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This study aimed at improving the reproduction effectiveness and synchronization of ovulation in the pikeperch, Sander lucioperca (L.), during induced spawning, which is one of the main bottlenecks in the aquaculture of this species. For this purpose, a new categorization of maturation stages in preovulatory oocytes was applied. It is generally based on two morphological indicators: germinal vesicle migration or its breakdown (GVBD) and di¡erent oil droplet coalescence rates. This categorization covered seven stages (from I to VII)^from the end of vitellogenesis to ovulation. The categorization was veri¢ed by controlled reproduction with the use of hormonal stimulation (500 IU of hCG per kg of female body weight) and low spawning temperature (12 1C), which extended the latency time. In addition, some morphological indicators (pseudo-gonadosomatic index, Fulton's condition coe⁄cient) of females were calculated in order to determine their usability in determining the maturation stage. However, these indicators proved to be ine¡ective for this purpose, further highlighting the need to determine the maturational stages in pre-ovulatory oocytes to synchronize ovulation in pikeperch. During the experiment, ovulation seemed to be synchronized among the experimental treatments. Statistical di¡erences were found in terms of latency time between experimental groups at di¡erent maturity stages (II^789 8 h; III^57^78 h; IV^48^58 h; V^32^49 h; VI^5^30 h) according to the proposed classi¢cation. This classi¢cation and the results presented in the study signi¢cantly improved the synchronization of ovulation, which may positively a¡ect the e¡ectiveness of pikeperch production under controlled conditions.

Summary This study determined the effect of two different activating solutions (‘Woynarovich’ and ‘Billard’) on the effectiveness of controlled insemination of eggs of the Eurasian perch, Perca fluviatilis L., compared to hatchery water. Moreover, the study established the period during which such eggs can be fertilised in each of these media. The experiments were conducted on eggs obtained by induced spawning of wild perch females, stimulated hormonally with HCG (500 IU kg−1). The eggs were divided into samples with about 200 eggs in each, which were activated with each of the test media. Subsequently, semen (0.05 mL) was added to each sample after 15, 30, 45, 60, 90, 120, 150 and 180 s following egg activation. The results were compared to a control group [semen was added to an egg sample before activation (0 s)]. Moreover, the sperm motility parameters and the time of sperm movement in each of the tested activating liquids were analysed. The results indicated that perch eggs activated with hatchery water remain capable of fertilisation for 150 s. The lowest survival rate of embryos was found in the control group, which could be attributed to the shortest motility time of spermatozoa (maximum 37 s) when activated with hatchery water. A similar time of egg fertilisation ability was recorded following the use of Billard solution (150 s), whereas eggs treated with Woynarovich solution remained capable of fertilisation throughout the experimental test period (180 s). The percentage of fertilisation was highest (P < 0.05) in that group (at least 88% of live embryos were observed at the eyed‐egg stage). The results indicated that Woynarovich solution (4 g of NaCl and 3 g of urea in 1 L of water) proved to be the most effective medium for controlled insemination of perch eggs. On the other hand, when clean hatchery water was used to activate eggs, semen should be added to water after several seconds, which may significantly improve the fertilisation rate in controlled insemination trials.

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Milt of the Leuciscus idus L. was collected from ¢ve experimental groups, and selected parameters of its quality were analysed for 36 h (group II), 60 h (group III), 84 h (group IV) and 108 h (group V), respectively, after hormonal stimulation with Ovopel (1granule kg À 1 of body weight). The control (group I) ¢sh were not subjected to hormonal stimulation. The highest milt volume was obtained from the ¢sh in group IV (0.70 AE 0.55 mL), where the largest volume of milt expressed per kilogram was also obtained (3.03 AE 1.94 mL kg À 1 ). Signi¢cant di¡erences were also found in milt volumes obtained between group I and groups III (Po0.01) and IV (Po0.05). The highest percentage of motile spermatozoa was found in the milt of group IV (59%); signi¢cant di¡erences were found between group I and groups II (Po0.01) and III (Po0.001). The value of osmotic pressure of seminal plasma was the highest in group IV (203.19 AE 37.63 mOsm kg À 1 ), and the lowest in group I (118.31 AE 41.13 mOsm kg À 1 ). Parameters determining milt quality and quantity indicate that the period of 60^84 h after hormonal stimulation with Ovopel is optimal for obtaining milt from ide.