Prolonged‐release gonadotrophin‐releasing hormone analogue implants enhance oocyte final maturation and ovulation, and increase plasma concentrations of sulphated C₂₁ steroids in North Sea plaice

Abstract

Reproductively mature female plaice were implanted with or without 50 g of gonadotrophinreleasing hormone analogue (GnRHa), suspended in either coconut oil or methacrylate resin. The weight of the GnRHa-treated fish increased significantly (due to hydration of the oocytes) and reached a peak between 10 and 14 days. The fish produced several batches of eggs, which were consistently bigger than those produced by control fish. Plasma concentrations of free 17 -oestradiol and glucuronidated testosterone rose briefly (4 days) in response to the GnRHa, but then fell continuously till the end of the experiment (20 days). Plasma concentrations of sulphated 5 -pregnane-3 ,17,20 -triol and 5 -pregnane-3 ,17,20 -triol (which are putative metabolites of 17,20 -dihydroxy-4-pregnen-3-one, the oocyte maturation-inducing steroid) increased significantly at 4 days and reached a peak between 12 and 16 days. Concentrations were still very elevated on day 20. Plasma concentrations of sulphated 3 ,17,21-trihydroxy-5pregnan-20-one showed a slight increase on day 4 but did not change thereafter. There was a highly significant difference in the amounts of GnRHa released into the bloodstream by the two methods of administration on day 4. However, this was not matched by significant differences in the concentrations of any of the steroids. 1999 The Fisheries Society of the British Isles

Immunoreactive changes in pituitary FSH and LH cells during seasonal reproductive and spawning cycles of female chub mackerel Scomber japonicus

“…When GnRHa is injected, it degrades within a few days [24]. As spawning of chub mackerel in captivity generally continues over a month, injected GnRHa plays a role as a trigger for spawning, but a series of spawnings may be induced by endogenous GnRH, which controls pituitary GtH secretion.…”

“…In early June 2005, chub mackerel reared in sea cages were transferred to the Fishery Research Laboratory of Kyushu University in Fukutsu City, Fukuoka Prefecture and moved into a concrete tank with running seawater. The next day, after anesthetizing the fish with 2-phenoxyethanol (200 ppm), females with oocytes greater than 600 lm in diameter and spermiating males were selected as described previously [22] and injected intramuscularly with GnRHa (des Gly 10 -D-[Ala 6 ] LHRH ethylamide; Sigma-Aldrich, St. Louis, MO, USA) (400 lg/kg BW) combined with coconut oil [24]. After GnRHa injection, 28 fish were divided into two groups (each group consisting of seven females and seven males) and kept in two 3000-l flow-through seawater tanks with running seawater under natural day length and water temperature.…”

Time course of final oocyte maturation and ovulation in chub mackerelScomber japonicusinduced by hCG and GnRHa

“…In Experiment 2, 40 fish were injected with GnRHa [des‐Gly 10 ‐(D‐Ala 6 ) LHRH ethylamide, 400 μg/kg BW, Sigma‐Aldrich, St. Louis, MO, USA] suspended in coconut oil 9 intramuscularly at 14:00 and 02:00 hours. Four to 10 fish were sampled at times between 24 and 48 h after GnRHa injection.…”

Changes in the expression of pituitary gonadotropin subunits during reproductive cycle of multiple spawning female chub mackerel Scomber japonicus

“…Before the treatment, suitable chub mackerel consisted of spermiating males and females that possessed oocytes greater than 600 lm were selected according to Shiraishi et al (2005). GnRHa injections were prepared by mixing the des Gly 10 -D-[Ala 6 ] LHRH ethylamide (SigmaAldrich) into molten coconuts oil according to the method of Scott et al (1999). A group of suitable chub mackerel (6-15 of each sex) was injected intramuscularly with GnRHa at a dose of 400 lg/kg BW and maintained in 3-m 3 tanks with circulating seawater.…”

“…By injecting GnRHa combined with coconut oil into a group of chub mackerel, we induced continuous spawning for over a month during the spawning season. Since the exogenous GnRHa was cleared 4 days post-injection (Scott et al 1999), the GnRHa-induced multiple spawning observed after 1 week was likely controlled by the endogenous GnRH-GtH system. In captive chub mackerel, the time course from the initiation of FOM to ovulation/ spawning has been determined (Shiraishi et al 2008).…”