The effects on carp reproduction were investigated in females of the Dor-70 strain and a cross-breed of this line with a Hungarian one of carp pituitary and Ovopel as ovulation stimulators. It was clear that, in the case of the Ovopel treatment, a higher percentage of females spawned, although the weight of eggs obtained was less than that yielded by hypophysed ®sh, the differences being highly signi®cant (P`0.01) with respect to the weight in grams and to percentage of female body weight. No statistically signi®cant differences were determined in the quality of eggs, measured by both the fertilization percentage and the percentage of living embryos, obtained after the two stimulators were used. Neither the provenance of females nor the interaction of female provenance and the stimulator has any effect on the traits investigated. The correlation between the percentage of fertilization and the percentage of live embryos was 0.54 for strain Dor-70 and 0.95 for the cross-breed. The multiple regression equations were calculated for strain Dor-70 and for cross-breed 5 separately, where the percentage of living embryos constituted a dependent variable and the mass of a female, mass of eggs in grams and the percentage of fertilization were independent variables. We appraised the regressions as signi®cant for Dor-70 (P`0.04) and highly signi®cant for the cross-breed (P`0.0001).

Investigations of the e¡ects of controlled reproduction were conducted on carp females of Polish strain 6 and Hungarian strain W after ovulation stimulation with carp pituitary homogenate (CPH) (0.3 mg1 2.7 mg kg À1 body weight), Ovopel (1/511pellet kg À1 body weight) or Dagin (1dose kg À1 body weight). In both strains, the highest percentage of spawning females was found after the Ovopel treatment. After treatments with CPH and Dagin this percentage did not di¡er in strain 6; however, after Dagin, it was higher in ¢sh of strainW. After CPH or Ovopel stimulation the females of line 6 yielded eggs of higher weight compared with line W. After the Dagin treatment the weight of eggs obtained from females, both strains was similar but much lower than after the two remaining agents. The quality of eggs expressed both by the percentage of fertilization and that of living embryos after 24 and 36 h incubation was similar in the two strains only in the group treated with Ovopel. After CPH application eggs of better quality were obtained from strain 6 compared with strainW; however, after the treatment with Ovopel, eggs of much better quality were noted in strain W. In general, the best e¡ects of reproduction were recorded in the case of Ovopel and the poorest in that of Dagin. Females of strain 6 yielded eggs of a higher weight but the percentages of spawning females were higher in strain W after each of the applied spawning agents. A new approach to this problem consisted in investigating the interaction between ovulation stimulators and origin of females of ¢sh treated with Dagin.

The effect of reproduction was investigated on females of Hungarian strain W, French strain F, and their cross-breed 1X whose ovulation was stimulated with carp pituitary (0.3 mg kg À1 and, after 12 h, 2.7 mg kg À1 ) or Ovopel (one-fifth of a pellet per kg and, after 12 h, one pellet per kg). It was found that in the case of Ovopel treatment, the percentage of spawning females of strain F and the cross-breed 1X was higher than in the hypophysed fish compared. The applied ovulation stimulators did not significantly affect the weight of obtained eggs, whereas the significant (P < 0.01) effect was recorded with respect to the quality of eggs after 12-, 24-, 36-and 48-h of incubation. After Ovopel stimulation, the quality of eggs was better. The origin of the females had no statistically significant effect on the weight of eggs although the yield of eggs from fish of strain W was much smaller than that from females of strain F and the 1X cross-breed. The interaction between the ovulation stimulator and the provenance of the females was significant (P < 0.05) for the percentage of live embryos after 48-h of incubation of eggs. Eggs of the best quality (and highest weight) were obtained from fish of strain F and cross-breed 1X treated with Ovopel. In females of strain F that spawned within 6 and 10 h after the second Ovopel injection, the effect of the ovulation time on the weight of eggs was non-significant. It was significant with respect to the percentage of egg fertilization and of live embryos after 36-h of incubation (P < 0.01 and P < 0.05 respectively). The better quality of eggs (and their higher weight) was recorded when this time was shorter.

Ovulation was stimulated in carp females of Polish and Hungarian provenance using injections of (D-Ala 6 ) GnRH ProNHEt (Kobarelin) (20 mg kg ±1 ) with metoclopramide (10 mg kg ±1 ) or carp pituitary (3 mg kg ±1 ). For estimating the effects of the substance stimulating ovulation and of the female provenance, analysis of variance was carried out using the least squares method. It was found that the stimulating substance, provenance and interaction of these factors did not signi®cantly affect the weight of eggs obtained. On the other hand, the stimulating substance, provenance and interaction had a highly signi®cant (P < 0.0001) effect on the percentages of fertilization and live embryos. Females of Hungarian provenance treated with Kobarelin yielded eggs of much better quality but a smaller weight than after the pituitary treatment. In the case of carp females of Polish provenance, a yield of eggs of smaller weight and very poor quality was noted compared with the weight and quality of eggs obtained after hypophysation.

Ovulation was stimulated in four groups of European catfish, Silurus glanis L., using injections of des‐Gly10, [D‐Ala6]‐LHRH Ethylamide (20 μg kg–1) and pimozide (10 mg kg–1), Ovaprim (0.33 mL kg–1), and carp pituitary extract (4 mg kg–1, in one or two doses). A higher percentage of ovulating females (producing eggs of sufficient quality) was found after the LHRH‐a and Ovaprim treatments (100% and 80%) in relation to fish treated with the pituitary extract (60% and 66.67%). The greatest weight of eggs was obtained in the case of repeated hypophysation and LHRH‐a (1299.69 and 1298.57 g, respectively), and the smallest after single hypophysation (1144.08 g). After 60 h of incubation, the best quality of eggs was found in the group treated with Ovaprim (62.9% of live embryos) and the poorest in the two groups which underwent hypophysation (50.41% and 50.75%). No statistically significant effect by the ovulation stimulators on the characteristic qualitative and quantitative traits of obtained eggs was ascertained.