Gonadotrophin-releasing hormone agonist raises plasma concentrations of progestogens and enhances milt fluidity in male Atlantic halibut (Hippoglossus hippoglossus) |
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| Authors: | ELM Vermeirssen RJ Shields C Mazorra de Quero AP Scott |
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| Institution: | (1) Reproductive Biology and Behaviour Group, Research Center for Ornithology of the Max Planck Society, Postfach 1564, D-82305 Starnberg (Seewiesen), Germany;(2) Marine Farming Unit, Sea Fish Industry Authority, Ardtoe, Acharacle, Argyll, PH36 4LD, UK;(3) Institute of Aquaculture, University of Stirling, Stirling, FK9 4LA, UK;(4) Centre for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk, NR33 0HT, UK |
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| Abstract: | In two separate spawning seasons, spermiating male Atlantic halibut were implanted with pellets containing gonadotrophin-releasing hormone agonist (GnRHa). Males were bled repeatedly, and milt samples were collected. Blood samples were assayed for free and conjugated steroids: testosterone, 11-ketotestosterone, 17,20 -dihydroxy-4-pregnen-3-one (17,20-P), 17,20 -dihydroxy-4-pregnen-3-one (17,20-P), 17,20,21-trihydroxy-4-pregnen-3-one and steroids with a 17,20 configuration. Towards the end of the first season, pellets were implanted into three wild-caught and three hatchery-reared males. No control fish were available. The major progestogen in plasma was identified as sulphated 5-pregnane-3,17,20-triol (3,17,20-P-5-S). Concentrations of this steroid were stimulated by the GnRHa. Sulphated 17,20-P was also identified in the plasma, but at 10-fold lower concentrations than 3,17,20-P-5-S. In the middle of the second season, pellets were implanted into five hatchery-reared males; five unimplanted males were used as controls. Levels of androgens fell following GnRHa treatment, levels of progestogens rose briefly, and there was a significant increase in the fluidity of the milt. Of all the measured steroids, free and sulphated 17,20-P showed the best correlation with milt fluidity. |
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| Keywords: | androgens GnRHa halibut milt fluidity progestogens sperm steroid conjugates |
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