A new classification of pre-ovulatory oocyte maturation stages in pikeperch, Sander lucioperca (L.), and its application during artificial reproduction

Abstract

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.

Hormonal induction of ovulation in pikeperch (Sander lucioperca L.) using human chorionic gonadotropin (hCG) and mammalian GnRH analogue

“…All females were determined in stages II, III, IV before injection, and during the ovulation were also observed stages V and VI (Zarski et al 2012). The ovulation rate observed in the present study (88.5 and 80.8 % in the hCG-and mGnRHa-treated groups) is similar to those of Zakes and Demska-Zakes (2005) and Rónyai (2007), where two injections were performed for stimulation of ovulation.…”

Effect of different commercial spawning agents and thermal regime on the effectiveness of pikeperch, Sander lucioperca (L.), reproduction under controlled conditions

“…However, those authors used a double injection of both hCG and Ovopel with an interval of 24 h between them, and the dose of Ovopel was smaller (1.25 pellet kg -1 ) than the one used in this experiment. Moreover, the females they used were at an earlier maturity stage (according to the description, it was probably stage II in the classification proposed by _ Zarski et al 2012). GnRH analogues have been found to have a very short halflife period in fish (up to 23 min in gilthead seabream, Sparus aurata L.) (Gothilf and Zohar 1991).…”

“…Subsequently, the samples were fixed in Serra solution (70 % ethanol, 40 % formaldehyde and 99.5 % glacial acetic acid in proportion 6:3:1). After the cytoplasm clarification (after 2-3 min of exposure) the maturity of oocytes was determined based on the classification proposed for the pikeperch by _ Zarski et al (2012). Only those female fish for which the maturation was between stage III (n = 28) and IV (n = 32) were taken for further procedures.…”

“…Only those female fish for which the maturation was between stage III (n = 28) and IV (n = 32) were taken for further procedures. Fish at those stages were chosen because on the basis of the published results of reproduction of pikeperch ( _ Zarski et al 2012) and Eurasian perch, Perca fluviatilis ( _ Zarski et al 2011a), at different maturational stages it could be concluded that the best and the most comparable results of induction of ovulation are to inject the fish at maturation stage III and IV of the classification proposed by Zarski et al (2012). Subsequently, all the chosen (at the maturational stages III and IV) fish were labelled with the floy-tags and randomly divided into 10 groups.…”

“…This does not apply to percids, in which ovulation has been observed without the need to use hormonal preparations (Kucharczyk et al 1996(Kucharczyk et al , 1998(Kucharczyk et al , 2007Ronyai and Lengyel 2010). However, in that case, it is difficult to predict the moment of ovulation (Kucharczyk et al 2007;Szczerbowski et al 2009;_ Zarski et al 2011b_ Zarski et al , 2012, which greatly hinders obtaining eggs and their controlled fertilisation, and even makes it impossible, because pikeperch as well as Eurasian perch, Perca fluviatilis L., spontaneously release eggs in a tank (Ronyai and Lengyel 2010;_ Zarski et al 2011b_ Zarski et al , 2012. Thus, hormonal stimulation is used in artificial reproduction of the species (Kucharczyk et al 2007;Zakęś and Demska-Zakęś 2009), which induces final oocyte maturation (FOM) and ovulation.…”