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|Title: ||Muscle growth and flesh quality of farmed Atlantic halibut (Hippoglossus hippoglossus) in relation to season of harvest|
|Authors: ||Hagen, Ørjan|
|Supervisors: ||Johnston, Ian A.|
|Keywords: ||Atlantic halibut|
|Issue Date: ||2008|
|Abstract: ||In the present study, muscle growth and flesh quality have been investigated from both commercially farmed Atlantic halibut (Hippoglossus hippoglossus) (Aga marine AS, Norway)and halibut obtained from small-scale trials at Mørkvedbukta Research Station (Bodø
University College, Norway).
Morphometric techniques have been utilized to investigate fast muscle growth in halibut
ranging from circa 2 g to 100 kg, and it was established that fast muscle fibre recruitment ceases when the fish attain approximately 81 and 177 cm, in the case of males and females, respectively. Different muscle fibre types were distinguished using histochemical (myosin ATPase and succinic dehydrogenase) and immunohistochemical (S-58, an antibody against
slow muscle myosin) staining techniques. Females recruit twice as many fast muscle fibres
compared to males, which allows them to reach a larger final size. Furthermore, the seasonal
growth patterns during a one year production cycle in commercial farmed halibut revealed a
winter depression in growth leading to loss of biomass, which was attributed to the maturation
of males. Commercial farmed fish of equal size (~1.5 kg) showed sexual dimorphism of fast
muscle fibre number, caused by a significantly higher rate of fast muscle fibre recruitment in
females. During the winter season fast muscle fibres shrunk significantly, especially in male
fish, as a consequence of loss of appetite, low water temperatures and sexual maturation.
None of the female fish matured during the trial.
Flesh quality of halibut deteriorated during winter and spring, since it had a softer appearance
and significantly lower myotomal protein content, particularly in males. Cathepsin activity
was measured using spectroscopy and showed a strong negative correlation to protein content, displaying a seasonal variation. The proteolytic depletion of fast muscle proteins affected the
water holding capacity of the muscle (determined by centrifugation), which showed
concomitant changes with the increase in cathepsin activity and drop in protein content.
Despite the soft appearance, the firmness (shear force) of the flesh increased during the
winter. The hydroxylysyl pyridinoline cross-link content of the collagen matrix, determined
by HPLC, showed a strong correlation to the fillet texture. The increased firmness during the
winter, a period of little (female) or negative growth (males), was probably due to an
increased cross-linking of the collagen compartment.
Partial sequences of IGF-I and IGF-II were cloned from fast muscle of Atlantic halibut, and
their relative gene expression levels were determined along with those of cathepsin B,
cathepsin D and IGF-IRa in male halibut using qPCR during a fasting and refeeding trial.
Transcript levels of cathepsin B and to some extent cathepsin D were significantly higher
during fasting than refeeding, suggesting an increased enzyme production during periods of
food deprivation. A temporary increase in IGF-I transcripts was observed after 7 days
refeeding suggesting that this growth factor is involved in muscle growth control. Both IGF-
IRa and IGF-II were down-regulated during refeeding.|
|Publisher: ||University of St Andrews|
|Appears in Collections:||Biology Theses|
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