Stress-associated impacts of short-term holding on fishes

Most sources of stress in aquaculture, fish salvage, stocking programs, and commercial and sport fisheries may be unavoidable. Collecting, handling, sorting, holding, and transporting are routine practices that can have significant effects on fish physiology and survival. Nevertheless, an understanding of the stressors affecting fish holding can lead to practices that reduce stress and its detrimental effects. The stress-related effects of short-term holding are influenced by water quality, confinement density, holding container design, and agonistic and predation-associated behaviors. Physiological demands (e.g., resulting from confinement-related stresses) exceeding a threshold level where the fish can no longer compensate may lead to debilitating effects. These effects can be manifested as suppressed immune systems; decreased growth, swimming performance, or reproductive capacity; even death. Furthermore, holding tolerance may depend upon the species, life stage, previous exposure to stress, and behavior of the held fish. Water quality is one of the most important contributors to fish health and stress level. Fish may be able to tolerate adverse water quality conditions; however, when combined with other stressors, fish may be quickly overcome by the resulting physiological challenges. Temperature, dissolved oxygen, ammonia, nitrite, nitrate, salinity, pH, carbon dioxide, alkalinity, and hardness are the most common water quality parameters affecting physiological stress. Secondly, high fish densities in holding containers are the most common problem throughout aquaculture facilities, live-fish transfers, and fish salvage operations. Furthermore, the holding container design may also compromise the survival and immune function by affecting water quality, density and confinement, and aggressive interactions. Lastly, fishes held for relatively short durations are also influenced by negative interactions, associated with intraspecific and interspecific competition, cannibalism, predation, and determining nascent hierarchies. These interactions can be lethal (i.e., predation) or may act as a vector for pathogens to enter (i.e., bites and wounds). Predation may be a significant source of mortality for fisheries practices that do not sort by size or species while holding. Stress associated with short-term holding of fishes can have negative effects on overall health and well-being. These four aspects are major factors contributing to the physiology, behavior, and survival of fishes held for a relatively short time period.     

A review of tricaine methanesulfonate for anesthesia of fish

Tricaine methanesulfonate (TMS) is an anesthetic that is approved for provisional use in some jurisdictions such as the United States, Canada, and the United Kingdom (UK). Many hatcheries and research studies use TMS to immobilize fish for marking or transport and to suppress sensory systems during invasive procedures. Improper TMS use can decrease fish viability, distort physiological data, or result in mortalities. Because animals may be anesthetized by junior staff or students who may have little experience in fish anesthesia, training in the proper use of TMS may decrease variability in recovery, experimental results and increase fish survival. This document acts as a primer on the use of TMS for anesthetizing juvenile salmonids, with an emphasis on its use in surgical applications. Within, we briefly describe many aspects of TMS including the legal uses for TMS, and what is currently known about the proper storage and preparation of the anesthetic. We outline methods and precautions for administration and changes in fish behavior during progressively deeper anesthesia and discuss the physiological effects of TMS and its potential for compromising fish health. Despite the challenges of working with TMS, it is currently one of the few legal options available in the USA and in other countries until other anesthetics are approved and is an important tool for the intracoelomic implantation of electronic tags in fish.     

Effects of habitat enrichment and food availability on the foraging behaviour of juvenile Atlantic Cod (<Emphasis Type="Italic">Gadus morhua L</Emphasis>)

The environment can play an important role in shaping how an animal behaves, and how well the animal performs in a particular environment can be influenced by early experiences. The tradition of releasing captive-reared juveniles into the wild in an effort to strengthen wild fish populations has often had little success owing to high post-release mortality. Fish reared under standard hatchery conditions are provided with fewer stimuli and they receive excess quantities of pellet food that are easy to handle and consume. Captive reared fish therefore appear to be under-stimulated and overfed. Several studies have demonstrated that simple structural enrichment in the rearing facilities promotes flexible behaviour compared to fish reared in plain, standard hatchery tanks. Less attention has been given to the effects of the diet. Here we use a cross-factored design to test the relative role of food ration and spatial enrichment on foraging behaviour. Our results show that fish from enriched environments, regardless of previous food-ration size, were more reluctant to start feeding on the first day in a novel arena. On day two and three, however, fish with prior experience of a low food ration showed greater foraging activity and efficiency than fish fed on full rations. On the second and third day, prior experience with enrichment was less important. We discuss how early feeding experience in combination with structural enrichment may contribute in producing fish that are better suited for release into the wild.     

Behavioural and physiological stress responses to handling in wild guanacos

Both ethology and physiology can provide insights about stress conditions in wild animals during handling. Lama guanicoe (guanaco) is the major large herbivore inhabiting arid zones in Argentina. Since 2005, the Payún Matrú Cooperative, a business established and run by native people, has captured and handled guanacos for shearing at Payunia Reserve, Mendoza Province, Argentina, to market the species’ fibre for clothing and other products. The aim of our study was to evaluate the behavioural and physiological stress responses to handling of wild guanacos during these shearing activities. We evaluated stress conditions in guanacos by monitoring the frequency of agonistic behaviour in the holding corrals, following capture, the rate of vocalisation and agonistic behaviour during handling, and by estimating cortisol levels in handled animals. Crowding increased agonistic behaviour; this appeared to be related to dominance conflicts between males in the corrals. Time of corralling increased rate of agonistic behaviour and vocalisations during handling. The rate of behavioural stress responses was negatively related to cortisol levels in males; which may be due to animal fatigue or because behavioural stress responses may help mitigate physiological stress responses. Incorporating our results into animal welfare practices could help reduce stress conditions in wild guanacos. Our results suggest that both behavioural and physiological responses are important measures of stress in handled animals, and that behavioural stress responses cannot be used as a simple surrogate for glucocorticoid levels.     

Evaluation of pulsed gastric lavage on the survival of captive shovelnose sturgeon

Little is known about the diet of the endangered pallid sturgeon, Scaphirhynchus albus. Because of this endangered status non‐lethal methods to ascertain their food habits must be evaluated. Tests of pulsed gastric lavage (PGL) were conducted on shovelnose sturgeon S. platorynchus, as a surrogate for the pallid sturgeon, to determine if PGL negatively affected their survival. Nine sequential trials containing eight shovelnose sturgeon (N = 72) were conducted with wild fish collected from the Platte River near Louisville, Nebraska. Each trial group was placed into one of two tanks, with each tank containing three pulsed gastric lavaged fish and one control fish. Fish were weighed, measured, and tagged with a passive integrated transponder (PIT tag) before being transported to holding tanks for acclimation and PGL treatment. Sturgeon were acclimated 4–6 days prior to PGL, then held for 15 days after treatment. Temperature, dissolved oxygen, ammonia, and nitrite were monitored daily. No significant difference between the survival of PGL fish and control fish was detected. Because the test required these fish to endure the additional stress of transport and handling, PGL seems a viable technique that can be safely used to evaluate food habits of shovelnose sturgeon, and could be considered safe for pallid sturgeon food habit studies.     

The effects of capture, handling, confinement and ectoparasite load on plasma levels of cortisol, glucose and lactate in the coral reef fish Hemigymnus melapterus

Tropical labrids Hemigymnus melapterus sampled underwater had low plasma levels of cortisol, glucose, and lactate. Plasma cortisol levels were elevated by capture stress within 5–6 min, while glucose and lactate levels were not. Plasmalevels of cortisol and glucose increased after 2–4 h of handling and transport to the laboratory. Levels of cortisol and glucose fell with laboratory acclimation back to values similar to those found in wild fish. Parasitism by gnathiid isopods across an order of magnitude of isopod numbers had no effect on plasma levels of cortisol or glucose. Thus, H. melapterus has a stress response similar to that shown by temperate species, and relatively high parasite loads are not apparently stressful to fish in the wild. This may be related to the counterproductive effects of physiological stress responses on the immune system or behaviour-modulated processes that counter parasitic invasion.     

Advancing the surgical implantation of electronic tags in fish: a gap analysis and research agenda based on a review of trends in intracoelomic tagging effects studies

Early approaches to surgical implantation of electronic tags in fish were often through trial and error, however, in recent years there has been an interest in using scientific research to identify techniques and procedures that improve the outcome of surgical procedures and determine the effects of tagging on individuals. Here we summarize the trends in 108 peer-reviewed electronic tagging effect studies focused on intracoleomic implantation to determine opportunities for future research. To date, almost all of the studies have been conducted in freshwater, typically in laboratory environments, and have focused on biotelemetry devices. The majority of studies have focused on salmonids, cyprinids, ictalurids and centrarchids, with a regional bias towards North America, Europe and Australia. Most studies have focused on determining whether there is a negative effect of tagging relative to control fish, with proportionally fewer that have contrasted different aspects of the surgical procedure (e.g., methods of sterilization, incision location, wound closure material) that could advance the discipline. Many of these studies included routine endpoints such as mortality, growth, healing and tag retention, with fewer addressing sublethal measures such as swimming ability, predator avoidance, physiological costs, or fitness. Continued research is needed to further elevate the practice of electronic tag implantation in fish in order to ensure that the data generated are relevant to untagged conspecifics (i.e., no long-term behavioural or physiological consequences) and the surgical procedure does not impair the health and welfare status of the tagged fish. To that end, we advocate for (1) rigorous controlled manipulations based on statistical designs that have adequate power, account for inter-individual variation, and include controls and shams, (2) studies that transcend the laboratory and the field with more studies in marine waters, (3) incorporation of knowledge and techniques emerging from the medical and veterinary disciplines, (4) addressing all components of the surgical event, (5) comparative studies that evaluate the same surgical techniques on multiple species and in different environments, (6) consideration of how biotic factors (e.g., sex, age, size) influence tagging outcomes, and (7) studies that cover a range of endpoints over ecologically relevant time periods.     

How parasitism and pollution affect the physiological homeostasis of aquatic hosts

Parasitism poses a serious threat to hosts under certain circumstances, while the well-being of organisms is also negatively affected by environmental pollution. Little information is available on the simultaneous effects of parasites and pollutants on the physiological homeostasis of organisms. The present paper demonstrates that parasites: (i) may influence the metabolism of pollutants in infected hosts, (ii) interact with pollution in synergistic or antagonistic ways, and (iii) may induce physiological reactions in hosts which were thought to be pollutant-induced. Experimental studies on the uptake and accumulation of metals by fish reveal that fish infected with acanthocephalans have lower metal levels than uninfected hosts; e.g. Pomphorhynchus laevis reduces lead levels in fish bile, thereby diminishing or impeding the hepatic intestinal cycling of lead, which may reduce the quantity of metals available for fish. Alterations in pollutant uptake and accumulation in different intermediate and final hosts due to parasites are thus very important in the field of ecotoxicology. In addition to such alterations, there is a close interaction between the effects of pollutants and parasites which seems to be mediated at least partly by the endocrine system, which itself is closely related to the immune system in fish. Laboratory studies on eels experimentally infected with the swimbladder nematode Anguillicola crassus reveal that toxic chemicals such as polychlorinated biphenyls produce immunosuppressive effects which facilitate parasite infection. Similarly, an increase in serum cortisol concentration in eels due to chemical exposure and infection is correlated with decreasing levels of anti-A. crassus antibodies. Furthermore, parasites are able to elicit physiological changes which are attributed to chemicals with endocrine disrupting activity, e.g. the cestode Ligula intestinalis is known to suppress gonad development in roach. The most thoroughly documented examples of endocrine disruption in wild fish are in roach, and it is conceivable that this disruption is not only due to chemical activity but also to parasites such as L. intestinalis or species of the phylum Microspora.     

Survival of captured and relocated adult spring-run Chinook salmon Oncorhynchus tshawytscha in a Sacramento River tributary after cessation of migration

We studied the efficacy of the process for capture and upstream relocation of 26 adult spring-run Chinook salmon in Butte Creek, California in 2009. These fish had ceased volitional upstream migration prior to reaching their summer holding habitat. The purpose of the relocation was to move fish upstream of two water diversion dams and release them in a part of the stream from which they could presumably swim to cool summer holding habitat, then spawn in the fall. Fish were netted, transported by truck, given an esophageal radio tag/temperature tag, and released. Radio tagging proved to be a useful technique for determining the survival and movement of relocated fish and temperature tags provide useful information to determine thermal exposure and time of death. Twenty-three tags (88 %) were recovered, compared with a 10 % tag recovery rate for an earlier study using fin clips. Most tags were recovered within 3.5 km upstream and 1 km downstream of the release site. A single tag was recovered 6 km upstream. No fish were determined to have survived to spawn. Temperature tag data indicate that most of the salmon died within 2–6 days after the relocation operation. After preventative measures have been exhausted, future relocations efforts, in any setting, should consider (1) intervention as soon as fish cease volitional migration but before they are exposed to further deleterious conditions (2) monitoring environmental conditions to choose appropriate release sites (3) evaluation of disease transmission risk, and (4) handling practices that minimize potential stress due to air immersion and thermal shock.     

The importance of parentage in assessing temperature effects on fish early life history: a review of the experimental literature

Climate change and human development are altering aquatic thermal regimes, highlighting the need to understand how fish fitness may be impacted across a generational boundary. We reviewed experimental temperature studies investigating the links between parents and progeny, asking questions regarding the taxa studied, broodfish used, offspring traits examined, experimental durations and research motivations. We identified forty-one peer-reviewed articles examining the effects of pre-spawning adult temperature holding on offspring. These studies showed a strong focus on the order Salmoniformes (46% of studies) and aquaculturally driven research (66%). The use of wild broodfish was rare (12%) and the majority of experiments (83%) did not examine offspring consequences beyond hatch. We also identified 56 articles investigating how incubation temperature and parental influences affect embryonic and larval development. We demonstrate that these studies are not common in comparison to the majority of incubation thermal experiments that do not employ controlled parental breeding designs. However, 52 out of 56 studies we reviewed reported maternal, paternal or family identity influenced offspring responses to temperature. In characterizing these studies, Salmoniformes were the most studied order (52%), wild broodfish were more commonly used (55%), aquaculture motivations were less evident (23%), and few studies investigated offspring performance or traits beyond endogenous yolk stages. Overall, we suggest it is beneficial to experimentally examine temperature with consideration to parent-progeny relationships. To broaden our current understanding of intergenerational temperature effects, we recommend an increased focus on wild populations, offspring physiological and performance measures, later offspring development stages, and expanding research in non-salmonid species.     

Mechanisms influencing competition between hatchery and wild juvenile anadromous Pacific salmonids in fresh water and their relative competitive abilities

Avoiding negative effects of competition from released hatchery salmonids on wild fish is a primary concern for recovery efforts and fisheries management. Several factors affect competition among juvenile salmonids including: (1) whether competition is intra- or interspecific, (2) duration of freshwater cohabitation of hatchery and wild fish, (3) relative body size, (4) prior residence, (5) environmentally induced developmental differences, and (6) fish density. Intraspecific competition is expected to be greater than interspecific because of greater niche overlap between conspecific hatchery and wild fish. Competition is expected to increase with prolonged freshwater cohabitation. Hatchery smolts are often larger than wild, and larger fish are usually superior competitors. However, wild fish have the advantage of prior residence when defending territories and resources in natural streams. Hatchery-induced developmental differences are variable and can favor both hatchery and wild fish. Although all these factors influence competitive interactions, fish density of the composite population (wild + hatchery fish) in relation to habitat carrying capacity likely exerts the greatest influence. The extent of competition and relative competitive ability of wild and hatchery fish can be determined by additive and substitutive experimental designs, respectively, and the limited body of substitutive experiments suggests that the relative competitive ability of hatchery and wild fish is approximately equal when measured as growth. Conducting substitutive experiments becomes difficult as the spatial and temporal scales increase. Large-scale experiments comparing supplemented and control reaches or streams hold some promise for quantifying the effects of released hatchery fish on wild fish behavior, growth and survival.     

Effect of holding duration on the immune system of western rock lobster, Panulirus cygnus

Live holding of lobsters is a major part of the post-harvest process in lobster fisheries. Following capture, animals are placed in factory tanks and held for varying lengths of time for recovery from stress due to handling, air exposure, disturbance and environmental variations. The aim of the present study was to determine the pattern of response of a range of immune and physiological parameters over varying holding periods and assess their possible application as a measure of recovery from stress of post-harvest procedures and in the determination of an appropriate duration of acclimation prior to live transport. The effect of holding duration on the following immune parameters: total haemocyte counts (THC), haemolymph clotting times, haemolymph pH, haemolymph protein concentration and the differential proportion of haemocytes, was assessed. Lobsters brought to the factory were placed in holding tanks and sampled over a period of up to 10 days. Two studies were conducted, the first on lobsters from different catch groups and the second on lobsters from the same day's catch from the same area. Experiments were conducted on adult animals (10-12 animals/treatment group) with a different group of lobsters being sampled at each time point. Various immune parameters showed alterations with time during holding. A consistent observation was significantly prolonged clotting times following four days of holding. The haemolymph pH showed a strong positive correlation to clotting time and the hyaline cell proportion showed a strong negative correlation with semi-granular cells. Although the levels of THC, clotting time and differential cell counts after one day of holding were similar to those observed in other studies on rested post-harvest lobsters, suggesting that the lobsters had recovered from the acute stress of capture and transport, subsequent alterations in pH, clotting time and differential cell counts indicated other physiological adjustments were still occurring for up to 4 days post capture. Overall the results suggest that though the effects of post-harvest procedures on the immune parameters appear to be resolved after a short duration of holding at low temperatures, no single immune parameter can provide predictable indication of the acclimation process.     

Factors affecting the outcome of territorial contests between hatchery and naturally reared coho salmon parr in the laboratory

In aquarium experiments using coho salmon as a model species, prior residents dominated intruders of the same size but intruders with a 6% length advantage were equally matched against prior residents. Prior winning experience (distinct from individual recognition) also strongly influenced competitive success and overcame a prior residence effect. Coho salmon reared in a hatchery dominated size-matched fish from the same parental population reared in a stream. Hatchery-reared salmon also dominated naturally spawned salmon, even when the wild salmon were prior residents. Thus the combined effects of greater size and rearing experience of hatchery-produced salmon were sufficient to overcome a wild salmon's advantage of prior residence. Efforts to rehabilitate salmonid populations must consider such behavioural interactions if displacement of wild fish is to be prevented.     

Condition dependent intra-individual repeatability of stress-induced cortisol in a freshwater fish

The glucocorticoid (GC) stress response is thought to be an individual trait associated with behaviour and life history strategies. Studies exploring such relationships typically assume measured hormone values to be repeatable within an individual. However, repeatability of GCs has proven variable in wild animals and underlying reasons remain unknown. We assessed individual repeatability of circulating stress-induced cortisol, the primary GC in teleost fish, and glucose concentrations in a wild teleost fish held under consistent laboratory conditions. We also tested the hypothesis that the magnitude of intra-individual variability in stress-induced cortisol concentrations (“cortisol variability”) is influenced by body condition. Wild-caught bluegill sunfish (Lepomis macrochirus) were subjected to repeated standardized stressors and blood sampled (3 times over 6 days) once cortisol concentrations peaked. Various indicators of fish condition, both whole body and physiological, were also measured. Overall, stress-induced circulating cortisol concentrations were repeatable but stress-induced glucose was not. Cortisol variability was related to Fulton's condition factor and size (eviscerated mass) where smaller fish in poor condition exhibited increased cortisol variability. The findings have implications for the interpretation of studies that examine correlates of GC concentrations as they suggest consistency in stress responsiveness is influenced by factors such as size and condition.     

Evaluation of water entry into the coelom and different levels of aseptic technique during surgical implantation of electronic tags in freshwater fish

We reviewed the literature in an attempt to determine the importance of aseptic technique when implanting electronic tags in fish. Given that there was negligible information on this topic we embarked on a study where bluegill (Lepomis macrochirus) were used as a model to investigate the effects of different aseptic surgical techniques for the intracoelomic implantation of electronic tags in fish. First we tested the effects of water entry into the incision using five treatments: lake, distilled and saline water introduced into the incision, water-free controls, and non-surgery controls. For fish in the water treatments, 1 mL of the sample was introduced into their coelom prior to incision closure. Fish were held for 10 days to monitor survival and at the end of the study, the survivors were blood sampled and euthanized to evaluate condition and health using the health assessment index. In a second experiment, four aseptic treatments were used: non-sterile, field-based, high-grade sterility, and non-surgery controls and fish were monitored as in the first experiment. For both experiments, no differences in physiological status, health or mortality were noted among treatment groups. However, in the aseptic techniques experiment, surgical times were approximately twice as long for fish in the sterile treatment as compared to other groups and the costs of surgical supplies was greater than that of the less-sterile treatments. Although we failed to document any benefit of keeping water out of the incision or using aseptic technique for bluegill, in other situations and for other species, such approaches may be important. As such, we encourage fish surgeons practicing intracoelomic implants to attempt to prevent water entry into the coelom. We also encourage, at least some level of infection control (e.g., non-sterile gloves, clean tags and surgical tools) consistent with good veterinary practices to maintain the welfare status of tagged fish and ensure that the data from tagged fish representative of untagged conspecifics. However, the most prudent and ethical approach would be to work with veterinarians to incorporate formal sterilization procedures, equipment (e.g., sterile gloves) and aseptic technique into field surgical techniques.     

Training considerations for the intracoelomic implantation of electronic tags in fish with a summary of common surgical errors

Training is a fundamental part of all scientific and technical disciplines. This is particularly true for all types of surgeons. For surgical procedures, a number of skills are necessary to reduce mistakes. Trainees must learn an extensive yet standardized set of problem-solving and technical skills to handle challenges as they arise. There are currently no guidelines or consistent training methods for those intending to implant electronic tags in fish; this is surprising, considering documented cases of negative consequences of fish surgeries and information from studies having empirically tested fish surgical techniques. Learning how to do fish surgery once is insufficient for ensuring the maintenance or improvement of surgical skill. Assessment of surgical skills is rarely incorporated into training, and is needed. Evaluation provides useful feedback that guides future learning, fosters habits of self-reflection and self-remediation, and promotes access to advanced training. Veterinary professionals should be involved in aspects of training to monitor basic surgical principles. We identified attributes related to knowledge, understanding, and skill that surgeons must demonstrate prior to performing fish surgery including a “hands-on” assessment using live fish. Included is a summary of common problems encountered by fish surgeons. We conclude by presenting core competencies that should be required as well as outlining a 3-day curriculum for training surgeons to conduct intracoelomic implantation of electronic tags. This curriculum could be offered through professional fisheries societies as professional development courses.     

Relative physiological effects of laparoscopic surgery and anesthesia with tricaine methanesulfonate (MS‐222) in Atlantic sturgeon Acipenser oxyrinchus oxyrinchus

Laparoscopy is a reliable, minimally‐invasive technique to obtain reproductive information from wild and captive sturgeon. While generally considered safe, the physiological consequences of laparoscopy in sturgeon are unknown. Therefore clinical pathology changes in juvenile, Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) following experimental laparoscopy at 10 and 22°C were described. Control fish were anesthetized with MS‐222 according to the same protocols as surgical fish, but were not incised. Surgical procedures did not affect heart and ventilation rates, signs of stress (skin redness) or time to recover from anesthesia in comparison to control fish. Anesthesia with MS‐222 produced a transient (by 1 h) hemo‐concentration (elevated protein and electrolytes), erythrocyte swelling (increased PCV and MCV) and stress response (elevated cortisol and glucose); and a delayed (by 24 h) increase in RBC, leukopenia and increased N : L ratio. Surgical procedures resulted in a delayed (by 24 h) decrease in plasma proteins, electrolytes, RBC and PCV relative to control fish, which may have resulted from surgically‐induced hemorrhage. Plasma enzyme activities increased in response to anesthesia and surgery and may indicate general stress and tissue damage. Anesthesia had a greater effect on blood value response than surgery, and the proportion of effect increased with temperature as MS‐222 potency and toxicity increases with water temperature. Repeated handling and blood draws within 24 h resulted in a 7% increase in cortisol, 10–14% increase in CK and 9–11% increase in LDH values. Except for plasma enzyme activities, blood values of all fish recovered within 1 week following anesthesia and surgeries. Relative experience of surgeons had no effect on hematology and biochemistry of fish, but healing rates of incisions were improved with better suture technique. Results of this study conclude that the physiological effects of laparoscopy are largely related to the anesthetic, MS‐222, and are generally mild and short‐lived. Improvements in laparoscopic technique might be gained by exploring alternate anesthetic protocols with faster induction and recovery times and reduced physiological effects.     

Effects of body size and predators on intracohort competition in wild and domesticated juvenile salmon in a stream

Competition between masu salmon (Oncorhynchus masou) of wild and aquaculture origin was investigated. Fry were individually marked and released in stream enclosures with and without a piscivorous predator. The aim was to assess the effects of predators and salmon body size on survival and growth of the two types of fish under natural conditions. The presence of predaceous Japanese huchen (Hucho perryi) resulted in lower mean growth rates of surviving fry. Relatively large fish survived and grew better than relatively small fish in the absence of predators, but not in their presence. This probably indicates an indirect effect of predation risk on within-cohort competitive behavior among salmon juveniles, with larger fish forced to give up their position as superior competitors. Domesticated fish survived in larger numbers and grew much faster than wild fish, irrespective of predator presence. Comparison with similar field studies revealed a pattern that the pre-experimental environment influenced the outcome of competition between wild and domesticated juvenile salmon. Domesticated fish were superior competitors even in the absence of an initial size advantage, which commonly gives a further advantage to hatchery-raised fish in natural streams. Therefore, caution dictates to avoid the release or escape of such fish into the wild.     

Physiological effects of dominance hierarchies: laboratory artefacts or natural phenomena?

Studies of fish behaviour have demonstrated the existence of social interactions that result in dominance hierarchies. In environments in which resources, such as food, shelter and mates, are limited, social competition results in some fish becoming dominant and occupying the most profitable positions. This behaviour has been observed in natural environments and also in many laboratory‐based experiments. When two fish have been confined in a small tank, one of them usually has exhibited behaviour that suggests it is dominant over the other submissive animal. Physiological consequences of social interaction can be seen in both dominants and subordinates but are more extreme in the subordinate. However, this scenario is without doubt an artificial situation. Fewer experiments have been conducted using laboratory experiments that are more socially and physically complex than those experienced by dyads in tanks. In simple fluvial tanks, through which water is recirculated, the physiological responses of fish to social competition have generally been qualitatively similar to those recorded among dyads. However, when environmental disturbances, complex resource distributions, increase in water flushing, presence of predators and competing species of fish have been included in experimen‐tal designs, there have been fewer, diminished or no physiological dierences between dominant and subordinate fish. There have been very few studies of physiology in relation to dominance in natural habitats, and those that have been conducted suggest that under some circumstances hierarchies may cause less intense physiological responses than have been suggested based on results of laboratory studies in simple environments. Possible reasons for these variations are discussed. The need is identified for a well structured experimental approach to the investi‐gation of the causes and consequences of hierarchies if the ecology of wild fish is to be modelled eectively based on physiological processes. It is also suggested that the further development and application of techniques for monitoring physiologies of fish in the wild is important.     

Effects of nutritional status on metabolic rate, exercise and recovery in a freshwater fish

The influence of feeding on swimming performance and exercise recovery in fish is poorly understood. Examining swimming behavior and physiological status following periods of feeding and fasting is important because wild fish often face periods of starvation. In the current study, researchers force fed and fasted groups of largemouth bass (Micropterus salmoides) of similar sizes for a period of 16 days. Following this feeding and fasting period, fish were exercised for 60 s and monitored for swimming performance and physiological recovery. Resting metabolic rates were also determined. Fasted fish lost an average of 16 g (nearly 12%) of body mass, while force fed fish maintained body mass. Force fed fish swam 28% further and required nearly 14 s longer to tire during exercise. However, only some physiological conditions differed between feeding groups. Resting muscle glycogen concentrations was twofold greater in force fed fish, at rest and throughout recovery, although it decreased in both feeding treatments following exercise. Liver mass was nearly three times greater in force fed fish, and fasted fish had an average of 65% more cortisol throughout recovery. Similar recovery rates of most physiological responses were observed despite force fed fish having a metabolic rate 75% greater than fasted fish. Results are discussed as they relate to largemouth bass starvation in wild systems and how these physiological differences might be important in an evolutionary context.