Rates of oxygen consumption and tolerance of hypoxia and desiccation in Chinese black sleeper(Bostrichthys sinensis)and mudskipper(Boleophthalmus pectinirostris)embryos

The rates of oxygen consumption, tolerance of hypoxia and desiccation of the Chinese black sleeper （ Bostrichthys sinensis） and mudskipper （Boleophthalmus pectinirostris） embryos were investigated. The pattern of oxygen consumption of the Chinese black sleeper embryos was similar to that of the mudskipper ones. The lowest rates of oxygen consumption [ （ 1.65 ±0. 66） nmol/ （ind. ·h） ] of the Chinese black sleeper embryos 16 h after fertilization and the lowest rates of oxygen consumption [ （0.79± 0.08 ）nmolf（ ind. · h） ] of the mudskipper embryos 6 h after fertilization were recorded, respectively. Then the rates of oxygen consumption of these two species embryos increased gradually until hatching [ （8.26 ± 1.70 ） nmolf（ ind.· h） in the Chinese black sleeper, （2.69 ± 0.23 ）nmolf（ ind. · h） in mudskipper]. After exposure to hypoxia water （0.16 mg/dm^3）, bradycardia of the embryos occurred in both the Chinese black sleeper and the mudskipper. However, the Chinese black sleeper embryos survived approximately 45 min longer than the mudskipper ones. After exposure to desiccation at a relative humidity of 58%, bradycardia of the embryos was observed in both the Chinese black sleeper and the mudskipper, and the Chinese black sleeper embryos lived approximately 9 min longer than the mudskipper ones.

Digestive enzyme activities in mudskipper Boleophthalmus pectinirostris and Chinese black sleeper Bostrichthys sinensis

The mudskipper Boleophthalmus pectinirostris and Chinese black sleeper Bostrichthys sinensis occupy the intertidal zone.However,both species have their own unique diet.The former is an herbivore and the latter is a carnivore.In order to reveal the relationship between digestive enzyme activities and diets in the two species,the activities of protease(P),non-specific bile salt-activated lipase(BAL) and α-amylase(A) were determined in the stomach and intestine of adult mudskipper B.pectinirostris and Chinese black sleeper B.sinensis.The results showed that the activities of protease,BAL and α-amylase in the intestine of B.pectinirostris were significantly(P<0.05) higher than those in the stomach.In B.sinensis,gastric protease activity was not different from the intestinal protease(P>0.05),while BAL and α-amylase activities of the intestine were significantly(P<0.05) higher than those of the stomach.The activity of gastric protease in B.sinensis was significantly(P<0.05) higher than that in B.pectinirostris,while the activities of intestinal protease were not different between the two fish species(P>0.05).BAL activities of the stomach and intestine in B.sinensis were significantly(P<0.05) higher than those in B.pectinirostris,while α-amylase activities of the stomach and intestine in B.pectinirostris were significantly(P<0.05) higher than those in B.sinensis.The ratios of P/BAL,A/P and A/BAL of the digestive tract in B.pectinirostris were 1.5,107.3 and 158.6,respectively;and those in B.sinensis were 0.2,1.6 and 0.2,respectively.It can be concluded that food digestion in the adult B.pectinirostris is mainly carried out in the intestine,whereas in the adult B.sinensis it is initiated in the stomach and finishes in the intestine.The activities of BAL and α-amylase in B.pectinirostris and B.sinensis are well correlated with their diets.However,a clear-cut correlation between protease activity and diets is not found in these two species.