Xu Yongli

AVibrio anguillarum strain associated with skin ulcer on cultured flounder,Paralichthys olivaceus

The characteristics of a bacterium strain M3, isolated from cultured flounderParalichthys olivaceus with remarkable external sign of skin ulcer during an epizootic outbreak, indicated that the bacterium belonged to the speciesVibrio anguillarum. Challenge by I.M. (intramuscular injection), bath, and oral administration with M3 showed that it was highly pathogenic forParalichthys olivacues. The LD50 dose was 5.144×103 CFU/ per fish infection by I.M. injection. Recovered inoculated bacteria from the surviving fish revealed that the asymptomatic carriers could be a latent contagious source. Study of the effect of bacterial culture CFS (cell-free-supernatant) showed that the exotoxins produced by M3 play an important role in its pathogenicity for flounder. The resistance of M3 to 36 out of 41 antibiotics indicated that the bacterial disease outbreak was mainly attributable to the frequent and excessive use of antimicrobial agents; and that vaccination would be an effective precaution against bacterial disease.

Study on embryonic development and early growth of triploid and gynogenetic diploid left-eyed flounder,Paralichthys olivaceus (T. et S.)

The early effects of chromosomal manipulation of eggs and sperm on the yields of triploid and gynogenetic diploid larvae ofParalichthys olivaceus were investigated Triploidy was achieved by cold shocking fertilized eggs at 0–2°C for 45 minutes duration 5 minutes after, fertilization, and the induced triploidy rates were 31.2%–50% and the relative hatching rates were 53.3%–99%. Gynogenetic diploids were obtained when eggs were inseminated with irradiated sperm and cold shocked at 0–2°C for 45 minutes duration 5 minutes after fertilization. The induced gynogenetic diploid rates and the relative hatching rates were 94%–96% and 48.5%–68.5% respectively. The embryonic development of the triploid experimental group and of the gynogenetic diploid experimental group was delayed at first compared with the control group. But from the gastrula stage, it was not delayed anymore. There were no significant differences in the growth of the triploid experimental group larvae and the control group larvae, and in the growth of the gynogenetic diploid experimental group larvae and the control group larvae according to Student’s t-test (α=0.05). The relationship between the early growth of the triploid experimental group larvae and that of gynogenetic diploid experimental group larvae was also studied.The early effects of chromosomal manipulation of eggs and sperm on the yields of triploid and gynogenetic diploid larvae ofParalichthys olivaceus were investigated Triploidy was achieved by cold shocking fertilized eggs at 0–2°C for 45 minutes duration 5 minutes after, fertilization, and the induced triploidy rates were 31.2%–50% and the relative hatching rates were 53.3%–99%. Gynogenetic diploids were obtained when eggs were inseminated with irradiated sperm and cold shocked at 0–2°C for 45 minutes duration 5 minutes after fertilization. The induced gynogenetic diploid rates and the relative hatching rates were 94%–96% and 48.5%–68.5% respectively. The embryonic development of the triploid experimental group and of the gynogenetic diploid experimental group was delayed at first compared with the control group. But from the gastrula stage, it was not delayed anymore. There were no significant differences in the growth of the triploid experimental group larvae and the control group larvae, and in the growth of the gynogenetic diploid experimental group larvae and the control group larvae according to Student’s t-test (α=0.05). The relationship between the early growth of the triploid experimental group larvae and that of gynogenetic diploid experimental group larvae was also studied.

Analysis of IL-2-like factor in lymphocyte culture supernatant of olive flounder,Paralichthys oliveaceus

To study immune mechanism of fish lymphocyte we performed a proliferation assay and ELISA using monoclonal antibody against human IL-2. The result showed that an interleukin-2 (IL-2)-like factor was detected in the supernatant of plant haemoglutinin (PHA)-stimulated lymphocyte culture from peripheral blood, spleen and head kidney of olive flounder,Paralichthys olivaceus. The quantities of IL-2-like factor in the supernatant from different lymphoid tissues were quite different. The IL-2 like factor in the supernatant from cultured head kidney lymphocytes was much higher than those of peripheral blood lymphocytes and spleen lymphocytes (P<0.01). The IL-2 activity was found in either mouse thymocyte proliferation assay or flounder head kidney lymphocyte proliferation assay and shown to have obvious enhancing effect on proliferation of the above two types of cell. The recombinant human IL-2, (rhIL-2) was able to stimulate flounder thymocyte proliferation and used to detect the IL-2 receptor (IL-2R) on the surface of flounder lymphocyte. The cross-reaction between the lymphocytes of flounder peripheral blood and CD25(IL-2R) was detected with flow cytometry and shown that the percentage of CD25-positive cell in peripheral blood was 7.74±0.67%.

Endocrine changes ofParalichthys olivaceus after oral administration with exogenous growth hormone

Recombinant salmon growth hormone contained in yeast was given for 5 months to flounder in its diet. Both free and total specific binding sites for the growth hormone were examined in liver membranes of control and treated fish. The association constants of both free and total specific binding sites were of the same order (1 nM−1), and no significant difference was found between any two groups in the capacity of their free binding sites. The capacity of total binding sites in the liver of treated fish increased significantly compared with that of control.Insulin-like growth factor I (IGF-I) levels in the plasma of treated fish increased by 22.61% (P<0.05), compared with that of control. While the T4 levels in plasma did not increase significantly (from 1.35±0.91 ng/ml to 2.29±1.13 ng/ml), T3 levels were elevated significantly (from 1.78±1.14 ng/ml to 4.87±1.22 ng/ml, P<0.01), as compared with that of control.

Up-regulation of hepatic receptor for growth hormone in the flounder (Paralichthys olivaceus) after oral administration with exogenous GH

The iodination efficiency of salmon GH(sGH) was 38.82%, using a modification of the chloramine-T method. The specific activity of the125I-sGH was about 40 μCi/μg protein. The results of binding assay showed a single class of high affinity and low-capacity binding site in flounder liver. Long-term administration with exogenous GH can induce the up-regulation of hepatic GH receptor in total binding capacity though there was no significant difference in capacity of free binding sites of livers from control and experimental fish, this result also indicated that the liver from experimental fish, compared to that from control fish, had more occupied binding sites.The iodination efficiency of salmon GH(sGH) was 38.82%, using a modification of the chloramine-T method. The specific activity of the125I-sGH was about 40 μCi/μg protein. The results of binding assay showed a single class of high affinity and low-capacity binding site in flounder liver. Long-term administration with exogenous GH can induce the up-regulation of hepatic GH receptor in total binding capacity though there was no significant difference in capacity of free binding sites of livers from control and experimental fish, this result also indicated that the liver from experimental fish, compared to that from control fish, had more occupied binding sites.