Baker, Dan

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    [Pre-print] The effect of substrate rearing on the growth, aerobic scope, and physiology of larval white sturgeon (Acipenser transmontanus)
    (John Wiley & Sons, Inc., 2018-04-24) Boucher, Marcus A.; Baker, Daniel W.; Brauner, Colin J.; Shrimpton, J. Mark
    The effect of substrate on growth and metabolic rate was assessed in larval white sturgeon (Aciperser transmontanus). Yolk sac larvae (YSL) were reared in bare tanks or tanks with gravel as substrate from hatch until approximately 16 days post hatch (dph). The effect of an artificial substrate was also evaluated for growth alone. Substrate had a significant effect on weight, with larvae reared in gravel and artificial substrate being larger than those reared without substrate. Respirometry measurements of resting (routine) metabolic rates in fish reared without gravel were significantly greater than those reared with gravel during the yolk sac phase. Aerobic scope (the difference between maximum and routine metabolic rate) was significantly lower for YSL and feeding larvae (FL) in bare tanks than those reared with gravel, particularly before fish started feeding exogenously. Routine factorial scope (maximum metabolic rate divided by routine metabolic rate) indicated that the ability to elevate metabolic rate above routine in the early ontogeny of white sturgeon is extremely limited (< 1.7). These findings suggest that YSL reared without substrate may divert more of their energy to non-growth related processes, such as exercise, as higher activity levels were observed but not quantified in YSL sturgeon reared without substrate. These results underscore the importance of adequate rearing substrate for growth and development, and may provide support for habitat restoration and alternative hatchery rearing methods.
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    Preferential intracellular pH regulation: Hypotheses and perspectives
    (The Company of Biologists, 2016-08) Shartau, Ryan B.; Baker, Daniel W.; Crossley, Dane A. II; Brauner, Colin J.
    The regulation of vertebrate acid–base balance during acute episodes of elevated internal PCO2 is typically characterized by extracellular pH (pHe) regulation. Changes in pHe are associated with qualitatively similar changes in intracellular tissue pH (pHi) as the two are typically coupled, referred to as ‘coupled pH regulation’. However, not all vertebrates rely on coupled pH regulation; instead, some preferentially regulate pHi against severe and maintained reductions in pHe. Preferential pHi regulation has been identified in several adult fish species and an aquatic amphibian, but never in adult amniotes. Recently, common snapping turtles were observed to preferentially regulate pHi during development; the pattern of acid–base regulation in these species shifts from preferential pHi regulation in embryos to coupled pH regulation in adults. In this Commentary, we discuss the hypothesis that preferential pHi regulation may be a general strategy employed by vertebrate embryos in order to maintain acid–base homeostasis during severe acute acid–base disturbances. In adult vertebrates, the retention or loss of preferential pHi regulation may depend on selection pressures associated with the environment inhabited and/or the severity of acid–base regulatory challenges to which they are exposed. We also consider the idea that the retention of preferential pHi regulation into adulthood may have been a key event in vertebrate evolution, with implications for the invasion of freshwater habitats, the evolution of air breathing and the transition of vertebrates from water to land.
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    Exceptional CO2 tolerance in white sturgeon (Acipenser transmontanus) is associated with protection of maximum cardiac performance during hypercapnia in situ
    (University of Chicago Press, 2011) Baker, Daniel W.; Hanson, Linda M.; Farrell, Anthony; Brauner, Colin J.
    White sturgeon rank among the most CO2-tolerant fish species examined to date. We investigated whether this exceptional CO2 tolerance extended to the heart, an organ generally viewed as acidosis intolerant. Maximum cardiac output (Qmax) and maximum cardiac power output (POmax) were assessed using a working, perfused, in situ heart preparation. Exposure to a Pco2 of 3 kPa for 20 min had no significant effect on maximum cardiac performance, while exposure to 6-kPa Pco2 reduced heart rate, Qmax, POmax, and rate of ventricular force generation (FO) by 23%, 28%, 26%, and 18%, respectively; however, full recovery was observed in all these parameters upon return to control conditions. These modest impairments during exposure to 6-kPa Pco2 were associated with partially compensated intracellular ventricular acidosis. Maximum adrenergic stimulation (500 nmol L−1 adrenaline) during 6-kPa Pco2 protected maximum cardiac performance via increased inotropy (force of contraction) without affecting heart rate. Exposure to higher CO2 levels associated with morbidity in vivo (i.e., 8-kPa Pco2) induced arrhythmia and a reduction in stroke volume during power assessment. Clearly, white sturgeon hearts are able to increase cardiac performance during severe hypercapnia that is lethal to other fishes. Future work focusing on atypical aspects of sturgeon cardiac function, including the lack of chronotropic response to adrenergic stimulation during hypercapnia, is warranted.
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    Juvenile Atlantic and shortnose sturgeons (family: Acipenseridae) have different hematological responses to acute environmental hypoxia
    (University of Chicago Press, 2005) Baker, Daniel W.; Wood, A.M.; Kieffer, J.D.
    Experiments were conducted to determine the behavioral and physiological responses to acute hypoxic challenges in Atlantic (Acipenser oxyrinchus) and shortnose (Acipenser brevirostrum) sturgeons. We measured the ventilatory rate following a 45‐mmHg hypoxic challenge, as well as a variety of hematological parameters, including O2 transport and hormonal, ionic, and metabolic variables, following a 1‐h exposure to either 75‐ or 30‐mmHg hypoxic challenges. Compared to fish in normoxic conditions (Pwo2 150 mmHg), juveniles of both species increased their ventilatory rate by approximately 40% when exposed to a 1‐h challenge at 45 mmHg Pwo2. Hematological variables (e.g., hematocrit, hemoglobin, and Na+ and Cl− levels) did not change substantially following a 1‐h challenge at 75 mmHg Pwo2. Conversely, a severe hypoxic challenge of 30 mmHg caused changes in several hematological variables (e.g., whole blood glucose and plasma cortisol and lactate levels). Most of these hematological parameters returned to prehypoxic levels within 2 h. Severe environmental hypoxia elicited the same basic pattern of response in both species; however, maximal plasma lactate levels were higher in Atlantic sturgeons, and maximal cortisol levels were higher in shortnose sturgeons. Whether these species differences are related to dissimilar hypoxia‐tolerance, ecological, and/or endocrinological characteristics between these two species is not entirely clear.
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    Lab-on-a-chip technology for a non-invasive and real-time visualisation of metabolic activities in larval vertebrates
    (SPIE, 2015-06-01) Zhu, Feng; Baker, Daniel W.; Skommer, Joanna; Sewell, Mary; Wlodkowic, Donald
    Non-invasive and real-time visualisation of metabolic activities in living small organisms such as zebrafish embryo and larvae has not yet been attempted due to profound analytical limitations of existing technologies. Significant progress in the development of physico-optical oxygen sensors using luminescence quenching by molecular oxygen has recently been made. Sensing using such microsensors is, however, still performed in small glass chambers that hold single specimens and thus not amenable for high-throughput data acquisition. In this work, we present a proof-of-concept approach by using microfluidic Lab-on-a-Chip (LOC) technologies combined with sophisticated optoelectronic sensors. The LOC device is capable of immobilising live zebrafish embryos with continuous flow perfusion, while the sensor uses innovative Fluorescence Ratiometric Imaging (FRIM) technology that can kinetically quantify the temporal patterns of aqueous oxygen gradients at a very fine scale based on signals coming from an optical sensor referred to as a sensor foil. By embedding the sensor foil onto the microfluidic living embryo array system, we demonstrated in situ FRIM on developing zebrafish embryos. Future integration of microfluidic chip-based technologies with FRIM technology represents a noteworthy direction to miniaturise and revolutionise research on metabolism and physiology in vivo.