Effects of acute and chronic hypoxia on acid–base regulation, hematology, ion, and osmoregulation of juvenile American paddlefish

Abstract

Despite the increasing prevalence of hypoxia in natural habitats occupied by the American paddlefish, basal bony fish, and ram ventilator, information about its response to hypoxia is scarce. To understand the physiological and biochemical responses of juvenile paddlefish (~150 g) to acute (<24 h) and chronic hypoxia (≥24 h), blood oxygen transport, blood acid-base balance, and metabolic stress were evaluated under four different partial pressures of oxygen [pO; normoxia (148 mmHg), mild hypoxia (89 mmHg), moderate hypoxia (59 mmHg), and extreme hypoxia (36 mmHg)], all at 21 °C. Arterial blood samples were collected from paddlefish after they had been exposed to treatments for 0.25, 2, 6, 24, and 72 h, and analyzed for hematocrit, pO, total oxygen content, oxygen saturation, pCO, pH, hemoglobin, Na, K, Ca, Cl, glucose, and lactate. Mild hypoxia only caused a reduction in blood pO and oxygen saturation. Both acute and chronic moderate and extreme hypoxia caused a decrease in blood pH, pO, total oxygen content, plasma Na, and Cl at all time points. Acute moderate and extreme hypoxia resulted in an increase in blood pCO, plasma glucose, lactate, and hematocrit. Chronic exposure to moderate hypoxia resulted in an increase in plasma lactate, red blood cell count, and hemoglobin. This study shows that paddlefish are able to physiologically compensate for mild hypoxia, but exhibit secondary stress responses and are unable to return to homeostasis when exposed to both acute and chronic moderate hypoxia, and die after 3-8 h of extreme hypoxia.

Haematological and oxidative stress responses inPiaractus mesopotamicusunder temperature variations in water

“…The MCV showed a high index in all treatments when compared with the control. Higher temperatures may be related to an increase in red blood cell volume in order to increase the supply of oxygen to metabolic activities (Gillooly & Zenil‐Ferguson, ), while at lower temperatures, the high MCV may due to a possible functional hypoxia from blood alkalosis (Perry & Gilmour, ), which interferes with the oxygen transport and consequently a decrease in the aerobic capacity of ATP generation (Aboagye & Allen, ; Jayasundara, Healy, & Somero, ). A relevant point to be considered is that an increase in levels of circulating catecholamines (which may occur in stress situations as lower temperatures) increases the sodium permeability of the red blood cells, which may lead to an increase in MCV due to water retention (Thomas & Perry, ).…”

Secondary stress responses to hypoxia and re‐oxygenation at different temperatures in pacu (Piaractus mesopotamicus) juveniles

“…Maintaining blood pH at homeostatic levels in fish is essential for enzyme function and protein stability (Aboagye & Allen, 2018).…”

“…Immediate re-oxygenation ensures the re-establishment of substrates for ATP generation, as well as instant oxygen increase and normalization of blood pH levels. However, normalization of extracellular pH creates an extreme H + gradient that can trigger the 'reverse mode' TA B L E 2 Blood variables of pacu juveniles (Piaractus mesopotamicus) evaluated at 1, 3 or 12 hr after 12 hr of hypoxia (2.02 mg O 2 L -1 ) followed by rapid (0.5 hr) or gradual (5 hr) reoxygenation, or maintained only under normoxia (6.39 mg O 2 L -1 ) at low (18.08°C), medium (23.10°C) or high (27.80°C) temperature that can lead to an overload of reactive oxygen species (Aboagye & Allen, 2018). In the current study, the re-oxygenation rates, however, apparently interfered less than temperature in blood pH values.…”

“…In order to repair this blood pH decrease, the Na + /H + exchanger is activated. In addition, the Na + /H + β adrenergic exchanger is located in the erythrocyte membrane, which controls the erythrocyte pH for higher or lower affinity of haemoglobin for oxygen (Aboagye & Allen, 2018), which also interferes with haematocrit values. Decreased blood pH levels could still be a compensatory response in which low blood pH levels would be offset by an increase in haemoglobin and erythrocyte variables, to hypoxia with or without re-oxygenation (Onukwufor, Stevens, & Kamunde, 2017).…”

A high-density SNP-based genetic map in Pelteobagrus vachelli and mapping of growth, sex determination and hypoxia tolerance related loci

“…Acute and chronic stress responses, which are important for the health of cultured organisms (such as their growth, reproduction, immunity, and other energy demanding activities), are the result of exposure to hypoxia [ 24]. A lot of environmental factors (i.e., elevated temperatures, decomposition, algal blooms, and organic matter accumulation via faeces and unconsumed food, and the high stocking density of intensive fish culture systems) will lead to rising biological oxygen demand and make the hypoxia status more serious for animals in the system [ 25].…”