The dissertation thesis focuses on predator ecology in artificial water bodies. Paper I deals with the importance of chemical cues for predator-prey interactions in an aquatic environment. Here, I demonstrate that the ability to detect chemical cues represents a survival benefit for prey species. Paper II points out gillnet methodological bias, which may have subsequent repercussions in field evaluation of a predator's presence and assessment of larger fish abundance in general. Papers III and IV focus on asp Leuciscus aspius spawning grounds. In Paper III, I demonstrate how males maximize their spawning chances by early arrival and in Paper IV, I evaluate the predation pressure of asp prey, Alburnus alburnus, directed on asp eggs.

This Ph.D. Thesis is focused mainly on the biology of two typical European predatory fishes, European catfish (Silurus glanis) and perch (Perca fluviatilis). Catfish is a typical apex predator, whereas perch is a smaller species that plays role of a mesopredator. Although, catfish is the third largest freshwater fish in the world, only few studies dealing with this species have been revealed thus far. The main reason is connected with capturing of the species that is inefficient by standard ichthyologic methods. Studies, that have been revealed recently, focused mainly on expansions of catfish to the West and South Europe. Catfish is unwanted in these localities due to a potential negative impact on native fish community, thus its reduction is desirable. In contrast, catfish occurrence is important in native localities where it plays a key role as a biomanipulative species (I). Catfish is a true generalist, which is a typical feature for large-bodied apex predators connected with high energy consumption of their bodies. The second typical feature is a wide diet plasticity and thus good adaptability to new food sources. It is associated with distribution of various food sources among individuals within the population (II). By contrast, perch is one of the most studied fish in the world and hundreds of studies with IF are revealed every year. However, the more information about biology of perch have been known, the more questions have been arisen. Several phenomena are revealed also in this thesis. For instance, crucial impact of juvenile perch on the entire ecosystem is described. High predation pressure on zooplankton may induce piscivory in primarily zooplanktivorous fish (III). Further, juvenile perch utilize hypoxic pelagic zones as a refuge against predation (IV). The last surprising phenomenon is described in the study dealing with both species, catfish and perch. Their coexistence may lead in strong discrimination of one species caused by special predation that was supposed to be implausible (V).

Insight into environments and habitats that contribute recruits to adult fish stocks in riverine systems is vital for effective population management and conservation. Catfishes are important recreational species in the Mississippi River and are commercially harvested. However, contributions from main channel and tributary habitats to catfish recruitment in large rivers such as the middle Mississippi River (between St. Louis, MO and Cairo, IL) are unknown. Stable isotope and trace elemental signatures in otoliths have been useful for determining environmental history of fishes in a variety of aquatic systems, including the Mississippi River. The objectives of this study were to identify the principle natal environments of channel catfish Ictalurus punctatus and blue catfish I. furcatus in the middle Mississippi River (MMR) using otolith stable oxygen isotopic composition (δ18O) and strontium:calcium ratios (Sr:Ca). Catfish were sampled in the MMR during July-October 2013 and 2014 and lapilli otoliths were analyzed for δ18O and Sr:Ca. Water samples from the MMR and tributaries were collected seasonally from 2006-2014 to characterize site-specific signatures. Persistent differences in water δ18O and Sr:Ca among the MMR and tributaries (including the upper Mississippi, Illinois, and Missouri rivers as well as smaller tributaries) were evident, enabling identification of natal environment for individual fish. Results indicated that blue and channel catfish stocks in the MMR primarily recruited from the largest rivers (Missouri and Mississippi rivers) in our study area and received minimal influence from smaller tributaries. Recruitment and year class strength investigations and efforts aimed at enhancing blue and channel catfish spawning and nursery habitats should be focused in the large rivers with less emphasis in the smaller tributaries.

The use of fatty acid (FA) analysis has become an important tool in recent years to investigate a broad spectrum of questions in fisheries and aquatic ecology. One of these applications has been the use of FA profiles as biomarkers for indicating diet and recent feeding history of fishes and other aquatic consumers. Differences in forage FA profiles and spatial differences in food web structure within aquatic systems may lead to corresponding spatial patterns of FA profiles in consumers, thereby facilitating the potential applicability of FA biomarkers as indicators of habitat use and origin for mobile consumers such as fishes. However, little information is available regarding differences in FA profiles among habitat types in river-floodplain ecosystems and the time-scale over which fish FA profiles change when fish move between habitats that differ in the FA profiles of prey resources. The objectives of this study were to test whether the tissue FA profiles of channel catfish (Ictalurus punctatus) differed among three reaches of the lower Kaskaskia River and its floodplain lakes, to determine the time-course of tissue FA profile turnover when fish are relocated to a new habitat type, and to compare FA profiles among muscle, liver, and adipose fin tissues in channel catfish. Fatty acid profiles of channel catfish were significantly different among sites, especially between upper and lower river sites, and between river channel and oxbow lake sites, suggesting differing energy sources among habitats and river reaches in the Kaskaskia system. More specifically, there was a significant increase in the essential FAs, 18:2n-6 and 18:3n-3, in channel catfish with increasing distance downstream, which could reflect an increase in river-floodplain connectivity at downstream sites. Channel catfish transplanted from the Kaskaskia River to ponds at Southern Illinois University Carbondale showed a significant linear decrease in n-3 and medium-chain polyunsaturated FAs (MC-PUFA), and a significant linear increase in monounsaturates (MUFA) with longer residence time in a lentic environment. Liver tissue exhibited the fastest turnover rate of the three tissue types (< 2 weeks), with muscle and adipose fin tissue both displaying similar, longer turnover times (approximately 10 weeks). Results of this study support the use of FA profiles as indicators of energy sources for fishes in large river-floodplain ecosystems, including the potential for indentifying habitat-specific (river channel vs. floodplain lake) or river reach-specific energy sources. Additionally, results of this study provide a timeline for FA turnover in channel catfish tissues when fish move among habitats with distinct FA signatures, which is crucial for detecting temporal shifts in use of habitat-specific energy sources by channel catfish. Results also suggest that adipose fin tissue samples may be a less invasive alternative to muscle tissue for analysis of FA profiles in channel catfish. Improved understanding of which habitats or river reaches provide trophic support for riverine fishes through use of FA profile analysis has potentially important implications for habitat conservation and rehabilitation in river-floodplain ecosystem.

Metals are ubiquitous and naturally occurring; however, anthropogenic activities have elevated metal concentrations in river sediments above what would be expected naturally. One of the primary anthropogenic sources of metals in freshwater is contamination by mine tailings, a toxic slurry of waste rock and chemicals left over after ore minerals or coal extraction. Mining waste is most often stored in retention ponds, which sometimes leak or fail. One of the worst mine tailings disasters on record occurred on the Tisza River of Central Europe in the winter of 2000, releasing over 240,000 tons of mine tailings laced with metals into the natural environment. Elevated metals in freshwater can negatively affect fish and other aquatic organisms, raising concerns as to the long-term ecological consequences of the spill. Therefore, the objectives of this dissertation were to describe the ecological implications of metals pollution from mining on freshwater systems through an empirical case study of the Tisza River combined with controlled laboratory experiments of chronic cadmium exposure on a model species, channel catfish (Ictalurus punctatus). Specific research questions discussed in the following chapters include: (1.) What is the current distribution of metals in the lower Tisza River Basin and are metals transported from the main channel to floodplain habitats?; (2.) Is there evidence for bioaccumulation and/or trophic transfer of metals to fish in the Tisza?; (3.) What are angler’s perceptions and fish consumption risks in the lower Tisza river basin?; and (4.) What are the effects of sub-lethal exposure to cadmium on growth, development, metabolism, and stress response in a model fish species? The case study of the Tisza River Basin was conducted during early summer in 2013 and 2014. Water, sediment, and fish were collected from the Tisza River as well oxbow lakes along the lower basin. Samples were screened for metals via GF-AAS following standard methods. Additionally, we conducted interviews at each sampling location to determine fish consumption habits. Controlled laboratory exposures were conducted during summer of 2015. Eggs of channel catfish (Ictalurus punctatus) were fertilized in treatment water and raised to 6 month old fingerlings. Treatments of cadmium included concentrations of 0.5 µg L-1 (control), 2 L-1 (low) and 6 L-1 (high), with endpoints of growth, development, cellular stress, metabolism, and general stress response. Results indicate that lakes with the greatest connectivity trended toward elevated metals; however, chlorophyll a concentrations decreased suggesting dilution of nutrients from surrounding agriculture. River connectivity therefore increases ecosystem health of floodplain lakes by ameliorating eutrophication, but as a trade-off with potential contamination of metals. This may have implications for management strategies in the basin as fish from the oxbow lakes also trended toward higher concentrations of metals compared to the river main stem. Although we did not detect any indication that metals are biomagnifying through the fish community, fish are clearly taking up contaminants from the water and sediment. Additionally, although fish fillets generally fell below human consumption guidelines, surveys collected at field sites indicate disparities between health risks and perceptions of those risks. For example, many people believe that fish from the oxbow lakes present a lower risk for metals than the river main stem, converse to our findings. Exposure of channel catfish to cadmium concentrations similar to those observed in the Tisza Basin indicate that negative physiological effects, such as altered carbohydrate metabolism and subsequently growth, can occur in fish at muscle concentrations below consumption guidelines. Although cadmium in Tisza fish fillets were lower than expected, metals may still be problematic for the basin as they may disproportionately affect early life stages of fish. This could skew life histories of exposed populations compared to unaffected fish, potentially reducing growth rates, size at maturity, reproductive output, and lifespan; indicating the need for more paired field and laboratory assessments of chronic metals exposure.

Orientador: Carlos Alberto de Magalhães Lopes / Banca: Silvio Luis de Oliveira / Banca: Vidal Haddad Junior / Banca: Mônica Valdyrce dos Anjos Lopes Ferreira / Banca: Itamar Alves Martins / Resumo: Nossos estudos objetivaram caracterizar as respostas imune inata e específica induzidas pelas peçonhas do muco e do ferrão do bagre Cathorops agassizii . A coleta dos espécimes foi realizada no complexo Baía-Estuário de Santos e São Vicente, localizado no litoral sul do Estado de São Paulo. As peçonhas (do Muco e do Ferrão) apresentaram perfil eletroforético similar entre si. Induzida a inflamação aguda em um modelo experimental murino, as peçonhas apresentaram igualmente a capacidade de induzir aumento da permeabilidade vascular e também edema de pata. A detecção de Leucotrieno B4 e Prostaglandina E2 no lavado da cavidade peritoneal dos camundongos injetados, com ambas as peçonhas, corroboram esta hipótese. Nossos resultados através da microscopia intravital mostraram que as peçonhas induzem um grande número de leucócitos rolantes nas vênulas pós-capilares com focos de extravasamento leucocitário, principalmente de neutrófilos seguido pelo influxo de macrófagos. Além disso, a peçonha do Ferrão induziu uma resolução mais rápida do influxo leucocitário ao contrário da peçonha do Muco que manteve o infiltrado macrofágico por até 7 dias. De maneira interessante, somente a citocina IL-6 foi detectada no lavado peritoneal induzida principalmente pela peçonha do Muco e as quimiocinas KC e MCP-1, por ambas as peçonhas, expressando naquele momento, a participação destes mediadores no recrutamento de neutrófilos e macrófagos para o sítio da lesão. As peçonhas foram eficazes ao induzir uma produção primária e secundária de anticorpos das classes IgM e IgG anti-venenos. Observamos ainda, uma especificidade dos anticorpos produzidos para os componentes das próprias peçonhas e também uma reatividade antigênica cruzada entre elas. / Abstract: Our studies aimed to characterize the innate and specific immune responses induced by poisons of the mucus and sting of the catfish Cathorops agassizii. The collection of specimens was accomplished in the complex Bay-Estuary System of Santos and São Vicente located in the south coast of the São Paulo State. Poisons of the Mucus and Sting presented similarities in their electrophorectical profiles. In basis of an Induced process of inflammation throughout an experimental murine model, both poisons equally showed the capacity to increase the vascular permeability and also paw edema. The Leucotrien B4'S and Prostaglandine E2 detection in washings of mice peritoneal cavity injected with both poisons corroborates this hypothesis. Our results through an intravital microscopy procedure also showed that the poisons induced a great number of rolling leukocytes in the post-capillary venules with focus on the leukocyte overflow mainly neutrophiles followed by macrophage influx. Besides, the sting poison Sting induced a faster resolution of the leukocyte influx, as well as, the Mucus poison unlike maintained a macrophage infiltrated for up to 7 days. In an interesting way, only the cytokine IL-6 was detected in peritoneal washings induced mainly by the Mucus poison although Quimiokinins KC and MCP-1 were for both poisons, expressing on that moment the participation of these mediators in the neutrophile and macrophage recruitment for the lesion site. The poisons were also effective in the induction of a primary and secondary production of IgM and IgG classes of antibodies. In this research we still observed a specificity of the antibodies produced for the components of the own poisons and also a crossed antigenic reactivity among them. / Doutor

In the Kruger National Park (KNP), pansteatitis in sharptooth catfish, Clarias gariepinus (Burchell), was shown to be a serious problem in the inlets to large man-made lakes fed by rivers arising in the polluted catchments of the Olifants and Sabie rivers. An increasing prevalence of pansteatitis was recorded in catfish from the Olifants River gorge. A low prevalence was found in catfish upstream of the gorge at two further sites. No pansteatitis was detected in catfish from a rain-filled dam distant from the potential pollution sources affecting the Olifants River and in rivers arising outside of the park that were not dammed. Analysis of stomach content indicated a higher prevalence of fish in the diet of catfish affected by pansteatitis than in those not affected. Significant pathology in catfish was limited to changes associated with a generalised necrosis and inflammation of adipose tissues (pansteatitis), and there was evidence that lesions accumulated over time. Similar pathology was found in a captive population of catfish with known nutritional pansteatitis. Pathology in other organs that might have been attributed to pollution could not be demonstrated. Examination of blood smears and measurement of haematocrit, blood haemoglobin, serum vitamin E and erythrocyte glutathione peroxidase values did not prove useful as monitoring tools, probably because of the episodic exposure to oxidative stress and the chronic nature of the condition. Pansteatitis-affected catfish, kept in an experimental pond for 11 months after the inciting nutritional cause had been removed, retained steatitis lesions almost unaltered. Whereas lipolysis appeared to be reduced by pansteatitis, adipogenesis appeared to be unaffected. Juvenile catfish confined in experimental tanks with sediments from sites where pansteatitis occurred remained healthy, and no pathology developed after 14 months, suggesting that sediments were not directly toxic. The results of the study present the first record of pansteatitis in both wild and farmed African sharptooth catfish and emphasize the ecological importance and complexity of nutritional oxidative stress in a disturbed aquatic environment. Nutrient entrapment and the consumption of phytoplankton-feeding fish rich in polyunsaturated fats, particularly silver carp, Hypophthalmichthys molitrix (Valenciennes), a species alien to Africa but present in the Olifants River, is proposed as the dietary cause of the pansteatitis. / Thesis (PhD)--University of Pretoria, 2012. / Paraclinical Sciences / unrestricted

In 2015, Illinois changed size and harvest limits for catfishes (blue catfish Ictalurus furcatus, flathead catfish Pylodictis olivaris, and channel catfish Ictalurus punctatus) in the Ohio River to match those of neighboring states in order to provide continuity of the regulations and promote a trophy catfish fishery. Regulations imposed a daily limit of one blue catfish or flathead catfish ≥ 35 inches (88.9 cm) and one channel catfish ≥ 28 inches (71.1 cm) per fisher and a 13 inch (33.0 cm) minimum length limit for all species with no bag limit. Although management regulations were implemented, potential efficacy of the implemented regulations and appropriate (i.e. most precise or accurate with fewest samples) monitoring protocols were unknown. Furthermore, there was general lack of understanding of early life movements, natal dispersal timing and principal recruitment sources that aide in determining appropriate spatial scale for monitoring and managing lower Ohio River catfish stocks.To fill these knowledge gaps the following methods were employed: 1) simulation modeling was used to evaluate precision in estimating catch and size distribution metrics for monitoring population trends with increasing sample size (i.e., sampling events), 2) N-mixture modeling was used to estimate size selectivity of multiple gears using detection probability as a robust alternative to size-specific catchability coefficients, 3) otolith microchemistry (Sr:Ca and Ba:Ca) was employed to determine principal recruitment sources, early life movement patterns, and provide fisheries managers with a better understanding of the spatial extent to which management actions should be implemented, 4) Bayesian modeling was used to estimate growth and mortality, 5) Yield-per-recruit modeling was used to estimate and evaluate fishing mortality rates that would result in growth overfishing (FMAX) and yield at FMAX (YPRMAX) for three management scenarios (no regulation, minimum length limit [33.0 cm or greater] and a permissive slot limit [33.0 cm – 88.9 cm; blue catfish and flathead catfish]). The simulation models presented account for the uncertainty associated with heterogeneous selectivity of a gear, and minimize the impact of rare or extreme catch values. Trotlines and low pulse (15-pps) electrofishing generally required the fewer samples to achieve stable values of catch per unit of effort (CPUE), proportional size distribution (quality; PSDQ), and coefficient of variation (CV) than other gears based on simulation modeling. Abundance and detection probabilities were estimated separately for each species of catfish by length category within and across gears, producing a species-gear-size correction for catch bias used in estimating Proportional Size Distribution - Quality (PSDQ). Corrected (i.e., accounting for detection) PSDQ values were lower than uncorrected estimates suggesting a positive bias for larger fish across the entire sampling regime. Managers should use a combination of low pulse electrofishing, trotlines, and high pulse (60-pps) electrofishing in their monitoring efforts for all three species. Based on microchemistry, ictalurid catfishes in the lower Ohio River appear to recruit from multiple sources and make movements across a broad geographic scale. Additionally, some catfish may be originating from outside the portion of the Ohio River that is managed by Illinois (lower 214 km). Fisheries managers should take this into account when implementing management actions. However, most ictalurid catfishes originated from riverine (e.g., Ohio and Mississippi River) natal environments and not from smaller tributaries, and managers should not expect tributaries to compensate for weak year-classes within the river. Based on yield per recruit modeling, catfish stocks are unlikely to benefit from current regulations or a theoretical minimum size limit given the near complete overlap of YPRMAX confidence intervals for all estimable scenarios and the small statistical difference (1 – 3%) based on FMAX between the most permissive and most restrictive scenarios. While statistical differences in FMAX exist, they are likely biologically irrelevant, exceeding the precision of estimation methods for F. While there is some indication that alignment and continuity of management regulations is warranted based on microchemistry, the efficacy of the current permissive slot regulations is questionable based on the models presented and the life history of these fishes. There is no advantage to implementing any of the modeled regulations in terms of increasing FMAX or YPRMAX.

Myxozoans are cnidarian parasites of primarily freshwater and marine fish, with some being important pathogens of aquacultured fish species worldwide. Their life cycles have waterborne actinospores released from aquatic annelid definitive hosts and myxospore stages in fish intermediate hosts. In the southeastern United States, catfish aquaculture is burdened by annual losses to a myriad of infectious diseases. Henneguya ictaluri, the causative agent of proliferative gill disease in channel catfish Ictalurus punctatus and female channel catfish x male blue catfish Ictalurus furcatus hybrids, is the most commonly diagnosed parasitic disease of catfish in Mississippi. Other myxozoans infect these ictalurid fish, but their impact on catfish production is unknown. Surveys of actinospores from the oligochaete Dero digitata and myxospore stages from fish revealed an unexpected diversity for these production systems. Six genetically distinct actinospores representing four collective groups were observed from D. digitata. Herein, two novel Henneguya spp. are described from the gills and a novel Unicauda sp. is described from the intestinal tract of channel catfish. One Henneguya sp. was linked to its actinospore stage and represents the fourth known life-cycle in the genus. In addition to catfish, smallmouth buffalo Ictiobus bubalus polycultured with catfish were examined and two Myxobolus spp. were characterized from the gills. Phylogenetic analyses strongly support a clade of ictalurid Henneguya spp. and a clade of catostomid Myxobolus spp. Although diverse, H. ictaluri is the only myxozoan in catfish attributed to significant losses. With no feasible method of control or treatment, investigations into less susceptible fish were initiated and showed promise. Infectivity trials characterizing H. ictaluri development in channel, blue, and hybrid catfish were performed. Channel catfish were suitable hosts with myxospores developing in the gills by six weeks and persisting for at least 14 weeks. In hybrid catfish arrested or limited development was observed with no pseudocysts observed during Trial 1 and only two at 14 weeks during Trial 2. These results may suggest a possible way of decreasing losses attributed to PGD through hybrid catfish monoculture or fish crop rotation to reduce the number of infectious myxospores released into the pond.

According to USDA-FSIS reports, L. monocytogenes and Salmonella are two important foodborne pathogens that are prevalent throughout catfish environment. Channel catfish (Ictalurus punctatus) is the most important aquaculture species in the United States accounting for more than 60% of its aquaculture production. The objectives of this study were to determine the effect of strain, temperature concentration on the growth, survival and biofilm formation of L. monocytogenes and Salmonella using catfish mucus extract on different food-contact surfaces. Growth and survival of L. monocytogenes and Salmonella was greater at the higher concentration of mucus extract at both 10°C and 22°C. In 15 micrograms/ml catfish mucus extract L. monocytogenes and Salmonella counts increased to 4.5 log CFU/ml after 72 h at 10°C and 5-7 log CFU/ml counts after 32-48 h at 22°C. In 375 micrograms/ml catfish mucus extract L. monocytogenes and Salmonella counts increased to 6-7 log CFU/ml counts after 72 h at 10°C and 8-9 log CFU/ml counts after 32-48 h at 22°C. L. monocytogenes and Salmonella were able to grow and survive for more than 63 days with at least 4-6 log CFU/ml at 10°C and 6-8 log CFU/ml in 375 micrograms/ml and 15 micrograms/ml of catfish mucus extract respectively. No differences (P > 0.05) among L. monocytogenes and Salmonella strains were observed to form biofilms in the presence catfish mucus extract on the stainless steel surface. The biofilm formation by L. monocytogenes and Salmonella in catfish mucus extract was less (P < 0.05) on buna-n rubber when compared to stainless steel, polyethylene and polyurethane surfaces. Therefore, the findings in this study show that catfish mucus promotes L. monocytogenes and Salmonella to grow and subsequently form biofilms on different food-contact surfaces also promotes growth and survival of these pathogens for longer period of time in catfish processing industries.