Daily change of genetic variability in hatchery offspring of red sea bream during spawning season

ABSTRACT:   In order to assess a daily change of genetic variability during spawning season, hatched larvae of red sea bream sampled on different dates were assayed by polymorphic markers such as microsatellite DNA (msDNA) and mitochondria DNA (mtDNA) control region. Based on the microsatellite loci, the average number of alleles per locus ranged between 13.7 and 18.3. The expected heterozygosities ranged between 0.843 and 0.919. A total of 23 mtDNA haplotypes were detected via digestion of mtDNA D-loop sequences with five endonucleases: Taq  I, Alu  I, Mbo  I, Rsa  I and Hinf  I. Significant fluctuation of genetic variability during spawning season was detected by both types of DNA markers. It was suggested that the genetic variability was maintained by pooling the seed fish collected on different spawning dates in a hatchery.     

Hypoxic conditions induce centrum defects in red sea bream Pagrus major (Temminck and Schlegel)

A previous study elucidated that an extreme hypoxia during somitogenesis induced the most frequent skeletal malformation centrum defects in red sea bream (RSB), Pagrus major. In this study, details of the hypoxic conditions to induce them in RSB, dissolved oxygen (DO) concentration and exposure time to hypoxia, were investigated. Fertilized eggs were exposed to seawater of six DO concentrations (0%, 10%, 25%, 50%, 75% and 100% of saturation) for seven different periods (5, 10, 30, 60, 120, 240 and 360 min) during somitogenesis. Somitic disturbances in newly hatched larvae were induced by exposure to 0% and 10% DO concentration for 10 and 120 min and longer respectively. Rearing eggs exposed to hypoxic condition of 10% DO for 240 min for 40 days post‐hatch showed that the location and the frequency of somitic disturbances in larvae and centrum defects in juveniles were significantly correlated (P<0.01). Dissolved oxygen concentration of the interstitial water in the egg high density layer formed at the water surface in a stationary state abruptly decreased to 3.7% within 7 min. Centrum defect induction by exposure of eggs to extreme low DO concentrations for a short period, which is the probable situation in the practical juvenile production, suggests that careful maintenance of DO concentration is important in the incubating water of fertilized eggs during egg sorting and transportation, where eggs are made into a pile and undergo hypoxia, for the prevention of centrum defects.     

Morphological aspects of feeding and improvement in feeding ability in the early larval stages of red sea bream Pagrus major

The present study examined the appearance, ossification and growth of the bones that form the oral cavity in early larval stages of laboratory reared red sea bream ( Pagrus major ) for 380 h after hatching. The fundamental elements of the oral cavity appeared 11 h after initial mouth opening (HAMO). Development in the red sea bream, based on the osteological development of the feeding apparatus, was divided into three phases following the first feeding (24 HAMO; mean total body length 3.3 mm). The first phase was the early sucking phase (24 to 80–100 HAMO; approximately 3.9 mm), during which the head and bones increased in size. The intensified sucking phase (to 200–220 HAMO; approximately 4.9 mm) was defined by the appearance of new structural elements and a continued enlargement of the head and bones. Finally, during the transition phase (beyond 300 HAMO; approximately 5.6 mm), larvae used grasping as well as sucking to feed, new elements appeared, ossification began, size increased and teeth were acquired. As the larvae advanced through these three phases, the ability to feed by sucking was enhanced by the appearance and growth of new bones. The developmental phases appear to be linked to the transition from endogenous to exogenous nutrition resources under laboratory rearing conditions and to diversification in the size and components of wild food organisms.     

Establishment and characterization of a fibroblast cell line derived from the dorsal fin of red sea bream,Pagrus major (Temminck & Schlegel)

The establishment and partial characterization of a continuous cell line from the dorsal fin of red sea bream, Pagrus major, are described. The cell line, designated RSBF‐2, has been subcultured for more than 100 passages since its initiation in November 2000. It was optimally maintained at 28 °C in Leibovitz L‐15 medium with 10% foetal bovine serum. Propagation of RSBF‐2 cells was serum dependent and exhibited low plating efficiency (<1.7%). Aside from long‐term cryopreservation, the cells could also be kept at 4 °C for 72 days. The distribution of the chromosome number was 38–98 with a mode of 48. The RSBF‐2 cell line was susceptible to red sea bream iridovirus but only produced a few rounded and refractory cells. Virus‐inoculated RSBF‐2 cells were then subcultured to generate a persistently infected cell line. RSBF‐2 was also very sensitive to the extracellular products of Photobacterium damselae ssp. piscicida and produced significant fluorescent signals after transfection with pEGFP‐C3. Analysis of mitochondrial cytochrome b gene sequences revealed 99% identity between the cell line and Pagrus major.     

Effects of protein and lipid sources on the growth and survival of red sea bream Pagrus major and Japanese flounder Paralichthys olivaceus receiving micro-bound diets during larval and early juvenile stage

The effects of dietary protein and lipid sources on growth and survival of the red sea bream Pagrus major (30‐days old) and Japanese flounder Paralichthys olivaceus (15‐days old) were examined using four zein‐microbound diets (MBD) containing the following nitrogen and lipid sources: MBD‐1, SBP‐1000 (soybean peptides with molecular weights of about 1000) + fish oil calcium soap (FOCS); MBD‐2, SBP‐3000 (molecular weights of about 3000) + FOCS; MBD‐3, soybean protein isolate (SPI) + FOCS; MBD‐4, SBP‐1000 + stearoyl calcium lactate (SCL). Six groups of the test fish were maintained on the following diets for 30 days; group 1, live food; group 2, 1/2 live food + 1/2 MBD‐1; group 3, MBD‐1; group 4, MBD‐2; group 5, MBD‐3; group 6, MBD‐4. In the red sea bream, high performance in terms of total length (TL) and body weight gain (BWG) was obtained in groups 1, 2, 3 and 4. However, the fish receiving MBD‐3 (group 5) and MBD‐4 (group 6) had shorter TL and lower BWG than those receiving the other diets. Regarding the Japanese flounder, high performance in terms of TL, BWG, and survival rate (SR) was obtained in groups 1 and 2. Group 3 receiving MBD‐1 gave the BWG and SR close to those of group 2 but lower than group 1. In contrast, groups 5 and 6 receiving MBD‐3 or MBD‐4 alone had significantly (P < 0.05) shorter TL and lower BWG than groups 1 and 2. The present study thus indicated that soybean peptides with molecular weights of 1000–3000 and FOCS are superior to SPI and SCL as nitrogen and lipid sources of MBD for the red sea bream and Japanese flounder at larval and early juvenile stage.     

海南三亚斑节对虾野生种群mtDNA 16S rRNA基因和控制区序列的多态性

采用聚合酶链式反应(PCR)技术对海南三亚野生斑节对虾(Penaeus monodon)20个个体的mtDNA 16S rRNA基因和控制区序列进行扩增,PCR产物经纯化后进行测序,得到16S rRNA基因的495 bp的核苷酸序列和控制区序列470 bp的核苷酸片段。用Clustal X软件对16S rRNA和控制区序列进行了比对,通过ARLEQUIN 2000软件对所得线粒体16S rRNA基因片段和控制区序列进行了比较分析。16S rRNA序列检测出17个多态位点,8种单倍型；控制区序列检测出100个多态位点,17种单倍型。该种群16S rRNA序列基因多样度(H)和碱基多样度(π)分别为0．700和0．0045；控制区序列的H和π分别为0．984和0．0480。研究结果表明：16S rRNA序列不适应斑节对虾的种群遗传多样性分析；控制区序列适应斑节对虾种群遗传多样性研究。