Search

Puffer and porcupine fishes (families Diodontidae and Tetraodontidae, order Tetradontiformes) are known for their extraordinary ability to triple their body size by swallowing and retaining large amounts of seawater in their accommodating stomachs. This inflation mechanism provides a defence to predation; however, it is associated with the secondary loss of the stomach's digestive function. Ingestion of alkaline seawater during inflation would make acidification inefficient (a potential driver for the loss of gastric digestion), paralleled by the loss of acid-peptic genes. We tested the hypothesis of stomach inflation as a driver for the convergent evolution of stomach loss by investigating the gastric phenotype and genotype of four distantly related stomach inflating gnathostomes: sargassum fish, swellshark, bearded goby and the pygmy leatherjacket. Strikingly, unlike in the puffer/porcupine fishes, we found no evidence for the loss of stomach function in sargassum fish, swellshark and bearded goby. Only the pygmy leatherjacket (Monochanthidae, Tetraodontiformes) lacked the gastric phenotype and genotype. In conclusion, ingestion of seawater for inflation, associated with loss of gastric acid secretion, is restricted to the Tetraodontiformes and is not a selective pressure for gastric loss in other reported gastric inflating fishes.

The excretion of nitrogenous waste products in the form of ammonia (NH3) and ammonium (NH4 (+)) is a fundamental process in aquatic organisms. For mytilid bivalves, little is known about the mechanisms and sites of excretion. This study investigated the localization and the mechanisms of ammonia excretion in mytilid mussels. An Rh protein was found to be abundantly expressed in the apical cell membrane of the plicate organ, which was previously described as a solely respiratory organ. The Rh protein was also expressed in the gill, although at significantly lower concentrations, but was not detectable in mussel kidney. Furthermore, NH3/NH4 (+) was not enriched in the urine, suggesting that kidneys are not involved in active NH3/NH4 (+) excretion. Exposure to elevated seawater pH of 8.5 transiently reduced NH3/NH4 (+) excretion rates, but they returned to control values following 24 h acclimation. These mussels had increased abundance of V-type H(+)-ATPase in the apical membranes of plicate organ cells; however, NH3/NH4 (+) excretion rates were not affected by the V-type H(+)-ATPase specific inhibitor concanamycin A (100 nmol l(-1)). In contrast, inhibition of ciliary beating with dopamine and increased seawater viscosity significantly reduced NH3 excretion rates under control pH (8.0). These results suggest that NH3/NH4 (+) excretion in mytilid mussels takes place by passive NH3 diffusion across respiratory epithelia via the Rh protein, facilitated by the water current produced for filter feeding, which prevents accumulation of NH3 in the boundary layer. This mechanism would be energy efficient for sessile organisms, as they already generate water currents for filter feeding.

Soluble adenylyl cyclase (sAC) is poised to play multiple physiological roles as an acid/base (A/B) sensor in aquatic organisms. Many of these roles are probably similar to those in mammals; a striking example is the evolutionary conservation of a mechanism involving sAC, carbonic anhydrase and vacuolar H+-ATPase that acts as a sensor system and regulator of extracellular A/B in shark gills and mammalian epididymis and kidney. Additionally, the aquatic environment presents unique A/B and physiological challenges; therefore, sACs from aquatic organisms have likely evolved distinct kinetic properties as well as distinct physiological roles. sACs from aquatic organisms offer an excellent opportunity for studying the evolution of A/B sensing at both the molecular and whole organism levels. Moreover, this information could help understand and predict organismal responses to environmental stress based on mechanistic models.This article is part of a Special Issue entitled "The Role of Soluble Adenylyl Cyclase in Health and Disease," guest edited by J. Buck and L. R. Levin.

Coastal California experiences large-scale blooms of Synechococcus cyanobacteria, which are predicted to become more prevalent by the end of the 21st century as a result of global climate change. This study investigated whether exposure to bloom-like concentrations of two Synechococcus strains, CC9311 and CC9902, alters fish behaviour. Black perch (Embiotoca jacksoni) were exposed to Synechococcus strain CC9311 or CC9902 (1.5 × 10(6) cells ml(-1)) or to control seawater in experimental aquaria for 3 days. Fish movement inside a testing arena was then recorded and analysed using video camera-based motion-tracking software. Compared with control fish, fish exposed to CC9311 demonstrated a significant preference for the dark zone of the tank in the light-dark test, which is an indication of increased anxiety. Furthermore, fish exposed to CC9311 also had a statistically significant decrease in velocity and increase in immobility and they meandered more in comparison to control fish. There was a similar trend in velocity, immobility and meandering in fish exposed to CC9902, but there were no significant differences in behaviour or locomotion between this group and control fish. Identical results were obtained with a second batch of fish. Additionally, in this second trial we also investigated whether fish would recover after a 3 day period in seawater without cyanobacteria. Indeed, there were no longer any significant differences in behaviour among treatments, demonstrating that the sp. CC9311-induced alteration of behaviour is reversible. These results demonstrate that blooms of specific marine Synechococcus strains can induce differential sublethal effects in fish, namely alterations light-dark preference behaviour and motility.

The average surface pH of the ocean is dropping at a rapid rate due to the dissolution of anthropogenic CO2, raising concerns for marine life. Additionally, some coastal areas periodically experience upwelling of CO2-enriched water with reduced pH. Previous research has demonstrated ocean acidification (OA)-induced changes in behavioural and sensory systems including olfaction, which is due to altered function of neural gamma-aminobutyric acid type A (GABAA) receptors. Here, we used a camera-based tracking software system to examine whether OA-dependent changes in GABAA receptors affect anxiety in juvenile Californian rockfish (Sebastes diploproa). Anxiety was estimated using behavioural tests that measure light/dark preference (scototaxis) and proximity to an object. After one week in OA conditions projected for the next century in the California shore (1125 ± 100 μatm, pH 7.75), anxiety was significantly increased relative to controls (483 ± 40 μatm CO2, pH 8.1). The GABAA-receptor agonist muscimol, but not the antagonist gabazine, caused a significant increase in anxiety consistent with altered Cl- flux in OA-exposed fish. OA-exposed fish remained more anxious even after 7 days back in control seawater; however, they resumed their normal behaviour by day 12. These results show that OA could severely alter rockfish behaviour; however, this effect is reversible. © 2013 The Author(s) Published by the Royal Society. All rights reserved.

In the present study, the influence of short-term osmotic variations on some electrophysiological properties related to NaCl absorption across posterior gills of Chasmagnathus granulatus was investigated. The transepithelial potential difference (V[sub te]) of isolated and perfused gills increased significantly when hyposmotic saline (699mosmoll[sup -1]) was used instead of isosmotic solution (1045 mosmol 1[sup -1]). A reduction of the concentration of Na[sup +] or CI[sup -] at constant osmolarity did not produce any change in V[sub te]. Transepithelial short-circuit current (I[sub sc]) and conductance (G[sub te]), measured with split gill lamellae mounted in a modified Ussing chamber, also increased after changing to hyposmotic salines (I[sub sc]: from -89.0±40.8 μA cm[sup -2] to -179.3±37.0 μA cm[sup -2]; G[sub te]: from 40.5±16.9mScm[sup -2] to 47.3±l5.8mS cm[sup - 2]). The observed effects of reduced osmolarity were fast, reversible and gradually dependent on the magnitude of the osmotic variation. The acitivity of the Na[sup +]/K[sup +]-ATPase increased significantly after perfusion with hyposmotic saline, from 18.73±6.35 μmol P[sub i] h[sup -1] mg[sup -1] to 41.84±14.54 μmol P[sub i] h[sup 1-] mg[sup -1]. Theophylline maintained part of the elevated V[sub te] induced by hyposmotic saline, suggesting that an increased cellular cyclic AMP level is involved in the response to reduced osmolarity. In summary, the results indicate that the hemolymph osmolarity regulates active transbranchial NaCl absorption by modulating the activity of the basolateral Na[sup +]/K[sup +]-ATPase and by changing a conductive pathway, probably at the apical membrane. [ABSTRACT FROM AUTHOR]

1. The ability to oxidize quinate is elicited in Acinetobacter calco-aceticus not only by growth on quinate but also by growth on protocatechuate or its precursors such as shikimate and p-hydroxybenzoate. Accordingly the synthesis of a quinate dependent dehydrogenase was found to be induced by protocatechuate. Moreover, this enzyme seems to belong to the same coordinate block of enzymes responsible for the conversion of shikimate to β-ketoadipyl-CoA. 2. Analogies between quinate and shikimate oxidation m A. calco-aceticus have been substantiated by showing that both quinate dehydrogenase and shikimate dehydrogenase activities rely on a single enzyme. 3. Several auxotrophs that have lost the ability to utile both quinate and shikimate as sole source of carbon and energy have been isolated. Particutarly relevant for this study are two of these mutants in which the dehydrogenase is severely impaired and correspondingly their ability to oxidize the mentioned hydroaromatic compounds is substantially reduced. The properties of these auxotrophs and their revertants confirm the key role of the dehydrogenase in the dissimilation of both quinate and shikimate. The rationale of the control of this enzyme by protocatechuate is discussed. [ABSTRACT FROM AUTHOR]

Aim: To identify the physiological role of the acid-base sensing enzyme, soluble adenylyl cyclase (sAC), in red blood cells (RBC) of the model teleost fish, rainbow trout., Methods: We used: (i) super-resolution microscopy to determine the subcellular location of sAC protein; (ii) live-cell imaging of RBC intracellular pH (pH i ) with specific sAC inhibition (KH7 or LRE1) to determine its role in cellular acid-base regulation; (iii) spectrophotometric measurements of haemoglobin-oxygen (Hb-O 2 ) binding in steady-state conditions; and (iv) during simulated arterial-venous transit, to determine the role of sAC in systemic O 2 transport., Results: Distinct pools of sAC protein were detected in the RBC cytoplasm, at the plasma membrane and within the nucleus. Inhibition of sAC decreased the setpoint for RBC pH i regulation by ~0.25 pH units compared to controls, and slowed the rates of RBC pH i recovery after an acid-base disturbance. RBC pH i recovery was entirely through the anion exchanger (AE) that was in part regulated by HCO 3 - -dependent sAC signaling. Inhibition of sAC decreased Hb-O 2 affinity during a respiratory acidosis compared to controls and reduced the cooperativity of O 2 binding. During in vitro simulations of arterial-venous transit, sAC inhibition decreased the amount of O 2 that is unloaded by ~11%., Conclusion: sAC represents a novel acid-base sensor in the RBCs of rainbow trout, where it participates in the modulation of RBC pH i and blood O 2 transport though the regulation of AE activity. If substantiated in other species, these findings may have broad implications for our understanding of cardiovascular physiology in vertebrates., (© 2024 The Author(s). Acta Physiologica published by John Wiley & Sons Ltd on behalf of Scandinavian Physiological Society.)

Marine fishes excrete excess H + using basolateral Na + -K + -ATPase (NKA) and apical Na + /H + exchanger 3 (NHE3) in gill ionocytes. However, the mechanisms that regulate H + excretion during exposure to environmentally relevant hypercapnia (ERH) remain poorly understood. Here, we explored transcriptomic, proteomic, and cellular responses in gills of juvenile splitnose rockfish ( Sebastes diploproa ) exposed to 3 days of ERH conditions (pH ∼7.5, ∼1,600 μatm Pco 2 ). Blood pH was fully regulated at ∼7.75 despite a lack of significant changes in gill 1 ) mRNAs coding for proteins involved in blood acid-base regulation, 2 ) total NKA and NHE3 protein abundance, and 3 ) ionocyte density. However, ERH-exposed rockfish demonstrated increased NKA and NHE3 abundance on the ionocyte plasma membrane coupled with wider apical membranes and greater extension of apical microvilli. The observed gill ionocyte remodeling is consistent with enhanced H + excretion that maintains blood pH homeostasis during exposure to ERH and does not necessitate changes at the expression or translation levels. These mechanisms of phenotypic plasticity may allow fishes to regulate blood pH during environmentally relevant acid-base challenges and thus have important implications for both understanding how organisms respond to climate change and for selecting appropriate metrics to evaluate its impact on marine ecosystems. NEW & NOTEWORTHY Splitnose rockfish exposed to environmentally relevant hypercapnia utilize existing proteins (rather than generate additional machinery) to maintain homeostasis.

The inner ear of teleost fish regulates the ionic and acid-base chemistry and secretes protein matrix into the endolymph to facilitate otolith biomineralization, which is used to maintain vestibular and auditory functions. The otolith is biomineralized in a concentric ring pattern corresponding to seasonal growth, and this calcium carbonate (CaCO 3 ) polycrystal has become a vital aging and life-history tool for fishery managers, ecologists, and conservation biologists. Moreover, biomineralization patterns are sensitive to environmental variability including climate change, thereby threatening the accuracy and relevance of otolith-reliant toolkits. However, the cellular biology of the inner ear is poorly characterized, which is a hurdle for a mechanistic understanding of the underlying processes. This study provides a systematic characterization of the cell types in the inner ear of splitnose rockfish ( Sebastes diploproa ). Scanning electron microscopy revealed the apical morphologies of six inner ear cell types. In addition, immunostaining and confocal microscopy characterized the expression and subcellular localization of the proteins Na + -K + -ATPase, carbonic anhydrase, V-type H + -ATPase, Na + -K + -2Cl - -cotransporter, otolith matrix protein 1, and otolin-1 in six inner ear cell types bordering the endolymph. This fundamental cytological characterization of the rockfish inner ear epithelium illustrates the intricate physiological processes involved in otolith biomineralization and highlights how greater mechanistic understanding is necessary to predict their multistressor responses to future climate change.

The gills of most teleost fishes lack plasma-accessible carbonic anhydrase (paCA) that could participate in CO2 excretion. We tested the prevailing hypothesis that paCA would interfere with red blood cell (RBC) intracellular pH regulation by β-adrenergic sodium-proton exchangers (β-NHE) that protect pH-sensitive haemoglobin-oxygen (Hb-O2) binding during an acidosis. In an open system that mimics the gills, β-NHE activity increased Hb-O2 saturation during a respiratory acidosis in the presence or absence of paCA, whereas the effect was abolished by NHE inhibition. However, in a closed system that mimics the tissue capillaries, paCA disrupted the protective effects of β-NHE activity on Hb-O2 binding. The gills are an open system, where CO2 generated by paCA can diffuse out and is not available to acidifying the RBCs. Therefore, branchial paCA in teleosts may not interfere with RBC pH regulation by β-NHEs, and other explanations for the evolutionary loss of the enzyme must be considered., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2023. Published by The Company of Biologists Ltd.)

The regulation of ionic, osmotic and acid-base (IOAB) conditions in biological fluids is among the most fundamental functions in all organisms; being surrounded by water uniquely shapes the IOAB regulatory strategies of water-breathing animals. Throughout its centennial history, Journal of Experimental Biology has established itself as a premier venue for publication of comparative, environmental and evolutionary studies on IOAB regulation. This Review provides a synopsis of IOAB regulation in aquatic animals, some of the most significant research milestones in the field, and evolving views about the underlying cellular mechanisms and their evolutionary implications. It also identifies promising areas for future research and proposes ideas for enhancing the impact of aquatic IOAB research., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2023. Published by The Company of Biologists Ltd.)

Diatoms, dinoflagellates, and coccolithophores are dominant groups of marine eukaryotic phytoplankton that are collectively responsible for the majority of primary production in the ocean. 1 These phytoplankton contain additional intracellular membranes around their chloroplasts, which are derived from ancestral engulfment of red microalgae by unicellular heterotrophic eukaryotes that led to secondary and tertiary endosymbiosis. 2 However, the selectable evolutionary advantage of these membranes and the physiological significance for extant phytoplankton remain poorly understood. Since intracellular digestive vacuoles are ubiquitously acidified by V-type H + -ATPase (VHA), 3 proton pumps were proposed to acidify the microenvironment around secondary chloroplasts to promote the dehydration of dissolved inorganic carbon (DIC) into CO 2 , thus enhancing photosynthesis. 4 , 5 We report that VHA is localized around the chloroplasts of centric diatoms and that VHA significantly contributes to their photosynthesis across a wide range of oceanic irradiances. Similar results in a pennate diatom, dinoflagellate, and coccolithophore, but not green or red microalgae, imply the co-option of phagocytic VHA activity into a carbon-concentrating mechanism (CCM) is common to secondary endosymbiotic phytoplankton. Furthermore, analogous mechanisms in extant photosymbiotic marine invertebrates 6 , 7 , 8 provide functional evidence for an adaptive advantage throughout the transition from endosymbiosis to symbiogenesis. Based on the contribution of diatoms to ocean biogeochemical cycles, VHA-mediated enhancement of photosynthesis contributes at least 3.5 Gtons of fixed carbon per year (or 7% of primary production in the ocean), providing an example of a symbiosis-derived evolutionary innovation with global environmental implications., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

We investigated whether CO 2 -induced ocean acidification (OA) affects dopamine receptor-dependent behavior in bicolor damselfish (Stegastes partitus). Damselfish were kept in aquaria receiving flow through control (pH ~ 8.03; pCO 2  ~ 384 μatm) or OA (pH ~ 7.64; CO 2  ~ 1100 μatm) seawater at a rate of 1 L min -1 . Despite this relatively fast flow rate, fish respiration further acidified the seawater in both control (pH ~7.88; pCO 2  ~ 595 μatm) and OA (pH ~7.55; pCO 2  ~ 1450 μatm) fish-holding aquaria. After five days of exposure, damselfish locomotion, boldness, anxiety, and aggression were assessed using a battery of behavioral tests using automated video analysis. Two days later, these tests were repeated following application of the dopamine D 1 receptor agonist SKF 38393. OA-exposure induced ceiling anxiety levels that were significantly higher than in control damselfish, and SKF 38393 increased anxiety in control damselfish to a level not significantly different than that of OA-exposed damselfish. Additionally, SKF 38393 decreased locomotion and increased boldness in control damselfish but had no effect in OA-exposed damselfish, suggesting an alteration in activity of dopaminergic pathways that regulate behavior under OA conditions. These results indicate that changes in dopamine D 1 receptor function affects fish behavior during exposure to OA. However, subsequent measurements of seawater sampled using syringes during the daytime (~3-4 pm local time) from crevasses in coral reef colonies, which are used as shelter by damselfish, revealed an average pH of 7.73 ± 0.03 and pCO 2 of 925.8 ± 62.2 μatm; levels which are comparable to Representative Concentration Pathway (RCP) 8.5 predicted end-of-century mean OA levels in the open ocean. Further studies considering the immediate environmental conditions experienced by fish as well as individual variability and effect size are required to understand potential implications of the observed OA-induced behavioral effects on damselfish fitness in the wild., Competing Interests: Declaration of competing interest The authors declare no competing interests., (Copyright © 2023 Elsevier B.V. All rights reserved.)