Changes In Gill Morphology Research Articles

Impact of turbidity on the gill morphology and hypoxia tolerance of eastern sand darter (Ammocrypta pellucida).

Anthropogenic stressors such as agriculture and urbanization can increase river turbidity, which can negatively impact fish gill morphology and growth due to reduced oxygen in the benthic environment. We assessed the gill morphology, field metabolic rate (FMR), and two hypoxia tolerance metrics (oxygen partial pressure at loss of equilibrium, PO2 at LOE, and critical oxygen tension, Pcrit) of eastern sand darter (Ammocrypta pellucida), a small benthic fish listed as threatened under the Species at Risk Act in Canada, from rivers in southern Ontario. Field trials were conducted streamside in the Grand River (August 2019; mean NTU 8) and in the comparatively more turbid Thames River (August 2020; mean NTU 94) to test the effect of turbidity on each physiological endpoint. Gills were collected from incidental mortalities and museum specimens, and were assessed using hematoxylin and eosin and immunofluorescent staining. The between-river comparison indicated that turbidity significantly increased interlamellar space and filament width but had no significant influence on other gill morphometrics or FMR. Turbidity significantly increased PO2 at LOE (i.e., fish had a lower hypoxia tolerance) but did not significantly impact Pcrit. Therefore, although turbidity influences hypoxia tolerance through LOE, turbidity levels were not sufficiently high in the study rivers to contribute to measurable changes in gill morphology or metabolism in the wild. Determining whether changes in gill morphology or metabolism occur under higherturbidity levels would help resolve the ecological importance of turbidity on species physiology in urban and agricultural ecosystems.

Road salt compromises functional morphology of larval gills in populations of an amphibian

Across the planet, winter de-icing practices have caused secondary salinization of freshwater habitats. Many amphibians are vulnerable because of permeable skin and reliance on small ponds, where salinity can be high. Early developmental stages of amphibians are especially sensitive to salt, and larvae developing in salt-polluted environments must osmoregulate through ion exchange in gills. Though ionoregulation in amphibian gills is generally understood, the role of gill morphology remains poorly described. Yet gill structure should affect ionoregulatory capacity, for instance in terms of available surface area. As larval amphibian gills also play critical roles in gas exchange and foraging, changes in gill morphology from salt pollution potentially affect not only osmoregulation, but also respiration and feeding. Here, we used an exposure experiment to quantify salinity effects on larval gill morphology in wood frogs (Rana sylvatica). We measured a suite of morphological traits on gill tufts—where ionoregulation and gas exchange occur—and on gill filters used in feeding. Larvae raised in elevated salinity developed larger gill tufts but with lower surface area to volume ratio. Epithelial cells on these tufts were less circular but occurred at higher densities. Gill filters showed increased spacing, likely reducing feeding efficiency. Many morphological gill traits responded quadratically, suggesting that salinity might induce plasticity in gills at intermediate concentrations until energetic demands exceed plasticity. Together, these changes likely diminish ionoregulatory and respiratory functionality of gill tufts, and compromise feeding functionality of gill filters. Thus, a singular change in aquatic environment from a widespread pollutant appears to generate a suite of consequences via changes in gill morphology. Critically, these changes in traits likely compound the severity of fitness impacts in populations dwelling in salinized environments, whereby ionoregulatory energetic demands should increase respiratory and foraging demands, but in individuals who possess structures poorly adapted for these functions.

Emersion behaviour underlies variation in gill morphology and aquatic respiratory function in the amphibious fish Kryptolebias marmoratus

Fishes acclimated to hypoxic environments often increase gill surface area to improve O2 uptake. In some species, surface area is increased via reduction of an interlamellar cell mass (ILCM) that fills water channels between gill lamellae. Amphibious fishes, however, may not increase gill surface area in hypoxic water because these species can, instead, leave water and breathe air. To differentiate between these possibilities, we compared wild amphibious mangrove rivulus Kryptolebias marmoratus from two habitats that varied in O2 availability - a hypoxic freshwater pool versus nearly anoxic crab burrows. Fish captured from crab burrows had less gill surface area (as ILCMs were enlarged by ∼32%), increased rates of normoxic O2 consumption and increased critical O2 tension compared with fish from the freshwater pool. Thus, wild mangrove rivulus do not respond to near-anoxic water by decreasing metabolism or increasing O2 extraction. Instead, fish from the crab burrow habitat spent three times longer out of water, which probably caused the observed changes in gill morphology and respiratory phenotype. We also tested whether critical O2 tension is influenced by genetic heterozygosity, as K. marmoratus is one of only two hermaphroditic vertebrate species that can produce both self-fertilized (inbred) or out-crossed (more heterozygous) offspring. We found no evidence for inbreeding depression, suggesting that self-fertilization does not impair respiratory function. Overall, our results demonstrate that amphibious fishes that inhabit hypoxic aquatic habitats can use a fundamentally different strategy from that used by fully aquatic water-breathing fishes, relying on escape behaviour rather than metabolic depression or increased O2 extraction ability.

Humic acid of commercial origin causes changes in gill morphology of silver catfish Rhamdia quelen exposed to acidic water: Response of silver catfish gills to low pH and humic acid.

The effect of dissolved organic carbon (DOC) against the burden of low pH was assessed in silver catfish Rhamdia quelen through the gills. A commercial humic acid (HA) was used as the source of DOC at 0 (control), 10, 25, and 50mg/l. For each HA concentration, two pH levels were tested: 6.5 (control) and 5.5. After 40 days of exposure, the gills were removed and morphological variables were analyzed through light and scanning electronic microscopy. The low water pH caused a reduction in the length of filaments, number of lamellae, and gill respiratory surface area (GRSA) and an increase in chloride cells (CCs) number in the filament epithelium. When HA was added to the test water, GRSA increased and CCs proliferated in lamellae, suggesting ionic and respiratory disturbances. Scanning electronic microscopy revealed that CC morphometric variables, that is, apical area, fractional area, and density, were undisturbed by the pH reduction, but increased in the presence of HA. This study indicates that the commercial HA did not protect silver catfish against low pH stress. Instead, it caused changes that may affect vital processes such as ion regulation and ventilation and, consequently, reduce growth.

Acclimation to prolonged hypoxia alters hemoglobin isoform expression and increases hemoglobin oxygen affinity and aerobic performance in a marine fish

Hemoglobin (Hb) multiplicity is common in fish, yet despite its ubiquitous nature, the functional significance is unclear. Here we explore the hypothesis that Hb multiplicity plays a role in hypoxia tolerance using the red drum (Sciaenops ocellatus). Red drum is an economically and ecologically important species native to coastal regions and estuaries of the Gulf of Mexico – habitats that routinely experience pronounced hypoxic events. Using a transcriptomic approach, we demonstrate that red drum red blood cells express 7 and 5 Hbα and Hbβ isoforms, respectively. Phylogenetic analysis grouped these isoforms into distinct isoHb clades, and provided evidence of lineage specific expression of particular isoHbs. In normoxia, three isoHbs predominated (Hbα-3.1, -3.2, and Hbβ-3.1). A three-week hypoxia acclimation (48 mmHg) resulted in significant up-regulation of Hbα-2, Hbα-3.2, and Hbβ-3.1, effectively switching the predominantly expressed isoforms. Changes in subunit expression were correlated with a decrease in non-stripped hemolysate P50. Similarly, hypoxia acclimation resulted in a 20% reduction in whole animal critical oxygen threshold (Pcrit). Hypoxia acclimation was not associated with changes in gill morphology, hematocrit, or relative ventricular mass. Overall, these data provide support for the hypothesis that Hb isoform switching can provide a physiological benefit to counteract environmental stress in fishes.

Pathological and histometric analysis of the gills of female Hyphessobrycon eques (Teleostei:Characidae) exposed to different concentrations of the insecticide Dimilin®

Female individuals of Hyphessobrycon eques were exposed to Diflubenzuron (Dimilin®) in order to determine whether exposure to sublethal levels of this insecticide causes changes in gill morphology. Fish were exposed to 0.01, 0.1 and 1.0mgL−1 for 96h and 17 days and then submitted to pathological and histometric evaluation. Pathological lesions, such as hyperplasia, lamellar fusion, vascular congestion, secondary lamellar disarray, vasodilatation, hemorrhage and increased lamellar epithelium, were significantly more common in the gills of fish exposed to Dimilin® than the control. Histometric analysis documented significant changes in blood vessel diameter, primary lamellae width and secondary lamellae length, and the appearance of hemorrhage foci in all concentrations tested. Even at low Dimilin® concentrations, the histopathological alteration index was mild to moderate, thereby indicating that the function of this tissue was compromised. These findings indicate that indiscriminate use of Dimilin® can adversely affect the structural integrity of the gills of H. eques, which can cause numerous problems for fish farming systems.

Alterations in gill structure in tropical reef fishes as a result of elevated temperatures

Tropical regions are expected to be some of the most affected by rising sea surface temperatures (SSTs) because seasonal temperature variations are minimal. As temperatures rise, less oxygen dissolves in water, but metabolic requirements of fish and thus, the demand for effective oxygen uptake, increase. Gill remodelling is an acclimation strategy well documented in freshwater cyprinids experiencing large seasonal variations in temperature and oxygen as well as an amphibious killifish upon air exposure. However, no study has investigated whether tropical reef fishes remodel their gills to allow for increased oxygen demands at elevated temperatures. We tested for gill remodelling in five coral reef species (Acanthochromis polyacanthus, Chromis atripectoralis, Pomacentrus moluccensis, Dascyllus melanurus and Cheilodipterus quinquelineatus) from populations in northern Papua New Guinea (2° 35.765′ S; 150° 46.193′ E). Fishes were acclimated for 12–14days to 29 and 31°C (representing their seasonal range) and 33 and 34°C to account for end-of-century predicted temperatures. We measured lamellar perimeter, cross-sectional area, base thickness, and length for five filaments on the 2nd gill arches and qualitatively assessed 3rd gill arches via scanning electron microscopy (SEM). All species exhibited significant differences in the quantitative measurements made on the lamellae, but no consistent trends with temperature were observed. SEM only revealed alterations in gill morphology in P. moluccensis. The overall lack of changes in gill morphology with increasing temperature suggests that these near-equatorial reef fishes may fail to maintain adequate O2 uptake under future climate scenarios unless other adaptive mechanisms are employed.

Acid–base and ion balance in fishes with bimodal respiration

The evolution of air breathing during the Devonian provided early fishes with bimodal respiration with a stable O2 supply from air. This was, however, probably associated with challenges and trade-offs in terms of acid-base balance and ionoregulation due to reduced gill:water interaction and changes in gill morphology associated with air breathing. While many aspects of acid-base and ionoregulation in air-breathing fishes are similar to water breathers, the specific cellular and molecular mechanisms involved remain largely unstudied. In general, reduced ionic permeability appears to be an important adaptation in the few bimodal fishes investigated but it is not known if this is a general characteristic. The kidney appears to play an important role in minimizing ion loss to the freshwater environment in the few species investigated, and while ion uptake across the gut is probably important, it has been largely unexplored. In general, air breathing in facultative air-breathing fishes is associated with an acid-base disturbance, resulting in an increased partial pressure of arterial CO2 and a reduction in extracellular pH (pHE ); however, several fishes appear to be capable of tightly regulating tissue intracellular pH (pHI ), despite a large sustained reduction in pHE , a trait termed preferential pHI regulation. Further studies are needed to determine whether preferential pHI regulation is a general trait among bimodal fishes and if this confers reduced sensitivity to acid-base disturbances, including those induced by hypercarbia, exhaustive exercise and hypoxia or anoxia. Additionally, elucidating the cellular and molecular mechanisms may yield insight into whether preferential pHI regulation is a trait ultimately associated with the early evolution of air breathing in vertebrates.

Interspecific Differences in Hypoxia-Induced Gill Remodeling in Carp

The gills of many fish, but in particular those of crucian carp (Carassius carassius) and goldfish (Carassius auratus), are capable of extensive remodeling in response to changes in oxygen (O2), temperature, and exercise. In this study, we investigated the interspecific variation in hypoxia-induced gill modeling and hypoxia tolerance in 10 closely related groups of cyprinids (nine species, with two strains of Cyprinus carpio). There was significant variation in hypoxia tolerance, measured as the O2 tension (P(O2)) at which fish lost equilibrium (LOEcrit), among the 10 groups of carp. In normoxia, there was a significant, phylogenetically independent relationship between mass-specific gill surface area and LOEcrit, with the more hypoxia-tolerant carp having smaller gills than their less hypoxia-tolerant relatives. All groups of carp, except the Chinese bream (Megalobrama pellegrini), increased mass-specific gill surface area in response to 48 h of exposure to hypoxia (0.7 kPa) through reductions in the interlamellar cell mass (ILCM) volume. The magnitude of the hypoxia-induced reduction in the ILCM was negatively correlated with LOEcrit (and thus positively correlated with hypoxia tolerance), independent of phylogeny. The hypoxia-induced changes in gill morphology resulted in reduced variation in mass-specific gill surface area among species and eliminated the relationship between LOEcrit and mass-specific gill surface area. While behavioral responses to hypoxia differed among the carp groups, there were no significant relationships between hypoxia tolerance and the Po2 at which aquatic surface respiration (ASR) was initiated or the total number of ASR events observed during progressive hypoxia. Our results are the first to show that the extent of gill remodeling in cyprinids is associated with hypoxia tolerance in a phylogenetically independent fashion.

Effects of sublethal, environmentally relevant concentrations of hexavalent chromium in the gills of Mytilus galloprovincialis

Hexavalent chromium Cr(VI) is an important contaminant released from both domestic and industrial effluents, and represents the predominant chemical form of the metal in aquatic ecosystems. In the marine bivalve Mytilus galloprovincialis exposure to non-toxic, environmentally relevant concentrations of Cr(VI) was shown to modulate functional parameters and gene expression in both the digestive gland and hemocytes. In this work, the effects of exposure to Cr(VI) (0.1–1–10μgL−1animal−1 for 96h) in mussel gills were investigated. Gill morphology and immunolocalization of GSH-transferase (GST), of components involved in cholinergic (AChE and ChAT), adrenergic (TH) and serotoninergic (5-HT3 receptor) systems, regulating gill motility, were evaluated. Total glutathione content, activities of GSH-related enzymes (glutathione reductase – GSR, GST), of catalase, and of key glycolytic enzymes (phosphofructokinase – PFK and pyruvate kinase – PK) were determined. Moreover, mRNA expression of selected Mytilus genes (GST-π, metallothionein isoforms MT10 and MT20, HSP70 and 5-HT receptor) was assessed by RT-q-PCR. Cr(VI) exposure induced progressive changes in gill morphology and in immunoreactivity to components involved in neurotransmission that were particularly evident at the highest concentration tested, and associated with large metal accumulation. Cr(VI) increased the activities of GST and GSR, and total glutathione content to a different extent at different metal concentrations, this suggesting Cr(VI) detoxication/reduction at the site of metal entry. Cr(VI) exposure also increased the activity of glycolytic enzymes, indicating modulation of carbohydrate metabolism. Significant changes in transcription of different genes were observed. In particular, the mRNA level for the 5-HTR was increased, whereas both decreases and increases were observed for GST-π, MT10, MT20 and HSP70 mRNAs, showing sex- and concentration-related differences. The results demonstrate that Cr(VI) significantly affected functional and molecular parameters in mussel gills, and indicate that this tissue represents the major target of exposure to environmentally relevant concentrations of the metal.

Does the presence of a seawater gill morphology induced by dietary salt loading affect Cl− uptake and acid–base regulation in freshwater rainbow trout Oncorhynchus mykiss

The goal of this study was to determine the effect of the changes in gill morphology induced by dietary salt feeding on several aspects of gill function in rainbow trout Oncorhynchus mykiss maintained in fresh water with specific emphasis on Cl(-) uptake (J(IN)Cl(-)) and acid-base regulation. The addition of 11% NaCl to the diet caused J(IN)Cl(-) to be reduced by c. 45% from 214·4 ± 26·7 to 117·3 ± 17·4 µmol kg(-1) h(-1) (mean ± s.e.). Rates of Cl(-) efflux (J(OUT)Cl(-)), net Cl(-) flux (J(NET)Cl(-)), J(NET) Na(+) and plasma levels of Na(+) or Cl(-) were unaffected by salt feeding. On the basis of significant effect of the salt diet on decreasing the maximal uptake rate of Cl(-)(J(MAX)Cl(-)), it would appear that internal salt loading caused a decrease in the number of functional ion transport proteins involved in Cl(-) uptake (e.g. Cl(-) -HCO(3)(-) exchangers) and decreased the transporting capacity of existing proteins. The acid-base regulating capacity of control fish and salt-loaded fish was assessed by monitoring arterial blood acid-base status [partial pressure of CO(2) (PCO(2)), pH and HCO(3)(-)] during exposure to external hypercapnia (nominally 7·5 mm Hg). Both groups of fish exhibited typical compensatory responses to sustained hypercapnia consisting of the gradual accumulation of plasma HCO(3) (-) and thus metabolic restoration within 24 h of the initial respiratory acidosis elicited by hypercapnia. Overall, the results demonstrate that while Cl(-) uptake capacity is reduced in salt-fed fish, there is no associated alteration in acid-base regulating capability.

Gill morphology and acute hypoxia: responses of mitochondria-rich, pavement, and mucous cells in the Amazonian oscar (Astronotus ocellatus) and the rainbow trout (Oncorhynchus mykiss), two species with very different approaches to the osmo-respiratory compromise

The hypoxia-intolerant rainbow trout ( Oncorhynchus mykiss (Walbaum, 1792)) exhibits increased branchial ion permeability and Na+influx during acute exposure to moderate hypoxia (Po2 = 80 torr; 1 torr = 133.3224 Pa), manifesting the usual trade-off between gas exchange and electrolyte conservation. In contrast, the hypoxia-tolerant oscar ( Astronotus ocellatus (Agassiz, 1831)) is unusual in exhibiting decreased branchial ion permeability to ions and Na+influx during acute exposure to severe hypoxia (Po2 = 10–20 torr). These different physiological approaches to the osmo-respiratory compromise correlate with rapid, oppositely directed changes in gill morphology. In oscar, pavement cells (PVCs) expanded, partially covering neighboring mitochondria-rich cells (MRCs), which were recessed and reduced in size. Those remaining open were transformed from “shallow-basin” to “deep-hole” forms with smaller openings, deeper apical crypts, and smaller numbers of subapical microvesicles, changes that were largely reversed during normoxic recovery. In contrast, moderate hypoxia caused outward bulging of MRCs in rainbow trout with increases in size, surface exposure, and number of subapical microvesicles, accompanied by PVC retraction. These changes were partially reversed during normoxic recovery. In both rainbow trout and oscar, hypoxia caused discharge of mucus from enlarged mucous cells (MCs). Rapid, divergent morphological changes play an important role in explaining two very different physiological approaches to the osmo-respiratory compromise.

Complete intracellular pH protection during extracellular pH depression is associated with hypercarbia tolerance in white sturgeon,Acipenser transmontanus

Sturgeons are among the most CO2 tolerant of fishes investigated to date. However, the basis of this exceptional CO2 tolerance is unknown. Here, white sturgeon, Acipenser transmontanus, were exposed to elevated CO2 to investigate the mechanisms associated with short-term hypercarbia tolerance. During exposure to 1.5 kPa Pco2, transient blood pH [extracellular pH (pHe)] depression was compensated within 24 h and associated with net plasma HCO3- accumulation and equimolar Cl- loss, and changes in gill morphology, such as a decrease in apical surface area of mitochondrial-rich cells. These findings indicate that pHe recovery at this level of hypercarbia is accomplished in a manner similar to most freshwater teleost species studied to date, although branchial mechanisms involved may differ. White sturgeon exposed to more severe hypercarbia (3 and 6 kPa Pco2) for 48 h exhibited incomplete pH compensation in blood and red blood cells. Despite pHe depression, intracellular pH (pHi) of white muscle, heart, brain, and liver did not decrease during a transient (6 h of 1.5 kPa Pco2) or prolonged (48 h at 3 and 6 kPa Pco2 blood acidosis. This pHi protection was not due to high intrinsic buffering in tissues. Such tight active cellular regulation of pHi in the absence of pHe compensation represents a unique pattern for non-air-breathing fishes, and we hypothesize that it is the basis for the exceptional CO2 tolerance of white sturgeon and, likely, other CO2 tolerant fishes. Further research to elucidate the specific mechanisms responsible for this tremendous pH regulatory capacity in tissues of white sturgeon is warranted.

The effect of hypoxia on gill morphology and ionoregulatory status in the Lake Qinghai scaleless carp, Gymnocypris przewalskii

Goldfish and crucian carp at low temperature exhibit plasticity in gill morphology during exposure to hypoxia to enhance gas exchange. Hypoxia-induced changes in gill morphology and cellular ultrastructure of the high altitude scaleless carp from Lake Qinghai, China, were investigated to determine whether this is a general characteristic of cold water carp species. Fish were exposed to acute hypoxia (0.3 mg O2 l(-1)) for 24 h followed by 12 h recovery in normoxic water (6 mg O2 l(-1) at 3200 m altitude), with no mortality. Dramatic alterations in gill structure were initiated within 8 h of hypoxia and almost complete by 24 h, and included a gradual reduction of filament epithelial thickness (>50%), elongation of respiratory lamellae, expansion of lamellar respiratory surface area (>60%) and reduction in epithelial water-blood diffusion distance (<50%). An increase in caspase 3 activity in gills occurred following 24 h exposure to hypoxia, indicating possible involvement of apoptosis in gill remodeling. Extensive gill mucous production during hypoxia may have been part of a general stress response or may have played a role in ion exchange and water balance. The large increase in lamellar surface area and reduction in diffusion distance presumably enhances gas transfer during hypoxia (especially in the presence of increased mucous production) but comes with an ionoregulatory cost, as indicated by a 10 and 15% reduction in plasma [Na+] and [Cl-], respectively, within 12-24 h of hypoxia. Within 12 h of hypoxia exposure, ;wavy-convex'-mitochondria rich cells (MRCs) with large apical crypts and numerous branched microvilli were transformed into small ;shallow-basin' cells with a flattened surface. As the apical membrane of MRCs is the site for active ion uptake from the water, a reduction in apical crypt surface area may have contributed to the progressive reduction in plasma [Na+] and [Cl-] observed during hypoxia. The changes in the macro- and ultra-structure of fish gills, and plasma [Na+] and [Cl-] during hypoxia were reversible, showing partial recovery by 12 h following return to normoxia. Although the large morphological changes in the gill observed in the scaleless carp support the hypothesis that gill remodeling during hypoxia is a general characteristic of cold water carp species, the reduced magnitude of the response in scaleless carp relative to goldfish and crucian carp may be a reflection of their more active lifestyle or because they reside in a moderately hypoxic environment at altitude.

Oxidative stress and changes in locomotor behavior and gill morphology of Gambusia affinis exposed to chromium

Sublethal effects of chromium trioxide on mosquito fish, Gambusia affinis, were carried out for 28 days on day 4, 8, 12, 16, 20, 24, and 28. The sublethal effects of chromium (LC10, 77.62 mg L−1) on antioxidant enzymes, thiobarbituric acid reactive substance (TBARS), locomotor behavior, and gill morphology were studied. The antioxidant enzymes like superoxide dismutase (SOD) and catalase were induced throughout the exposure span of 28 days. Percent induction was also increase with the days of exposure. Lipid peroxidation product, malondialdehyde was enhanced in the viscera tissue of chromium-exposed fish. Perturbation of locomotor behavior like decrease in distance travelled (m min−1) and in swimming speed (cm s−1) was observed in exposed fish. Chromium toxicity caused alterations in gill morphology like hypertrophy and hyperplasia in secondary lamellae followed by detached epithelium with severe necrosis. It can be concluded from the results that Cr intoxication in Gambusia fish, caused induction in antioxidant enzymes and lipid peroxidation, plus changes in gill morphology and locomotor behavior.

Plasticity of respiratory structures — Adaptive remodeling of fish gills induced by ambient oxygen and temperature

While a large surface area combined with short diffusion distances make fish gills well suited for gas exchange, these properties leads to costly water and ion fluxes and exposure to toxic substances and pathogens. Thus, gill morphology is likely to be a compromise between opposing demands. It has become clear that some fishes have the ability to modify gill structure in response to environmental parameters such as oxygen levels and temperature. Maybe the most dramatic example of gill plasticity is the adaptive and reversible changes in gill surface area displayed by crucian carp (Carassius carassius) and goldfish (Carassius auratus). Here, a cell mass is filling up the space between the lamellae during normoxic and cold conditions (i.e. when oxygen demands are low). Hypoxia or high temperature induce apoptosis and suppress mitosis in the interlamellar cell mass causing it to retract and the lamellae to protrude. The functional importance of oxygen and temperature induced changes in gill morphology and the underlying mechanisms are discussed.

Ontogenetic changes in gill morphology and potential significance for food acquisition in the scallop Placopecten magellanicus

Sources of mortality in both wild and cultured populations of marine bivalves during postlarval stages remain largely unknown, but may be partly associated with the inability to meet energetic demands during intense morphogenesis. The development of the gills in postsettlement scallops (Placopecten magellanicus) from 0.35 to 14 mm in shell height (SH) was investigated using scanning electron microscopy to determine the degree of size-specific differentiation of the gills and evaluate potential ontogenetic constraints in food acquisition. Key transitional stages in morphogenesis, likely to exert pronounced effects on feeding function, were identified and correlated with scallop size. The gill was initially homorhabdic, with unreflected inner demibranchs forming a basket-like structure maintained by ciliary junctions. Gill reflection, immediately followed by accelerated proliferation of gill filaments and formation of outer demibranchs, occurred at ~1 mm SH. Outer demibranchs were fully formed at ~2 mm SH. Suspension-feeding is probably rather inefficient prior to attaining 1–2 mm sizes. The onset of the heterorhabdic, adult form of the gill, which allows bidirectional particle transport and the potential for selection and for volume regulation of ingested material on the gill, occurred fairly late in development, at ~3.3–5.0 mm SH. Full development of gill plication was delayed until scallops attained ~7 mm. Gill differentiation in this species is thus relatively protracted and punctuated by critical transitional stages, which may be important in determining feeding and growth capacity of postlarval wild and cultured populations.

Ontogenetic changes in gill morphology and potential significance for food acquisition in the scallop Placopecten magellanicus

Ontogenetic changes in gill morphology and potential significance for food acquisition in the scallop Placopecten magellanicus

The effects of hypercapnia on branchial and renal calcium fluxes in the rainbow trout ( Oncorhynchus mykiss )

Whole body calcium influx, branchial calcium efflux, and renal Ca2+ excretion were measured in rainbow trout (Oncorhynchus mykiss) exposed to hypercapnia. These experiments were performed to assess the potential impact on Ca2+ balance of the changes in gill morphology known to accompany respiratory acidosis in this species. After 48 h of hypercapnia, gill filamental chloride cell fractional area was significantly reduced. Despite this reduction and the presumed involvement of the chloride cell in calcium influx, whole body calcium influx was increased after 12 h of hypercapnia and remained elevated for 48 h. Branchial calcium efflux was unaltered during hypercapnia exposure, whereas renal Ca2+ excretion was elevated over preflux values only at 6 h of hypercapnia. Measurement of the kinetics of whole body calcium influx after 48 h of hypercapnia revealed a significant increase in the maximal uptake rate of Ca2+, yet the affinity constant of Ca2+ uptake was unaffected. Measurements of high-affinity Ca2+ -ATPase activities and ATP-dependent Ca2+ transport of gill basolateral membrane vesicles revealed that the ATP-dependent Ca2+ extrusion mechanism of the gills was not affected by hypercapnia. The results of the present study clearly show that the reduced chloride cell surface area that accompanies hypercapnia in trout does not impair calcium homeostasis. Although adjustments to the basolateral membrane high affinity Ca2+ transporter do not appear to play a role, the mechanism(s) underlying the maintenance of calcium homeostasis under hypercapnic conditions are unresolved.

Changes in gill morphology of Atlantic salmon ( Salmo salar) smolts due to addition of acid and aluminum to stream water

One-year-old Atlantic salmon smolts were held in three artificial channels adjacent to a softwater (mean sp. cond. 30 μS cm −1, circumneutral stream. Water in one channel was untreated (mean pH 6.25); the others received additions of acid (to mean pH 5.6), or acid plus aluminum (to mean pH 5.5; mean exchangeable Al 158 μg litre −1). Gills were sampled after 16 and 23 days of exposure for morphometric examination. On primary lamellae, chloride cells were more numerous in both experimental treatments than in controls. In contrast, numbers of chloride cells on secondary lamellae were elevated only in fish exposed to acid without added Al. Chloride cell size and shape also varied with time and treatment. Fewer gill mucous cells were found in fish exposed to acid plus Al than in controls. Chloride cell proliferation and structural changes may represent an attempt to compensate for increased ionic effluxes with low pH stress by increasing uptake. However, if Al concentrations are high, chloride cells do not proliferate along the secondary lamellae, or proliferating cells are damaged and lost. This may limit the potential to increase ionic uptake.