Evaluation of the potency of azagly-nafarelin (GnRH analogue), administered in combination with different formulations of pimozide, on LH secretion, ovulation and egg quality in common carp (Cyprinus carpio L.) under laboratory, commercial hatchery and natural conditions

Abstract

The study was performed in order to evaluate the effects of the GnRH analogue, azagly-nafarelin (AZAGLY), in combination with pimozide (dopamine receptor antagonist), on LH secretion, ovulation and egg quality of common carp. Experiments were performed in laboratory, commercial hatchery and natural conditions during 3 consecutive years (1998–2000). AZAGLY action was compared with GnRH agonists already used in aquaculture practice: d-Arg6 Des-Gly10 salmon GnRH analogue (sGnRHa) and d-Ala6 Des-Gly10 LHRH analogue, a component of a commercially available product, Ovopel. In addition, the potency of pimozide, administered to fish using different formulations (suspensions or solutions), to potentiate the action of AZAGLY or sGnRHa was tested. It was shown that combined treatment of AZAGLY+pimozide (in dissolved form) is highly efficient in stimulating LH secretion and ovulation in common carp. The number of ovulated females as well as egg quality is not different and in some cases even better than after Ovopel treatment. The best results were obtained when the total dose of AZAGLY (20 μg kg−1 b.w.) and pimozide (5 mg kg−1 b.w.) was administered in two portions (10+90%) at 6- or 12-h intervals. Additional experiments performed in 1998 showed that the relatively low potency of AZAGLY and sGnRHa treatment in 1998 experiments was caused by the insufficient inhibition of dopamine action by pimozide administered intraperitoneally in a form of suspension. Significantly higher LH concentrations were obtained if pimozide was given in a dissolved form. Combined treatment of AZAGLY+pimozide was also shown to be very effective in stimulating the natural spawning of common carp under an unfavourable thermal regime.