Behavioural changes following intraperitoneal vaccination in Atlantic salmon (Salmo salar)

Heart rate as an indicator of stress during the critical swimming speed test of farmed Atlantic salmon (Salmo salar L.)

A swim tunnel is to fish as a treadmill is to humans, and is a device used for indirect measuring of the metabolic rate. This study aims to explore the fish stress (if any) during the critical swimming test routines (fish handling, confinement, and swimming) using heart rate (fH , heartbeat per minute) bio-loggers in farmed Atlantic salmon (Salmo salar L.). In addition, the recovery dynamics of exercised fish using fH were explored for 48 h post swim tests. Continuous fH data were acquired following the surgical implantation and throughout the trials, such as during fish handling, swim tests (critical swimming speed, Ucrit ), and 48 h post swim tests. After 3 weeks of surgical recovery, fH stabilized at 46.20 ± 1.26 beats min-1 , equalizing a ~38% reduction in fH recorded post-surgical tachycardia (74.13 ± 1.44 beats min-1 ). Interestingly, fH was elevated by ~200% compared to baseline levels not only due to the Ucrit (92.04 ± 0.23 beats min-1 ) but also due to fish handling and confinement in the swim tunnel, which was 66% above the baseline levels (77.48 ± 0.34 beats min-1 ), suggesting fish stress. Moreover, significantly higher plasma cortisol levels (199.56 ± 77.17 ng mL-1 ) corresponding to a ~300% increase compared to baseline levels (47.92 ± 27.70 ng mL-1 ) were identified after Ucrit , predicting post-swim test stress (physiological exhaustion). These findings reinforce the importance of fish acclimation in the swim tunnel prior to the swimming tests. However, fH dropped over the course of the 48-h post-swim test, but remained comparatively higher than the basal levels, suggesting fish should be given at least 48 h to recover from handling stress for better fish welfare. This study further explored the influence of fish tagging on Ucrit , which resulted in reduced swimming capabilities of tagged fish (1.95 ± 0.37 body lengths s-1 ) compared to untagged fish (2.54 ± 0.42 body length s-1 ), although this was not significant (p = 0.06), and therefore future tagging studies are warranted.

Pain Recognition in Fish

Empirical evidence has demonstrated that fish experience pain, and so to ensure their good welfare, it is vital that we can recognize and assess pain. A range of general, behavioral, and physiologic indicators can be used when assessing pain in fish. Many of these can be used at the tank side and are termed operational welfare indicators, whereas some require further computer or laboratory analysis. Behavioral indicators are valid and have been shown to profoundly differ between nonpainful and painful treatments in fish. However, these are not universal, and species-specific differences exist in behavioral responses to pain.

Comparative study on antigen persistence and immunoprotective efficacy of intramuscular and intraperitoneal injections of squalene - aluminium hydroxide (Sq + Al) adjuvanted viral hemorrhagic septicaemia virus vaccine in olive flounder (Paralichthys olivaceus)

The profitability of the olive flounder (Paralichthys olivaceus) aquaculture industry in Korea depends on high production and maintenance of flesh quality, as consumers prefer to eat raw flounders from aquaria and relish the raw muscles as 'sashimi'. For sustaining high production, easy-to-deliver and efficient vaccination strategies against serious pathogens, such as viral hemorrhagic septicemia virus (VHSV), is very important as it cause considerable losses to the industry. Whereas, a safe and non-invasive vaccine formulation that is free from unacceptable side-effects and does not devalue the fish is needed to maintain flesh quality. We previously developed a squalene-aluminium hydroxide (Sq + Al) adjuvanted VHSV vaccine that conferred moderate to high protection in flounder, without causing any side effects when administered through the intraperitoneal (IP) injection route. However, farmers often demand intramuscular (IM) injection vaccines as they are relatively easy to administer in small fishes. Therefore, we administered the developed vaccine via IP and IM routes and investigated the safety and persistency of the vaccine at the injection site. In addition, we conducted a comparative analysis of vaccine efficacy and serum antibody response. The clinical and histological observation of the IM and IP groups showed that our vaccine remained persistence at the injection sites for 10-17 weeks post vaccination (wpv), without causing any adverse effects to the fish. The relative percentage of survival were 100% and 71.4% for the IP group and 88.9% and 92.3% for the IM group at 3 and 17 wpv, respectively. Thus, considering the persistency period (24 wpv) and both short and long-term efficacy of our vaccine, the present study offers an option to flounder farmers in selecting either IM or IP delivery strategy according to their cultured fish size and harvesting schedule - IM vaccination for small-sized fish and IP vaccination for table-sized fish.

Mucin modified SPR interfaces for studying the effect of flow on pathogen binding to Atlantic salmon mucins

Knowledge on host-pathogen interactions contributes to the development of approaches to alleviate infectious disease. In this work, we developed a surface plasmon resonance (SPR) based method for investigating bacteria/mucins interactions. Furthermore, we investigated adhesion of three pathogens, Aeromonas salmonicida, Aeromonas hydrophila and Vibrio harveyi, to Atlantic salmon mucins isolated from different epithelial sites, using SPR and microtiter-based binding assays. We demonstrated that performing bacterial binding assays to mucins using SPR is feasible and has advantages over microtiter-based binding assays, especially under flow conditions. The fluid flow in the SPR is linear and continuous and SPR enables real-time reading of mucin-bacterial bonds, which provides an in vivo-like setup for analysis of bacterial binding to mucins. The variation between technical replicates was smaller using SPR detection compared to the adenosine 5'-triphosphate (ATP) bioluminescence assay in microtiter plates. Furthermore, we demonstrated that the effect of flow on pathogen-mucin interaction is significant and that bacterial adhesion differ non-linearly with flow rates and depend on the epithelial source of the mucin.

The Controversy on Fish Pain: A Veterinarian's Perspective

Fish welfare is still a relatively new field. As such, regulations and protocols to ensure fish welfare are currently limited and vary considerably in different jurisdictions. This is in part because of the ongoing controversy as to whether or not fish feel pain. This controversy has persisted for several years, yet veterinarians have been mostly absent from the discussion so far. This essay aims to address this issue. Here, it is argued that while this controversy has its place, it is unlikely to be resolved in the near future. Fish welfare could instead be improved by pursuing more clinically applicable research to increase knowledge of fishes' behavior and physiology. Such research would assist in learning the optimal environment for their specific needs, as well as compiling some verified indicators of pain in fish. This would then lead to improved studies that could help to determine if and when analgesic drugs can be beneficial in fish, as they are in many other species.

Impact of stress, fear and anxiety on the nociceptive responses of larval zebrafish

Both adult and larval zebrafish have been demonstrated to show behavioural responses to noxious stimulation but also to potentially stress- and fear or anxiety- eliciting situations. The pain or nociceptive response can be altered and modulated by these situations in adult fish through a mechanism called stress-induced analgesia. However, this phenomenon has not been described in larval fish yet. Therefore, this study explores the behavioural changes in larval zebrafish after noxious stimulation and exposure to challenges that can trigger a stress, fear or anxiety reaction. Five-day post fertilization zebrafish were exposed to either a stressor (air emersion), a predatory fear cue (alarm substance) or an anxiogenic (caffeine) alone or prior to immersion in acetic acid 0.1%. Pre- and post-stimulation behaviour (swimming velocity and time spent active) was recorded using a novel tracking software in 25 fish at once. Results show that larvae reduced both velocity and activity after exposure to the air emersion and alarm substance challenges and that these changes were attenuated using etomidate and diazepam, respectively. Exposure to acetic acid decreased velocity and activity as well, whereas air emersion and alarm substance inhibited these responses, showing no differences between pre- and post-stimulation. Therefore, we hypothesize that an antinociceptive mechanism, activated by stress and/or fear, occur in 5dpf zebrafish, which could have prevented the larvae to display the characteristic responses to pain.

Sickness behaviour in the cricket Gryllus texensis: Comparison with animals across phyla

Immune activation alters behaviour (i.e. sickness behaviour) in animals across phyla and is thought to aid recovery from infection. Hypotheses regarding the adaptive function of different sickness behaviours (e.g. decreased movement and appetite) include the energy conservation and predator avoidance hypotheses. These hypotheses were originally developed for mammals (e.g. Hart, 1988), however similar sickness behaviours are also observed in insects (e.g., crickets). We predicted that immune-challenged crickets (Gryllus texensis) would reduce feeding, grooming, and locomotion as well as increase shelter use, consistent with the energy conservation and predator avoidance hypotheses. We found evidence of illness-induced anorexia in adult and juvenile crickets, consistent with previous research (Adamo et al., 2010), but contrary to expectations, we found an increase in grooming, and no evidence that crickets decreased locomotion or increased shelter use in response to immune challenge. Therefore, our results do not support the energy conservation or predator avoidance hypotheses. The difference in sickness behaviour between insects and mammals is probably due, in part, to the lack of physiological fever in insects. We hypothesize that the lack of physiological fever reduces the need for energy conservation, decreasing the benefits of some sickness behaviours such as increased shelter use. These results, taken together with others in the literature, suggest that ectotherms and endotherms may differ significantly in the selective forces leading to the evolution of most sickness behaviours.

Pain in aquatic animals

Recent developments in the study of pain in animals have demonstrated the potential for pain perception in a variety of wholly aquatic species such as molluscs, crustaceans and fish. This allows us to gain insight into how the ecological pressures and differential life history of living in a watery medium can yield novel data that inform the comparative physiology and evolution of pain. Nociception is the simple detection of potentially painful stimuli usually accompanied by a reflex withdrawal response, and nociceptors have been found in aquatic invertebrates such as the sea slug Aplysia. It would seem adaptive to have a warning system that allows animals to avoid life-threatening injury, yet debate does still continue over the capacity for non-mammalian species to experience the discomfort or suffering that is a key component of pain rather than a nociceptive reflex. Contemporary studies over the last 10 years have demonstrated that bony fish possess nociceptors that are similar to those in mammals; that they demonstrate pain-related changes in physiology and behaviour that are reduced by painkillers; that they exhibit higher brain activity when painfully stimulated; and that pain is more important than showing fear or anti-predator behaviour in bony fish. The neurophysiological basis of nociception or pain in fish is demonstrably similar to that in mammals. Pain perception in invertebrates is more controversial as they lack the vertebrate brain, yet recent research evidence confirms that there are behavioural changes in response to potentially painful events. This review will assess the field of pain perception in aquatic species, focusing on fish and selected invertebrate groups to interpret how research findings can inform our understanding of the physiology and evolution of pain. Further, if we accept these animals may be capable of experiencing the negative experience of pain, then the wider implications of human use of these animals should be considered.

Aeromonas salmonicida binds differentially to mucins isolated from skin and intestinal regions of Atlantic salmon in an N-acetylneuraminic acid-dependent manner

Aeromonas salmonicida subsp. salmonicida infection, also known as furunculosis disease, is associated with high morbidity and mortality in salmonid aquaculture. The first line of defense the pathogen encounters is the mucus layer, which is predominantly comprised of secreted mucins. Here we isolated and characterized mucins from the skin and intestinal tract of healthy Atlantic salmon and studied how A. salmonicida bound to them. The mucins from the skin, pyloric ceca, and proximal and distal intestine mainly consisted of mucins soluble in chaotropic agents. The mucin density and mucin glycan chain length from the skin were lower than were seen with mucin from the intestinal tract. A. salmonicida bound to the mucins isolated from the intestinal tract to a greater extent than to the skin mucins. The mucins from the intestinal regions had higher levels of sialylation than the skin mucins. Desialylating intestinal mucins decreased A. salmonicida binding, whereas desialylation of skin mucins resulted in complete loss of binding. In line with this, A. salmonicida also bound better to mammalian mucins with high levels of sialylation, and N-acetylneuraminic acid appeared to be the sialic acid whose presence was imperative for binding. Thus, sialylated structures are important for A. salmonicida binding, suggesting a pivotal role for sialylation in mucosal defense. The marked differences in sialylation as well as A. salmonicida binding between the skin and intestinal tract suggest interorgan differences in the host-pathogen interaction and in the mucin defense against A. salmonicida.