Showing papers in "Fish Physiology in 1984"

1 General Anatomy of the Gills

Abstract: Publisher Summary This chapter describes the general anatomy of the gills in fish. The gills form a highly characteristic feature of fishes and their presence has a marked effect on the anatomy and functioning of the rest of the animal. A gill septum separates two adjacent gill pouches and a series of filaments is attached to its surface. In the most primitive groups, the septum forms a complete partition between the pharynx and the outer body wall. Its extension forms a flap-valve for the next posterior slit. In more advanced groups, there is a progressive reduction in the septum and the consequent freeing of the filaments at their tips. Filaments form the most distinctive respiratory structure of fish gills and are sometimes referred to as “primary lamellae.” In adult fish, the number of filaments does not increase so markedly as during the juvenile growth period, but there is a very significant increase in the length of each of them as the fish grows. The lamellae are the most important units of the gill system from the point of view of gas exchange. The rest of the basic anatomy is directed to providing a suitable support for these structures and to enable the water and blood to come into close proximity.

5 Oxygen and Carbon Dioxide Transfer Across Fish Gills

Abstract: Publisher Summary This chapter discusses oxygen and carbon dioxide transfer across fish gills. The gills of fish are the major site, though not the only one, for oxygen and carbon dioxide transfer. The skin and fins may also serve in this capacity and many fish have evolved accessory air-breathing organs. These may be the modifications of the skin, buccal, pharyangeal, or gill surface, or they may be the regions of the gut or the swim bladder. In general, the gills of fish are the major pathway for oxygen and carbon dioxide transfer between the environment and the body tissues. The oxygen stores within the body, with the exception of that in the swim bladder, are small. Carbon dioxide stores in the body are large as compared with the rate of production. At resting rates of CO 2 production, it would take the animal several hours to accumulate the equivalent of the body CO 2 stores. Thus, minor changes in the magnitude of the CO 2 stores—for example, related to the acidification of the body tissues—can have a marked effect on CO 2 excretion across the gills.

6 Acid-Base Regulation in Fishes*

Abstract: Publisher Summary This chapter focuses on acid–base regulation in fishes. The maintenance of a constant pH in body fluids at a given temperature is one of the important tasks of the regulatory systems for homeostasis in animals. During normal steady-state conditions, there is a continuous production of surplus H+ or OH– ions, which are eliminated from the body fluids by the excretory organs of animals at the same rate as they are produced, such that pH in the body compartments is kept constant within narrow limits. Any description of the acid–base status of fish must focus on the pH value as a parameter of large significance for many biological functions. The pH in a body compartment can be affected by the addition or removal of H+ ions from the compartment fluid. This can result from changes in the concentration of the volatile anhydride of carbonic acid, CO2, or that of nonvolatile H+-dissociating substances (acids) and substances capable of transferring H+ ions into the nondissociated state (bases), induced by changed metabolic production. The chapter discusses the techniques used for the measurement of acid–base ion transfer. The acid–base status of fish is frequently stressed in addition to the endogenous steady-state load of surplus acid-base relevant ions by various endogenous and environmental factors. The chapter discusses the effect of some of these factors on the acid–base status and on ionic transfer processes.

5 The Chloride Cell: The Active Transport of Chloride and the Paracellular Pathways

Abstract: Publisher Summary This chapter discusses the active transport of chloride and the paracellular pathways. The anatomic element directly associated with the secretion of salts is the chloride cell located on the gill filaments, mainly on its proximal end. These large columnar cells are present in greater quantities in the seawater-adapted fish and are less frequent in the freshwater-adapted fish. The tissue lining the opercular cavity of Fundulus heteroclitus consists of a stratified epithelium with an underlying layer of connective tissue. The method utilized for the isolation and study of isolated chloride cell-rich opercular epithelia is described in the chapter. The electrical potential difference of opercular epithelia of Fundulus heteroclitus oscillates between 10 and 35 mV. The flat sheet of opercular epithelium contains considerable numbers of chloride cells and it is clear that potential difference, short-circuit current, and ion flux will be directly related to the presence of so many chloride cells. Several agents or drugs related to transport mechanisms or specific effects that are used to interpret membrane phenomena have also tested for their action on chloride fluxes. In all instances, either stimulations or inhibitions were correlated with an increase of chloride transport by the chloride cells of the epithelia studied.

8 The Roles of Gill Permeability and Transport Mechanisms in Euryhalinity

Abstract: Publisher Summary This chapter discusses the roles of gill permeability and transport mechanisms in euryhalinity. The best-studied examples of the euryhaline species are the members of the families, Salmonidae, Cyprinodontidae, Anguillidae, Pleuronectidae, and Mugilidae. These and various other species are able to maintain quite consistent blood osmolarities and ionic concentrations over a wide range of salinities. Extrinsic factors, such as calcium concentrations, may also play a significant role in determining euryhalinity by the alteration of passive ionic permeability. It appears that prolactin is necessary in lowered salinities for reduction in both ionic and osmotic permeabilities, while epinephrine stimulates an active uptake of at least Na+ and osmotic uptake of water. With the exception of this latter effect, these responses to both hormones are adaptive for osmoregulation in reduced salinities. Data have been accumulating that the mechanisms for NaCl uptake are actually resident in the branchial epithelium of marine fish. The relative roles of efflux versus influx modulation in acclimation to lowered salinities are also discussed in the chapter.

2 Gill Internal Morphology

Abstract: Publisher Summary This chapter presents an overview of the internal morphology of gills. Each gill arch skeleton is jointed with the posterior skull dorsally and with the copula ventrally. The septum contains nerves and blood vessels and bears the filaments. Two rows of filaments are generally inserted on each gill arch. This whole forms the so-called holobranchs. The mode of the insertion of filaments on the gill arch depends on the morphology of the septum and varies with the group of fish. In some groups (Chondrostei and the holostean Lepisosteus), certain arches—the hyoidean and the mandibular only—bear a single row of filaments, called “hemibranchs.” In other groups or species, these arches are completely devoid of filaments or absent, such as in Amia (Holostei), which has a mandibular but no hyoidean arch. The presence of lamellae on gill arches corresponds with the distribution of true aortic arches. The pattern of branchial arch organization is relatively constant among teleosts, but differs significantly in lower groups. In Myxinoidei, the variable number of gill slits correspond to a series of pouches connected by narrower tubes with the gut and body surface.

3 Innervation and Pharmacology of the Gills

Abstract: Publisher Summary This chapter focuses on the innervation and pharmacology of the gills in fish. In fish, eleven pairs of cranial nerves are present: terminal, olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, acoustic, glossopharyngeal, and vagus. There are no accessory vagus or hypoglossal nerves in fish; instead the nerves leaving the central nervous system (CNS) behind the vagus in the occipital region are referred to as “spinal nerves.” The branchial nerves are the branches of the facial, glossopharyngeal, and vagus nerves; in gnathostome fish, the glossopharygeal and vagus form large trunks that enter the dorsal part of the gill arches. The branchial nerves are composed of a variety of fibers, which are both sensory (afferent) and motor (efferent), but anatomic studies indicate that most fibers are sensory. The chapter outlines the basic anatomy of the branchial innervation to discuss in more detail some of the functions of different sensory and motor components of the branchial nerves. It also discusses the autonomic innervation of the gill vasculature, along with the effects of some drugs on the branchial blood flow.

2 Branchial Ion Movements in Teleosts: The Roles of Respiratory and Chloride Cells

Abstract: Publisher Summary This chapter examines the roles of respiratory and chloride cells in branchial ion movements in teleosts. The branchial epithelium is an extremely complex tissue in both histological structure and blood circulation. In fish, the branchial and systemic circulations are in series, the heart driving the blood at a sufficiently high pressure to maintain an adequate perfusion of the entire system in spite of the flow resistance encountered in the gills. The chapter presents a study in which the ratios of the radioactive concentrations of venous and arterial efferent liquids at isotopic equilibrium were used to determine whether, after passing over the lamellar epithelium, the perfusion liquid increased in radioactivity on passing through the venous sinus. The difference between the total Na + and Cl - influxes and effluxes shows that there is a net excretion of Na + and Cl - through the seawater-adapted trout gill. In both freshwater- and seawater-adapted fish, ammonium is excreted by the lamellar epithelium. Dorsoventral arterial clearance measurements show that in both media the quantity of ammonium extracted from the blood during its passage through the lamellar epithelium is equal to the amount of NH 4+ appearing in the external medium.

3 Ion Transport and Gill Atpases

Abstract: Publisher Summary This chapter describes the ion transport and gill ATPases in the fish gills. The gill epithelium is located between two liquid compartments of very different ionic composition. The gills are not only the site of entry for selected ions essential to life but also for the extrusion of other ions, such as HCO3-, NH3+ , and H+, which are the ionic forms of metabolic by-products. The magnitude of unidirectional fluxes, as well as the degree and direction of net fluxes, is dependent on the equilibrium established between the fish and its environment. Membranes are gently treated with ionic detergents, such as deoxycholate, dodecyl sulfate, or chaotropic agents, to release proteic constituents that are less strongly associated with phospholipids, (Na+, K+)-ATPase remaining in situ. Euryhaline species are an attractive model to compare branchial physiology from the adaptation medium and to relate physiological and biochemical aspects of ionic transport. The Ca2+-ATPase is also a membrane ATPase whose role in the cell is essential and evident, but it could also play a role in transepithelial transport and be implicated in the regulation of plasma Ca2+ concentration.

4 Transepithelial Potentials in Fish Gills

Abstract: Publisher Summary This chapter describes the different aspects of transepithelial potentials in fish gills. The knowledge of the transepithelial potential is essential in the interpretation of the movements of ions across an epithelium. The transepithelial potential observed in the gills of a teleost is generated by a diffusion potential, arising from the difference in composition between the blood plasma and the external medium and a metabolically maintained component, arising from the active transport of ions. In euryhaline fishes, the potentials approximate to the Nernst potentials for sodium, depolarizing as the external concentration falls and even reversing in hypoosmotic solutions. The substitution of sodium by the larger, less permeant organic ion, choline, also depolarizes the gills, whereas the substitution of organic anions for chloride hyperpolarizes them, but to a smaller extent. Calcium ions modulate the permeability of the gill in both seawater and fresh water, but whereas seawater always contains about 20 mEq l − l , fresh water usually contains somewhere between 0.1 and 1.0 mEq l −1 and some waters have calcium concentrations that lie even outside this range. Bicarbonate ions in the external medium stimulate chloride efflux in the toadfish, Opsanus tau, but have no significant effect on the transepithelial potential.

10 Perfusion Methods for the Study of Gill Physiology

Abstract: Publisher Summary This chapter discusses perfusion methods for the study of gill physiology A large number of perfused gill preparations have been developed to study gill physiology In general, isolated or in situ perfused gills allow to control or measure many variables concerning gill function The control of perfusate composition, pressure, and flow and the exclusion of postbranchial circulation, together with an increased accuracy of measurements, are the principal advantages of perfusion methods Perfused gill preparations fall into four main groups: isolated branchial arches, branchial baskets including all arches, heads, and whole bodies Isolated branchial arches exclude tissues, such as the central nervous system, buccal and opercular epithelium, and pseudobranch, and represent truly isolated gills The cost of isolation is the impairment of recurrent circulation, abnormal ventilation, and mechanical stresses The lamellar blood channels of fish gills are perfused with blood under arterial pressure and in that sense bear a close resemblance to the capillaries of a glomerular kidney Experiments designed to study branchial ion transport have also been conducted, primarily on intact animals

4 Model Analysis of Gas Transfer in Fish Gills

Abstract: Publisher Summary This chapter presents the model analysis of gas transfer in fish gills The Countercurrent model follows from the anatomic arrangement of the gill elements and their blood vessels wherein water flow through the interlamellar space and blood flow in the lamellae are in opposite directions On the basis of this anatomic evidence, the countercurrent system is now generally accepted as the appropriate model for branchial gas exchange The chapter applies to fish gills the basic principles and methods that have proved successful in the analysis of gas exchange in mammalian lungs In doing so, it focuseson the model that applies to fish gills—that is, the countercurrent model—as opposed to the ventilated pool system of mammalian lungs The chapter discusses the basic countercurrent model for branchial gas transfer, with its relevant quantities and relationships In this model, a water flow and a blood flow, both continuous and constant, are arranged in countercurrent manner Gas transfer takes place through a barrier that is homogeneous and of constant thickness and width, its diffusive conductance or diffusing capacity (transfer factor) being D The chapter also discusses compound models for functional inhomogeneities and diffusion resistance of interlamellar water

9 The Pseudobranch: Morphology and Function

Abstract: Publisher Summary This chapter examines the morphology and function of the pseudobranch. Teleostean pseudobranch is a hemibranch and is maximally developed in highly evolved fish. In the teleosts, the pseudobranch is located in the cranial part of the subopercular cavity to which it is attached by one of its sides. Histological serial sections and cast preparations demonstrate that the pseudobranch has an arterio-arterial vasculature similar to that of the gill. The afferent pseudobranchial artery gives rise to successive arteries supplying filaments. Different types of pseudobranch organization have been observed according to the fresh- or saltwater origin of the fish, but it has been noticed that forms, sizes, and external structures vary widely within orders, families, and species without any obvious reason, whereas vascular organization and innervation keep a similar organization throughout. In some part of the pseudobranch with free lamellae, the epithelium consists of typical chloride cells in place of pseudobranchial cells. In the pseudobranch, chloride cells exhibit the characteristic differences of fresh- and saltwater species.

7 Metabolism of the Fish Gill

Abstract: Publisher Summary This chapter discusses different aspects of the metabolism of the fish gill. The branchial epithelium of fish possesses a wide variety of different physiological functions and the gills constitute the major organ for respiratory gas exchange, play important roles for ionic and osmotic balance, and are the main location for the excretion of nitrogenous substances. All of these different processes are facilitated through the anatomic arrangement of the tissue, which includes its large surface area, its short diffusion distances, and its countercurrent arrangement of water and blood flow. In the apparent absence of an ample supply of endogenous oxidative substrate, gill tissue will have to rely on blood-borne substrates to maintain its high metabolic throughput. Under stress conditions, in this case mild hypoxia, gill tissue replaces lactate with some other substrate, presumably one that does not pose the redox problems that can potentially arise from the utilization of lactate. It has been shown that the energy status of the gill tissue as a functional unit strongly depends on external factors, such as environmental pH.

6 Hormonal Control of Water Movement Across the Gills

Abstract: Publisher Summary This chapter discusses the hormonal control of water movement across the gills of fishes The great majority of fish species live in either hypoosmotic or hyperosmotic media and face a constant problem of osmotic water gain or loss Lahlou and Giordan measured weight changes and urine flow in goldfish, Carassius auratus, as well as drinking rate in a small sample, which appeared not to influence the results They found that osmotic and diffusional permeability was decreased by hypophysectomy Osmotic permeability of hypophysectomized fish could be maintained by prolactin, which also increased water turnover in intact goldfish Prolactin also restored the reduced water turnover following hypophysectomy in killifish, Fundulus kansae, in fresh water, and prolactin restored, at least for the first few days after operation, the reduced water turnover rate of hypophysectomized dogfish, Scyliorhinus canicula Prolactin decreased osmotic influx or outflux in the gills of the tilapia, Oreochromis mossambicus, incubated in hypoosmotic or hyperosmotic salines, although it had no effect on the gills of fish kept in high-calcium water Cortisol and adrenocorticotrophic hormone produce increases in water turnover in intact goldfish and cortisol reverses the reduced water turnover produced by hypophysectomy In the anesthetized European eel under conditions of low blood pressure and flow, visual examination has shown that there are no unperfused lamellae, although, unless adrenaline is injected or the animal starts to recover from anesthesia, erythrocyte flow is confined to the marginal and basal channels

1 Water and Nonelectrolyte Permeation

Abstract: Publisher Summary This chapter examines the water and nonelectrolyte permeation in the fish gill The study of nonelectrolyte gill exchanges is important because it permits the elucidation of various phenomena The fish gill can be considered as the sum of two epithelia: the respiratory and nonrespiratory The comparison of branchial morphology of fishes adapted to fresh water or seawater pointed out structural modifications of two pathways: the membranes of chloride cells, which represent the exchange surface of the nonrespiratory epithelium (4% of the total area) and, (c) the intercellular junctions The number of chloride cells increases in seawater by a factor of about three and loose junctions, permeable to lanthanum ions, appear among chloride cells on the apical side The selective increase in the permeability of small lipophilic molecules under adrenaline action in freshwater-adapted fish indicates an effect of the catecholamine on the lipid mobility of the plasmalemma An intermediate compartment, probably consisting of intracellular water, exists for water exchange Two barriers exist that water molecules must successfully pass to cross the epithelium: external and internal membranes The basal barrier is about eight times less permeable, and thus is the limiting factor for water diffusion, as well as ionic exchanges in the gills