Studies On Post-embryonic Development Of Qinglong Grouper (Epinephelus Coioides♀×E. Lanceolatus♂) And Histochemistry And Immunohistochemistry Of Digestive Tract In Juveniles

1. Allometric growth of grouper hybrid (Epinephelus coioides♀×E.lanceolatus) larvae and juvenilesWe evaluated the pattern of allometric growth in hybrid Qinglong grouper(Epinephelus coioides (♀)×E. lanceolatus (♂)) during the larval and juvenile stages. Wemeasured the total length, pre-anal length, trunk height, head length, eye diameter,mouth width, the second dorsal fin spine, pelvic fin spine, pectoral fin, anal fin, and tailfin of Qinglong grouper (from hatch to28d) and captured images of each individualusing Q-Capture Pro6. The average total length of newly hatched larvae was1.62±0.26mm. After28d, the total length of juveniles was16.58±1.09mm at a water temperatureof30±1°C and a salinity of28±1ppt. The growth in total length of Qinglong grouperwas divided into three stages. The growth rate during the first, second, and third stageswas0.11mm/d (from hatch to7d),0.37mm/d (from8to21d), and1.51mm/d,respectively. There was a significant difference in the growth rate between larval andjuvenile stages (P<0.05). Some of the organs exhibited allometric growth in earlyontogeny. Head length and trunk height were positively allometric up to the inflexionpoint, then switched to isometric and negatively allometric, respectively. Pre-anal lengthwas characterized by isometric growth and had no inflexion point during the larval andjuvenile stages. The growth in the head (inflexion point at21–22d) and sensory organs(inflexion point at20–21d) was positive up to the inflexion point, then becameisometric and negatively allometric, respectively. The second dorsal fin spine and pelvicfin spine exhibited strong positive allometry at first, before becoming negatively allometric. The inflexion point of the second dorsal fin spine was between20and21d,whereas that of the pelvic fin spine was at17d. The second dorsal fin spine and pelvicfin spine reached a maximum at24d. From hatch to day26, pectoral and tail fin growthwas positively allometric, and their inflexion points were between14and15d, and22and23d, respectively. Anal fin growth was positively allometric and had no inflexionpoint. This pattern of growth results in rapid improvement in swimming ability, therebyallowing individuals to search for food and escape predators. Our results suggest thatthe organs involved in feeding, sensing, and swimming developed most rapidly duringthe early developmental stages in Qinglong grouper. To increase the survival rate ofQinglong grouper during early life stages, it is critical to provide environmentalconditions that account for the priority order of organ development.2. Differentiation of fin during early developmental stages of Qinglonggrouper (E. coioides♀×E. lanceolatus♂)The ontogeny of the fin on larvae of Qinglong grouper (Epinephelus coioides♀×E.lanceolatus♂) during early developmental stages was observed. The development ofthe fin had a vital role on feeding, growth and survival during the larval and juvenilestages. Pectoral fin of Qinglong grouper formed the earliest, and then tail fin, pelvic fin,dorsal fin, anal fin. The3DAH larvae of pectoral fin and tail fin had ability to promoteand maintain body balance. The extension and shrinkage of the pelvic spine and thesecond dorsal spine represented the most apparently changes during the post embryonicdevelopment of Qinglong grouper. The larvae of7DAH appeared pelvic fin spine, andat8DAH appeared the second dorsal fin spine. The second dorsal fin spine and pelvicfin spine reached a maximum at24DAH. The second dorsal spine and pelvic fin spinelength has been contracted by the (5.55±0.11) mm and (4.54±0.32) mm at28DAH.The fins of30DAH were similar to adult: dorsal finⅩ~Ⅺ-15, anal fin Ⅲ-8, pectoralfin18~19, pelvic finⅠ-5, tail fin16~17.3. Studies on post-embryo development of the digestive system ofQinglong grouper (E. coioides♀×E. lanceolatus♂)Using the morphological and histological technology to study the development of digestive system of Qinglong grouper, and described its digestive organs processes andstructure of organization. Studies showed that the digestive system development ofQinglong grouper could be divided into three stages: the endogenous vegetative stage(0to3DAH), the larvae completely relied onthe yolksac, and didn’t have the feeding anddigestion. The mixed vegetative stage (4to5DAH), the mouth and anus opened, thedigestive tract ran through. The exotrophic stage (after6DAH), the yolk sac had beencompletely absorbed. The structure and function of the digestive system of Qinglonggrouper at25DAH developed gradually. In conclusion，development of the digestivesystem of Qinglong grouper were in accord with the growth，morphology developmentand perfection of functions during the early development.4. Histochemistry and immunohistochemistry of digestive tract injuveniles Qinglong grouper (E. coioides♀×E. lanceolatus♂)We studied the histochemistry and immunohistochemistry in the digestive tract ofQinglong grouper by using AB-PAS and SABC. Result showed that mucous cells inesophagus were of TypeⅠ,TypeⅡ, TypeⅢ and TypeⅣ containing neutral and acidicmucoitin. The cardiac stomach had mucous cells of TypeⅠ,TypeⅡand TypeⅣ. Thepyloric stomach had mucous cells of TypeⅠcontaining neutral mucointin. Pyloric caecaand intestines contained neutral and acidic mucointin. Pyloric caeca had a maximum ofmucous cells TypeⅡ, and less of TypeⅢ mucous cells. Foregut, midgut and hindguthad four types of mucous cells. The density of intestinal mucous cells: midgut>hindgut> foregut. Using the immunohistochemistry to study the distribution of gastrincells in the digestive tract, indicating that the entire intestinal and pyloric caeca hadgastrin cells, but the esophagus and stomach were not found. Intestinal tract had lots ofgastrin cells, because the intestine was the main site of digestion and absorption of food.Through a systematic study of mucous and gastrin cells of the digestive tract ofQinglong grouper, we had further understanding of the physiological and biochemicalfunctions of the digestive tract.