . Diffusion processes and receptor binding chemistry, for example, may be affected by the
reduced surface area to volume ratio of enlarged cells. Fish erythrocytes are nucleated and contain the oxygen-binding protein haemoglobin,
which is critical for the delivery of oxygen to metabolising tissues. Triploid salmonids Ž
. possess fewer and larger erythrocytes Benfey and Sutterlin, 1984; Benfey et al., 1984 ,
Ž .
and thus erythrocyte count and haematocrit Hct
measurements are a less useful measure of oxygen carrying capacity than is haemoglobin concentration. Atlantic salmon
Ž .
triploids have lower blood haemoglobin concentration Benfey and Sutterlin, 1984 , although this is not always the case with triploids of other species, including some
Ž .
salmonids Benfey, 1999 . Additional factors affecting blood oxygen transport which might be influenced by
Ž erythrocyte dimensions are the rheological flow characteristics of blood including
. Ž
viscosity and erythrocyte deformability , and blood oxygen affinity notably regulation .
by pH and erythrocyte ATP . These aspects are poorly understood in triploid fish, yet they are likely to be important in regulating oxygen delivery during the stresses imposed
by handling and exercise, confinement, and temperature and oxygen perturbations. It appears that triploid salmonids may be more sensitive to the stresses imposed by
handling and seawater transfer during routine farm management, and suffer higher Ž
mortality rates under sub-optimal environmental conditions Johnson et al., 1986; Quillet .
and Gaignon, 1990; Jungawalla, 1991; Yamamoto and Iida, 1994a; Ojolick et al., 1995 . Therefore, we examined the above-aspects of the blood oxygen transport system with a
view to discerning whether differences in the respiratory component of the stress response might account for higher mortality in triploids. Accordingly, we have subjected
Ž diploid and triploid Atlantic salmon to handling and confinement stress see Pickering,
. 1992 , and compared haematological variables, and the plasma metabolites glucose and
lactate before and after the stress regime. Further, the response of blood oxygen affinity to pH, and the effect of shear rate on blood viscosity, were assessed to evaluate
functional differences, if any, between the two groups.
2. Materials and methods
Kategori