The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system Nevertheless, substantial questions about the evolution of these mechanisms and control remain

https://people.clas.ufl.edu/devans/files/PRVGill.pdf

The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste

Unbiased Stereology. Three‐Dimensional Measurement in Microscopy.

More than 200 genes annotated as Na+/H+ hydrogen exchangers (NHEs) currently reside in bioinformation databases such as GenBank and Pfam. We performed detailed phylogenetic analyses of these NHEs i...

/pdf/evolutionary-origins-of-eukaryotic-sodium-proton-exchangers-41hdaqdz8e.pdf

Evolutionary origins of eukaryotic sodium/proton exchangers.

Fish display robust neuroendocrine and physiologic stress responses to noxious stimuli. Many anesthetic, sedative, or analgesic drugs used in other vertebrates reduce stress in fish, decrease handling trauma, minimize movement and physiologic changes in response to nociceptive stimuli, and can be used for euthanasia. But extrapolating from limited published anesthetic and sedative data to all fish species is potentially harmful because of marked anatomic, physiologic, and behavioral variations; instead, a stepwise approach to anesthetizing or sedating unfamiliar species or using unproven drugs for familiar species is advisable. Additionally, knowledge of how water quality influences anesthesia or sedation helps limit complications. The most common method of drug administration is through immersion, a technique analogous to gaseous inhalant anesthesia in terrestrial animals, but the use of injectable anesthetic and sedative agents (primarily intramuscularly, but also intravenously) is increasing. Regardless of the route of administration, routine preprocedural preparation is appropriate, to stage both the animals and the supplies for induction, maintenance, and recovery. Anesthetic and sedation monitoring and resuscitation are similar to those for other vertebrates. Euthanasia is most commonly performed using an overdose of an immersion drug but injectable agents are also effective. Analgesia is an area in need of significant research as only a few studies exist and they provide some contrasting results. However, fish have mu and kappa opiate receptors throughout the brain, making it reasonable to expect some effect of at least opioid treatments in fish experiencing noxious stimuli.

Fish Sedation, Anesthesia, Analgesia, and Euthanasia: Considerations, Methods, and Types of Drugs

This review explores the fundamental neuranatomical and functional bases for integration of the respiratory and cardiovascular systems in vertebrates and traces their evolution through the vertebrate groups, from primarily water-breathing fish and larval amphibians to facultative air-breathers such as lungfish and some adult amphibians and finally obligate air-breathers among the reptiles, birds, and mammals. A comparative account of respiratory rhythm generation leads to consideration of the changing roles in cardiorespiratory integration for central and peripheral chemoreceptors and mechanoreceptors and their central projections. We review evidence of a developing role in the control of cardiorespiratory interactions for the partial relocation from the dorsal motor nucleus of the vagus into the nucleus ambiguus of vagal preganglionic neurons, and in particular those innervating the heart, and for the existence of a functional topography of specific groups of sympathetic preganglionic neurons in the spinal cord. Finally, we consider the mechanisms generating temporal modulation of heart rate, vasomotor tone, and control of the airways in mammals; cardiorespiratory synchrony in fish; and integration of the cardiorespiratory system during intermittent breathing in amphibians, reptiles, and diving birds. Concluding comments suggest areas for further productive research.

Central Control of the Cardiovascular and Respiratory Systems and Their Interactions in Vertebrates

Predominantly, Hoplias malabaricus inhabits stagnant O2 poor environments, whereas Hoplias lacerdae occurs in well-aerated streams. The present study evaluates the influence of mode of life on O2 uptake and gill ventilation in equally-sized (300 g) specimens of this genus at 25° C. Comparing the species, H. lacerdae was characterized by the highest O2 uptake and gill ventilation combined with a relatively higher cost of breathing and a lower O2 extraction. Both species substantially increased ventilation in response to hypoxia with the difference that H. malabaricus exclusively augmented tidal volume, whereas H. lacerdae also increased breathing frequency.

Respiratory responses to hypoxia in relation to mode of life of two erythrinid species (Hoplias malabaricus and Hoplias lacerdae)

Ventilation and oxygen uptake were measured in the elephant trunk snake, Acrochordus javanicus, during normal, undisturbed breathing. Ventilation is periodic, with ventilatory periods (VP) lasting 2.5-3.5 min, interrupted by nonventilatory periods (NVP) averaging 10 times longer at 25 C. Average tidal volumes ranged from 27.8 to 47.7 ml·kg⁻¹, while breathing frequency during VP ranged from 78 h⁻¹ to 155 h⁻¹. Total ventilation ($\dot{V}_{I}$) ranged from 250 to 543 ml·kg⁻¹·h⁻¹ BTPS (body temperature and pressure, saturated with water vapor). Oxygen uptake ($\dot{V}_{O_{2}}$) averaged 16.6 mlO₂· kg⁻¹·h⁻¹ STPD (standard temperature and pressure, dry) at 20 C and 29.3 mlO₂· kg⁻¹·h⁻¹ at 30 C. Corresponding ventilations were 225 ml·kg⁻¹·h⁻¹ and 504 ml·2kg⁻¹· h⁻¹ BTPS. Ventilatory requirements, $\dot{V}_{I}/\dot{V}_{O_{2}}$, were 13.8 and 17.2 for 20 and 30 C. Both ventilation and oxygen uptake are low in Acrochordus, compared with other reptiles. Also, the $\dot{V}_{I}/\dot{V}_{O_{2}}$ ratio is much lower for A...

Control of Breathing in Acrochordus javanicus, an Aquatic Snake

Central chemoreceptor drive to breathing in unanesthetized toads, Bufo paracnemis.

The effects of changes in environmental temperature and oxygen tension on gill ventilation, arterial P O 2 , P CO 2 pH and [HCO 3 − ] were evaluated in carp ( Cyprinus carpio L.). Gill ventilation was measured continuously in specimens acclimated to 10 or 20°C, combining the method of electromagnetic flow determination with the application of a rubber mask technique. After establishing control values in airequilibrated water the environmental water P O 2 (Pw O 2 ) was reduced from about 150 mmHg (20 kPa) during control conditions to 110 or 75 mm Hg (14.7 or 10 kPa), respectively. Measurements of blood gases and acid-base parameters were performed repeatedly before, and 1 and 4 h after, initiation of hypoxia. Regardless of temperature, these moderately hypoxic conditions caused considerable and lasting increases in gill ventilation of about 70% (PW O 2 =110 mm Hg/l4.7kPa) or 180% (Pw O 2 =75 mm Hg/10kPa), relative to the respective normoxic control values of about 50 ml kg −1 min −1 at 10°C and 230 ml kg −1 min −1 at 20°C. These increases in ventilation reduced P CO 2 substantially, resulting in a rise in pHa by about 0.1 units at Pw O 2 of 110 mmHg (14.7 kPa) and by about 0.2 units at Pw CO 2 of 75 mmHg (lOkPa). Arterial P O 2 was low under normoxic conditions at both temperatures (≈15 mmHg, ≈2kPa). During hypoxia, Pa O 2 was marginally reduced, whereas the arterial O 2 content and saturation remained at normoxic levels, mainly because of the increase in the blood O 2 -affinity induced by respiratory alkalosis. Thislack of any clear relationship between arterial O2 content and ventilatory response to moderate hypoxia contrasts with previously reported data for trout, and supports the hypothesis that a change in P O 2 is an adequate stimulus for the adjustment of ventilation in carp.

Combined effects of environmental PO2 and temperature on ventilation and blood gases in the carp Cyprinus carpio L.

Lungfishes (Dipnoi) occupy an evolutionary transition between water and air breathing and possess well-developed lungs and reduced gills. The South American species, Lepidosiren paradoxa, is an obligate air-breather and has the lowest aquatic respiration of the three extant genera. To study the relative importance, location and modality of reflexogenic sites sensitive to oxygen in the generation of cardio-respiratory responses, we measured ventilatory responses to changes in ambient oxygen and to reductions in blood oxygen content. Animals were exposed to aquatic and aerial hypoxia, both separately and in combination. While aerial hypoxia elicited brisk ventilatory responses, aquatic hypoxia had no effect, indicating a primary role for internal rather than branchial receptors. Reducing haematocrit and blood oxygen content by approximately 50% did not affect ventilation during normoxia, showing that the specific modality of the internal oxygen sensitive chemoreceptors is blood P o 2 per se and not oxygen concentration. In light of previous studies, it appears that the heart rate responses and the changes in pulmonary ventilation during oxygen shortage are similar in lungfish and tetrapods. Furthermore, the modality of the oxygen receptors controlling these responses is similar to tetrapods. Because the cardio-respiratory responses and the modality of the oxygen receptors differ from typical water-breathing teleosts, it appears that many of the changes in the mechanisms exerting reflex control over cardio-respiratory functions occurred at an early stage in vertebrate evolution.

Mogens L. Glass

Papers

Respiratory responses to hypoxia in relation to mode of life of two erythrinid species (Hoplias malabaricus and Hoplias lacerdae)

Control of Breathing in Acrochordus javanicus, an Aquatic Snake

Central chemoreceptor drive to breathing in unanesthetized toads, Bufo paracnemis.

Combined effects of environmental PO2 and temperature on ventilation and blood gases in the carp Cyprinus carpio L.

The differential cardio-respiratory responses to ambient hypoxia and systemic hypoxaemia in the South American lungfish, Lepidosiren paradoxa.