Comparing a bioenergetics model with feeding rates of caged European starlings

We tested a bioenergetics model integrated within a mortality model that estimates numbers of European starlings (Sturnus vulgaris) poisoned with the avicide, Compound DRC-1339 Concentrate. The bioenergetics model predicted daily metabolic rate. Accuracy and reliability of this variable is critical because other algorithms (e.g., toxicity regressions, feeding behavior) in the mortality model depend on metabolic rate to calculate the amount of DRC-1339 ingested per bird. We tested the bioenergetics model by comparing its estimates of metabolic rate with those generated from measuring feeding rates of caged starlings during a feeding trial conducted outdoors during January 2008. Over the 12-day feeding trial, daily feeding rates of caged starlings indicated that metabolic rates ranged from 157 kJ/bird per day to 305 kJ/bird per day. The bioenergetics model predicted metabolic rates ranging from 208 kJ/bird per day to 274 kJ/bird per day. There was no difference between these 2 independently derived estimates of daily metabolic rate (paired t-test: t₍₁₁₎ = 1.4, P = 0.18). Using 95% confidence intervals calculated from variation of feeding rates among cages (n = 4, 6 birds/cage), the bioenergetics model's estimates were within 95% confidence intervals on 9 of 12 days and greater than the upper 95% confidence interval on 3 days. Daily estimates of metabolic rate were directly correlated between the bioenergetics model and the feeding-rate model (r₁₂ = 0.57, P = 0.05). A broad range of temperatures (−17°C to 14°C), wind speeds (0–40 km/hr), and percent cloud cover (0–100%) were encountered during the feeding trial. The bioenergetics model's predictions appeared robust to varying meteorological conditions typical of winters in middle latitudes of the interior United States. Compound DRC-1339 Concentrate is used by USDA Wildlife Services to manage chronic infestations of starlings at livestock facilities, which occur mainly during fall and winter. Compared to other methods used for estimating DRC-1339 mortality (e.g., counting birds pre- and posttreatment), bioenergetics modeling should improve the mortality model's overall accuracy and precision. © The Wildlife Society, 2011     

Tradeoffs between respiration and feeding in Sacramento blackfish,Orthodon microlepidotus

Synopsis Suspension-feeding fishes use gill structures for both respiration (lamellae) and food capture (rakers). During hypoxic exposure in eutrophic lakes or poorly circulated sloughs, many fishes, including Sacramento blackfish, Orthodon microlepidotus, increase their gill water flows, in part by increasing ventilatory stroke volumes. Stroke volume increases could compromise particle sieving efficiency by spreading interdigitated gill rakers from adjacent gill arches, although blackfish capture food particles by raker-guided water flows to a sticky buccal root. Using van Dam-type respirometers, blackfish respiratory variables and feeding efficiency (Artemia nauplii) were measured under normoxia (> 130 torr PO₂) and hypoxia (60 torr PO₂). Compared with non-feeding, normoxic conditions, gill ventilation volume, frequency, stroke volume, and gape all increased, while O₂ uptake efficiency decreased, during hypoxia and during feeding. O₂ consumption increased during feeding treatments, and % uptake of nauplii showed no difference between normoxic and hypoxic groups. Thus, blackfish display respiratory adaptations, including increased ventilatory stroke volumes, to survive in hypoxic environments such as Clear Lake, California. Importantly, they have also evolved a particle capture mechanism that allows efficient suspension-feeding under both normoxic and hypoxic conditions.     

Effect of meal size on excess post-exercise oxygen consumption in fishes with different locomotive and digestive performance

Effects of feeding on pre-exercise VO₂ and excess post-exercise oxygen consumption (EPOC) after exhaustive exercise were investigated in sedentary southern catfish, active herbivorous grass carp, omnivorous crucian carp, and sluggish omnivorous darkbarbel catfish to test whether feeding had different effects on EPOC and to compare EPOC in fishes with different ecological habits. For fasting fish, the pre-exercise and peak post-exercise VO₂ were higher and recovery rates were faster in crucian carp and grass carp compared to those of darkbarbel catfish and southern catfish. EPOC magnitudes of grass carp and southern catfish were significantly larger than those of crucian carp and darkbarbel catfish. Feeding had no significant effect on peak post-exercise VO₂, recovery rate, and EPOC magnitude in grass carp. Both the pre-exercise and peak post-exercise VO₂ increased with meal size, while the EPOC magnitude and duration decreased significantly in the larger meal size groups of crucian carp and southern catfish. In darkbarbel catfish, both the pre-exercise and peak post-exercise VO₂ increased with meal size, but the VO₂ increment elicited by exercise was larger in feeding groups compared with the fasting group. These results suggest that (1) the characteristics of the post-exercise VO₂ profile, such as peak post-exercise VO₂ and recovery rate, were closely related to the activity of fishes, whereas the EPOC magnitude was not and (2) the effects of feeding on EPOC were more closely related to the postprandial increase in VO₂.     

Temperature Effects on the Activity of the Alternative Respiratory Pathway in Chill-Sensitive Cucumis sativus

After 48 hours at 2°C, hypocotyls from chill-sensitive Cucumis sativus seedlings showed a burst of O₂ uptake. The alternative pathway became engaged to close to 45% full capacity during this postchilling respiratory burst. However, it only accounted for up to 50% of this increased respiratory O₂ uptake. By 24 hours after chilling, when the seedlings were fully recovered from visible symptoms of chilling injury, the flux through the alternative pathway was back to the level (about 10%) found before chilling. Blocking chilling-induced ethylene production with aminoethoxyvinylglycine had no effect on this increased utilization of the alternative pathway.     

Comparing correlative and bioenergetics‐based habitat suitability models for drift‐feeding fishes

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Changes in dormancy of Sisymbrium officinaleseeds do not depend on changes in respiratory activity

Effects of dark incubation at different temperatures were studied on dormancy and respiratory activity of seeds of Sisymbrium officinale (L.) Scop. Because germination of this species absolutely depends on the simultaneous action of light and nitrate, changes in dormancy could be studied in darkness without the interference of early germination events. Upon the start of incubation rates of O₂ uptake and CO₂ release rose. This was followed by a gradual decrease until stable levels of O₂ uptake and CO₂ release were achieved. Seeds kept for prolonged periods at 24^°C, showed neither a change in germination capacity nor in rates of O₂ uptake and CO₂ release. Respiratory quotients were 0.55–0.7. The initial rise in O₂ uptake correlated with the rate of water uptake and with breaking of primary dormancy. However, the subsequent decline in O₂ uptake was not generally linked to induction of secondary dormancy. An increased O₂ uptake was not required during breaking of secondary dormancy. It is concluded that changes in dormancy are not generally related to changes in respiratory activity. However, germination strongly depends on respiration. The increase in O₂ uptake started well before radicle protrusion. A far red irradiation only reversed this increase when it was given before germination escaped from its red light antagonising action. The contribution of different respiratory pathways was followed during prolonged incubation at 24^°C in darkness. KCN at 1.5 mM was needed to inhibit the cytochrome pathway (CP) and benzohydroxamic acid (BHAM) at 30 mM to inhibit the alternative pathway (AP). These concentrations did not exert any side effects. Electron flow was predominantly via the CP, maximally 10% was via the AP. Flow through the CP declined during the first 6 days and residual respiration remained constant. Therefore, the contribution of residual respiration became relatively more important with prolonged incubation. KCN at concentrations that almost completely inhibited flow through the CP, did not dramatically reduce germination. BHAM already inhibited germination at concentrations that do not inhibit oxygen uptake.     

Properties of heterocysts isolated with colloidal silica

A method is described for the isolation of heterocysts that are virtually free of contaminating cell debris after sonication of aerobically grown Anabaena 7120. Isolated heterocysts reduced acetylene in a light-dependent process in the absence of exogenously provided ATP; heterocysts supplied with ATP and Na₂S₂O₄ reduced acetylene slowly in the dark but still showed a marked light activation. Nitrogenase activity was greatest in fractions containing intact heterocysts. Up to 13% of the activity of the intact filaments was accounted for in the isolated heterocyst preparation.Isolated heterocysts took up O₂ in a light-independent process; O₂ uptake with added NADP⁺ was enhanced by pyruvate, isocitrate and intermediates of the oxidative pentose pathway.     

Photoreduction of O(2) Primes and Replaces CO(2) Assimilation

A mass spectrometer with a membrane inlet system was used to monitor directly gaseous components in a suspension of algae. Using labeled oxygen, we observed that during the first 20 seconds of illumination after a dark period, when no net O₂ evolution or CO₂ uptake was observed, O₂ evolution was normal but completely compensated by O₂ uptake. Similarly, when CO₂ uptake was totally or partially inhibited, O₂ evolution proceeded at a high (near maximal) rate. Under all conditions, O₂ uptake balanced that fraction of the O₂ evolution which could not be accounted for by CO₂ uptake.     

Temperature effects on oxidative metabolism of dormant sugar pine seeds

When dormant sugar pine (Pinus lambertiana L.) seeds were imbibed at 5°C, they showed a rapid increase in O₂ uptake, ATP level, and moisture content during the first 4 days. This was followed by a plateau phase until 60 days, after which a second significant increase in all three features occurred as dormancy was broken. During the plateau phase, conventional CN-sensitive respiration accounted for 74 to 79% of the total O₂ uptake. When dormant sugar pine seeds were imbibed at and maintained at 25°C, a different pattern occurred. Water uptake was much more rapid during the first 4 days and no second increase occurred after 60 days because the seeds did not break dormancy. There was an initial burst of O₂ uptake and ATP formation, but these both declined abruptly after 24 to 48 hours. Levels about half those of seeds at 5°C were maintained through the rest of a 90-day period. CN-sensitive respiration declined during imbibition at 25°C, and accounted for only 55 to 61% of the total O₂ uptake. The inability of dormant sugar pine seeds to germinate at temperatures above about 17°C may therefore result from initial temperature effects on membrane properties, leading to reduced O₂ uptake, reduced cytochrome oxidase electron transport activity, and lowered ATP levels.     

Effects of hypoxia on aerobic metabolism and active electrosensory acquisition in the African weakly electric fish Marcusenius victoriae

Environmental hypoxia has effected numerous and well-documented anatomical, physiological and behavioural adaptations in fishes. Comparatively little is known about hypoxia's impacts on sensing because it is difficult to quantify sensory acquisition in vivo. Weakly electric fishes, however, rely heavily on an easily-measurable sensory modality—active electric sensing—whereby individuals emit and detect electric organ discharges (EODs). In this study, hypoxia tolerance of a mormyrid weakly electric fish, Marcusenius victoriae, was assessed by examining both its metabolic and EOD rates using a critical threshold (p_crit) paradigm. The routine metabolic rate was 1.42 mg O₂ h⁻¹, and the associated critical oxygen tension was 14.34 mmHg. Routine EOD rate was 5.68 Hz with an associated critical tension of 15.14 mmHg. These metabolic indicators of hypoxia tolerance measured in this study were consistent with those in previous studies on M. victoriae and other weakly electric fishes. Furthermore, our results suggest that some aerobic processes may be reduced in favour of maintaining the EOD rate under extreme hypoxia. These findings underscore the importance of the active electrosensory modality to these hypoxia-tolerant fish.     

Re-interpreting anaerobic metabolism: an argument for the application of both anaerobic glycolysis and excess post-exercise oxygen consumption (EPOC) as independent sources of energy expenditure

Due to current technical difficulties and changing cellular conditions, the measurement of anaerobic and recovery energy expenditure remains elusive. During rest and low-intensity steady-state exercise, indirect calorimetric measurements successfully represent energy expenditure. The same steady-state O₂ uptake methods are often used to describe the O₂ deficit and excess post-oxygen consumption (EPOC): 1 l O₂ = 5 kcal = 20.9 kJ. However, an O₂ deficit plus exercise O₂ uptake measurement ignores energy expenditure during recovery, and an exercise O₂ uptake plus EPOC measurement misrepresents anaerobic energy expenditure. An alternative solution has not yet been proposed. Anaerobic glycolysis and mitochondrial respiration are construed here as a symbiotic union of metabolic pathways, each contributing independently to energy expenditure and heat production. Care must be taken when using O₂ uptake alone to quantify energy expenditure because various high-intensity exercise models reveal that O₂ uptake can lag behind estimated energy demands or exceed them. The independent bioenergetics behind anaerobic glycolysis and mitochondrial respiration can acknowledge these discrepancies. Anaerobic glycolysis is an additive component to an exercise O₂ uptake measurement. Moreover, it is the assumptions behind steady-state O₂ uptake that do not permit proper interpretation of energy expenditure during EPOC; 1 l O₂≠ 20.9 kJ. Using both the O₂ deficit and a modified EPOC for interpretation, rather than one or the other, leads to a better method of quantifying energy expenditure for higher intensity exercise and recovery. Accepted: 23 September 1997     

Feeding habits of ocellate spot skate,Okamejei kenojei (Müller & Henle, 1841), in coastal waters of Taean,Korea

The feeding habits of Okamejei kenojei were studied using 592 specimens collected in the coastal waters of Taean, Korea from April 2008 to March 2009. O. kenojei is a bottom‐feeding carnivore that consumes mainly shrimp, fishes, and crabs. Its diet also includes small quantities of amphipods, mysids, cephalopods, euphausiids, copepods, isopods, and polychaetes. The total length (TL) of individuals in this study ranged from 8.2 to 49.0 cm. Cluster analysis based on %IRI (index of relative importance) identified three size classes. Group A (< 20 cm TL) ate primarily caridean shrimp and amphipods; group B (20–30 cm TL) ate exclusively shrimp; and group C (> 30 cm TL) ate penaeoidean shrimp, fishes, and crabs. O. kenojei showed ontogenetic changes in feeding habits. Although shrimps were the primary food consumed by all size groups, the proportion of shrimp in the total diet decreased and the consumption of fishes and crabs gradually increased with the body size of O. kenojei. Size of the prey organisms also increased. Smaller individuals fed mainly on small prey, such as amphipods, mysids, and small shrimp, whereas larger individuals preferred larger prey, such as larger shrimp, fishes, and crabs. The size‐related diet breadth and the percentage of empty stomachs were significant; the diet breadth gradually increased with body size, whereas the percentage of empty stomachs decreased. Seasonal changes in the O. kenojei diet were not significant, but shrimp constituted 97.3% of the summer diet by %IRI. Seasonal changes in diet breadth and the percentage of empty stomachs were not significant.     

The evolution of Root effect hemoglobins in the absence of intracellular pH protection of the red blood cell: insights from primitive fishes

The Root effect, a reduction in blood oxygen (O₂) carrying capacity at low pH, is used by many fish species to maximize O₂ delivery to the eye and swimbladder. It is believed to have evolved in the basal actinopterygian lineage of fishes, species that lack the intracellular pH (pH_i) protection mechanism of more derived species’ red blood cells (i.e., adrenergically activated Na⁺/H⁺ exchangers; βNHE). These basal actinopterygians may consequently experience a reduction in blood O₂ carrying capacity, and thus O₂ uptake at the gills, during hypoxia- and exercise-induced generalized blood acidoses. We analyzed the hemoglobins (Hbs) of seven species within this group [American paddlefish (Polyodon spathula), white sturgeon (Acipenser transmontanus), spotted gar (Lepisosteus oculatus), alligator gar (Atractosteus spatula), bowfin (Amia calva), mooneye (Hiodon tergisus), and pirarucu (Arapaima gigas)] for their Root effect characteristics so as to test the hypothesis of the Root effect onset pH value being lower than those pH values expected during a generalized acidosis in vivo. Analysis of the haemolysates revealed that, although each of the seven species displayed Root effects (ranging from 7.3 to 40.5% desaturation of Hb with O₂, i.e., Hb O₂ desaturation), the Root effect onset pH values of all species are considerably lower (ranging from pH 5.94 to 7.04) than the maximum blood acidoses that would be expected following hypoxia or exercise (pH_i 7.15–7.3). Thus, although these primitive fishes possess Hbs with large Root effects and lack any significant red blood cell βNHE activity, it is unlikely that the possession of a Root effect would impair O₂ uptake at the gills following a generalized acidosis of the blood. As well, it was shown that both maximal Root effect and Root effect onset pH values increased significantly in bowfin over those of the more basal species, toward values of similar magnitude to those of most of the more derived teleosts studied to date. This is paralleled by the initial appearance of the choroid rete in bowfin, as well as a significant decrease in Hb buffer value and an increase in Bohr/Haldane effects, together suggesting bowfin as the most basal species capable of utilizing its Root effect to maximize O₂ delivery to the eye.     

Temporal plasticity in thermal‐habitat selection of burbot Lota lota a diel‐migrating winter‐specialist

In this study, animal‐borne telemetry with temperature sensors was coupled with extensive habitat temperature monitoring in a dimictic reservoir, to test the following hypotheses: behavioural thermoregulation occurs throughout the year and temperature selection varies on a diel and seasonal basis, in a winter‐specialist diel‐migrating fish. Burbot Lota lota demonstrated nightly behavioural thermoregulation throughout the year, with a large seasonal shift between selection for very cold temperatures (<2° C) optimal for reproduction during the spawning period and selection for warmer temperatures (12–14° C) optimal for hunting and feeding during non‐reproductive periods. During daylight hours, while L. lota avoided habitats warmer than optimal for reproduction and feeding during the spawning and non‐reproductive periods, respectively, active selection was limited to selection for 4–6° C habitat during the prespawning period. Although behavioural thermoregulation explained the night‐time migration, behavioural thermoregulation only partially explained daytime behaviour, indicating that diel migration is best explained by a combination of factors. Thus, thermal‐habitat selection was a good predictor of night‐time habitat occupancy in a diel‐migrating species. Together, these results show that thermal‐habitat selection by fishes may be important throughout the year and a more seasonally plastic behaviour than previously recognized.     

Respiration of juvenile Arctic cod (Boreogadus saida): effects of acclimation,temperature, and food intake

Oxygen consumption (VO₂) of juvenile Arctic cod (Boreogadus saida) was investigated at low tempera tures (six temperatures; range -0.5 to 2.7°C). Small (mean wt. 6–8 g) and large (mean wt. 14 g) fish were acclimated, or adjusted to a constant temperature (0.4°C), for 5 months and then tested for metabolic cold adaptation (elevated metabolic rates in polar fishes). Short-term (2 weeks) acclimated fish showed elevated VO₂ similar to previously established values for polar fishes, but there was no such evidence after longterm acclimation. Long-term acclimation caused VO₂ values to drop significantly (from 86.0 to 46.5 mg O₂·kg^–1·h^–1, at 0.4°C), which showed that metabolic cold adaptation was a phenomenon caused by insufficien: acclimation time for fish in respiration experiments. We also measured the effects of temperature and feeding on VO₂. A temperature increase of 2.3°C resulted in relatively large increases in VO₂ for both longand short-term acclimated fish (Q₁₀ = 6.7 and 7.1, respectively), which suggests that metabolic processes are strongly influenced by temperature when it is close to zero. Feeding individuals to satiation caused significant increases in VO₂ above pre-fed values (34–60% within 1–2 days after feeding). Respiration budgets of starved and fed Arctic cod at ambient temperatures in Resolute Bay N.W.T., Canada, were used to model annual respiration costs and potential weight loss. Low respiration costs for Arctic cod at ambient temperatures result in high growth efficiency during periods of feeding and low weight loss during periods of starvation.     

Utilization of metabolic scope in relation to feeding and activity by individual and grouped zebrafish, Brachydanio rerio (Hamilton-Buchanan)

Metabolic scope and its utilization in relation to feeding and activity were measured in individual and grouped zebrafish (weight range, 430–551 mg) at 24° C by respirometry. Mean maximum metabolic rate, induced by swimming to exhaustion, R_max(i), was 1223 (s.d. , 157) mg O₂, kg^?1 h^?1 for individuals. Standard metabolic rate, R_s. was 364 mg O₂ kg^?1 h^?1, as estimated by extrapolating to zero activity from measurements of unfed, spontaneously active individuals. Mean routine metabolic rate, R_rout, of individuals was 421 (s.d. , 58) mg O₂, kg_-1 h_-1. The mean voluntary maximum metabolic rate, R_max(v), following transfer of minimally exercised fish to the respirometer, was 1110 (s.d. , 83) mg O₂ kg ^?1 h^?1 for groups of six fish, and was not significantly different from the value measured for individuals, 1066 (s.d. , 122) mg O₂, kg^?1 h^?1. Grouped fish acclimated to the respirometer more slowly than individual fish and exhibited significantly higher R_rout, apparently a result of greater social interaction and activity in groups. Mean R_rout for groups was 560 (s.d. , 78) mg O₂, kg^?1 h^?1. While groups of zebrafish fed a ration of 5% wet body weight day^?1 exhibited consistently higher metabolic rates than fish fed rations of 2.5% wet body weight day^?1 the high ration group still used only a maximum of 77% of the metabolic scope. Zebrafish of the size studied do not appear to demonstrate a high degree of conflict in utilization of metabolic scope by different respiratory components. The metabolic rates measured for zebrafish are among the highest yet measured for fish of similar size and at similar temperatures.     

A COMPARISON OF PHOTOSYNTHETIC ELECTRON TRANSPORT RATES IN MACROALGAE MEASURED BY PULSE AMPLITUDE MODULATED CHLOROPHYLL FLUOROMETRY AND MASS SPECTROMETRY

The relationship between whole chain photosynthetic electron transport and PSII activity was investigated in Porphyra columbina (Montagne) (Rhodophyta), Ulva australis (Areschoug) (Chlorophyta), and Zonaria crenata ( J. Agardh) (Phaeophyta). Mass spectrometric measurements of gross O₂ evolution and gross O₂ uptake were combined with simultaneous measurement of pulse-modulated chl fluorescence under a range of irradiances and inorganic carbon (C_i) concentrations. At light-limiting irradiance, a good correlation between gross O₂ evolution and the electron transport rate (ETR) calculated from chl fluorescence ((F_m′− F_s)/F_m′) was found in the optically thin species (Ulva and Porphyra). The calculated ETR was equivalent to the theoretical electron requirement in these species but overestimated gross O₂ evolution in the thicker species Zonaria. In saturating light, especially when C_i availability was low, ETR overestimated gross O₂ evolution in all species. Excess electron flow could not be accounted for by an increase in gross O₂ uptake; thus neither Mehler-ascorbate-peroxidase reaction nor the photosynthetic carbon oxidation cycle were enhanced at high irradiance or low C _i. Alternative explanations for the loss of correlation include cyclic electron flow around PSII that may be engaged under these conditions or nonphotochemical energy quenching within PSII centers. The loss of correlation between ETR and linear photosynthetic electron flow as irradiance increased from limiting to saturating or at low C_i availability and in the case of optically thick thalli limits the application of this technique for measuring photosynthesis in macroalgae.     

The limitations of heart rate as a predictor of metabolic rate in fish

Although telemetered heart rate (f_H) has been used as a physiological correlate to predict the metabolic rate (as oxygen consumption, V?O₂) of fish in the field, it is our contention that the method has not been validated adequately for fish. If f_H in fish is to be used to estimate V?O₂, a single linear (or log-linear) relationship must be established for each species between the two variables which allows V?O₂ to be predicted accurately under all environmentally relevant conditions. Our analyses of existing data indicate that while a good linear (or log-linear) relationship can be established between f_H and V?O₂, the conditions under which the relationship applies may be quite restricted. Physiological states and environmental factors affect the relationship between f_H and V?O₂ significantly such that several curves can exist for a single species. In addition, there are situations in which f_H and V?O₂ do not covary in a significant manner. In some situations f_H can vary over much of its physiological range while V?O₂ remains constant; in others V?O₂ may vary while f_H is invariate. The theoretical basis for this variability is examined to explain why the use of telemetered f_H in predicting V?O₂ of fish may be limited to certain specified applications.