Study On The Ontogenetic Development Of The Digestive System And Feeding Biology In Pikeperch(Sander Lucioperca) Larvae

Pikeperch(Sander lucioperca) has become an important aquacultural and fishing sport fish in the world. High mortalities during the larval stage and weaning time have hindered the pikeperch culture industry. In this study, through researches on Point of No Return(PNR), ontogenetic development of digestive morphology and functionality of larval pikeperch and prey matching strategy during adult pikeperch culture. Such information will surely provide valuable theoretical basis for pikeperch cultivation.1. Early growth and Point of No Return of Pikeperch(Sander Lucioperca) LarvaeArtificial propagation of pikeperch( Sander lucioperca) was performed at15±2℃.Yolk sac absorption, oil globule absorption, larval growth and the first initial feeding rate were observed to analyze the early development and to determine the Point of No Return(PNR) of pikeperch larvae. Results are as follows: After the exhaustion of the yolk sac and oil globule from 14 DAH, growth difference appeared between the control group and the starvation group. There was no significant difference in the yolk sac volume(VY) and oil globule volume(Vog) between control and starvation groups on each day. During the mixed nourishment stage, which lasted for 4-5 days, larvae consumed the oil globule. Initial feeding began at day 8 after hatching(DAH) and reached a maximum initial feeding rate of 82.7% at 14 DAH. The point of No Return appeared to occur during 15-16 DAH; and at a water temperature of 15±2℃, the earliest feeding time for pikeperch larvae is 8 DAH, If the first feeding is later than 15 DAH, the pikeperch larvae will entered the PNR,which may result inmass motality.2. Ontogenetic development of digestive system in pikeperch(Sander lucioperca) larvaeOntogenetic development of the digestive system in pikeperch( Sander lucioperca)larvae was histologically and enzymatically analyzed from hatching to 60 day after hatching(DAH). The development of digestive system in pikeperch larvae can be divided into three phases: phase I started from hatching to exogenous feeding(8DAH); phase II started from first feeding and ended at the formation of gastric glands(30 DAH); phase III started from the appearance of gastric glands to the appearance of pyloric caeca(60 DAH). The specific activities of amylase and lipase were firstly detected since 2 DAH and 40 DAH respectively, with low level till the end of this study. The specific activity of pepsin was first detected at 14 DAH and showed a sharp increasing trend up from 30 DAH. The composition of digestive enzymes indicates that larvae are able to digest protein, lipid and carbohydrate at early stages,and the higher requirements for protein in the feed. The appropriate weaning time for pikeperch larvae is recommended from 30 DAH(Total length 15.6mm).3. Prey fish matching strategy for adult pikeperch cultureThe gape width determines the carnivorous fishes’ choice of prey fish specifications. Morphological measurement of gape widths and total length of pikeperch as well as the total lengths and body depths of silver carp(Hypophthalmichthys molitrix), grass carp(Ctenopharyngodon idellus), gold crucian carp(carassius auratus), mrigal carp(Cirrhina mrigola)and Squaliobarbus curriculus were made. Based on the traditional foraging theory that animals should maximize their net rate of energy return when selecting prey, regression analysis was used to search for the optimum prey fish for different-sized pikeperch. Results are as follow:Silver carp is the optimum prey fish when the total length of pikeperch is less than 47.9mm, as well as the total length of silver carp is less than 24.3 mm. Mrigal carp is the optimum prey fish when the total length of pikeperch between 47.9 mm and 185.3 mm and the total length of mrigal carp is less than 87.3 mm. S. curriculus is the optimumprey fish when the total length of pikeperch is more than 185.3 mm. Being with S.curriculus as main prey fish species, supplemented with silver carp, gold crucian carp according to seasonal balance is the appropriate prey fish matching scheme during pikeperch culture.4. The effects of artificial feed and prey fish on condition factor,hepatosmatic index, liver histological structure and composition of fatty acids in muscle and liver of pikeperch(Sander lucioperca)The experiment was conducted to study the effects of artificial feed(AF) and prey fish(PF) on condition factor, hepatosmatic index, liver histological structure and composition and content of fatty acids in muscle and liver of pikeperch. The results showed that: The condition factor of pikeperch(PF) was significantly higher than pikeperch(AF). Whereas, the hepatosmatic index of pikeperch(AF) was significantly higher than the pikeperch(PF). Tissue section analysis showed that the pikeperch(AF)liver cells appeared nutritional fatty liver symptoms: arranged disorderly, vacuolated and the nucleus offset. On the contrary, the pikeperch(PF) liver cells were arranged compactly and the nucleus was located in the central cell. 21 kinds of fatty acids were detected in muscle and liver of pikeperch AF and PF. The highest content of fatty acids in muscle was saturated fatty acid in pikeperch(AF) and pikeperch(PF), 69.2 % and59.8 % respectively. Compared with the pikeperch(AF), the proportion of saturated fatty acids(SFA) in the pikeperch(PF) liver declined significantly, whereas the proportions of unsaturated fatty acids especially the polyunsaturated fatty acids(PUFA), increased significantly.