Amoebic gill disease increases energy requirements and decreases hypoxia tolerance in Atlantic salmon (Salmo salar) smolts.

Globally, Atlantic salmon (Salmo salar Linnaeus) aquaculture is now routinely affected by amoebic gill disease (AGD; Neoparamoeba perurans). The disease proliferates throughout the summer and is implicated in decreasing tolerance of salmon to environmental perturbations, yet little empirical evidence exists to support these observations. Using salmon acclimated to 15 or 19 °C, our aim was to determine the effects of clinically light-moderate (industry-relevant) AGD on metabolism (MO2rest and MO2max), aerobic scope (MO2max - MO2rest), excess post-exercise oxygen consumption (EPOC), and hypoxia tolerance. An increase in MO2rest (~8% and ~ 13% increase within the 15 and 19 °C acclimation groups, respectively) with increasing disease signs demonstrated an increase in baseline energy requirements as the disease progressed. Conversely, MO2max remained stable at both temperatures (~364 mg O2 kg-1 h-1), resulting in a decline in aerobic scope by 13 and 19% in the 15 and 19 °C groups, respectively. There was evidence of a decrease in hypoxia tolerance as the dissolved oxygen concentrations at loss of equilibrium increased by ~8% with more severe lesion coverage of the gills. These results suggest an increase in basal energy requirements and reduction in hypoxia tolerance as AGD proliferates, lending support to the idea that AGD reduces environmental tolerance. However, the lack of an effect of acclimation temperature indicates that the temperature-disease interaction may be more complicated than currently thought.

Measurement and relevance of maximum metabolic rate in fishes.

Maximum (aerobic) metabolic rate (MMR) is defined here as the maximum rate of oxygen consumption (M˙O2max ) that a fish can achieve at a given temperature under any ecologically relevant circumstance. Different techniques exist for eliciting MMR of fishes, of which swim-flume respirometry (critical swimming speed tests and burst-swimming protocols) and exhaustive chases are the most common. Available data suggest that the most suitable method for eliciting MMR varies with species and ecotype, and depends on the propensity of the fish to sustain swimming for extended durations as well as its capacity to simultaneously exercise and digest food. MMR varies substantially (>10 fold) between species with different lifestyles (i.e. interspecific variation), and to a lesser extent (

Experimental methods in aquatic respirometry: the importance of mixing devices and accounting for background respiration.

In light of an increasing trend in fish biology towards using static respirometry techniques without the inclusion of a mixing mechanism and without accurately accounting for the influence of microbial (background) respiration, this paper quantifies the effect of these approaches on the oxygen consumption rates (MO2 ) measured from juvenile barramundi Lates calcarifer (mean ± s.e. mass = 20·31 ± 0·81 g) and adult spiny chromis damselfish Acanthochromis polyacanthus (22·03 ± 2·53 g). Background respiration changed consistently and in a sigmoidal manner over time in the treatment with a mixing device (inline recirculation pump), whereas attempts to measure background respiration in the non-mixed treatment yielded highly variable estimates of MO2 that were probably artefacts due to the lack of water movement over the oxygen sensor during measurement periods. This had clear consequences when accounting for background respiration in the calculations of fish MO2 . Exclusion of a mixing device caused a significantly lower estimate of MO2 in both species and reduced the capacity to detect differences between individuals as well as differences within an individual over time. There was evidence to suggest that the magnitude of these effects was dependent on the spontaneous activity levels of the fish, as the difference between mixed and non-mixed treatments was more pronounced for L. calcarifer (sedentary) than for A. polyacanthus (more spontaneously active). It is clear that respirometry set-ups for sedentary species must contain a mixing device to prevent oxygen stratification inside the respirometer. While more active species may provide a higher level of water mixing during respirometry measurements and theoretically reduce the need for a mixing device, the level of mixing cannot be quantified and may change with diurnal cycles in activity. To ensure consistency across studies without relying on fish activity levels, and to enable accurate assessments of background respiration, it is recommended that all respirometry systems should include an appropriate mixing device.

Heart rate responses to temperature in free-swimming Pacific bluefin tuna (Thunnus orientalis).

The bluefin tuna heart remains at ambient water temperature (Ta) but must supply blood to warm regions of the body served by countercurrent vascular heat exchangers. Despite this unusual physiology, inherent difficulties have precluded an understanding of the cardiovascular responses to Ta in free-swimming bluefin tunas. We measured the heart rate (f(H)) responses of two captive Pacific bluefin tunas (Thunnus orientalis; 9.7 and 13.3 kg) over a cumulative period of 40 days. Routine f(H) during fasting in the holding tank at a Ta of 20°C was 45.1±8.0 and 40.7±6.5 beats min(-1) for Tuna 1 and Tuna 2, respectively. f(H) decreased in each fish with a Q10 temperature coefficient of 2.6 (Tuna 1) and 3.1 (Tuna 2) as Ta in the tank was slowly decreased to 15°C (~0.4°C h(-1)), despite a gradual increase in swimming speed. The same thermal challenge during digestion revealed similar thermal dependence of f(H) and indicated that the rate of visceral cooling is not buffered by the heat increment of feeding. Acutely decreasing Ta from 20 to 10°C while Tuna 1 swam in a tunnel respirometer caused a progressive increase in tail-beat frequency and oxygen consumption rate (M(O2)). f(H) of this fish decreased with a Q10 of 2.7 as Ta decreased between 20 and 15°C, while further cooling to 10°C saw a general plateau in f(H) around 35 beats min(-1) with a Q10 of 1.3. A discussion of the relationships between f(H), and haemoglobin-oxygen binding sheds further light on how bluefin cardiorespiratory systems function in a changing thermal environment.

Blood lactate loads of redthroat emperor Lethrinus miniatus associated with angling stress and exhaustive exercise.

Baseline, post-angling and maximum attainable blood lactate concentrations were measured for the fishery species redthroat emperor Lethrinus miniatus to gain insight into the condition of fish released following c. 30 s angling and <45 s air exposure. Mean ± S.D. baseline blood lactate was 1·5 ± 0·6 mmol l⁻¹, which increased and plateaued around 6 mmol l⁻¹ at 15-30 min post-angling. These values were significantly lower than those obtained from fish maximally exhausted with a prolonged chase and air exposure protocol following capture (10·9 ± 1·8 mmol l⁻¹), suggesting that L. miniatus is not maximally exhausted during standard angling practices.

The efficacy of field techniques for obtaining and storing blood samples from fishes.

Prompted by the dramatic increase in the use of blood analyses in fisheries research and monitoring, this study investigated the efficacy of common field techniques for sampling and storing blood from fishes. Three questions were addressed: (1) Do blood samples taken via rapid caudal puncture (the 'grab-and-stab' technique) yield similar results for live v. sacrificed groups of fishes? (2) Do rapidly obtained caudal blood samples accurately represent blood properties of fishes prior to capture? (3) Does storage of whole blood in an ice slurry for a working day (8·5 h) modify the properties of the plasma? It was shown that haematocrit, plasma ions, metabolites, stress hormones and sex hormones of caudal blood samples were statistically similar when taken from live v. recently sacrificed groups of adult coho salmon Oncorhynchus kisutch. Moreover, this study confirmed by using paired blood samples from cannulated O. kisutch that blood acquired through the caudal puncture technique (mean ±s.e. 142 ± 26 s after capture) was representative of fish prior to capture. Long-term (8·5 h) cold storage of sockeye salmon Oncorhynchus nerka whole blood caused significant decreases in plasma potassium and chloride, and a significant increase in plasma glucose. Previous research has suggested that these changes largely result from net movements of ions and molecules between the plasma and erythrocytes, movements that can occur within minutes of storage. Thus, blood samples from fishes should be centrifuged as quickly as practicable in the field for separation of plasma and erythrocytes to prevent potentially misleading data.

An exposé of Frappellian Motion.

Contrary to the well-recognised role of an abstract in helping to summarise the main points of the following article, this abstract takes its influence from Peter B. Frappell ('Frapps') and, therefore, is distracted from its key purpose. While the abstract was supposed to discuss the serious phenomenon of 'Frappellian Motion' (FM), someone just passed along some gossip that is heaps more exciting, so "let's go grab a beer and I'll talk at you".

Bio-sensing technologies in aquaculture: how remote monitoring can bring us closer to our farm animals.

Farmed aquatic animals represent an increasingly important source of food for a growing human population. However, the aquaculture industry faces several challenges with regard to producing a profitable, ethical and environmentally sustainable product, which are exacerbated by the ongoing intensification of operations and increasingly extreme and unpredictable climate conditions. Fortunately, bio-sensors capable of measuring a range of environmental, behavioural and physiological variables (e.g. temperature, dissolved gases, depth, acceleration, ventilation, heart rate, blood flow, glucose and l-lactic acid) represent exciting and innovative tools for assessing the health and welfare of farmed animals in aquaculture. Here, we illustrate how these state-of-the-art technologies can provide unique insights into variables pertaining to the inner workings of the animal to elucidate animal-environment interactions throughout the production cycle, as well as to provide insights on how farmed animals perceive and respond to environmental and anthropogenic perturbations. Using examples based on current challenges (i.e. sub-optimal feeding strategies, sub-optimal animal welfare and environmental changes), we discuss how bio-sensors can contribute towards optimizing the growth, health and welfare of farmed animals under dynamically changing on-farm conditions. While bio-sensors currently represent tools that are primarily used for research, the continuing development and refinement of these technologies may eventually allow farmers to use real-time environmental and physiological data from their stock as 'early warning systems' and/or for refining day-to-day operations to ethically and sustainably optimize production. This article is part of the theme issue 'Measuring physiology in free-living animals (Part I)'.

Aerobic and anaerobic movement energetics of hybrid and pure parental abalone.

The underlying mechanisms controlling growth heterosis in marine invertebrates remain poorly understood. We used pure blacklip (Haliotis rubra) and greenlip (Haliotis laevigata) abalone, as well as their hybrid, to test whether differences in movement and/or aerobic versus anaerobic energy use are linked to a purported increased growth rate in hybrids. Abalone were acclimated to control (16 °C) and typical summer temperatures (23 °C), each with oxygen treatments of 100% air saturation (O2sat) or 70% O2sat. The experiment then consisted of two phases. During the first phase (chronic exposure), movement and oxygen consumption rates (MO2) of abalone were measured during a 2 day observation period at stable acclimation conditions. Additionaly, lactate dehydrogenase (LDH) and tauropine dehydrogenase (TDH) activities were measured. During phase two (acute exposure), O2sat was raised to 100% for abalone acclimated to 70% O2sat followed by an acute decrease in oxygen to anoxia for all acclimation groups during which movement and MO2 were determined again. During the chronic exposure, hybrids and H. laevigata moved shorter distances than H. rubra. Resting MO2, LDH and TDH activities, however, were similar between abalone types but were increased at 23 °C compared to 16 °C. During the acute exposure, the initial increase to 100% O2sat for individuals acclimated to 70% O2sat resulted in increased movement compared to individuals acclimated to 100% O2sat for hybrids and H. rubra when compared within type of abalone. Similarly, MO2 during spontaneous activity of all three types of abalone previously subjected to 70% O2sat increased above those at 100% O2sat. When oxygen levels had dropped below the critical oxygen level (Pcrit), movement in hybrids and H. laevigata increased up to 6.5-fold compared to movement above Pcrit. Differences in movement and energy use between hybrids and pure species were not marked enough to support the hypothesis that the purportedly higher growth in hybrids is due to an energetic advantage over pure species.

Effects of suspended coal particles on gill structure and oxygen consumption rates in a coral reef fish.

Large quantities of coal are transported through tropical regions; however, little is known about the sub-lethal effects of coal contamination on tropical marine organisms, including fish. Here, we measured aerobic metabolism and gill morphology in a planktivorous coral reef damselfish, Acanthochromis polyacanthus to elucidate the sub-lethal effects of suspended coal particles over a range of coal concentrations and exposure durations. Differences in the standard oxygen consumption rates (MO2) between control fish and fish exposed to coal particles (38 and 73 mg L-1) were minimal and generally not dose dependent; however, the MO2 of fish exposed to 38 mg coal L-1 (21 days) and 73 mg coal L-1 (31 days) were both significantly higher than the MO2 of control fish. Chronic coal exposure (31 days) altered gill structure in the higher coal treatments (73 and 275 mg L-1), with fish exposed to 275 mg L-1 exhibiting significant reductions in gill mucous and thinning of lamellar and filament epithelium. These findings contribute to our limited understanding of the potential impacts of coal on tropical reef species; however, most of the observed effects occurred at high coal concentrations that are unlikely under most coal spill scenarios. Future studies should investigate other contamination scenarios such as the impacts of chronic exposures to lower concentrations of coal.

Postprandial metabolism of Pacific bluefin tuna (Thunnus orientalis).

Specific dynamic action (SDA) is defined as the energy expended during ingestion, digestion, absorption and assimilation of a meal. This study presents the first data on the SDA response of individual tunas of any species. Juvenile Pacific bluefin tunas (Thunnus orientalis; body mass 9.7-11.0 kg; N=7) were individually fed known quantities of food consisting primarily of squid and sardine (meal energy range 1680-8749 kJ, approximately 4-13% of tuna body mass). Oxygen consumption rates (M(O2)) were measured in a swim tunnel respirometer during the postprandial period at a swimming speed of 1 body length (BL) s(-1) and a water temperature of 20 degrees C. was markedly elevated above routine levels in all fish following meal consumption [routine metabolic rate (RMR)=174+/-9 mg kg(-1) h(-1)]. The peak M(O2) during the SDA process ranged from 250 to 440 mg kg(-1) h(-1) (1.5-2.3 times RMR) and was linearly related to meal energy content. The duration of the postprandial increment in M(O2) ranged from 21 h to 33 h depending upon meal energy content. Consequently, the total energy used in SDA increased linearly with meal energy and ranged from 170 kJ to 688 kJ, such that the SDA process accounted for 9.2+/-0.7% of ingested energy across all experiments. These values suggest rapid and efficient food conversion in T. orientalis in comparison with most other fishes. Implanted archival temperature tags recorded the increment in visceral temperature (T(V)) in association with SDA. M(O2) returned to routine levels at the end of the digestive period 2-3 h earlier than T(V). The qualitative patterns in M(O2) and T(V) during digestion were similar, strengthening the possibility that archival measurements of T(V) can provide new insight into the energetics and habitat utilization of free-swimming bluefin in the natural environment. Despite efficient food conversion, SDA is likely to represent a significant component of the daily energy budget of wild bluefin tunas due to a regular and high ingestion of forage.

Moving with the beat: heart rate and visceral temperature of free-swimming and feeding bluefin tuna.

Owing to the inherent difficulties of studying bluefin tuna, nothing is known of the cardiovascular function of free-swimming fish. Here, we surgically implanted newly designed data loggers into the visceral cavity of juvenile southern bluefin tuna (Thunnus maccoyii) to measure changes in the heart rate (fH) and visceral temperature (TV) during a two-week feeding regime in sea pens at Port Lincoln, Australia. Fish ranged in body mass from 10 to 21 kg, and water temperature remained at 18-19 degrees C. Pre-feeding fH typically ranged from 20 to 50 beats min(-1). Each feeding bout (meal sizes 2-7% of tuna body mass) was characterized by increased levels of activity and fH (up to 130 beats min(-1)), and a decrease in TV from approximately 20 to 18 degrees C as cold sardines were consumed. The feeding bout was promptly followed by a rapid increase in TV, which signified the beginning of the heat increment of feeding (HIF). The time interval between meal consumption and the completion of HIF ranged from 10 to 24 hours and was strongly correlated with ration size. Although fH generally decreased after its peak during the feeding bout, it remained elevated during the digestive period and returned to routine levels on a similar, but slightly earlier, temporal scale to TV. These data imply a large contribution of fH to the increase in circulatory oxygen transport that is required for digestion. Furthermore, these data oppose the contention that maximum fH is exceptional in bluefin tuna compared with other fishes, and so it is likely that enhanced cardiac stroke volume and blood oxygen carrying capacity are the principal factors allowing superior rates of circulatory oxygen transport in tuna.

Thermal effects on the blood respiratory properties of southern bluefin tuna, Thunnus maccoyii.

Thermal effects on the blood respiratory properties of southern bluefin tuna (Thunnus maccoyii) at 10, 23 and 36 degrees C, and at 0.5 and 1.5% CO(2) were investigated. A reversed temperature effect occurred as the oxygen partial pressure required for 50% haemoglobin saturation (P(50)) at 0.5% CO(2) decreased from 2.9 kPa at 10 degrees C to 1.7 kPa at 23 degrees C (apparent heat of oxygenation, DeltaH degrees , =+27 kJ mol(-1)). However, oxygen binding was essentially independent of temperature at warmer temperatures (P(50)=1.7-2.0 kPa from 23-36 degrees C at 0.5% CO(2); DeltaH degrees =-6.5 kJ mol(-1)). Hill's coefficient (n(H)) ranged from 1.3 to 1.6, and there was a large effect of temperature on the Bohr factor (DeltalogP(50)/DeltapH=-1.6 at 10 degrees C and -0.9 at 36 degrees C). This is the first study of whole blood to demonstrate the thermal dependence of DeltaH degrees itself, whereby the oxygen equilibrium curve is more sensitive to temperature in the lowest thermal range examined. We suggest that the functional basis for these observations lies in the necessity to ensure a sufficient oxygen supply to all tissues, including the heart and liver, without suffering from premature or excessive oxygen unloading around the heat exchanger prior to delivery of oxygen to organs and tissues that lie efferent to the exchanger.

Predicting rate of oxygen consumption from heart rate while little penguins work, rest and play.

The relationship between heart rate (f(H)) and rate of oxygen consumption (V(.)O2) was investigated under changing conditions of ambient temperature, digestive state and exercise state in the little penguin (Eudyptula minor). Both f(H) and V(.)O2 were recorded simultaneously from 12 little penguins while they each (a) rested and exercised within their reported thermo-neutral zone (TNZ), (b) rested and exercised below their reported TNZ and (c) digested a meal of sardines within their reported TNZ. Contrary to our expectations, we found that minimum V(.)O2 did not vary between the two temperatures used. Comparison with values from the literature suggests that both minimum V(.)O2 and the extent of the TNZ in this species may vary along a latitudinal gradient. Furthermore, while minimum V(.)O2 was unchanged at the lower temperature, minimum f(H) was significantly higher, suggesting a hitherto undescribed cardiac response to lowered ambient temperature in an avian species. This response was maintained when the penguins exercised within and below their apparent TNZ as f(H) was significantly greater in cold conditions for a given level of V(.)O2. Furthermore, both f(H) and V(.)O2 were slightly but significantly elevated for a given walking speed during exercise at the lower temperature. This suggests that the penguins may have been close to their TNZ and that the measures employed to counteract heat loss while at rest may have been compromised during exercise. There was no significant difference in the relationship between f(H) and V(.)O2 while the penguins were inactive ina post-digestive state or inactive and digesting a meal within their TNZ, though both of these relationships were significantly different from that during exercise. This suggests that while digestion has no effect on the f(H)/V(.)O2 relationship, for little penguins at least, it is of little value in deriving a predictive relationship for application to active free-ranging animals.

Micronutrient supplements and mortality of HIV-infected adults with pulmonary TB: a controlled clinical trial.

SETTING: Zomba and Blantyre, Malawi, Africa. OBJECTIVES: To determine whether daily micronutrient supplementation reduces the mortality of human immunodeficiency virus (HIV) infected adults with pulmonary tuberculosis (TB). DESIGN: A randomised, controlled clinical trial of micronutrient supplementation for HIV-positive and HIV-negative adults with pulmonary TB. Participants were enrolled at the commencement of chemotherapy for sputum smear-positive pulmonary TB and followed up for 24 months. RESULTS: A total of 829 HIV-positive and 573 HIV-negative adults were enrolled. During follow-up, 328 HIV-positive and 17 HIV-negative participants died. The proportion of HIV-positive participants who died in the micronutrient and placebo groups was 38.7% and 40.4%, respectively (P = 0.49). Micronutrient supplementation did not reduce mortality (hazard ratio [HR] 0.93, 95%CI 0.75-1.15) among HIV-positive adults. CONCLUSIONS: Micronutrient supplementation at the doses used in this study does not reduce mortality in HIV-positive adults with pulmonary TB in Malawi.

Physiological response to feeding in little penguins.

Specific dynamic action (SDA), the increase in metabolic rate above resting levels that accompanies the processes of digestion and assimilation of food, can form a substantial part of the daily energy budget of free-ranging animals. We measured heart rate (fH) and rate of oxygen consumption (VO2) in 12 little penguins while they digested a meal of sardines in order to determine whether they show specific dynamic action. In contrast to some studies of other penguin species, little penguins showed a substantial SDA, the magnitude of which was proportional to the size of the meal. The energy utilized in SDA was equivalent to 13.4% of the available energy content of the fish. Furthermore, animals such as penguins that forage in a cold environment will probably expend further energy in heating their food to body temperature to facilitate efficient digestion. It is estimated that this additional energy expenditure was equivalent to 1.6%-2.3% of the available energy content of the fish, depending on the time of year and therefore the temperature of the water. Changes in fH during digestion were qualitatively similar to those in VO2, implying that there were no substantial circulatory adjustments during digestion and that the relationship between fH and VO2 in penguins is unaffected by digestive state.

Effects of streptovaricins and their degradation products on RNA-directed DNA polymerase of Rauscher leukemia virus.

The activities of streptovaricin complexes, streptovaricins, streptovals, and streptovarinic degradation products were elevated against RNA-directed DNA polymerases of Rauscher leukemia virus, DNA-dependent DNA polymerase of bacterial and mammalian cells, and DNA-dependent RNA polymerases of mammalian origin. The activities of streptovaricins were also listed for comparison purposes. The effects of streptovaricin complexes on viral DNA polymerases varied significantly from lot to lot, and streptovaricin complex lot 7 was the most active. All the streptovals and streptovaricin degradation products except varicinal A showed a marked improvement (twofold to tenfold) in activity against the viral enzyme over the parent streptovaricins. None of these compounds, however, displayed any significant effect on either the DNA polymerase of L1210 leukemia cells and Escherichia coli or the RNA polymerase of isolated nuclei of mouse liver. As a result of tests in these systems, some specific inhibitors of RNA-directed DNA polymerases of Rauscher leukemia virus were selected.

Effects of streptovaricins and their degradation products on infectivity of Rauscher leukemia virus.

The virucidal effects of streptovaricin (Sv) A, SvC, SvD, streptoval (Sval) C, Sval Fc, and streptovarone were evaluated by incubation of the drug with Rauscher leukemia virus (RLV) at 37 degrees C for 60 minutes prior to dillution and addition to cells (in vitro assay) or before ip injection into animals (in vivo assay). The in vitro and in vivo assays were plaque formation and splenomegaly, respectively. A dose-related effect was observed with all six compounds with the in vitro assay. On an equimolar basis, the Sv degradation products, i.e., Sval C, Sval Fc, and streptovarone were most inhibitory, followed by SvD; SvA and SvC were least active. At 0.0625 mumoles, the three Sv degradation products inactivated over 90% of the RLV. Similar results were obtained through the in vivo assay. At 0.06 mumoles, streptovarone, Sval C, and SvD showed 78,62, and 29% inhibition of splenomegaly, respectively; SvA and SvC were essentially inactive. A direct relationship was observed between inhibition on RNA-directed DNA polymrase of RLV by these compounds and their virucidal effects. No drug given at the time of injection, however, showed any significant effect on virus infective processes in vitro or in vivo. The reason for the lack of therapeutic effects of these compounds is discussed.