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¹ University of South Bohemia České Budějovice, Faculty of Fisheries and Protection of Waters, South Bohemian Research Centre of Aquaculture and Biodiversity of Hydrocenoses, Zátiší 728/II, 389 25 Vodnany, Czech Republic DOI : 10.4194/1303-2712-v15_2_46 Viewed : 4002 - Downloaded : 3987 Various induction protocols were compared with the aim to reach ovulation in northern pike (Esox lucius L.). The effectiveness of salmon D-Arg6Pro9NEt-GnRHa at two doses in combination with various additives were tested: 50 and 100 μg kg-1 (groups GnRHa 1 and 2), GnRHa at 50 and 100 μg kg-1 in combination with 8 mg kg-1 metoclopramide (groups 3 and 4), GnRHa at 50 and 100 μg kg-1 emulsified in Freund´s incomplete adjuvant (FIA) (groups 5 and 6), and GnRHa at 50 and 100 μg kg-1 emulsified with FIA 8 mg kg-1 and metoclopramide (groups GnRHa 7 and 8). These treatments were compared to indoor controlled conditions (Group ICC, injected with saline solution, without hormonal treatment) and two traditional treatments: 3 mg kg-1 carp pituitary (Group CP) and ambient outdoor conditions (Group AOC, injected with saline solution only, without hormonal treatment). All fish in Group CP and 70% of those in Group AOC ovulated. The latency periods for Group CP was 96 ± 4 h and 264±58 h for Group AOC. One Group-3 female ovulated spontaneously 108 h post-injection, whereas none of the other GnRHa injected or Group ICC fish ovulated. The pseudogonadosomatic index was 19.3±5.9%; 18.5% and 17.8±7.5% in the AOC, Group 3 and CP, respectively. The fertilization rate reached 88.6±4.5%; 85.5±12.0% and 66.0±13.7% in AOC, Group 3 and CP, respectively. The hatching rate was 68.6±9.9%; 65.5±7.5% and 54.4±8.0% in AOC, Group 3 and CP, respectively. The ovarian fluid pH was significantly higher (8.27±0.03) in AOC compared to CP group (8.11±0.02) (P>0.05). Ovarian fluid of the spontaneously ovulated Group-3 fish had a pH of 8.35. There were no significant differences in egg size and weight among successfully reproduced groups – AOC and CP (P>0.05). Keywords : carp pituitary, GnRHa, injection, reproduction, fertilization, hatching rate