Understanding causal relationships within complex business environments represents an essential c... more Understanding causal relationships within complex business environments represents an essential component in a decision-maker's toolset when evaluating alternative aquaculture production technologies. This article assesses the utility of employing signed digraph qualitative modeling to support technology selection decision-making through evaluating the adoption of three alternative production expansion strategies (offshore production, IMTA, or land-based RAS) by the Atlantic salmon industry. Results underlined the benefits of strategically understanding the dynamics of demand growth, emphasized the requirement to address societal concerns early; and indicated that levels of ambiguity are lowest with expansion offshore and highest with land-based RAS growout. The research suggests that signed digraph modeling can provide an objective perspective on the levels of uncertainty and causal linkages within a business environment when exploring aquaculture adoption technology scenarios.
Physiological and Biochemical Zoology, Jul 1, 2017
Exposure to developmental hypoxia can have long-term impacts on the physiological performance of ... more Exposure to developmental hypoxia can have long-term impacts on the physiological performance of fish because of irreversible plasticity. Wild and captive-reared Atlantic salmon (Salmo salar) can be exposed to hypoxic conditions during development and continue to experience fluctuating oxygen levels as juveniles and adults. Here, we examine whether developmental hypoxia impacts subsequent hypoxia tolerance and aerobic performance of Atlantic salmon. Individuals at 87C were exposed to 50% (hypoxia) or 100% (normoxia) dissolved oxygen (DO) saturation (as percent of air saturation) from fertilization for ∼100 d (800 degree days) and then raised in normoxic conditions for a further 15 mo. At 18 mo after fertilization, aerobic scope was calculated in normoxia (100% DO) and acute (18 h) hypoxia (50% DO) from the difference between the minimum and maximum oxygen consumption rates (M Á O 2 min and M Á O 2 max , respectively) at 107C. Hypoxia tolerance was determined as the DO at which loss of equilibrium (LOE) occurred in a constantly decreasing DO environment. There was no difference in M Á O 2 min , M Á O 2 max , or aerobic scope between fish raised in hypoxia or normoxia. There was some evidence that hypoxia tolerance was lower (higher DO at LOE) in hypoxiaraised fish compared with those raised in normoxia, but the magnitude of the effect was small (12.52% DO vs. 11.73% DO at LOE). Acute hypoxia significantly reduced aerobic scope by reducing M Á O 2 max , while M Á O 2 min remained unchanged. Interestingly, acute hypoxia uncovered individual-level relationships between DO at LOE and M Á O 2 min , M Á O 2 max , and aerobic scope. We discuss our findings in the context of developmental tra-jectories and the role of aerobic performance in hypoxia tolerance.
Growth hormone (GH)-transgenic Atlantic salmon display accelerated growth rates compared with non... more Growth hormone (GH)-transgenic Atlantic salmon display accelerated growth rates compared with non-transgenics. GH-transgenic fish also display cardiorespiratory and metabolic modifications that accompany the increased growth rate. An elevated routine metabolic rate has been described for pre-and post-smolt GH-transgenic salmon that also display improvements in oxygen delivery to support the increased aerobic demand. The early ontogenic effects of GH transgenesis on the respiratory and cellular physiology of fish, especially during adverse environmental conditions, and the effect of polyploidy are unclear. Here, we investigated the effects of GH transgenesis and polyploidy on metabolic, heart and ventilation rates and heat shock protein (HSP) levels after exposure to acute hypoxia in post-hatch Atlantic salmon yolk-sac alevins. Metabolic rate decreased with decreasing partial pressures of oxygen in all genotypes. In normoxia, triploid transgenics displayed the highest mass-specific metabolic rates in comparison to diploid transgenics and non-transgenic triploids, which, in contrast, had higher rates than diploid non-transgenics. In hypoxia, we observed a lower massspecific metabolic rate in diploid non-transgenics compared with all other genotypes. However, no evidence for improved O 2 uptake through heart or ventilation rate was found. Heart rate decreased in diploid non-transgenics while ventilation rate decreased in both diploid non-transgenics and triploid transgenics in severe hypoxia. Regardless of genotype or treatment, inducible HSP70 was not expressed in alevins. Following hypoxia, the constitutive isoform of HSP70, HSC70, decreased in transgenics and HSP90 expression decreased in all genotypes. These data suggest that physiological changes through GH transgenesis and polyploidy are manifested during early ontogeny in Atlantic salmon.
Developing an understanding of economic variance (risk) is critical when evaluating alternative a... more Developing an understanding of economic variance (risk) is critical when evaluating alternative aquaculture production technologies. This article assesses the efficacy of employing a quantitative stochastic analysis technique to support technology selection decision making by undertaking a case study investment assessment of three alternative production expansion strategies (offshore sea-pens, land-based RAS growout and larger post-smolt) for the Tasmanian salmon industry. Results demonstrate that salmon aquaculture is undertaken with considerable underlying levels of economic risk, expansion offshore probably represents the lowest initial capital investment and greatest economic return, and that levels of financial uncertainty increase with land-based RAS production. The study highlights stochastic modeling provides significant "addedvalue" over single-point deterministic analysis and that developing an appreciation of the input variability is a key component in critically evaluating alternative production technologies.
Fluctuations in reproductive performance (i.e., spawning success, hatching rate, larval survival)... more Fluctuations in reproductive performance (i.e., spawning success, hatching rate, larval survival) are a common occurrence in abalone breeding programs, in particular during the early stages of their development. Such fluctuations affect the numbers of families available for progeny testing and selection, and can have consequences for genetic gains and inbreeding. We used stochastic computer simulations to understand how genetic gains and levels of inbreeding are affected when greenlip (Haliotis laevigata) breeding programs encounter varying severity and frequency of reproductive failure. We simulated breeding programs for greenlip abalone with both conservative and aggressive selection approaches over 35 y (10 generations). Without reproductive failure, genetic improvements of 36%-55% could be achieved after 10 y of selection in a single trait in a commercial abalone breeding program with a conservative selection approach, and gains of twice that could be achieved with a selection approach that allowed high rates of inbreeding. A conservative selection approach would be sustainable even at high rates of reproductive failure, whereas a more aggressive approach would lead to nearly twice the recommended level of inbreeding. It was concluded that breeding programs for greenlip abalone may be buffered against unexpected fluctuations in reproductive performance if the selection approach is chosen strategically.
Exposure to developmental hypoxia can have long-term impacts on the physiological performance of ... more Exposure to developmental hypoxia can have long-term impacts on the physiological performance of fish because of irreversible plasticity. Wild and captive-reared Atlantic salmon (Salmo salar) can be exposed to hypoxic conditions during development and continue to experience fluctuating oxygen levels as juveniles and adults. Here, we examine whether developmental hypoxia impacts subsequent hypoxia tolerance and aerobic performance of Atlantic salmon. Individuals at 8°C were exposed to 50% (hypoxia) or 100% (normoxia) dissolved oxygen (DO) saturation (as percent of air saturation) from fertilization for ∼100 d (800 degree days) and then raised in normoxic conditions for a further 15 mo. At 18 mo after fertilization, aerobic scope was calculated in normoxia (100% DO) and acute (18 h) hypoxia (50% DO) from the difference between the minimum and maximum oxygen consumption rates ([Formula: see text] and [Formula: see text], respectively) at 10°C. Hypoxia tolerance was determined as the DO...
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2022
Globally, Atlantic salmon (Salmo salar Linnaeus) aquaculture is now routinely affected by amoebic... more 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 (ṀO2rest and ṀO2max), aerobic scope (ṀO2max - ṀO2rest), excess post-exercise oxygen consumption (EPOC), and hypoxia tolerance. An increase in ṀO2rest (~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, ṀO2max 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.
The underlying mechanisms controlling growth heterosis in marine invertebrates remain poorly unde... more 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 (ṀO2) 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 ṀO2 were determined again. During the chronic exposure, hybrids and H. laevigata moved shorter distances than H. rubra. Resting ṀO2, 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, ṀO2 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.
Hypoxia in aquatic ecosystems is becoming increasingly prevalent, potentially reducing fish perfo... more Hypoxia in aquatic ecosystems is becoming increasingly prevalent, potentially reducing fish performance and survival by limiting the oxygen available for aerobic activities. Hypoxia is a challenge for conserving and managing fish populations and demands a better understanding of the short- and long-term impacts of hypoxic environments on fish performance. Fish acclimate to hypoxia via a variety of short- and long-term physiological modifications in an attempt to maintain aerobic performance. In particular, hypoxia exposure during early development may result in enduring cardio-respiratory modifications that affect future hypoxia acclimation capacity, yet this possibility remains poorly investigated. We incubated Atlantic salmon (Salmo salar) in normoxia (~100% dissolved oxygen [DO, as percent air saturation]), moderate hypoxia (~63% DO) or cyclical hypoxia (100–25% DO daily) from fertilization until 113 days post-fertilization prior to rearing all groups in normoxia for a further 8 ...
Hyperoxia has been shown to affect growth, survival and cellular homeostasis in fish. Previous fi... more Hyperoxia has been shown to affect growth, survival and cellular homeostasis in fish. Previous findings on chronic hypoxia (low environmental O 2) exposure in Atlantic salmon alevins indicate that re-exposure to normoxic conditions after hypoxia exposure (relative hyperoxia) elevates metabolism above normal. Hence, we here investigated whether acute hyperoxia above normoxic conditions also alters O 2 uptake and whether chronic hyperoxia affects O 2 uptake under normoxic and hypoxic conditions. To this end, the effects of acute and chronic hyperoxia exposure on metabolic rate and cardiorespiratory function (heart rate and ventilation rate) in Atlantic salmon (Salmo salar) alevins incubated at 4°C were investigated, and how it is affected by an increase in ambient temperature (4°C and 8°C). Hyperoxia (15-18 days at 28 kPa) reared alevins display advanced development compared with normoxia incubated animals. While acute hypoxia generally leads to metabolic depression (≈70%, 21 kPa compared with 5 kPa), acute hyperoxia (28 kPa) causes hypermetabolism (≈30% compared with normoxia at 4°C and ≈20% at 8°C). Chronic hyperoxic rearing on the other hand did not alter metabolic rate at 4°C or 8°C in acute hyperoxia, normoxia or hypoxia. Heart rates and ventilation rates were also unaltered with acute hyperoxia and were unaffected by chronic hyperoxia exposure. It is shown that acute hyperoxia increases O 2 uptake above normoxic conditions but chronic hyperoxia does not result in long term physiological changes. This adds further proof that O 2 uptake is not limited by O 2 transport capacity but by O 2 availability at this developmental stage in salmonids.
Understanding causal relationships within complex business environments represents an essential c... more Understanding causal relationships within complex business environments represents an essential component in a decision-maker's toolset when evaluating alternative aquaculture production technologies. This article assesses the utility of employing signed digraph qualitative modeling to support technology selection decision-making through evaluating the adoption of three alternative production expansion strategies (offshore production, IMTA, or land-based RAS) by the Atlantic salmon industry. Results underlined the benefits of strategically understanding the dynamics of demand growth, emphasized the requirement to address societal concerns early; and indicated that levels of ambiguity are lowest with expansion offshore and highest with land-based RAS growout. The research suggests that signed digraph modeling can provide an objective perspective on the levels of uncertainty and causal linkages within a business environment when exploring aquaculture adoption technology scenarios.
Many hybrids of marine molluscs show improved growth in comparison to their pure parental species... more Many hybrids of marine molluscs show improved growth in comparison to their pure parental species. Yet, little is known about the physiological mechanisms underlying the better hybrid performance. In this study, movement, oxygen consumption rate () and heart rate were determined in 22 month old cultured abalone Haliotis rubra, H. laevigata and their interspecies hybrid, the latter of which exhibits improved growth rate. Abalone were exposed to an acute temperature increase following acclimation to 16 or 23°C at high and low oxygen levels (100% or 70% air saturation, respectively). Movement of hybrids and H. laevigata was generally not affected by temperature and oxygen levels, yet H. rubra showed a strong thermal response. Heart rate and /temperature slopes revealed that hybrids were least affected by oxygen levels. Arrhenius break-point temperatures of hybrids and H. laevigata, but not H. rubra, were generally higher when abalone were acclimated to 23°C in comparison to 16°C. Hybrids had more stable maximum heart rate and values across acclimation conditions in comparison to H. laevigata and H. rubra. Thus, it appears that hybrids are able to maintain physiological functions over a broader environmental range. This improved tolerance to environmental fluctuations may bolster energy metabolism and improve growth in variable environments such as aquaculture farms.
Understanding causal relationships within complex business environments represents an essential c... more Understanding causal relationships within complex business environments represents an essential component in a decision-maker's toolset when evaluating alternative aquaculture production technologies. This article assesses the utility of employing signed digraph qualitative modeling to support technology selection decision-making through evaluating the adoption of three alternative production expansion strategies (offshore production, IMTA, or land-based RAS) by the Atlantic salmon industry. Results underlined the benefits of strategically understanding the dynamics of demand growth, emphasized the requirement to address societal concerns early; and indicated that levels of ambiguity are lowest with expansion offshore and highest with land-based RAS growout. The research suggests that signed digraph modeling can provide an objective perspective on the levels of uncertainty and causal linkages within a business environment when exploring aquaculture adoption technology scenarios.
Physiological and Biochemical Zoology, Jul 1, 2017
Exposure to developmental hypoxia can have long-term impacts on the physiological performance of ... more Exposure to developmental hypoxia can have long-term impacts on the physiological performance of fish because of irreversible plasticity. Wild and captive-reared Atlantic salmon (Salmo salar) can be exposed to hypoxic conditions during development and continue to experience fluctuating oxygen levels as juveniles and adults. Here, we examine whether developmental hypoxia impacts subsequent hypoxia tolerance and aerobic performance of Atlantic salmon. Individuals at 87C were exposed to 50% (hypoxia) or 100% (normoxia) dissolved oxygen (DO) saturation (as percent of air saturation) from fertilization for ∼100 d (800 degree days) and then raised in normoxic conditions for a further 15 mo. At 18 mo after fertilization, aerobic scope was calculated in normoxia (100% DO) and acute (18 h) hypoxia (50% DO) from the difference between the minimum and maximum oxygen consumption rates (M Á O 2 min and M Á O 2 max , respectively) at 107C. Hypoxia tolerance was determined as the DO at which loss of equilibrium (LOE) occurred in a constantly decreasing DO environment. There was no difference in M Á O 2 min , M Á O 2 max , or aerobic scope between fish raised in hypoxia or normoxia. There was some evidence that hypoxia tolerance was lower (higher DO at LOE) in hypoxiaraised fish compared with those raised in normoxia, but the magnitude of the effect was small (12.52% DO vs. 11.73% DO at LOE). Acute hypoxia significantly reduced aerobic scope by reducing M Á O 2 max , while M Á O 2 min remained unchanged. Interestingly, acute hypoxia uncovered individual-level relationships between DO at LOE and M Á O 2 min , M Á O 2 max , and aerobic scope. We discuss our findings in the context of developmental tra-jectories and the role of aerobic performance in hypoxia tolerance.
Growth hormone (GH)-transgenic Atlantic salmon display accelerated growth rates compared with non... more Growth hormone (GH)-transgenic Atlantic salmon display accelerated growth rates compared with non-transgenics. GH-transgenic fish also display cardiorespiratory and metabolic modifications that accompany the increased growth rate. An elevated routine metabolic rate has been described for pre-and post-smolt GH-transgenic salmon that also display improvements in oxygen delivery to support the increased aerobic demand. The early ontogenic effects of GH transgenesis on the respiratory and cellular physiology of fish, especially during adverse environmental conditions, and the effect of polyploidy are unclear. Here, we investigated the effects of GH transgenesis and polyploidy on metabolic, heart and ventilation rates and heat shock protein (HSP) levels after exposure to acute hypoxia in post-hatch Atlantic salmon yolk-sac alevins. Metabolic rate decreased with decreasing partial pressures of oxygen in all genotypes. In normoxia, triploid transgenics displayed the highest mass-specific metabolic rates in comparison to diploid transgenics and non-transgenic triploids, which, in contrast, had higher rates than diploid non-transgenics. In hypoxia, we observed a lower massspecific metabolic rate in diploid non-transgenics compared with all other genotypes. However, no evidence for improved O 2 uptake through heart or ventilation rate was found. Heart rate decreased in diploid non-transgenics while ventilation rate decreased in both diploid non-transgenics and triploid transgenics in severe hypoxia. Regardless of genotype or treatment, inducible HSP70 was not expressed in alevins. Following hypoxia, the constitutive isoform of HSP70, HSC70, decreased in transgenics and HSP90 expression decreased in all genotypes. These data suggest that physiological changes through GH transgenesis and polyploidy are manifested during early ontogeny in Atlantic salmon.
Developing an understanding of economic variance (risk) is critical when evaluating alternative a... more Developing an understanding of economic variance (risk) is critical when evaluating alternative aquaculture production technologies. This article assesses the efficacy of employing a quantitative stochastic analysis technique to support technology selection decision making by undertaking a case study investment assessment of three alternative production expansion strategies (offshore sea-pens, land-based RAS growout and larger post-smolt) for the Tasmanian salmon industry. Results demonstrate that salmon aquaculture is undertaken with considerable underlying levels of economic risk, expansion offshore probably represents the lowest initial capital investment and greatest economic return, and that levels of financial uncertainty increase with land-based RAS production. The study highlights stochastic modeling provides significant "addedvalue" over single-point deterministic analysis and that developing an appreciation of the input variability is a key component in critically evaluating alternative production technologies.
Fluctuations in reproductive performance (i.e., spawning success, hatching rate, larval survival)... more Fluctuations in reproductive performance (i.e., spawning success, hatching rate, larval survival) are a common occurrence in abalone breeding programs, in particular during the early stages of their development. Such fluctuations affect the numbers of families available for progeny testing and selection, and can have consequences for genetic gains and inbreeding. We used stochastic computer simulations to understand how genetic gains and levels of inbreeding are affected when greenlip (Haliotis laevigata) breeding programs encounter varying severity and frequency of reproductive failure. We simulated breeding programs for greenlip abalone with both conservative and aggressive selection approaches over 35 y (10 generations). Without reproductive failure, genetic improvements of 36%-55% could be achieved after 10 y of selection in a single trait in a commercial abalone breeding program with a conservative selection approach, and gains of twice that could be achieved with a selection approach that allowed high rates of inbreeding. A conservative selection approach would be sustainable even at high rates of reproductive failure, whereas a more aggressive approach would lead to nearly twice the recommended level of inbreeding. It was concluded that breeding programs for greenlip abalone may be buffered against unexpected fluctuations in reproductive performance if the selection approach is chosen strategically.
Exposure to developmental hypoxia can have long-term impacts on the physiological performance of ... more Exposure to developmental hypoxia can have long-term impacts on the physiological performance of fish because of irreversible plasticity. Wild and captive-reared Atlantic salmon (Salmo salar) can be exposed to hypoxic conditions during development and continue to experience fluctuating oxygen levels as juveniles and adults. Here, we examine whether developmental hypoxia impacts subsequent hypoxia tolerance and aerobic performance of Atlantic salmon. Individuals at 8°C were exposed to 50% (hypoxia) or 100% (normoxia) dissolved oxygen (DO) saturation (as percent of air saturation) from fertilization for ∼100 d (800 degree days) and then raised in normoxic conditions for a further 15 mo. At 18 mo after fertilization, aerobic scope was calculated in normoxia (100% DO) and acute (18 h) hypoxia (50% DO) from the difference between the minimum and maximum oxygen consumption rates ([Formula: see text] and [Formula: see text], respectively) at 10°C. Hypoxia tolerance was determined as the DO...
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2022
Globally, Atlantic salmon (Salmo salar Linnaeus) aquaculture is now routinely affected by amoebic... more 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 (ṀO2rest and ṀO2max), aerobic scope (ṀO2max - ṀO2rest), excess post-exercise oxygen consumption (EPOC), and hypoxia tolerance. An increase in ṀO2rest (~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, ṀO2max 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.
The underlying mechanisms controlling growth heterosis in marine invertebrates remain poorly unde... more 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 (ṀO2) 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 ṀO2 were determined again. During the chronic exposure, hybrids and H. laevigata moved shorter distances than H. rubra. Resting ṀO2, 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, ṀO2 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.
Hypoxia in aquatic ecosystems is becoming increasingly prevalent, potentially reducing fish perfo... more Hypoxia in aquatic ecosystems is becoming increasingly prevalent, potentially reducing fish performance and survival by limiting the oxygen available for aerobic activities. Hypoxia is a challenge for conserving and managing fish populations and demands a better understanding of the short- and long-term impacts of hypoxic environments on fish performance. Fish acclimate to hypoxia via a variety of short- and long-term physiological modifications in an attempt to maintain aerobic performance. In particular, hypoxia exposure during early development may result in enduring cardio-respiratory modifications that affect future hypoxia acclimation capacity, yet this possibility remains poorly investigated. We incubated Atlantic salmon (Salmo salar) in normoxia (~100% dissolved oxygen [DO, as percent air saturation]), moderate hypoxia (~63% DO) or cyclical hypoxia (100–25% DO daily) from fertilization until 113 days post-fertilization prior to rearing all groups in normoxia for a further 8 ...
Hyperoxia has been shown to affect growth, survival and cellular homeostasis in fish. Previous fi... more Hyperoxia has been shown to affect growth, survival and cellular homeostasis in fish. Previous findings on chronic hypoxia (low environmental O 2) exposure in Atlantic salmon alevins indicate that re-exposure to normoxic conditions after hypoxia exposure (relative hyperoxia) elevates metabolism above normal. Hence, we here investigated whether acute hyperoxia above normoxic conditions also alters O 2 uptake and whether chronic hyperoxia affects O 2 uptake under normoxic and hypoxic conditions. To this end, the effects of acute and chronic hyperoxia exposure on metabolic rate and cardiorespiratory function (heart rate and ventilation rate) in Atlantic salmon (Salmo salar) alevins incubated at 4°C were investigated, and how it is affected by an increase in ambient temperature (4°C and 8°C). Hyperoxia (15-18 days at 28 kPa) reared alevins display advanced development compared with normoxia incubated animals. While acute hypoxia generally leads to metabolic depression (≈70%, 21 kPa compared with 5 kPa), acute hyperoxia (28 kPa) causes hypermetabolism (≈30% compared with normoxia at 4°C and ≈20% at 8°C). Chronic hyperoxic rearing on the other hand did not alter metabolic rate at 4°C or 8°C in acute hyperoxia, normoxia or hypoxia. Heart rates and ventilation rates were also unaltered with acute hyperoxia and were unaffected by chronic hyperoxia exposure. It is shown that acute hyperoxia increases O 2 uptake above normoxic conditions but chronic hyperoxia does not result in long term physiological changes. This adds further proof that O 2 uptake is not limited by O 2 transport capacity but by O 2 availability at this developmental stage in salmonids.
Understanding causal relationships within complex business environments represents an essential c... more Understanding causal relationships within complex business environments represents an essential component in a decision-maker's toolset when evaluating alternative aquaculture production technologies. This article assesses the utility of employing signed digraph qualitative modeling to support technology selection decision-making through evaluating the adoption of three alternative production expansion strategies (offshore production, IMTA, or land-based RAS) by the Atlantic salmon industry. Results underlined the benefits of strategically understanding the dynamics of demand growth, emphasized the requirement to address societal concerns early; and indicated that levels of ambiguity are lowest with expansion offshore and highest with land-based RAS growout. The research suggests that signed digraph modeling can provide an objective perspective on the levels of uncertainty and causal linkages within a business environment when exploring aquaculture adoption technology scenarios.
Many hybrids of marine molluscs show improved growth in comparison to their pure parental species... more Many hybrids of marine molluscs show improved growth in comparison to their pure parental species. Yet, little is known about the physiological mechanisms underlying the better hybrid performance. In this study, movement, oxygen consumption rate () and heart rate were determined in 22 month old cultured abalone Haliotis rubra, H. laevigata and their interspecies hybrid, the latter of which exhibits improved growth rate. Abalone were exposed to an acute temperature increase following acclimation to 16 or 23°C at high and low oxygen levels (100% or 70% air saturation, respectively). Movement of hybrids and H. laevigata was generally not affected by temperature and oxygen levels, yet H. rubra showed a strong thermal response. Heart rate and /temperature slopes revealed that hybrids were least affected by oxygen levels. Arrhenius break-point temperatures of hybrids and H. laevigata, but not H. rubra, were generally higher when abalone were acclimated to 23°C in comparison to 16°C. Hybrids had more stable maximum heart rate and values across acclimation conditions in comparison to H. laevigata and H. rubra. Thus, it appears that hybrids are able to maintain physiological functions over a broader environmental range. This improved tolerance to environmental fluctuations may bolster energy metabolism and improve growth in variable environments such as aquaculture farms.
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