Effects of sex on characteristics and expression levels of digestive enzymes in the adult guppy Poecilia reticulata

Background: Characteristics (pH 2 to 12 and temperature of 25 degrees C to 80 degrees 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 degrees C for acidic amylase, pH 7 at 55 degrees C for neutral amylase, pH 11 at 50 degrees C for alkaline amylase, pH 7 at 30 degrees C to 35 degrees C for lipase, pH 2 at 55 degrees C for acidic protease, pH 9 at 45 degrees C for alkaline protease, pH 8 at 50 degrees C for trypsin, and pH 9 at 50 degrees 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.