The effects of electroshock on immune function and disease progression in juvenile spring chinook salmon

Although much is known about the effects of electroshock on fish physiology, consequences to the immune system and disease progression have not received attention. Our objectives were to determine the effects of electroshock on selected immune function in juvenile spring chinook salmon Oncorhynchus tshawytscha, the mechanism of any observed alteration, and the effects of electroshock on disease progression. We found that the ability of anterior kidney leukocytes to generate antibody-producing cells (APC) was suppressed 3 h after a pulsed-DC electroshock (300 V, 50 Hz, 8 ms pulse width) but recovered within 24 h. This response was similar in timing and magnitude to that of fish subjected to an acute handling stress. The mechanism of suppression is hypothesized to be via an elevation of plasma cortisol concentrations in response to stress. Other monitored immune functions, skin mucous lysozyme levels, and respiratory burst activity were not affected by exposure to electroshock. The progression of a Renibacterium salmoninarum (RS) infection may have been altered after exposure to an electroshock. The electroshock did not affect infection severity or the number of mortalities, but may have accelerated the time to death. The limited duration of APC suppression and lack of effects on lysozyme and respiratory burst, as well as infection severity and mortality levels in RS-infected fish, led us to conclude that electrofishing under the conditions we tested is a safe procedure in regards to immunity and disease

The physiological stress response of salmonids: considerations for field procedures and environmental monitoring

Investigating the physiological state of wild salmonids is challenging on many levels. The sensitive nature of an integrated physiological stress response directs how biological data is collected in the field and, consequently, how the results are interpreted. This thesis is comprised of two main components. The first component encompasses laboratory-based studies addressing the potential confounding effects of: 1) anaesthesia with either tricaine methanesulphonate (tricaine) or clove oil (eugenol) prior to blood/tissue sampling, and 2) capture by electroshocking, on the immediate and short-term responses of plasma/serum cortisol and glucose concentrations, haematocrit, plasma/serum lysozyme activity, and total leucocyte abundance in juvenile chinook salmon (Oncorhynchus tshawytscha). The second component involves a field-based exploration of the in situ physiological status, using the same five physiological traits, of wild bull trout (Salvelinus confluentus) in the Torpy River watershed, B.C., in relation to selected habitat attributes (stream gradient, discharge rate, and riparian canopy-closure). Anaesthetization and electroshocking did not significantly alter values for the five physiological traits provided that post-capture blood sampling occurred immediately. Tricaine and clove oil immobilization produced similar effects on the physiological stress response of juvenile chinook salmon. Clove oil (eugenol) shows promise as a viable and safe alternative to tricaine for aquacultural purposes and in laboratory- and field-based research. Electroshocking is an acute stressor from which juvenile chinook salmon can recover physiologically (usually within 12-24 h). Handling without shocking, however, significantly reduced serum lysozyme activity for up to 2 wks post-stress. Radiographs indicated that while some degree of spinal abnormality exists naturally in domestic chinook juveniles, individuals exposed to a single brief shock incur significantly more spinal deformities. Some of the variation in the stress physiology and non-specific immune function of wild bull trout in the Torpy River system were explained by the combined effects of stream gradient, discharge rate, and riparian canopy-closure. The physiological measurements of wild bull trout generally did not differ from those reported in the literature for other salmonid species. The "background" effects of these habitat features on the physiology of wild salmonids must be considered when interpreting field-collected data.The original print copy of this thesis may be available here: http://wizard.unbc.ca/record=b120573

Physiological effects of the parasite ichthyophonus on spawning chinook salmon and their offspring in a Yukon River tributary

Thesis (M.S.) University of Alaska Fairbanks, 2015In recent years, Chinook salmon Oncorhynchus tshawytscha returns to the Yukon River, Alaska, have been substantially reduced. In summer 2010-2012, spawning Chinook salmon (n=51, 32, and 23, respectively) were collected from the Salcha River, a tributary of the Yukon River, to determine the effects of Ichthyophonus, a protozoan parasite, on salmon reproductive success. Eggs and milt from Ichthyophonus-infected and non-infected parents were collected in 2010 and cross-fertilized to investigate offspring survival and potential second-generation effects induced by the parasite. Proximate composition analysis of adult muscle, eggs, and alevins, and blood chemistry analysis of adult blood plasma and alevin whole body homogenates were analyzed to explore potential differences between Ichthyophonus-infected and non-infected salmon. Ichthyophonus infection prevalence was 7.8, 6.3, and 8.3 % in 2010, 2011, and 2012, respectively. Egg lipid content was significantly higher in eggs from Ichthyophonus-infected females, compared to eggs from Ichthyophonus-negative females. Survival of fertilized eggs to hatching was not significantly different between offspring from Ichthyophonus-infected parents (Mean±1SD: 24.4±29.8 % survival) and non-infected parents (41.0±24.8 % survival). Proximate composition (% lipid, % protein, kJ/g) of muscle from spawning adult salmon also did not differ, nor did total body composition or morphology of alevins produced by either Ichthyophonus-infected or non-infected parents. We found no significant differences in blood plasma cortisol concentrations (a stress indicator) between Ichthyophonus-positive and negative adults or their offspring. There were also no significant differences in blood chemistry parameters indicative of tissue damage between Ichthyophonus-positive and Ichthyophonus-negative adults or resulting alevins, with the exception of aspartate aminotransferase, which was unexpectedly higher in plasma of Ichthyophonus-negative adults. Overall, infection with Ichthyophonus does not appear to impact the spawning ability or spawning success of Chinook salmon in the Salcha River

Cool, pathogen free refuge lowers pathogen associated prespawn mortality of Willamette River Chinook salmon (Oncorhynchus tshawytscha)

Spring Chinook salmon, Oncorhynchus tshawytscha, are transported above dams in the Willamette River to provide access to blocked spawning habitat. However, 30-95% of these transplants may die before spawning in some years. To varying degrees, salmon in other tributaries--both blocked and unblocked--have similar prespawn mortality (PSM). Our study determined if holding in constant temperature, pathogen free conditions prior to spawning increased survival to spawn. In addition, we evaluated pathogens as a potential cause of PSM. Adult Chinook were captured early and late in the season from the lower Willamette River and from upper river tributaries and held in constant, cool temperature (13 ˚C), pathogen-free water at Oregon State University. Additional fish were sampled at time of transport from each of the collection sites. Finally, recent mortalities were collected from river surveys on holding and spawning reaches above traps. Necropsies were performed on all fish, and samples were processed for histology. Held fish were spawned to determine if progeny were viable. Held fish were less likely to be a PSM than fish that were outplanted to the river. However, bacterial infections were more prevalent in held fish than outplanted fish. Consistent with these observations, PSM in held fish was more likely to have higher burdens of pathogens than spawned fish. Held spawned fish were more likely to have Myxobolus sp. brain infections and less likely to be infected with the kidney myxozoan Parvicapusla minibicornis than spawned outplanted fish. The equal likelihood of other pathogens for held and outplanted spawned fish suggests interactive effects determine survival and that holding at 13 ˚C prevented expression of lethal pathogenesis. Progeny of held fish from all locations and collection dates were viable. Overall, holding could be a viable method to reduce PSM, but issues of transport stress, proliferative disease such as those caused by bacteria, and antibiotics remain

Distribution and coinfection of microparasites and macroparasites in juvenile salmonids in three upper Willamette River tributaries

Wild fish populations are typically infected with a variety of micro- and macroparasites that may affect fitness and survival, however, there is little published information on parasite distribution in wild juvenile salmonids in three upper tributaries of the Willamette River, OR. The objectives of this survey were to document (1) the distribution of select microparasites in wild salmonids and (2) the prevalence, geographical distribution, and community composition of metazoan parasites infecting these fish. From 2011-2013, I surveyed 279 Chinook salmon Oncorhynchus tshawytscha and 149 rainbow trout O. mykiss for one viral (IHNV) and four bacterial (Aeromonas salmonicida, Flavobacterium columnare, Flavobacterium psychrophilum, and Renibacterium salmoninarum) microparasites known to cause mortality of fish in Willamette River hatcheries. The only microparasite detected was Renibacterium salmoninarum, causative agent of bacterial kidney disease, which was detected at all three sites. I identified 23 metazoan parasite taxa in these fish. Nonmetric multidimensional scaling of metazoan parasite communities reflected a nested structure with trematode metacercariae being the basal parasite taxa at all three sites. The freshwater trematode Nanophyetus salmincola was the most common macroparasite observed at three sites. Metacercariae of N. salmincola have been shown to impair immune function and disease resistance in saltwater. To investigate if N. salmincola affects disease susceptibility in freshwater, I conducted a series of disease challenges to evaluate whether encysted N. salmincola metacercariae increase susceptibility of juvenile Chinook salmon to Flavobacterium columnare and Aeromonas salmonicida infection. These bacteria cause high mortality in juvenile hatchery salmonid populations in the Willamette River, and are a potential threat to wild juvenile salmonids. Juvenile Chinook salmon were first infected with N. salmincola through cohabitation with infected freshwater snails, Juga spp., then challenged through static immersion with either F. columnare or A. salmonicida. Cumulative percent mortality from F. columnare was higher in N. salmincola-parasitized compared to non-parasitized juvenile Chinook salmon. In contrast, cumulative percent mortality from A. salmonicida did not differ between N. salmincola-parasitized and non-parasitized juvenile Chinook salmon. No mortalities were observed in the N. salmincola-only and control groups from either challenge. These results show that a high infection intensity (>200 metacercariae per posterior kidney) of encysted N. salmincola metacercariae does not cause mortality alone, but can increase susceptibility to certain bacterial infections in juvenile Chinook salmon

Assessment of injury to New Zealand native fish by boat electrofishing

This study investigated the survival, incidence and severity of injuries and physiological reactions to stress caused by boat electrofishing in comparison with standard netting techniques in three New Zealand native fish species. Shortfin eel (Anguilla australis), grey mullet (Mugil cephalus) and common smelt (Retropinna retropinna) were captured from the Waikato River and its surrounding lakes with standardised boat electrofishing techniques (60-Hz pulsed direct current, 45-60% of range with the 0-500-V peak voltage machine setting, 3-4 Amps root mean square output). Fish were captured in water of 133-154 μScm─1 ambient conductivity at 18-21oC. Capture techniques used for comparison were fyke netting for eels, gill netting for grey mullet and beach seine netting for smelt. Survival was assessed in eels that held for 30 days after capture and smelt that were held for 30 min after capture. Several different methods were used to assess the incidence and severity of injuries. External examinations were used to assess branding and abrasions, and internal injuries were assessed by radiographic imaging and bilateral filleting to reveal haemorrhaging and spinal damage. Finally, physiological stress was determined by an analysis of haematocrit and haemoglobin concentration and an analysis of blood plasma ions (sodium, potassium, magnesium and calcium). Survival over 30 days of shortfin eels captured by electrofishing (92% for Lake Areare eels and 96% for Lake Rotongaro eels) was similar to that for fyke netting (92% for Lake Areare and 88% for Lake Rotongaro). Two eels appeared to have died from fungal infections as no haemorrhaging or spinal injuries were apparent among the mortalities. External examinations revealed that no abrasions or branding occurred in eels captured by electrofishing; however, abrasions occurred in eels captured by fyke netting (24% for Lake Areare eels and 16% for Lake Rotongaro eels). Rates of internal haemorrhaging immediately after electrofishing were inconsistent (0% in Lake Areare and 28% in Lake Rotongaro); in Lake Rotongaro, this was significantly greater than those captured by fyke netting, in which only 8% had haemorrhages. No haemorrhaging was observed in eels after 30 days from Lake Areare. Haemorrhages from electrofishing in our study appeared to heal within the 30-day holding period, as the incidence of haemorrhaging in Rotongaro eels reduced from 28% at capture to only 4% after 30 days in captivity. Rates of spinal injury in eels captured by electrofishing was also variable (12% in Lake Areare eels and 8% in Lake Rotongaro eels), compared to the rate of spinal injury in eels captured by fyke netting (0% in Lake Areare eels and 4% in Lake Rotongaro eels). The upper rate of haemorrhaging that we found for electrofishing in shortfin eels (28%) was similar to injury rates for electrofished American eels (25%), but our rates of spinal damage (8-12%) were much lower than for American eels (60%). In grey mullet, there was no significant difference (P > 0.101) in the occurrence of haemorrhages or spinal injuries between the two capture methods. However, physiological stress from electrofishing caused a significantly (t = 2.37, P = 0.02) reduced sodium ion concentration (139.38 ± 13.24 mM) compared to that of gill netting (149.06 ± 15.58 mM). Electrofishing also caused a significantly (t = 4.61, P < 0.001) lower concentration of haemoglobin (86.55 ± 9.21 g L-1) compared to that of grey mullet captured by gill netting (108.81 ± 23.86 g L-1). However, there were no significant differences between capture methods for the other blood plasma constituents tested (haematocrit and the blood plasma ions sodium, potassium, magnesium and calcium). Survival was high in smelt captured by both electrofishing (94.8%, n = 1217) and by seine netting (92.9%, n = 1271), with no statistically significant difference between the two fishing methods (t = −1.021, P = 0.320). In a subsample of smelt analysed for injuries (n = 40 for each method), external injuries were observed in 15% (n = 6) of smelt captured by electrofishing and in 20% (n = 8) of smelt captured by seine netting. No haemorrhages were detected in smelt for either of the capture methods and there was no significant difference (G = 0.215, P = 0.642) in the rate of spinal injuries in smelt captured by electrofishing (10%, n = 4) or by seine netting (5%, n = 2). These results suggest that boat electrofishing as practiced in New Zealand is in the long term generally no more harmful to shortfin eels, grey mullet, and common smelt than other comparable capture sampling techniques. Exceptions to this conclusion were increased haemorrhaging in electrofished shortfin eels, from which they recovered within 30 days, and reduced sodium and haemoglobin concentrations in electrofished grey mullet, which are signs of physiological stress. All fishing methods examined caused some level of injury, stress, or mortality in the three species studied. Netting techniques (fyke net, gill netting, and seine netting) that are commonly used will also cause harm and these techniques are currently used far more widely than boat electrofishing

Biological data and model development for management of longfinned eels

Objectives: 1. Estimate population parameters required for a management model. These include survival, density, age structure, growth, age and size at maturity and at recruitment to the adult eel fishery. Estimate their variability among individuals in a range of habitats. 2. Develop a management population dynamics model and use it to investigate management options. 3. Establish baseline data and sustainability indicators for long-term monitoring. 4. Assess the applicability of the above techniques to other eel fisheries in Australia, in collaboration with NSW. Distribute developed tools via the Australia and New Zealand Eel Reference Group

Biological data and model development for management of longfinned eels

Objectives: 1. Estimate population parameters required for a management model. These include survival, density, age structure, growth, age and size at maturity and at recruitment to the adult eel fishery. Estimate their variability among individuals in a range of habitats. 2. Develop a management population dynamics model and use it to investigate management options. 3. Establish baseline data and sustainability indicators for long-term monitoring. 4. Assess the applicability of the above techniques to other eel fisheries in Australia, in collaboration with NSW. Distribute developed tools via the Australia and New Zealand Eel Reference Group

Welfare Indicators for farmed Atlantic salmon: tools for assessing fish welfare

Fish welfare is a key issue in commercial farming and is central to many decisions that farmers take during their daily husbandry practices and longer term production planning. It is also a prominent topic for NGO’s, animal welfare organisations and charities, regulatory bodies, policy makers and consumers. Farmers have long been interested in optimising the welfare of their animals and actively employ strategies that address fish welfare concerns and attempt to minimise threats to fish welfare. Independent third party organisations have even developed fish welfare standards and certification schemes for certain aquaculture species (e.g. RSPCA welfare standards for farmed Atlantic salmon and rainbow trout, RSPCA, 2018a, b). The topic of fish welfare has also been covered in numerous aquaculture research and review papers over the years, both from a fundamental and also applied perspective. This wealth of information and documentation can be spread over a wide range of sources that may not be easily accessible for the farmer and other end users. In many cases the wealth of information requires interpretation and re-presentation before it is suitable for use out on the farm. Once the farmer has information on fish welfare, they need to implement it in their production systems and daily husbandry practices. This can be a serious challenge as even measuring fish welfare can be challenging and the tools available for measurement may not be suitable for all species or all life stages. To assess the overall welfare status of the fish we use Welfare Indicators (WIs). Welfare indicators can either be direct animal-based (something you get from the fish), or indirect resource-based (e.g. rearing environment, infrastructure etc.). However, some WIs may be too complex or too difficult to apply on a farm. WIs that are appropriate for on-farm use are termed Operational Welfare Indicators (OWIs). WIs that can be sampled on the farms, but need to be sent to a laboratory or other remote analytical facility are termed Laboratory-based Welfare Indicators (LABWIs). There are other potential WIs that cannot currently be classified as either OWIs or LABWIs, these are mainly used in research but may be useful in the future or under specific circumstances at present. From the suite of appropriate OWIs or LABWIs available, the end user then needs to apply these to different production systems and husbandry routines. This is the goal of this handbook – to assemble a farm-friendly toolbox of fit for purpose Operational Welfare Indicators (OWIs) and Laboratory-based Welfare Indicators (LABWIs) for use out on fish farms in different production systems and husbandry routines. It also includes advice on their implementation and interpretation

Welfare Indicators for farmed Atlantic salmon : tools for assessing fish welfare

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