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Blood sugar levels were determined in toadfish and catfish by the Folin reducing procedure and a specific enzymatic glucose procedure. The difference between the two values was considered to be the rest reduction (RR). After alloxan injection, the RR level increased greatly reaching a peak at one hour and then decreasing. The glucose level rose more slowly. An attempt was made to study these changes in blood by paper chromatography using silver nitrate to detect reducing compounds. In normal blood, glucose, an unidentified compound, and several other reducing compounds present in small amounts were separated. The large amount or RR present after alloxan could not be detected by silver nitrate. The significance of the results was discussed and future investigations were suggested. / Thesis / Master of Science (MSc)

Blue Catfish were introduced in the tidal tributaries of the Chesapeake Bay in the 1970s and 1980s to establish new fisheries during a time period when many fisheries were in decline due to pollution, habitat alteration, disease, overfishing, and environmental catastrophes. Having expanded their range to most Bay tributaries, the species has drawn concern from many stakeholders and scientists for its effects on at-risk and economically important native and naturalized species. My study focused on understanding the dynamics of this species based on multiple long-term monitoring data and evaluating potential management strategies to meet stakeholder needs. I sought to understand how is growth variability was partitioned over time and space, how Blue Catfish populations changed from 1994 to 2016, and how predation on native species and fishery-based performance measures may respond to management intervention. As Blue Catfish length-at-age is exceptionally variable in Virginia tributaries of the Chesapeake Bay, I evaluated the variability in growth using candidate non-linear mixed effects models that described variability in growth over time and space. Linear trend tests supported declines in growth over time within river systems, but did not support the presence of synchronous growth responses among river systems. To better understand population dynamics of Blue Catfish in the Chesapeake Bay watershed, I developed a statistical catch-at-length model for the James River to estimate population size, instantaneous fishing mortality, and size structure over time. The statistical catch-at-length model estimated that Blue Catfish abundance increased slowly and peaked in the mid-2000s before undergoing a recent decline. The model estimated a large spike in abundance due to an estimated large recruitment event in 2011, but may be an artifact of missing data in 2012 in both relative abundance indices examined. The newly developed statistical catch-at-length model provides most detailed information on population dynamics of Blue Catfish in the James River and can be expanded and updated as new data become available. Based on results of the statistical catch-at-length model, I examined population responses to unregulated, maximum length limit (60 cm), and harvest slot limit regulations (harvest allowed 25 –60 cm) in a management strategy evaluation framework. The management strategy evaluation supported that the James River Blue Catfish population could be reduced with increased harvest, but trophy-size fish would decline. Consequently, fishery managers tasked with invasive species management must consider this tradeoff of fishery economic benefits and predation on native populations, especially those prey in which population sizes are unknown. / Doctor of Philosophy / Blue Catfish are non-native to the Chesapeake Bay watershed, but were stocked in the 1970s and 1980s to provide fishing opportunities to the region. Unknowingly, Blue Catfish expanded downstream and beyond the boundaries of the rivers to which they were originally stocked and now exist in extremely dense populations in places. This expansion in population size and distribution has generated concern for the health of the Chesapeake Bay and calls for population control. I wanted to learn more about Blue Catfish in Virginia, specifically Blue Catfish growth rates, population dynamics, and how they might respond to control efforts. I examined Blue Catfish growth rates and found growth rates differed over time and across river systems. Blue Catfish tended to grow more slowly over time as their populations matured. As growth rates declined, population size increased with maximum population sizes in the late 2000s in the James River with a subsequent decline in abundance. Many invasive species exhibit this sort of phenomenon, where population sizes increase and reach a maximum before declining. Finally, I looked at Blue Catfish responses to different fishing regulations and harvest levels, finding that increased harvest could help control Blue Catfish population sizes. However, Blue Catfish management objectives are in conflict as regulations that limit predation of native species of interest also reduce the proportion of large fish in populations. Blue Catfish management will require stakeholder-driven approaches to ensure buy-in and reduce user conflicts.

This investigation examined the diet, growth, movement, population genetics, and possible consumption demands of an introduced blue catfish Ictalurus furcatus population in Lake Norman, North Carolina. Clupeids, Corbicula fluminea, and Chara were the predominant food items (percent stomach contents by weight) found in blue catfish, and varied by season, lake-region, and fish size-class. Lake Norman blue catfish grow at a slower rate than has been reported for other reservoir populations, with fair to poor body conditions (Wr<85) early in life, but improving with increases in length (Wr>95). Movements and home ranges of blue catfish in Lake Norman were extremely varied, but individual blue catfish did establish specific seasonal home ranges and exhibited site fidelity. A spawning area in the upper region of the lake was identified and data suggested that blue catfish may have segregated populations within Lake Norman. The Lake Norman blue catfish population exhibited relatively little genetic variability, and was genetically differentiated from populations from Santee-Cooper, SC, and Arkansas. Genetic diversity could have been limited by a population bottleneck at the founding of the population or in subsequent generations. A consumption model indicated that 5.0 kg/ha to 8.3 kg/ha of clupeid standing stock could be eaten annually by blue catfish in Lake Norman based on percent stomach contents by weight data, and 21 kg/ha to 42 kg/ha based on percent caloric contribution calculations. This may reduce the possible production of other game fish species, including the put-grow-take striped bass Morone saxatilis fishery. / Master of Science

Aquacultured products assist the human demands for seafood so that foodfish supplies can remain sustainable and consistent. Although the fish-farming industry has seen dramatic growth and intensification in recent years, the latter has led to an increase in bacterial diseases and fish health management problems, resulting in major economic losses around the world. In addition to the lack of understanding of fish physiology, these complications are exacerbated by the inappropriate and controversial use of antibiotics. This work addressed these issues in striped catfish (Pangasius hypophthalmus) and Nile tilapia (Oreochromis niloticus), two economically important foodfish, by investigating alternative, more cost-effective options to promote fish health. The first two studies established reference intervals for immunology, hematology and plasma chemistry analytes in striped catfish in a recirculating aquaculture system (RAS). In a third study, the immunomodulatory effects after directly feeding probiotic strains of Bacillus subtilis NZ86 and O14VRQ in Nile tilapia were ascertained. This last study revealed that supplementation with both of the probiotic strains for 51 days stimulated several local and systemic innate immune responses of tilapia. When these transient probiotic bacteria were present in the gut, a pro-inflammatory environment was developed as evidenced by the localized higher expression of the cytokines tumor necrosis factor (TNF) – α and interleukin (IL) – 1β. Significant increases (p < 0.05) were noted differentially by both probiotic strains throughout the trial in plasma lysozyme content, alternative complement activity, and in the peripheral blood leukocyte profiles. Additionally, there were trends for increased levels of phagocytosis and respiratory burst in leukocytes of the anterior kidney and spleen at the end of the trial, suggesting the potential use of these probiotic strains for improved immune-competence. These findings help to understand and clarify the potential mechanism of action associated with the increased disease resistance recorded in preliminary studies with the same probiotic strains. Implementation of the tools established and validated in this work could be useful in evaluating fish welfare situations involving striped catfish grown in RAS conditions, and also show promise for a healthier foodfish supply where antibiotic applications practices could be minimized. / Ph. D. / Aquaculture, or fish farming, is one of the most prosperous production sectors of animal-derived food. Despite the success story of aquaculture, the fish industry is heavily plagued by bacterial diseases, which cause losses in billions of dollars annually around the world, and directly contribute to increases in human food insecurity. Since the options to cost-effectively address diseases are limited, I explored alternative ways to more safely monitor and also ensure optimal health in striped catfish and tilapia, two globally important aquaculture fishes. I investigated the values of different cellular and chemical components of the blood to monitor the health of striped catfish when grown in indoor recirculating conditions, in order to understand normal catfish physiology. The values of these blood components were comparable to those of other freshwater fishes. As part of another study, I supplemented probiotics in the diet of the tilapia for 51 days, and assessed the effects of these on the immune system of the fish. Dietary supplementation of the probiotics resulted in the presence of the probiotics in the gut of the fish. Furthermore, the presence of these microbes was tightly linked to elevated values of numerous functions of the immune system. These functions included levels of lysozyme, alternative complement, and percentage of neutrophils, which are all related with a state of heightened immunity in the animal host. The tools that I established and validated in this study are promising alternatives to optimize the health of these two important foodfish. Moreover, they could be useful for the fish farmer because of their greater cost-effectiveness, and can potentially lead to a safer foodfish supply by decreasing the reliance on antibiotics.

Intensive Forschung hat in den vergangenen Jahrzehnten zu einer sehr detaillierten Charakterisierung des Geschmackssystems der Säugetiere geführt. Dennoch sind mit den bislang eingesetzten Methoden wichtige Fragestellungen unbeantwortet geblieben. Eine dieser Fragen gilt der Unterscheidung von Bitterstoffen. Die Zahl der Substanzen, die für den Menschen bitter schmecken und in Tieren angeborenes Aversionsverhalten auslösen, geht in die Tausende. Diese Substanzen sind sowohl von der chemischen Struktur als auch von ihrer Wirkung auf den Organismus sehr verschieden. Während viele Bitterstoffe potente Gifte darstellen, sind andere in den Mengen, die mit der Nahrung aufgenommen werden, harmlos oder haben sogar positive Effekte auf den Körper. Zwischen diesen Gruppen unterscheiden zu können, wäre für ein Tier von Vorteil. Ein solcher Mechanismus ist jedoch bei Säugetieren nicht bekannt. Das Ziel dieser Arbeit war die Untersuchung der Verarbeitung von Geschmacksinformation in der ersten Station der Geschmacksbahn im Mausgehirn, dem Nucleus tractus solitarii (NTS), mit besonderem Augenmerk auf der Frage nach der Diskriminierung verschiedener Bitterstoffe. Zu diesem Zweck wurde eine neue Untersuchungsmethode für das Geschmackssystem etabliert, die die Nachteile bereits verfügbarer Methoden umgeht und ihre Vorteile kombiniert. Die Arc-catFISH-Methode (cellular compartment analysis of temporal activity by fluorescent in situ hybridization), die die Charakterisierung der Antwort großer Neuronengruppen auf zwei Stimuli erlaubt, wurde zur Untersuchung geschmacksverarbeitender Zellen im NTS angewandt. Im Zuge dieses Projekts wurde erstmals eine stimulusinduzierte Arc-Expression im NTS gezeigt. Die ersten Ergebnisse offenbarten, dass die Arc-Expression im NTS spezifisch nach Stimulation mit Bitterstoffen auftritt und sich die Arc exprimierenden Neurone vornehmlich im gustatorischen Teil des NTS befinden. Dies weist darauf hin, dass Arc-Expression ein Marker für bitterverarbeitende gustatorische Neurone im NTS ist. Nach zweimaliger Stimulation mit Bittersubstanzen konnten überlappende, aber verschiedene Populationen von Neuronen beobachtet werden, die unterschiedlich auf die drei verwendeten Bittersubstanzen Cycloheximid, Chininhydrochlorid und Cucurbitacin I reagierten. Diese Neurone sind vermutlich an der Steuerung von Abwehrreflexen beteiligt und könnten so die Grundlage für divergentes Verhalten gegenüber verschiedenen Bitterstoffen bilden. / Intense research in the past decades has led to a detailed understanding of the mammalian taste system. Some important issues, however, have remained unanswered with the established methods that have been applied so far. One of these questions is whether different bitter substances can be distinguished. There are thousands of compounds which taste bitter to humans and elicit innate aversive behavior in animals. Moreover, these bitter substances are very heterogeneous regarding their structure as well as their effect on the organism. While many bitter tastants are potent poisons, others are harmless or even have beneficial effects in the amounts that are typically ingested. The ability to discriminate between those groups of bitter tastants could be an evolutionary advantage. Such a mechanism, however, is not known for mammals. The aim of this thesis was to study the processing of taste information in the first station of gustatory processing in the mouse brain, the nucleus of the solitary tract (NTS). Of particular interest was the question concerning discrimination of bitter tastants. To this end a new method was established for the taste system combining the advantages of methods used before while circumventing their disadvantages. The Arc catFISH method (cellular compartment analysis of temporal activity by fluorescent in situ hybridization), which allows the characterization of responses of large neuron populations to two stimuli, was used to analyze taste-processing cells in the NTS. In the course of this project a stimulus-induced Arc expression in the NTS was shown for the first time. The results demonstrated that Arc expression in the NTS appears specifically after stimulation with bitter tastants and that the Arc expressing neurons are located primarily in the gustatory part of the NTS. This indicates that Arc expression is a marker for bitter-processing gustatory neurons in the NTS. Upon stimulating twice with bitter compounds, distinct, yet overlapping neuron populations were identified, that reacted differently to the three bitter substances cycloheximide, quinine hydrochloride, and cucurbitacin I. Presumably these neurons are involved in the regulation of aversive reflexes and could form a basis for divergent behavior towards different bitter substances.

Master of Science / Division of Biology / Martha E. Mather / Understanding how and why fish distribution is related to specific habitat characteristics underlies many ecological patterns and is crucial for effective research and management. Blue Catfish, Ictalurus furcatus, are an important concern for many fisheries agencies; however, lack of information about their distribution and habitat use remains a hindrance to proper management. Here, over all time periods and across months, I quantified Blue Catfish distribution and environmental correlates of distribution in Milford Reservoir, the largest reservoir in Kansas. I tested relationships among acoustically tagged Blue Catfish and three groups of variables postulated to influence Blue Catfish distribution in the literature (i. localized microhabitat variables, ii. larger-scale mesohabitat variables, iii. biotic variables). Blue Catfish were consistently aggregated in two locations of the reservoir across five months during summer and fall, 2013. Using multiple linear regression and an information theoretic model selection approach, consistent correlates of distribution included localized, microhabitat variables (i.e., dissolved oxygen, slope) larger-scale, mesohabitat variables (i.e., distance to channel, river kilometer from the dam) and a biotic variable (i.e., Secchi depth). This research identified which 5 of the 12 variables identified in the literature were most influential in determining Blue Catfish distribution. As a guide for future hypothesis generation and research, I propose that Blue Catfish distribution was driven by three ecologically-relevant tiers of influence. First, Blue Catfish avoided extremely low dissolved oxygen concentrations that cause physiological stress. Second, Blue Catfish aggregated near the channel, an area of bathymetric heterogeneity that may offer a foraging advantage. Third, Blue Catfish aggregated near low Secchi depths, shown here to be associated with increased productivity and prey abundance. Building on my results, future research into the distribution and habitat use of Blue Catfish should incorporate aggregated distributions of fish into research designs, focus on how both small and large scale relationships interact to produce patterns of distribution, and explore further the mechanisms, consequences, and interactions among the three tiers of influence identified here.

Channel catfish have pectoral spines that lock to defend against gape-limited predators such as largemouth bass. Previous work indicated that spines increase survival of channel catfish exposed to bass but did not determine whether bass avoid catfish if less dangerous species are available. We presented bass with channel catfish and two alternatives, bluegill and goldfish, and compared order of ingestion, ingestion time, percent of successful strikes, and time spent chasing each prey species. We also presented the three species in a jar study that standardized position in the water column as well as in a net-pen study. The order of ingestion was suggestive of a preference for goldfish, then bluegill and finally channel catfish. Handling time was greater for channel catfish, less for bluegill, and the least for goldfish. Fewer catfish were eaten when other prey were available. Bass appear to avoid channel catfish if alternative prey is available.

Acoustically, teleost swimbladders have been considered resonant underwater bubbles. Contrary results indicating that bladders are tuned less sharply than such a bubble have been explained by damping of surrounding fish tissue. Recent findings in toadfish and weakfish, however, suggest that the bladder is a highly damped structure and that the frequency of the fish sounds is deternlined as a forced response to sonic muscle movement rather than by resonance of the bladder. In this study I examined acoustics and material properties of swimbladders in Tilapia (an auditory generalist) and the channel catfish (an auditory specialist). The swimbladder was struck with a piezoelectric impact hammer. Amplitude and timing characteristics of bladder sound and displacement were compared for strikes of different amplitudes. Most of the first cycle of sound occurs during swimbladder compression, indicating that the bladder rapidly contracts and expands as force increases during the strike. Harder hits are shorter in duration generate a similar displacement duration with an increasing number of shorter cycles and a 12-15 dB increase in sound amplitude. The frequency spectrum is broad, and the dominant frequency is driven by the strike and not the natural frequency of the bladder. The displacement waveform varies between species catfish exhibit a greater structural stiffness and lower amplitude movement and higher sound amplitude for an equivalent hammer strike. Material properties (peak load, stress, strain, Young's modulus), fiber direction (catfish only), and structural stiffiless of bladders exhibit various patterns suggesting that the bladder walls are not uniform structures. Additionally thickness varies regionally. Notably Young's modulus in both species is similar despite large difference in stress and strain. The modulus of catfish bladder increased 1600-fold when dried. Finally the bladder of both species had a high water content averaging about 70%. These data suggest that viscous damping caused by water in the bladder wall is a major factor responsible for acoustic properties of the teleost swimbladder.

Reproduction ability is the key factor for survival and dispersal of every species. There is, however, only limited information about reproduction of large-bodied fish. Males of European catfish, our biggest native fish, build nests in vegetation and mate there later with females. After succesful mating male guards the nest and takes care of eggs and fry. According to literature, the act of reproduction should take place at nights with water temperature from 18 to 24 řC. However, available records about reproductive behaviour are outdated, fragmentary or come from aquacultures. Thus, a study was designed to evaluate behaviour of European catfish in their natural environment in the Berounka river using radiotelemetry, the results of which I processed in this thesis. Spatial distribution of catfish was followed during the whole year, with special attention on separating mating season from the rest of the year. The goal was to determine conditions characteristic for the mating period and to verify that catfish in the field indeed reproduce in pairs. For this purpose, 10 adults were tracked for two-year period (2002-2004) in the Berounka river by radiotelemetry. Exact positions of all individuals were followed in fourteen-day cycles. In every tracking episode, the position of an individual fish was...