Introduction
The development of pikeperch (Sander lucioperca) production has accelerated over the last 20 years, thanks to significant R&D efforts. In addition to traditional pond production, the growth of intensive farming is also striking. The first step is the development of the controlled and programmed reproduction. At present, hatchery breeding using in vitro fertilisation (collection and dry fertilisation of the gametes) is the most researched area. In our previous studies, we demonstrated that sperm injected into the ovaries of externally fertilized fish retains its fertilizing ability several hours before induced ovulation. This method can be successfully used in combination with (Müller et al. 2018, 2020) or without hormonal treatment (Gazsi et al. 2021) in case of several species. The aim of our study was to investigate the efficiency of sperm ovarian lavage in case of pikeperch induced spawning in the absence of male. Additionally, in order to assess the appropriate moment for the lavage, we monitored the effect of carp pituarity (CP) suspension on final oocyte maturation and ovulation.
Materials and methods
The pikeperch broodstock was transported from the Nagyatád V95 LtD fish farm (Nagyatád, Hungary) to the Laboratory of MATE Kaposvár Campus. The fish were sorted by sex (10 females, 4 males) and individual females were separated in 250 l tanks, while male specimens were placed in pairs into two 300 l tanks. The tanks were in same water circuit and the water temperature was maintained between 13.2-14.7°C. Hormone treatment of singular injection of 7 mg/kg CP was administrated intraperitoneally. The maturation stages of oocytes (Zarski et al., 2012) were assessed following biopsy sampling of all females at three different moments - at the same time as hormone treatment (0 h), at 48 h and 70 h post-injection. Clarified oocytes were photographed and oocyte stage was evaluated. Artificial nest substrate (60×70 cm) was inserted for spawning, straight after sperm ovarian lavage. The method of sperm injection was as described by Müller et al. (2020). Briefly, 1 ml sperm per kg of female’s body weight was equally divided into two ovarian lobes 75 h after hormone treatment. The timing of sperm injection was determined based on the oocyte stage and previous studies so that the "ovarian storage time" would not exceed 40 h, the time when spermatozoa fertility greatly reduces (Müller et al., 2020).
Results
In total nine fish ovulated and released their eggs. The maturation dynamics of the 9 females showed large individual differences, visible in latency time being at 83h (n=1), 88h (n=1), 95h (n=5), 99h (n=1), 154 h (n=1). Several fish did not ovulate on the artificial substrate but disposed the eggs next to it (n=4). Fertility values measured at 72 h post-fertilisation showed large individual differences in total range 0-84%. There was no correlation between the fertilisation rate and ovulation time (sperm storage time).
Discussion
The ovarian lavage method was successfully used with different siluriform and cypriniform species (Müller et al., 2018, 2020; Gazsi et al, 2021). To the best of our knowledge, this is the first report on the application of this fertilisation method in pikeperch. The outcome of the technique appears to be rather variable, nevertheless, such variability was already described in pikeperch on different issues (Ljubobratović et al., 2017, Zarski et al., 2019; Colchen et al., 2020). Therefore, future studies are required to adapt this method to pikeperch and other perciforms respecting the biology of their gonads.
Acknowledgements
This work was supported by the National Research Development and Innovation Office of Hungary (NKFI K - 135824), the Higher Education Institutional Excellence Program FEKUT2019: TUDFO/ 47138/ 2019- ITM awarded by the Ministry of Human Capacities as well as the the Department for Angling and Fisheries, Ministry of Agriculture and the EFOP-3.6.3-VEKOP-16-2017-00008 project (the project is co-financed by the European Union and the European Social Fund) as well as 2020-1.2.4 TÉT Ipari TR (2021-00015) project.
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