Increased reliance on coronary perfusion for cardiorespiratory performance in seawater-acclimated rainbow trout

Salmonid ventricles are composed of spongy and compact myocardium, the latter being perfused via a coronary circulation. Rainbow trout (Oncorhynchus mykiss) acclimated to sea water have higher proportions of compact myocardium and display stroke volume-mediated elevations in resting cardiac output relative to freshwater-acclimated trout, probably to meet the higher metabolic needs of osmoregulatory functions. Here, we tested the hypothesis that cardiorespiratory performance of rainbow trout in sea water is more dependent on coronary perfusion by assessing the effects of coronary ligation on cardiorespiratory function in resting and exhaustively exercised trout acclimated to fresh water or sea water. While ligation only had minor effects on resting cardiorespiratory function across salinities, cardiac function after chasing to exhaustion was impaired, presumably as a consequence of atrioventricular block. Ligation reduced maximum O2 consumption rate by 33% and 17% in fish acclimated to sea water and fresh water, respectively, which caused corresponding 41% and 17% reductions in aerobic scope. This was partly explained by different effects on cardiac performance, as maximum stroke volume was only significantly impaired by ligation in sea water, resulting in 38% lower maximum cardiac output in seawater compared with 28% in fresh water. The more pronounced effect on respiratory performance in sea water was presumably also explained by lower blood O2 carrying capacity, with ligated seawater-acclimated trout having 16% and 17% lower haemoglobin concentration and haematocrit, respectively, relative to ligated freshwater trout. In conclusion, we show that the coronary circulation allows seawater-acclimated trout to maintain aerobic scope at a level comparable to that in fresh water

Echocardiography - a non-invasive alternative for assessing cardiac morphology and function in Atlantic salmon (Salmo salar L.)

publishedVersio

Prevalence and severity of cardiac abnormalities and arteriosclerosis in farmed rainbow trout (Oncorhynchus mykiss)

Cardiovascular disease may pose a major threat to the health and welfare of farmed fish. By investigating a range of established cardiovascular disease indicators, we aimed to determine the prevalence, severity and consequences of this affliction in farmed rainbow trout (Oncorhynchus mykiss) from an open cage farm in the Baltic Sea, an open cage farm in a freshwater lake, and a land-based recirculating aquaculture system. We also aimed to identify environmental, anthropogenic and physiological factors contributing towards the development of the disease. The majority of trout possessed enlarged hearts with rounded ventricles (mean height:width ratios of 1.0-1.1 c.f. similar to 1.3 in wild fish) and a high degree of vessel misalignment (mean angles between the longitudinal ventricular axis and the axis of the bulbus arteriosus of 28-31 degrees c.f. similar to 23 degrees in wild fish). The prevalence and severity of coronary arteriosclerosis was also high, as 92-100% of fish from the different aquaculture facilities exhibited coronary lesions. Mean lesion incidence and severity indices were 67-95% and 3.1-3.9, respectively, which resulted in mean coronary arterial blockages of 19-32%. To evaluate the functional significance of these findings, we modelled the effects of arterial blockages on coronary blood flow and experimentally tested the effects of coronary occlusion in a sub-sample of fish. The observed coronary blockages were estimated to reduce coronary blood flow by 34-54% while experimental coronary occlusion adversely affected the electrocardiogram of trout. Across a range of environmental (water current, predation), anthropogenic (boat traffic intensity, hatchery of origin, brand of feed pellets) and physiological factors (condition factor, haematological and plasma indices), the hatchery of origin was the main factor contributing towards the observed variation in the development of cardiovascular disease. Therefore, further research on the effects of selective breeding programs and rearing strategies on the development of cardiovascular disease is needed to improve the welfare and health of farmed fish

Bigger is not better: cortisol-induced cardiac growth and dysfunction in salmonids

acceptedVersio

Effect of Hydrogen Peroxide on Immersion Challenge of Rainbow Trout Fry with Flavobacterium psychrophilum

An experimental model for immersion challenge of rainbow trout fry (Oncorhynchus mykiss) with Flavobacterium psychrophilum, the causative agent of rainbow trout fry syndrome and bacterial cold water disease was established in the present study. Although injection-based infection models are reliable and produce high levels of mortality attempts to establish a reproducible immersion model have been less successful. Various concentrations of hydrogen peroxide (H₂O₂) were evaluated before being used as a pre-treatment stressor prior to immersion exposure to F. psychrophilum. H₂O₂ accelerated the onset of mortality and increased mortality approximately two-fold; from 9.1% to 19.2% and from 14.7% to 30.3% in two separate experiments. Clinical signs observed in the infected fish corresponded to symptoms characteristically seen during natural outbreaks. These findings indicate that pre-treatment with H₂O₂ can increase the level of mortality in rainbow trout fry after exposure to F. psychrophilum

Oxygen- and capacity-limited thermal tolerance: blurring ecology and physiology

No abstract available

Behavioural Thermoregulatory Tactics in Lacustrine Brook Charr, Salvelinus fontinalis

The need to vary body temperature to optimize physiological processes can lead to thermoregulatory behaviours, particularly in ectotherms. Despite some evidence of within-population phenotypic variation in thermal behaviour, the occurrence of alternative tactics of this behaviour is rarely explicitly considered when studying natural populations. The main objective of this study was to determine whether different thermal tactics exist among individuals of the same population. We studied the behavioural thermoregulation of 33 adult brook charr in a stratified lake using thermo-sensitive radio transmitters that measured hourly individual temperature over one month. The observed behavioural thermoregulatory patterns were consistent between years and suggest the existence of four tactics: two “warm” tactics with both crepuscular and finer periodicities, with or without a diel periodicity, and two “cool” tactics, with or without a diel periodicity. Telemetry data support the above findings by showing that the different tactics are associated with different patterns of diel horizontal movements. Taken together, our results show a clear spatio-temporal segregation of individuals displaying different tactics, suggesting a reduction of niche overlap. To our knowledge, this is the first study showing the presence of behavioural thermoregulatory tactics in a vertebrate

Continuous physiological welfare evaluation of European whitefish (Coregonus lavaretus) during common aquaculture practices leading up to slaughter

European whitefish (Coregonus lavaretus) is an aquaculture species with the potential for expanded cultivation in the fresh and brackish waters of Northern Europe. Yet, relatively little species-specific information is available regarding the stress responses and associated welfare implications for this species in captivity. We addressed this knowledge gap by using a combination of implantable heart rate bio-loggers and a range of traditional stress indicators (e.g. haematological parameters and plasma concentrations of cortisol, glucose and ions) to comprehensively evaluate the physiological responses of freely swimming whitefish in captivity, as well as when subjected to aquaculture practices and stressors that commonly occur prior to and during slaughter. Whitefish appeared to recover rapidly from surgery, as resting heart rate decreased within 36 h to stabilize at similar to 25 beats min(-1) for the next 18 days when fish were left relatively undisturbed (i.e. personnel were only present when feeding fish). In contrast with previous studies on farmed rainbow trout and Atlantic salmon, whitefish did not exhibit a clear circadian heart rate rhythm, which may be related to species-specific differences in diurnal locomotor activity. Whitefish also appear to have a well-developed capacity for thermal acclimation of heart rate, as daily resting heart rate did not change during the undisturbed period despite an increase in body temperature from similar to 6.8 to 11.2 degrees C. Following acute stressors such as crowding and transportation, the physiological response of whitefish typically involved transient elevations in heart rate, plasma cortisol and glucose, and red blood cell swelling, while plasma [K+] decreased. In contrast, the heart rate of whitefish plummeted following the combination of brailing (i.e. to haul in fish with a brail/net) and CO2 exposure prior to slaughter, while plasma cortisol, glucose and [Ca2+] significantly increased. An unforeseen finding concerns the substantial and long-lasting physiological stress response observed in whitefish when held in close proximity (i.e. within similar to 10 m) to a rainbow trout net pen, as the mean heart rate of whitefish increased from similar to 32 to 43 beats min(-1) (i.e. an increase of similar to 34%). This may represent an innate physiological response to the threat of predation, which consequently increases the allostatic load and energetic expenditure of whitefish when farmed alongside salmonids. To conclude, this study highlights the importance of performing long-term, species-specific evaluations of freely swimming fish in real aquaculture settings, and provides a platform for further research aiming to determine the welfare implications of simultaneously farming predatory and prey species in close proximity