Biochemical composition and digestive enzyme activities during the embryonic development of the redclaw crayfish, Cherax quadricarinatus

The biochemical composition and the activity of five digestive enzymes of embryos were studied during embryonic development in the redclaw crayfish, Cherax quadricarinatus (Von Martens, 1868), in order to investigate the relationship between embryonic development and the utilization of yolk. Carbohydrates remained a minor constituent of the yolk as a whole. The contents of total proteins and total amino acids (TAA) were all observed to decrease. Among the essential amino acids (EAA), the contents of leucine and arginine were relatively high, while of the non-essential amino acids (NEAA), the most important components were glutamine and aspartic acid. The contents of total lipids (TL) decreased during embryonic development, and the predominant fatty acids of both neutral lipids (NL) and polar lipids (PL) were C16:0, C18:0, C18:1ω9, and C18:3ω3. The five digestive enzymes tested all showed changes in their activities. The specific activities of pepsin and trypsin gradually increased in the earlier stages of embryonic development, pepsin decreased rapidly in later stages, while trypsin still kept a high level of activity. The specific activity of amylase changed in a "V" shape and reached high values again in later stages. The specific activities of cellulase and lipase showed relatively low values. It is shown that carbohydrates may play an important role in synthesizing many specific compounds to participate in signal transmission and in forming the carapace. Proteins and lipids were the dominating construction and energy substances; proteins were primarily consumed in the early stages, as against lipids in later stages. Saturated fatty acids (SFA) (16:0 and 18:0) and monounsaturated fatty acids (MUFA) (16:1ω7 and 18:1ω9) were always used for energetic purposes and polyunsaturated fatty acids (PUFA) (20:5ω3 and 22:6ω3) were important as structural components of cell membranes and in the development of the central nervous system. The activities of the digestive enzymes were controlled by their genes and expressed sequentially during embryonic development. They hydrolyse the yolk and provide construction substances and energy sources for the formation of tissues, organs, and various systems in general.