The Embryonic Development, The Digestive Tract And Digestive Enzymes Of Larval Symphysodon Discus Heckel

Symphysodon discus Heckel has been recognized gradually because of its economic and scientific research value.At present,this species is cultured in large scale as ornamental fish in the world.However,the techniques of breed and manufacture of formulated open-mouth starter diet are still problematic.This work tries to understand the underlying physiological mechanism for the unique feeding habit of Symphysodon discus larvae which feeds on surface mucus of parents in early days by observing the development of digestive tract and analyzing the digestive enzymes of larval discus.The embryonic development is described as well in this paper.Different developmental stages after fertilization of Symphysodon discus Heckel were observed under the anatomical microscope.The incubating temperature was 30±1℃and the pH was 5.5.The first cleavage could be seen in 50min after fertilization.It entered the blastula stage in 3h.The fertilized egg entered the gastrula stage in 9h30min.The blastopore closed in 20h.The muscles began throbbing in 32h.The heart beating occurred in 33h10min.The whole incubation lasted about 50 hours.The summation temperature was 1500±50(℃.h).The duration of cleavage stage and the gastrula stage are much shorter than Tilapia nilotica,but the duration of organic development stage is much longer than Tilapia nilotica.The development of the digestive tract of Symphysodon discus Heckel during early life stages was observed.At hatching,the digestive tract did not differentiate.At 3 DAH,a constriction between intestine and rectum that would become the intestine-rectal valve was visible,and at the same time,liver and pancreas could be seen.At 4 DAH,the yolk sac was depleted.At 7 DAH the stomach could be observed,but without stomach gland. The number of the intestine folds and mucus cell increased progressively.At 10 DAH the digestive system were almost completed and at 25 DAH,the morphology and function of digestive system were similar to the adult Symphysodon discus Heckel. The activities of four digestive enzymes in larvae Symphysodon discus Heckel could be detected,but the activity of amylase and acidic protease is very low.The optimum temperature for the amylase is 37℃,and 42℃for the acidic protease,32℃for the alkaline proteases,and 27-37℃for the lipase,respectively.