Influence of LHRHa and methyltestosterone on milt production of sea bass Lates calcarifer (Bloch)

Abstract only.Milt volume, sperm density, and number of spermatozoa were determined to quantify milt production of mature sea bass after a single injection of LHRHa [(D-Ala6,Pro9-N-ethylamiide)LHRH] in saline solution and 17α-methyltestosterone in corn oil (MT). Two measures of sperm density, sperm count and spermatocrit, were highly correlated (r=0.85). Compared with control, milt volume and the number of spermatozoa collected increased but sperm count decreased (24% at 24 h) after a LHRHa (20 µg/kg body weight treatment, suggesting a stimulation of spermatozoa production and not merely milt dilution. Further milt dilution (44%) was induced by 80 µg/kg LHRHa (LHRHa80) at 12 h post-treatment but not by 200 µg/kg MT (MT200) alone. A milt dilution of only 27% at 12 h after simultaneous injections of LHRHa80 and MT200 may indicate some inhibitory effect of MT on the efficiency of LHRHa. These results demonstrate that the stimulation of milt production by LHRHa involves testicular hydration resulting in milt dilution

Tolerance of seahorse Hippocampus kuda (Bleeker) juveniles to various salinities

In line with current conservation efforts, some success in the captive breeding of the seahorse Hippocampus kuda (Teleostei: Syngnathidae) has been achieved. To evaluate the salinity tolerance of these hatchery-bred juveniles, 9-week-old H. kuda were transferred without prior acclimatization from ambient full strength seawater (32–33 ppt) to salinities ranging from freshwater to 85 ppt. Survival, growth, and total body water content were determined after 4 and 18 days of exposure. Juvenile H. kuda are able to survive in dilute seawater (15 ppt) for at least 18 days without any compromise in growth (both wet and dry body weight), survival, and total body water. Fish abruptly transferred to freshwater succumbed within 4–24 h, while survival of 5 ppt-reared fish decreased to ca. 65% in 18 days. Although 10 ppt-reared seahorses had growth and survival comparable with the control (30 ppt seawater), total body water was significantly elevated indicating reduced adaptability. The upper limit of H. kuda salinity tolerance was 50 ppt. Fish reared at salinities ≥55 ppt succumbed within 24 h. Like several other marine teleosts, growth and survival of juvenile H. kuda tended to peak in diluted seawater salinities of 15 and 20 ppt. These results indicate the possibility of growing hatchery-bred H. kuda in brackishwater environments.The authors acknowledge the technical assistance of Messrs Tomas Gonzales, Ronald Maliao, and Dr Aurelio Delos Reyes. Dr Luis Maria B. Garcia made a critical review of the manuscript. At the time of the experiments, R.D.R. and C.M.H.G. were visiting students from the Iloilo National HS and the University of the Philippines College of Medicine, respectively. R.D.R. is grateful for the support of Dr Clarissa L. Marte. This study was funded by the SEAFDEC Aquaculture Department under study code Br-04-F95T of G.V.H-G

First measurement of the left-right cross-section asymmetry in Z boson production by e+ e- collisions

We present the first measurement of the left-right cross section asymmetry (A(LR)) for Z boson production by e+e- collisions. The measurement was performed at a center-of-mass energy of 91.55 GeV with the SLD detector at the SLAC Linear Collider which utilized a longitudinally polarized electron beam. The average beam polarization was (22.4 +/- 0.6)%. Using a sample of 10224 Z decays, we measure A(LR) to be 0.100 +/- 0.044(stat) +/- 0.004(syst), which determines the effective weak mixing angle to be sin2theta(W)eff=0.2378 +/- 0.0056(stat) +/- 0.0005(syst)