Features of the species composition and structure of fish communities in small anthropogenic reservoirs with different content of dissolved mineral nitrogen

In 22 small anthropogenic reservoirs with an area of 0.4 to 62 ha located in the territory of the Udmurt Republic, individuals of different fish species were captured and water samples were taken in late spring for analysis of NO3–, NO2– and NH4+ content. In many reservoirs, concentrations of ammonium exceed the maximum permissible according to the fishing standards for water quality, and in some this is also the case with nitrites. Ponds with zooplanktophages (bleak Alburnus alburnus (L.) and belica Leucaspius delineates (Heckel)) present in fish communities were statistically significantly different in the increased content of total dissolved mineral nitrogen from reservoirs where these two fish species were not registered. In perch and roach reservoirs, the numerical proportion of river perch Perca fluviatilis was negatively and statistically significantly related to the level of their contamination with nitrogen ionic forms.

Could Fish Feeding Behaviour and Size Explain Prevalence Differences of the Nematode Eustrongylides excisus among Species? The Case Study of Lake Garda

The nematode Eustrongylides excisus is a parasite of freshwater fish- and fish-eating birds, with known differences on prevalence values among fish species. Thus, the present study aims to explore the hypothesis that the feeding behavior and the size of fish belonging to different trophic levels could explain such differences. For that, 14 sampling sites were selected to perform a fish parasitological survey on Lake Garda (Italy) during spring-summer 2020. Amplification of nuclear ribosomal internal transcribed spacer (ITS) rDNA sequences of nematodes morphologically ascribable to the genus Eustrongylides allowed to identify them as E. excisus. From the five studied fish species (Perca fluviatilis, Lepomis gibbous, Coregonus lavaretus, Alosa fallax lacustris and Micropterus salmoides), only three presented the parasite E. excisus: P. fluviatilis, L. gibbous and M. salmoides, with significant differences in prevalence values among species (p = 0.002). Additionally, there were differences in prevalence values within the same fish species captured from different sampling sites. Findings showed that mainly piscivorous fish were positive for E. excisus and how the prevalence was highest in M. salmoides. As regard the fish size, a negative correlation between body size and E. excisus was found in P. fluviatilis due to the feeding habit of juvenile perch which feed mainly zooplankton and benthic invertebrates (i.e., oligochaetes, which are the first intermediate hosts of E. excisus). The study findings advance novel knowledge in the field of pathogens of zoonotic importance in the aquatic environment.

Linking behavioural type with cannibalism in Eurasian perch

The propensity to kill and consume conspecifics (cannibalism) varies greatly between and within species, but the underlying mechanisms behind this variation remain poorly understood. A rich literature has documented that consistent behavioural variation is ubiquitous across the animal kingdom. Such inter-individual behavioural differences, sometimes referred to as personality traits, may have far-reaching ecological consequences. However, the link between predator personality traits and the propensity to engage in cannibalistic interactions remains understudied. Here, we first quantified personality in Eurasian perch (Perca fluviatilis), measured as activity (time spent moving) and sociability (time spent near conspecifics). We then gave perch of contrasting behavioural types the option to consume either conspecific or heterospecific (roach, Rutilus rutilus) prey. Individual perch characterized by a social-active behavioural phenotype (n = 5) selected roach before being cannibalistic, while asocial-inactive perch (n = 17) consumed conspecific and heterospecific prey evenly. Thus, asocial-inactive perch expressed significantly higher rates of cannibalism as compared to social-active individuals. Individual variation in cannibalism, linked to behavioural type, adds important mechanistic understanding to complex population and community dynamics, and also provides insight into the diversity and maintenance of animal personality.

Monitoring of the ecological state of the city lake of Chita

Introduction. The paper presents the results of the studies on assessing the quality of the aquatic ecosystem of a lake located within the city. The European perch (Perca fluviatilis L.) and the Gibel carp (Carassius gibelio) were used as an indicator for determining the quality of the aquatic ecosystem by the method of fluctuating asymmetry. Problem Statement. The aim of the work was to conduct monitoring with the subsequent assessment of the quality of the ecosystem of the city lake using the method of fluctuating asymmetry (hereinafter FA). Theoretical and Practical Part. The quality of the urban lake aquatic ecosystem was assessed using the FA method (indicators: the European perch (Perca fluviatilis L.), 1758 and the Gibel carp (Carassius auratus Bloch), 1783). To identify the reasons for the high PFA values, a chemical analysis (in an accredited laboratory) of the gills of the Gibel carp for heavy metals was performed. Conclusions. As a result of the research, the FA indicators values for these indicators were obtained. According to the results of a laboratory study of the content of heavy metals in the gill arches of the Gibel carp, an excess of the maximum permissible concentration of 8 out of 10 analyzed elements was revealed. It has been established that the ecosystem of the city lake Kenon is experiencing a significant anthropogenic load (5 points — the critical quality of the aquatic environment) and it continues to increase towards the deterioration of the habitat.

Split it up and see: using proxies to highlight divergent inter-populational performances in aquaculture standardised conditions

Background Considering wild inter-populational phenotypic differentiation can facilitate domestication and subsequent production of new species. However, comparing all populations across a species range to identify those exhibiting suitable key traits for aquaculture (KTA; i.e. important for domestication and subsequent production) expressions is not feasible. Therefore, proxies highlighting inter-populational divergences in KTA are needed. The use of such proxies would allow to identify, prior to bioassays, the wild population pairs which are likely to present differentiations in KTA expressions in aquaculture conditions. Here, we assessed the relevance of three alternative proxies: (i) genetic distance, (ii) habitat divergence, and (iii) geographic/hydrologic distances. We performed this evaluation on seven allopatric populations of Perca fluviatilis for which divergences in KTA had already been shown. Results We showed differences in the correlation degree between the alternative proxy-based and KTA-based distance matrices, with the genetic proxy being correlated to the highest number of KTA. However, no proxy was correlated to all inter-populational divergences in KTA. Conclusion For future domestication trials, we suggest using a multi-proxy assessment along with a prioritisation strategy to identify population pairs which are of interest for further evaluation in bioassays.

Trophic Interactions Promoting Dominance by Cyanobacteria in a Freshwater Pelagic Food Web

<p>Cyanobacterial blooms have occurred in the Lower Karori Reservoir (Wellington) for approximately the last eight years. The dominant species in the past have been identified as Anabaena lemmermannii and A. circinalis. The reservoir was built in 1874 as part of the first water supply scheme for Wellington City and has been closed to the public since 1906. The catchment was created into a "predator-free" native wildlife sanctuary in 1999. The first severe bloom in the Lower Karori Reservoir occurred during the summer of 2000/01. The objectives of this study were: - To establish a baseline knowledge of the food web within the Lower Karori Reservoir. - To follow the chemical and biological dynamics of the Lower Karori Reservoir for an extended period of time to observe seasonal changes associated with the cyanobacterial blooms. - To experimentally manipulate the trophic levels of the food web to determine which factors (i.e. resources or consumers) were most significant in promoting the growth of cyanobacteria. I sampled temperature, dissolved oxygen, nutrient levels, and phytoplankton and zooplankton communities from 7 October 2003 to 7 July 2004. I also monitored the diet of the zooplanktivorous fish (perch, Perca fluviatilis) present in the lake. The dominant cyanobacteria species was found to be A. lemmermannii. Three other cyanobacteria species were present during the study at low abundances, including A. planktonica which had not been previously recorded in the reservoir. The bloom of cyanobacteria was associated with thermal stratification. Nutrient concentrations were at moderate levels, characteristic of mesotrophic lakes. The perch population consisted mostly of smallsized individuals that feed predominately on large species of zooplankton that were at low abundances within the lake. During March 2004, I conducted a food web manipulation experiment within the Lower Karori Reservoir. I sought to test the role of nutrient resources (bottom-up) versus cascading effects of zooplanktivorous perch (Perca fluviatilis) (top-down) in controlling cyanobacteria in this lake. Experimental treatments with perch had higher levels of cyanobacterial densities, lower zooplankton species diversity and zooplankton species were generally smaller-sized than in treatments without perch. Nutrient treatments were not favourable for cyanobacteria as the addition of nitrogen probably meant that nitrogen fixing Anabaena species lost competitive advantage over other phytoplankton taxa. It is not known by which mechanism perch promoted cyanobacterial growth since this was not directly measured. Plankton community composition was altered by all treatments. This study indicates that blooms of Anabaena species in the Lower Karori Reservoir are the result of a number of complex interactions within the lake food web. Low nitrogen levels favour dominance by the nitrogen fixing cyanobacteria, which bloom during thermal stratification as they are able to maintain their position in the water column due to buoyancy control. Predation pressure by perch is likely keeping large filter-feeding zooplankton at low levels and thus reducing grazing pressure on phytoplankton. Phosphorus excretion by perch also probably favours cyanobacteria. An eradication of perch within the Lower Karori Reservoir would probably contribute to prevent cyanobacteria predominance. The removal of perch from the reservoir should be reasonably simple due its small size and contained area. Other methods which may help reduce cyanobacterial blooms within the reservoir include artificial mixing to prevent stratification. However, these methods can be expensive to install and run.</p>

Trophic Interactions Promoting Dominance by Cyanobacteria in a Freshwater Pelagic Food Web

<p>Cyanobacterial blooms have occurred in the Lower Karori Reservoir (Wellington) for approximately the last eight years. The dominant species in the past have been identified as Anabaena lemmermannii and A. circinalis. The reservoir was built in 1874 as part of the first water supply scheme for Wellington City and has been closed to the public since 1906. The catchment was created into a "predator-free" native wildlife sanctuary in 1999. The first severe bloom in the Lower Karori Reservoir occurred during the summer of 2000/01. The objectives of this study were: - To establish a baseline knowledge of the food web within the Lower Karori Reservoir. - To follow the chemical and biological dynamics of the Lower Karori Reservoir for an extended period of time to observe seasonal changes associated with the cyanobacterial blooms. - To experimentally manipulate the trophic levels of the food web to determine which factors (i.e. resources or consumers) were most significant in promoting the growth of cyanobacteria. I sampled temperature, dissolved oxygen, nutrient levels, and phytoplankton and zooplankton communities from 7 October 2003 to 7 July 2004. I also monitored the diet of the zooplanktivorous fish (perch, Perca fluviatilis) present in the lake. The dominant cyanobacteria species was found to be A. lemmermannii. Three other cyanobacteria species were present during the study at low abundances, including A. planktonica which had not been previously recorded in the reservoir. The bloom of cyanobacteria was associated with thermal stratification. Nutrient concentrations were at moderate levels, characteristic of mesotrophic lakes. The perch population consisted mostly of smallsized individuals that feed predominately on large species of zooplankton that were at low abundances within the lake. During March 2004, I conducted a food web manipulation experiment within the Lower Karori Reservoir. I sought to test the role of nutrient resources (bottom-up) versus cascading effects of zooplanktivorous perch (Perca fluviatilis) (top-down) in controlling cyanobacteria in this lake. Experimental treatments with perch had higher levels of cyanobacterial densities, lower zooplankton species diversity and zooplankton species were generally smaller-sized than in treatments without perch. Nutrient treatments were not favourable for cyanobacteria as the addition of nitrogen probably meant that nitrogen fixing Anabaena species lost competitive advantage over other phytoplankton taxa. It is not known by which mechanism perch promoted cyanobacterial growth since this was not directly measured. Plankton community composition was altered by all treatments. This study indicates that blooms of Anabaena species in the Lower Karori Reservoir are the result of a number of complex interactions within the lake food web. Low nitrogen levels favour dominance by the nitrogen fixing cyanobacteria, which bloom during thermal stratification as they are able to maintain their position in the water column due to buoyancy control. Predation pressure by perch is likely keeping large filter-feeding zooplankton at low levels and thus reducing grazing pressure on phytoplankton. Phosphorus excretion by perch also probably favours cyanobacteria. An eradication of perch within the Lower Karori Reservoir would probably contribute to prevent cyanobacteria predominance. The removal of perch from the reservoir should be reasonably simple due its small size and contained area. Other methods which may help reduce cyanobacterial blooms within the reservoir include artificial mixing to prevent stratification. However, these methods can be expensive to install and run.</p>