The induced spawning of roach, Rutilus rutilus (L.), with the antioestrogens clomiphene and tamoxifen

Abstract

The induced spawning of gravid roach was investigated using the antioestrogens clomiphene and tamoxifen. Three dose levels ofeach were used: 0·1, l or 10 mgkg‐1, given twice with a 4‐day interval to groups of eight fish with saline controls. Running males were randomly distributed. Tamoxifen, when injected at a rate of l mg kg‐1 was found to be most successful. This treatment induced ovulation in five of the six females, and profuse spawning on 3 consecutive days, 4 days after the first injection. Clomiphene induced ovulation and spawning in one of six females at 2 × 10 mg kg‐1, and two of eight females at 2 × l mg kg‐1, respectively 6 and 7 days after the first injection. The eggs produced showed normal devel‐opment. No control fish ovulated or spawned. Both drugs probably act by indirect mechanisms, blocking sex steroid feedback inhibition of gonadotropin (GtH) secretion at the pituitary, thereby inducing a plasma GtH surge. The results of this experiment suggest that tamoxifen may be an effective substitute for pituitary preparations in the induced spawning of fish.