ABSTRACT:A qualitative assessment of the Eurasian perch Perca fluviatilis semen describing the basic parameters of seminal plasma was completed. The histological methods used in this study showed changes in perch gonads during a spawning and post-spawning period. At the late period of the spawning season, the structure of testes was clearly loosened and spermatozoa did not fill uniformly all the ampullae of the testes, leaving free spaces at their banks and no spermatids were observed. The results confirmed that there was an additional period after spawning in the annual reproductive cycle of the male Eurasian perch. In both years of investigations (2000)(2001), an essential decline in sperm motility at the late period of the spawning season was observed, from more than 85% to 56% in 2000. The sperm motility was not influenced by sperm concentrations because throughout the spawning time no changes in the sperm concentration were observed, 32.4 and 32.6 mld/ml at beginning and at the late period of spawning period, respectively. In contrast to sperm concentrations, protein concentrations in seminal plasma increased in the late period of spawning season, from 3.95 to 5.16 g/l in 2001. This study confirmed that protein concentrations in the seminal plasma of most fish are much lower than in the other vertebrates. Among the fish examined, perch is characterized by one of the highest values of protein concentrations in plasma. Our observations confirmed that a high water temperature influenced anatomical and functional parameters of the reproductive system in male perch.

Improving reproductive protocols is one crucial step towards aquaculture expansion of pikeperch (Sander lucioperca), which is still characterised by variable and/or low spawning effectiveness. One of the main challenges is to synchronise ovulation at a precisely planned time with a consistently satisfactory reproductive outcome. To this end, the present study examined the effect of different spawning agents (human chorionic gonadotropin [hCG] and salmon gonadotropin-releasing hormone analogue [sGnRHa]) with different doses and application modes (including double injection). The study covered three consecutive spawning seasons, which corresponded to three distinct experiments, where domesticated pikeperch broodstock, commercially grown in a recirculating aquaculture system, was used. In the first year of the study, the effect of different doses of sGnRHa (10, 25 and 50 μg kg -1 ) and hCG (250, 500 and 1000 IU kg -1 ) on the reproductive performance of the domesticated broodstock was evaluated. The results were also compared with literature data for wild fish. During the second and third years, typical indicators of spawning performance (ovulation rate, latency time and egg quality) were followed when a double sGnRHa injection was compared to a single 50 µg kg -1 or 500 IU kg -1 injection of sGnRHa or hCG, respectively; the best results were 2 obtained in the first and second experiments. The results of the present study clearly indicate that various hormonal treatments effectively induced domesticated pikeperch ovulation, although highly variable egg quality was observed throughout the three spawning seasons (maximum hatching rates were 60.6 ± 11.5, 37.7 ± 28.9 and 49.1 ± 24.7% in the first, second and third years of the study, respectively). However, additional analysis of the data from the entire study revealed for the first time that a significant proportion of the lower-quality eggs came from fish that responded 'early' to hormonal treatment (<120 h after injection) regardless of the hormone used. This group represented approximately 40% of the population each year.Further, most of the fish that responded to hormone treatment early exhibited this trait during all three consecutive spawning seasons. This finding indicates that early hormone response is a potential selection trait. The present study showed that controlled domesticated pikeperch broodstock reproduction may involve application of either hCG or sGnRHa, with no clear difference in their effectiveness, although the recommended doses are 500 IU kg -1 and 50 µg kg -1 , respectively.

The effect of supplemented commercial diets with crystalline L-tryptophan 10 and 20 g TRP kg -1 ) on cannibalism, survival and growth parameters of pikeperch postlarvae (Sander lucioperca) was evaluated. Fifteen-day-old pikeperch larvae (mean weight-6.8 mg) were reared during the next 28 days (20.5°C, 16L:8D) in glass aquaria in a recirculating aquaculture system. The enzyme-linked immunosorbent assay showed that TRP-supplemented diets were effective in increasing the levels of serotonin (5-HT) in the body tissue of pikeperch. TRP supplementation resulted in a slight decrease in both types of cannibalism, although the reduction in cannibalism impact did not amount to more than a few percent. TRP treatment had no significant influence on the final survival of pikeperch post-larvae (ranged from 20.1 ± 12.4 to 29.0 ± 12.9 %). However, contrary to the earlier studies conducted on other fish species, no significant difference in the growth rates and feeding behavior of pikeperch between TRP-fed and control group were found. The final body weight and growth rate ranged from 0.211 ± 0.014 to 0.243 ± 0.016 and from 12.19 ± 0.38 to 12.76 ± 0.35 % day -1 , respectively. To our knowledge, this is the first study reporting the effects of TRP supplementation on the cannibalism-survival-growth relations in fish in the post-larval stage.

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