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Vol. 52, 2013
Effects of sex on characteristics and expression levels of
digestive enzymes in the adult guppy Poecilia
reticulata
Karun
Thongprajukaew1,2* and Uthaiwan Kovitvadhi2,3
1Department
of Applied Science, Faculty of Science, Prince of Songkla University,
Songkhla 90112, Thailand
2Biochemical Research Unit for Feed Utilization
Assessment, Faculty of Science, Kasetsart University, Bangkok 10900,
Thailand
3Department of Zoology, Faculty of Science, Kasetsart
University, Bangkok 10900, Thailand
Abstract
Background: Characteristics (pH 2
to 12 and temperature of 25°C to 80°C) and expression levels of the
main digestive enzymes, including amylase, lipase, total protease,
trypsin, and chymotrypsin, were investigated in adult male and female
guppies Poecilia reticulata. A completely randomized design was used
during this experiment.
Results: Digestive enzyme studies indicated that
sex had a direct effect on characteristic profiles (n = 3) and expression levels (n = 10) of all digestive enzymes.
The most suitable conditions for studying digestive enzymes in general
were pH 2 at 50°C for acidic amylase, pH 7 at 55°C for neutral amylase,
pH 11 at 50°C for alkaline amylase, pH 7 at 30°C to 35°C for lipase, pH
2 at 55°C for acidic protease, pH 9 at 45°C for alkaline protease, pH 8
at 50°C for trypsin, and pH 9 at 50°C for chymotrypsin, regardless of
sex. Specific activities of amylase, total protease, trypsin, and
chymotrypsin were higher in females than males (p < 0.001), while the specific
activity of lipase was higher in males than females. These findings
were correlated with the higher growth capacity of females than males
(except for lipase), as indicated by differences in body weight (p < 0.001), length (p < 0.001), and the activity
ratio of trypsin (T) to chymotrypsin (C), i.e., the T/C ratio (p < 0.007).
Conclusions: Feeding habits of
adult guppies differed between sexes, as indicated by a difference in
the activity ratio between amylase and trypsin, i.e., the A/T ratio (p < 0.04). Information from
digestive enzyme studies, as well as using optimal conditions of
digestive enzymes to study in vitro nutrient utilization in guppies,
might be important to understand the effects of sex on nutritional
responses.
Key words: Characteristics; Digestive enzymes;
Guppy; Poecilia reticulata; Sex.
*Correspondence: E-mail:
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