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Electricity in Fish Research and Management, 2nd Edition provides a comprehensive discussion of the uses of both electricity and electrical principles in fishery management and research. It covers electric fishing (including theory, equipment, data analysis and practical factors affecting efficiency), fish barriers, fish counters and fish welfare issues. The book concentrates on Electric Fishing (or Electrofishing); an internationally accepted and widely used procedure for sampling fish. Over the past 50 years electric fishing has become a standard method for fishery studies and management e.g. establishing population densities and abundance. However, due to the potential hazards of the method (both to operators and fish) there is a continuing need to develop and promote best practice guidelines. The author has studied fish ecology for 40 years and understands the need for information that reaches out to all levels of understanding in the field. Previous books on this subject have either been collections of scientific papers and/or technical reports or very simple instruction manuals. In this book theory and practice is explained using non-technical language and simple equations. It brings depth as well as breadth in both information and principles behind the methods and should be an invaluable tool to both fisheries managers and researchers. Although the book is aimed at undergraduates, the clear explanation of the factors means that the book is suitable for all levels of practitioners.

The origin of tetrapods from their fish antecedents, approximately 400 million years ago, was coupled with the origin of terrestrial locomotion and the evolution of supporting limbs. Polypterus is a member of the basal-most group of ray-finned fish (actinopterygians) and has many plesiomorphic morphologies that are comparable to elpistostegid fishes, which are stem tetrapods. Polypterus therefore serves as an extant analogue of stem tetrapods, allowing us to examine how developmental plasticity affects the ‘terrestrialization’ of fish. We measured the developmental plasticity of anatomical and biomechanical responses in Polypterus reared on land. Here we show the remarkable correspondence between the environmentally induced phenotypes of terrestrialized Polypterus and the ancient anatomical changes in stem tetrapods, and we provide insight into stem tetrapod behavioural evolution. Our results raise the possibility that environmentally induced developmental plasticity facilitated the origin of the terrestrial traits that led to tetrapods. The most primitive extant bony fish, Polypterus , exhibits adaptive plasticity for life on land when raised on land rather than in water, suggesting that environmentally induced phenotypic plasticity might have facilitated the macroevolutionary transition to life on land. Best fin forward Bichirs (genus Polypterus ) are primitive ray-finned fish found in Africa — and sometimes in home aquaria — that have functional lungs derived from the swim bladder and powerful pectoral fins that provide support during occasional forays ashore. This study takes Polypterus senegalus as a model for the immediate ancestors of tetrapods and quantifies the anatomical and behavioural changes that occur when these fish are 'terrestrialized'. When raised on land, bichirs lift their heads higher off the ground, deploy their forelimbs closer to the midline and slip around much less often than those raised underwater and prompted to walk ashore for the first time. These observations, together with changes in bone structure and musculature, suggest that some of the postural changes seen in the earliest tetrapods, or rather their immediate antecedents, might have been made in response to the environment and assimilated by developmental plasticity.

A method for modelling time-varying dynamic stability in a natural marine fish community finds that seasonal patterns in community stability are driven by species diversity and interspecific interactions. Fish interactions and ecosystem stability Ecological theory suggests that ecosystem stability—the ability of an ecosystem to persist through perturbations—is influenced by changes in the interactions between different species. Masayuki Ushio and colleagues use a 12-year observational dataset of species interactions in a marine fish community in Maizuru Bay, Japan, to examine the link between fluctuations in interspecific interactions and community stability. They find that short-term changes in the interaction network influence the overall community dynamics, with weak interactions and higher species diversity promoting community stability. Ecological theory suggests that large-scale patterns such as community stability can be influenced by changes in interspecific interactions that arise from the behavioural and/or physiological responses of individual species varying over time 1 , 2 , 3 . Although this theory has experimental support 2 , 4 , 5 , evidence from natural ecosystems is lacking owing to the challenges of tracking rapid changes in interspecific interactions (known to occur on timescales much shorter than a generation time) 6 and then identifying the effect of such changes on large-scale community dynamics. Here, using tools for analysing nonlinear time series 6 , 7 , 8 , 9 and a 12-year-long dataset of fortnightly collected observations on a natural marine fish community in Maizuru Bay, Japan, we show that short-term changes in interaction networks influence overall community dynamics. Among the 15 dominant species, we identify 14 interspecific interactions to construct a dynamic interaction network. We show that the strengths, and even types, of interactions change with time; we also develop a time-varying stability measure based on local Lyapunov stability for attractor dynamics in non-equilibrium nonlinear systems. We use this dynamic stability measure to examine the link between the time-varying interaction network and community stability. We find seasonal patterns in dynamic stability for this fish community that broadly support expectations of current ecological theory. Specifically, the dominance of weak interactions and higher species diversity during summer months are associated with higher dynamic stability and smaller population fluctuations. We suggest that interspecific interactions, community network structure and community stability are dynamic properties, and that linking fluctuating interaction networks to community-level dynamic properties is key to understanding the maintenance of ecological communities in nature.

It was recently suggested that supplying the brain with new neurons could counteract Alzheimer's disease (AD). This provocative idea requires further testing in experimental models in which the molecular basis of disease-induced neuronal regeneration could be investigated. We previously found that zebrafish stimulates neural stem cell (NSC) plasticity and neurogenesis in AD and could help to understand the mechanisms to be harnessed for developing new neurons in diseased mammalian brains. Here, by performing single-cell transcriptomics, we found that amyloid toxicity-induced interleukin-4 (IL4) promotes NSC proliferation and neurogenesis by suppressing the tryptophan metabolism and reducing the production of serotonin. NSC proliferation was suppressed by serotonin via down-regulation of brain-derived neurotrophic factor (BDNF)-expression in serotonin-responsive periventricular neurons. BDNF enhances NSC plasticity and neurogenesis via nerve growth factor receptor A (NGFRA)/ nuclear factor 'kappa-light-chain-enhancer' of activated B-cells (NFkB) signaling in zebrafish but not in rodents. Collectively, our results suggest a complex neuron-glia interaction that regulates regenerative neurogenesis after AD conditions in zebrafish.

The scototaxis (dark/light preference) protocol is a behavioral model for fish that is being validated to assess the antianxiety effects of pharmacological agents and the behavioral effects of toxic substances, and to investigate the (epi)genetic bases of anxiety-related behavior. Briefly, a fish is placed in a central compartment of a half-black, half-white tank; following habituation, the fish is allowed to explore the tank for 15 min; the number and duration of entries in each compartment (white or black) are recorded by the observer for the whole session. Zebrafish, goldfish, guppies and tilapias (all species that are important in behavioral neurosciences and neuroethology) have been shown to demonstrate a marked preference for the dark compartment. An increase in white compartment activity (duration and/or entries) should reflect antianxiety behavior, whereas an increase in dark compartment activity should reflect anxiety-promoting behavior. When individual animals are exposed to the apparatus on only one occasion, results can be obtained in 20 min per fish.

Understanding how collective neuronal activity in the brain orchestrates behavior is a central question in integrative neuroscience. Addressing this question requires models that can offer a unified interpretation of multimodal data. In this study, we jointly examine video-recordings of zebrafish larvae freely exploring their environment and calcium imaging of the Anterior Rhombencephalic Turning Region (ARTR) circuit, which is known to control swimming orientation, recorded in vivo under tethered conditions. We show that both behavioral and neural data can be accurately modeled using a Hidden Markov Model (HMM) with three hidden states. In the context of behavior, the hidden states correspond to leftward, rightward, and forward swimming. The HMM robustly captures the key statistical features of the swimming motion, including bout-type persistence and its dependence on bath temperature, while also revealing inter-individual phenotypic variability. For neural data, the three states are found to correspond to left- and right-lateral activation of the ARTR circuit, known to govern the selection of left vs. right reorientation, and a balanced state, which likely corresponds to the behavioral forward state. To further unify the two analyses, we exploit the generative nature of the HMM, using neural sequences to generate synthetic swimming trajectories, whose statistical properties are similar to the behavioral data. Overall, this work demonstrates how state-space models can be used to link neuronal and behavioral data, providing insights into the mechanisms of self-generated action.

Habituation is a form of learning during which animals stop responding to repetitive stimuli, and deficits in habituation are characteristic of several psychiatric disorders. Due to technical challenges, the brain-wide networks mediating habituation are poorly understood. Here we report brain-wide calcium imaging during larval zebrafish habituation to repeated visual looming stimuli. We show that different functional categories of loom-sensitive neurons are located in characteristic locations throughout the brain, and that both the functional properties of their networks and the resulting behavior can be modulated by stimulus saliency and timing. Using graph theory, we identify a visual circuit that habituates minimally, a moderately habituating midbrain population proposed to mediate the sensorimotor transformation, and downstream circuit elements responsible for higher order representations and the delivery of behavior. Zebrafish larvae carrying a mutation in the fmr1 gene have a systematic shift toward sustained premotor activity in this network, and show slower behavioral habituation. Habituation is a process in which animals stop responding to repetitive stimuli, and habituation is altered in autism and other conditions. Here, the authors describe visual habituation networks across the zebrafish brain, and find that fmr1 mutants show slower brain-wide and behavioural habituation.

Determining how prey learn the identity of predators and match their vigilance with current levels of threat is central to understanding the dynamics of predator–prey systems and the determinants of fitness. Our study explores how feeding history influences the relative importance of olfactory and visual sensory modes of learning, and how the experience gained through these sensory modes influences behaviour and survival in the field for a juvenile coral reef damselfish. We collected young fish immediately prior to their settlement to benthic habitats. In the laboratory, these predator-naïve fish were exposed to a high- or low-food ration and then conditioned to recognize the olfactory cues (odours) and/or visual cues from two common benthic predators. Fish were then allowed to settle on reefs in the field, and their behaviour and survival over 70 h were recorded. Feeding history strongly influenced their willingness to take risks in the natural environment. Conditioning in the laboratory with visual, olfactory or both cues from predators led fish in the field to display risk-averse behaviour compared with fish conditioned with sea water alone. Well-fed fish that were conditioned with visual, chemical or a combination of predator cues survived eight times better over the first 48 h on reefs than those with no experience of benthic predator cues. This experiment highlights the importance of a flexible and rapid mechanism of learning the identity of predators for survival of young fish during the critical life-history transition between pelagic and benthic habitats.

Some of the densest microbial ecosystems in nature thrive within the intestines of humans and other animals. To protect mucosal tissues and maintain immune tolerance, animal hosts actively sequester bacteria within the intestinal lumen. In response, numerous bacterial pathogens and pathobionts have evolved strategies to subvert spatial restrictions, thereby undermining immune homeostasis. However, in many cases, it is unclear how escaping host spatial control benefits gut bacteria and how changes in intestinal biogeography are connected to inflammation. A better understanding of these processes could uncover new targets for treating microbiome-mediated inflammatory diseases. To this end, we investigated the spatial organization and dynamics of bacterial populations within the intestine using larval zebrafish and live imaging. We discovered that a proinflammatory Vibrio symbiont native to zebrafish governs its own spatial organization using swimming motility and chemotaxis. Surprisingly, we found that Vibrio's motile behavior does not enhance its growth rate but rather promotes its persistence by enabling it to counter intestinal flow. In contrast, Vibrio mutants lacking motility traits surrender to host spatial control, becoming aggregated and entrapped within the lumen. Consequently, nonmotile and nonchemotactic mutants are susceptible to intestinal expulsion and experience large fluctuations in absolute abundance. Further, we found that motile Vibrio cells induce expression of the proinflammatory cytokine tumor necrosis factor alpha (TNFα) in gut-associated macrophages and the liver. Using inducible genetic switches, we demonstrate that swimming motility can be manipulated in situ to modulate the spatial organization, persistence, and inflammatory activity of gut bacterial populations. Together, our findings suggest that host spatial control over resident microbiota plays a broader role in regulating the abundance and persistence of gut bacteria than simply protecting mucosal tissues. Moreover, we show that intestinal flow and bacterial motility are potential targets for therapeutically managing bacterial spatial organization and inflammatory activity within the gut.