Study On The Characteristics Of Reproduction And Molting In Neocaridina Denticulata Sinensis

Neocaridina denticulata sinensis, shrimps of small size and a short reproductive cycle,are not only important freshwater shrimps, but also good material for this research ofecological, physiology and toxicology. To research the biological zeros point and effectiveaccumulated temperature of the shrimp is helpful to understand its breeding season andannual generations, and it is an important basic work for further research on the reproductivebiology characteristics and experimental study. For proper growth and developmentcrustaceans need to shed their exoskeletons periodically, the study of which is an importantprecondition for study of the physiology and biochemistry of these edible animals. Theobjective of this study is to identify the shrimp N. denticulata sinensis the sequence ofmolt-cycle stages, to be used as a reference for the characteristics of Y-organ structure,exoskeleton structure and ecdysteroid levels in molting stages.This paper studies the development period, biological zeros point and effectiveaccumulated temperature of parental and offspring shrimp in embryonic development. Basedon the morphological observation, the molting cycle was divided in detail. Using paraffinsection technique, the change of the exoskeleton and Y-organ in N. denticulata sinensis wereobserved during the molt stages. As measured by ELISA, this research explores the featuresof changes in the hemolymph ecdysteroid levels during the molt cycle of N. denticulatasinensis. The following consequences were obtained in the study:At room temperature, the biological zeros point of N. denticulata sinensis in embryonic was7.07℃, and the effective accumulated temperature was358.58℃·d. The embryonicdevelopment period was with an average of (44.64±2.98) d and the time was (2.40±1.24) dfrom the first larvae hatched to all larvae hatched under12-22℃when the embryonicdevelopment period was with an average of (17±3.31) d and the time was (2.77±2.17) d fromthe first larvae hatched to all larvae hatched under26-30℃.Using the structural changes of the telson and applying Drach’s classification system, fourmolting periods (postmolt, intermolt, premolt and ecdysis) were divided for the molt cycle of N. denticulata sinensis. We identified five periods (C, D0-1, D2-4, E and A-B) in the molt cycleof N. denticulata sinensis. The construction of the integument of N. denticulata sinensis waschanged periodically. The epicuticle was synthesized before molt, and the endocuticle andexocuticle layer were synthesized after molt. The exoskeleton was most hard during theintermolt stage. The cells of YO have different shapes, and their sizes vary greatly in A-Bstage, and the diameter of nucleus was an average of (4.68±0.61) μm; the diameter of cellnucleus in C stage was an average of (4.46±0.42) μm, many inter-lobular spaces wereobserved at this stage; the cytoplasm started to increase in size at early premolt D0-1about(7.42±1.35) μm(p<0.05), reaching the maximum(8.32±1.15) μm(p<0.05) at D2-4stages whenno inter-lobular space was seen any longer, more and more Y-organ cell cords were observed.As measured by Elisa, the ecdysteroid levels increased during the A-B stages, peaked in thepremolt D2-4stage (p<0.05).