Induced ovulation in coho salmon ( Oncorhynchus kisutch). II. Preliminary study of the use of LH-RH and two high potency LH-RH analogues

LH-RH and two of its high potency analogues, D-Ala 6 des Gly 10-LH-RH(1–9) ethylamide and [D-Ser(Bu t) 6]-LH-RH(1–9) ethylamide in combination with SG-G100 (salmon gonadotropin) have been demonstrated to be effective agents for the induction of ovulation in coho salmon ( Oncorhynchus kisutch). In November 1978 two groups of seven fish were administered a primer injection (ip) of 0.1 mg/kg SG-G100 followed by three daily injections of either 1.6 mg/kg LH-RH or 0.2 mg/kg D-Ala 6 des Gly 10-LH-RH(1–9) ethylamide. A control group was injected with saline. The LH-RH and LH-RH analogue treated groups ovulated significantly earlier than the control with mean days to ovulation of 11.0 ± 1.6 and 10.0 ± 0.0 respectively as compared with 16.9 ± 6.8 for the control. Survival to the eyed stage and egg size for all groups fell within the normal range for this race of coho. In October 1978, a group of five fish was administered a 0.1 mg/kg SG-G100 primer injection followed by three daily injections of 2.0 mg/kg LH-RH. A control group of seven fish was injected with saline. While no significant differences in mean days to ovulation could be demonstrated by Day 11 of the experiment, 69% of the treated group had ovulated compared with 14.0% of the controls. Egg survival to the eyed stage and to hatching fell within the normal range of Big Qualicum coho. The egg diameters of treated fish were smaller than the normal range for this stock. In November 1978, injection of a 0.1 SG-G100 primer followed by three daily injections of either 1.0 mg/kg LH-RH or 0.1 mg/kg of the [D-Ser(Bu t) 6]-LH-RH(1–9) ethylamide analogue was shown to accelerate ovulation significantly compared with controls.