Stories of Želivka asp
This story will take us to the Švihov reservoir on the Želivka river. It is one of the most important dam reservoirs in the Czech Republic, which supplies the majority of the capital city of Prague and its surroundings with raw drinking water. It is less known that this reservoir hosts a very interesting population of Asp or rapacious carp (Leuciscus aspius). This fish is interesting in that it is our only species from the otherwise very successful and widespread family of cyprinid fish, which in adulthood feeds mainly on other fish.
Asp have always been successful in the Želivka river basin. The construction of a large reservoir often stirs up conditions in fish communities, but the Želivka asp has withstood this great change well. It learned to benefit from the increased supply of forage fish in the new reservoir and was able to solve even the seemingly most difficult problem of reproduction. In terms of reproduction, Bolen is a rheophilic species that needs a flowing environment for spawning and incubating eggs, which is lacking in the reservoir. The asp learned to utilize the rapids under the first weir above the reservoir upper end during the spawning period. Here, in the early spring, sexually mature fish from the entire reservoir gather. This leads to the accumulation of parental fish, which did not escape the attention of the reservoir administrators. They successfully embarked on the idea of using the stock of adult asp for artificial reproduction, and so during the 80s of the last century the technology of artificial breeding was developed and asp from Želivka was spread to many Czechoslovak and foreign localities. Thanks to this breeding primate, it is possible to follow the traces of the Želivka gene pool in a large part of Central Europe. This was one of the reasons why this unique site was included in the list of protected areas within the Natura 2000 system.
Massive occurrence of parental asp also attracted the attention of fisheries scientists. Its monitoring has been carried out since the 1980s under the leadership of Jiří Vostradovský, CSc. Many interesting questions arose in connection with the difficult predictability of the occurrence of fish in the spawning grounds and the observed alternation of strong and weak year classes. Simple monitoring, although associated with fish tagging, provided only limited information on the fascinating life history of this unique stock. A real revolution in the knowledge has meant the introduction of marking of asp by HDX passive chips and RFID technology for scanning the numbers of individual chips (passive telemetry). Unique codes of marked individuals can be "read" by special antennas up to a distance of about 1 meter from the antenna. Once marked, the fish is identified whenever it approaches the spawning ground.
The spawning of asp peaks at night
Over the years, the number of marked individuals has reached more than 2000 and antenna records allowed to describe the overall seasonal dynamics of spawning run and the fact that males are present in the spawning area much earlier and longer than females (Šmejkal et al. 2017a). A very fundamental new finding was the fact that the spawning of asp peaks at night (Šmejkal et al. 2018). The combination of passive telemetry and camera recordings revealed a compelling reason for such behaviour. Spawned asp eggs become abundant prey of the the bleak (Alburnus alburnus) that accompany the asp at the spawning grounds during the day (Šmejkal et al. 2017b), while at night the bleak disappear from the spawning area, so the asp can spawn uninterruptedly (Šmejkal et al. 2018). Bleak, which is normally a common prey of asp for most of the year, feed for a short time on their main predator.
Asp with unique code: 900_2300001333248. With tag reader.
Long-term monitoring using passive telemetry makes it possible to monitor well the dynamics of the spawning stock and also the development of the behaviour of individual individuals. The age of the spawning males ranged from 4 to 11 years. According to a just published study (Šmejkal et al. 2021), older and more experienced individuals come to spawn sooner and can occupy more advantageous habitats. At the same time, they visit the spawning grounds more often and for a longer period of time, so they never miss the spawning peak.
Females are more complicated
Assessment of females is a bit more complicated. Their number of records is smaller because they are less active overall and, in addition, they have been found to lose their chips implanted in the body cavity relatively easily. It happens that the chips leave the female body together with the laid eggs (Šmejkal et al. 2019). On average, approximately 15% of females and 2% of males lost their chip during several years of study. These losses can affect estimates of fish abundance and behaviour. In the case of large-scale marking projects, lost tags can also “pollute” the habitat. It is not that the bottom of the river is covered with a layer of tags, but even individual tags laying on the river bottom can send false signals simulating fish that may not be present at all (Šmejkal et al. 2020). In addition, current antennas can only recognize one chip at a time. If there is a lost tag near the antenna, typically called a ghost-tag, it may interfere with the detection of newly migrating individuals and invalidate the results. Before re-installing the antennas, it is very important to make sure that the place is free of ghost tags.
Hundreds of marked asps are still floating in Švihov reservoir, and the extensive monitoring program promises many other interesting results from the most important life phase of this interesting species. Interactions with other fish species and predators, as well as abiotic factors like peaking discharges and bottom quality, come into play for the success of new generations. But more on that will be reported on the occasion of the publication of future asp publications.
Spawning grounds of asp in the tributary of Švihov reservoir with recording antennas installed.
Šmejkal M., Ricard D., Vejřík L., Mrkvička T., Vebrová L., Baran R., Blabolil P., Sajdlová Z., Vejříková I., Prchalová M., Kubečka J. (2017) Seasonal and daily protandry in a cyprinid fish Scientific Reports 7: 4737. DOI: 10.1038/s41598-017-04827-x
Šmejkal M., Baran R., Blabolil P., Vejřík L., Prchalová M., Bartoň D. , Mrkvička T., Kubečka J. (2017) Early life-history predator-prey reversal in two cyprinid fishes Scientific Reports 7: 6924. DOI: 10.1038/s41598-017-07339-w
Šmejkal M., Souza A., Blabolil P., Bartoň D. , Sajdlová Z., Vejřík L., Kubečka J. (2018) Nocturnal spawning as a way to avoid egg exposure to diurnal predators Scientific Reports 8: 15377. DOI: 10.1038/s41598-018-33615-4
Šmejkal M., Blabolil P., Bartoň D., Duras J., Vejřík L., Sajdlová Z., Kočvara L., Kubečka J. (2019) Sex-specific probability of PIT tag retention in a cyprinid fish Fisheries Research 219: 105325. DOI: 10.1016/j.fishres.2019.105325
Šmejkal M., Bartoň D., Děd V., Souza A., Blabolil P., Vejřík L., Sajdlová Z., Říha M., Kubečka J. (2020) Negative feedback concept in tagging: Ghost tags imperil the long-term monitoring of fishes PLoS ONE 15: e0229350. DOI: 10.1371/journal.pone.0229350
Šmejkal M., Bartoň D., Brabec M., Sajdlová Z., Souza A., Ribeiro de Moraes K., Soukalová K., Blabolil P., Vejřík L., Kubečka J. (2021) Climbing up the ladder: male reproductive behaviour changes with age in a long-lived fish Behavioral Ecology and Sociobiology 75: 22. DOI: doi.org/10.1007/s00265-020-02961-7