Gill Surface Research Articles

The allometric scaling of oxygen supply and demand in the California Horn Shark, Heterodontus francisci.

The gill surface area of aquatic ectotherms is thought to be closely linked to the ontogenetic scaling of metabolic rate, a relationship that is often used to explain and predict ecological patterns across species. However, there are surprisingly few within-species tests of whether metabolic rate and gill area scale similarly. We examined the relationship between oxygen supply (gill area) and demand (metabolic rate) by making paired estimates of gill area with resting and maximum metabolic rates across ontogeny in the relatively inactive California Horn Shark, Heterodontus francisci. We found that the allometric slope of resting metabolic rate was 0.966±0.058 95% CI, while that of maximum metabolic rate was somewhat steeper (1.073±0.040). We also discovered that the scaling of gill area shifted with ontogeny: the allometric slope of gill area was shallower in individuals <0.203 kg body mass (0.564±0.261), but increased to 1.012±0.113 later in life. This appears to reflect changes in demand for gill-oxygen uptake during egg case development and immediately post hatch, while for most of ontogeny, gill area scales in between that of resting and maximum metabolic rate. These relationships differ from predictions of the Gill Oxygen Limitation Theory, which argues that the allometric scaling of gill area constrains metabolic processes. Thus, for the California Horn Shark, metabolic rate does not appear limited by theoretical surface area-to-volume ratio constraints of gill area. These results highlight the importance of data from paired and size-matched individuals when comparing physiological scaling relationships.

Gills, growth and activity across fishes

AbstractLife history theory suggests that maximum size and growth evolve to maximize fitness. In contrast, the Gill Oxygen Limitation Theory (GOLT) suggests that growth and maximum size in fishes and other aquatic, water‐breathing organisms is constrained by the body mass‐scaling of gill surface area. Here, we use new data and a novel phylogenetic Bayesian multilevel modelling framework to test this idea by asking the three questions posed by the GOLT regarding maximum size, growth and gills. Across fishes, we ask whether the body mass‐scaling of gill surface area explains (1) variation in the von Bertalanffy growth coefficient (k) above and beyond that explained by asymptomatic size (W∞), (2) variation in growth performance (a trait that integrates the tradeoff between k and W∞) and (3) more variation in growth performance compared to activity (as approximated by caudal fin aspect ratio). Overall, we find that there is only a weak relationship among maximum size, growth and gill surface area across species. Indeed, the body mass‐scaling of gill surface area does not explain much variation in k (especially for those species that reach the same W∞) or growth performance. Activity explained three to five times more variation in growth performance compared to gill surface area. Our results suggest that in fishes, gill surface area is not the only factor that explains variation in maximum size and growth, and that other covariates (e.g. activity) are likely important in understanding how growth, maximum size and other life history traits vary across species.

Constant temperature and fluctuating temperature have distinct effects on hypoxia tolerance in killifish (Fundulus heteroclitus).

Climate change is leading to rapid change in aquatic environments, increasing the mean and variability of temperatures, and increasing the incidence of hypoxia. We investigated how acclimation to constant temperatures or to diel temperature fluctuations affects hypoxia tolerance in mummichog killifish (Fundulus heteroclitus). Killifish were acclimated to constant cool (15°C), constant warm (25°C) or a diel temperature cycle (15°C at night, 25°C during day) for 6 weeks. We then measured hypoxia tolerance (time to loss of equilibrium in severe hypoxia, tLOE; critical O2 tension, Pcrit), whole-animal metabolism, gill morphology, haematology and tissue metabolites at 15°C and 25°C in a full factorial design. Among constant temperature groups, tLOE was highest and Pcrit was lowest in fish tested at their acclimation temperature. Warm-acclimated fish had lower metabolic rate at 25°C and greater gill surface area (less coverage of lamellae by interlamellar cell mass, ILCM), but cool-acclimated fish had greater brain glycogen stores. Therefore, effects of constant temperature acclimation on hypoxia tolerance were temperature specific and not exhibited broadly across test temperatures, and they were associated with different underlying mechanisms. Hypoxia tolerance was less sensitive to test temperature in fish acclimated to fluctuating temperatures compared with fish acclimated to constant temperature. Acclimation to fluctuating temperatures also increased haemoglobin-O2 affinity of the blood (decreased P50) compared with constant temperature groups. Therefore, acclimation to fluctuating temperatures helps maintain hypoxia tolerance across a broader range of temperatures, and leads to some distinct physiological adjustments that are not exhibited by fish acclimated to constant temperatures.

Gill surface area allometry does not constrain the body mass scaling of maximum oxygen uptake rate in the tidepool sculpin, Oligocottus maculosus.

The gill oxygen limitation hypothesis (GOLH) suggests that hypometric scaling of metabolic rate in fishes is a consequence of oxygen supply constraints imposed by the mismatched growth rates of gill surface area (a two-dimensional surface) and body mass (a three-dimensional volume). GOLH may, therefore, explain the size-dependent spatial distribution of fish in temperature- and oxygen-variable environments through size-dependent respiratory capacity, but this question is unstudied. We tested GOLH in the tidepool sculpin, Oligocottus maculosus, a species in which body mass decreases with increasing temperature- and oxygen-variability in the intertidal, a pattern consistent with GOLH. We statistically evaluated support for GOLH versus distributed control of [Formula: see text] allometry by comparing scaling coefficients for gill surface area, standard and maximum [Formula: see text] ([Formula: see text],Standard and [Formula: see text],Max, respectively), ventricle mass, hematocrit, and metabolic enzyme activities in white muscle. To empirically evaluate whether there is a proximate constraint on oxygen supply capacity with increasing body mass, we measured [Formula: see text],Max across a range of Po2s from normoxia to Pcrit, calculated the regulation value (R), a measure of oxyregulatory capacity, and analyzed the R-body mass relationship. In contrast with GOLH, gill surface area scaling either matched or was more than sufficient to meet [Formula: see text] demands with increasing body mass and R did not change with body mass. Ventricle mass (b = 1.22) scaled similarly to [Formula: see text],Max (b = 1.18) suggesting a possible role for the heart in the scaling of [Formula: see text],Max. Together our results do not support GOLH as a mechanism structuring the distribution of O. maculosus and suggest distributed control of oxyregulatory capacity.

Plastic loss of motile cilia in the gills of Polypterus in response to high CO2 or terrestrial environments.

The evolutionary transition of vertebrates from water to land during the Devonian period was accompanied by major changes in animal respiratory systems in terms of physiology and morphology. Indeed, the fossil record of the early tetrapods has revealed the existence of internal gills, which are vestigial fish-like traits used underwater. However, the fossil record provides only limited data on the process of the evolutionary transition of gills from fish to early tetrapods. This study investigated the gills of Polypterus senegalus, a basal ray-finned/amphibious fish which shows many ancestral features of stem Osteichthyes. Based on scanning electron microscopy observations and transcriptome analysis, the existence of motile cilia in the gills was revealed which may create a flow on the gill surface leading to efficient ventilation or remove particles from the surface. Interestingly, these cilia were observed to disappear after rearing in terrestrial or high CO2 environments, which mimics the environmental changes in the Devonian period. The cilia re-appeared after being returned to the original aquatic environment. The ability of plastic changes of gills in Polypterus revealed in this study may allow them to survive in fluctuating environments, such as shallow swamps. The ancestor of Osteichthyes is expected to have possessed such plasticity in the gills, which may be one of the driving forces behind the transition of vertebrates from water to land.

Revisiting a central prediction of the Gill Oxygen Limitation Theory: Gill area index and growth performance

AbstractThe Gill Oxygen Limitation Theory (GOLT) posits that a mismatch in oxygen supply and demand stemming from geometric constraints on gill surface area limits metabolic rate and energy available for biological processes. This theory has been suggested to explain numerous phenomena observed with warming yet is based upon a relationship among maximum size, growth, and gill surface area established over 40 years ago. However, the metric used in this relationship to characterize gill surface area, gill area index, fails to capture the known variability in the scaling of gill surface area and is biased by the sizes at which gills were measured. Here, we revisit a central prediction of the GOLT, asking four key questions that examine limitations in the original relationship. We find that gill area index does indeed explain variation in growth performance across 132 species of fish and this relationship is strikingly similar to the original relationship across 42 species. Yet, we argue that gill area index is not an adequate measure of gill surface area because (1) gill surface area has a non‐linear relationship with size and, thus, changes ontogenetically as an individual grows over time and (2) because it is based on mean estimates of both gill surface area and body mass. Indeed, we show that the value of gill area index for a given species is variable depending on how it is calculated. We therefore suggest a pathway forward for assessing whether gill surface area is an important factor in explaining variation in growth performance.

Growth performance and quality indicators of European seabass (Dicentrarchus labrax) fed diets including refined glycerol

Glycerol is a by-product of the biodiesel industry with growing availability and applicability in animal feeds. However, its use as a source of energy in aquafeeds has only been investigated in a small number of fish species. The effects of dietary refined glycerol inclusion rate on growth performance, nitrogen and energy balances, and fish quality were investigated in juvenile European seabass. Twelve fish were assigned to each of the nine tanks and used to test the experimental diets in triplicate. The diets comprised 0, 25, or 50 g kg−1 of refined glycerol (G0, G25, and G50, respectively), being not isoenergetic, although having similar digestible protein-to-energy ratios (22 mg kJ−1). Fish were fed twice a day to apparent satiation for 90 days. The G25 group displayed a higher absolute feed intake and a higher weight gain than the G0 or G50 groups, although feed efficiency and the use of protein as an energy source were similar between the three groups. Seabass fed the G25 diet also displayed a higher specific growth rate than fish fed the G50 diet. Higher hepato-somatic and visceral lipid-somatic indices of seabass were observed with increased levels of dietary glycerol, although proximal body composition remained similar across groups. The apparent digestibility coefficients for dry matter, crude protein, and energy increased with increasing dietary glycerol inclusion rate, whereas the apparent lipid digestibility coefficient was highest for the G25 group. No differences in the energy retained as protein, nitrogen efficiency, and total ammonia excretion rate were detected between seabass fed the different diets. At the end of the growth trial, physical and microbiological quality parameters of the skin and gill surfaces were assessed after 1 and 10 days of storage on ice. Fish quality decreased with storage time but was not affected by the dietary glycerol inclusion rate. In summary, the inclusion of refined glycerol in seabass diets may have economic benefits for feed manufacture and a positive effect on growth performance but does not change the efficiency of protein utilization in this carnivorous species.

Gill grooming in middle Cambrian and Late Ordovician trilobites

AbstractEfficient extraction of oxygen from ambient waters played a critical role in the development of early arthropods. Maximizing gill surface area enhanced oxygen uptake ability but, with gills necessarily exposed to the external environment, also presented the issue of gill contamination. Here we document setae inserted on the dorsal surface of walking legs of the benthic-dwelling middle CambrianOlenoides serratusand on the gill shaft of the Late OrdovicianTriarthrus eatoni. Based on their physical positions relative to gill filaments, we interpret these setae to have been used to groom the gills, removing particles trapped among the filaments. The coordination between setae and gill filaments is comparable to that seen among modern crustaceans, which use a diverse set of setae-bearing appendages to penetrate between gill filaments when grooming. Grooming is known relatively early in trilobite evolutionary history and would have enhanced gill efficiency by maximizing the surface area for oxygen uptake.

Interactions among deep-sea mussels and their epibiotic and endosymbiotic chemoautotrophic bacteria: Insights from multi-omics analysis.

Endosymbiosis with Gammaproteobacteria is fundamental for the success of bathymodioline mussels in deep-sea chemosynthesis-based ecosystems. However, the recent discovery of Campylobacteria on the gill surfaces of these mussels suggests that these host-bacterial relationships may be more complex than previously thought. Using the cold-seep mussel ( Gigantidas haimaensis) as a model, we explored this host-bacterial system by assembling the host transcriptome and genomes of its epibiotic Campylobacteria and endosymbiotic Gammaproteobacteria and quantifying their gene and protein expression levels. We found that the epibiont applies a sulfur oxidizing (SOX) multienzyme complex with the acquisition of soxB from Gammaproteobacteria for energy production and switched from a reductive tricarboxylic acid (rTCA) cycle to a Calvin-Benson-Bassham (CBB) cycle for carbon assimilation. The host provides metabolic intermediates, inorganic carbon, and thiosulfate to satisfy the materials and energy requirements of the epibiont, but whether the epibiont benefits the host is unclear. The endosymbiont adopts methane oxidation and the ribulose monophosphate pathway (RuMP) for energy production, providing the major source of energy for itself and the host. The host obtains most of its nutrients, such as lysine, glutamine, valine, isoleucine, leucine, histidine, and folate, from the endosymbiont. In addition, host pattern recognition receptors, including toll-like receptors, peptidoglycan recognition proteins, and C-type lectins, may participate in bacterial infection, maintenance, and population regulation. Overall, this study provides insights into the complex host-bacterial relationships that have enabled mussels and bacteria to thrive in deep-sea chemosynthetic ecosystems.

ВПЛИВ Zn2+ ВОДНОГО СЕРЕДОВИЩА НА ДОБОВУ ЦИКЛІЧНІСТЬ ДИХАННЯ АЛОВИДІВ PLANORBARIUS CORNEUS S. L. (MOLLUSCA, GASTROPODA, PLANORBIDAE)

We investigated the impact of the different concentrations of Zn2+ in the water (in the 0.5 MPL – 3 MPL range) on the chronological features of lung and direct diffusive respiration in representatives of superspecies complex of ramshorns Planorbarius corneus s. l. (“eastern” and “western” allospecies) from the Ukrainian river network. They have a bimodal respiration. Atmospheric oxygen goes into their true lungs through the breathing pore – pneumostome, – during the periodical rises up to the water surface tension film. And the oxygen soluble in the water is acquired by the osmosis through the epithelial body coverings and the surface of adaptive gill. Both ways are almost equally important for the oxygen supply of mollusks’ organisms.&#x0D; Zn2+ ions are the powerful toxins of local effect for ramshorns. The excess of the MPL may lead to the impairment of stable homeostasis. Both P. corneus allospecies s. l. have clearly expressed diurnal cyclicality of their lung respiration (in the “day-night” rhythm). They perform 1.2–1.3 times more “inhales” during the day with the shorter (1.3–1.4 times) intervals. This apparently is the consequence of physiological activity increasing in the period of their most intensive life-giving metabolic processes occurring. &#x0D; Under the 0.5 MPL of Zn2+ there were no statistically significant changes in lung and direct diffusive respirations indexes (comparing to the control) in both allospecies during the latent phase of their intoxication process. “Inhales” during the day were 1.1 time longer than during the night in experimental animals. This let mollusks replenish the amount of oxygen they underreceived due to the decreased number of night “inhales”.&#x0D; Under MPL Zn2+ level the respirational indexes of ramshorns (number, length and volume of “inhales” and intervals between them) increased in average 1.1 times. Their feeding and moving behaviors visibly activated, which promoted the increasing of the daily frequency of their respiration rhythm. Under the 2 MPL concentration of Zn2+ there was further significant increasing (p

Optimization of Low-Biomass Sample Collection and Quantitative PCR-Based Titration Impact 16S rRNA Microbiome Resolution.

The major aquatic interface between host and environment in teleost finfish species is the gill. The diversity of this infraclass, high complexity of the organ, and its direct exposure to the surrounding environment make it an ideal candidate for furthering our understanding of the intertwined relationships between host and microbiome. Capturing the structure and diversity of bacterial communities from this low-biomass, inhibitor-rich tissue can, however, prove challenging. Lessons learned in doing so are directly applicable to similar sample types in other areas of microbiology. Through the development of a quantitative PCR assay for both host material and 16S rRNA genes, we tested and developed a robust method for low-biomass sample collection which minimized host DNA contamination. Quantification of 16S rRNA facilitated not only the screening of samples prior to costly library construction and sequencing but also the production of equicopy libraries based on 16S rRNA gene copies. A significant increase in diversity of bacteria captured was achieved, providing greater information on the true structure of the microbial community. Such findings offer important information for determining functional processes. Results were confirmed across fresh, brackish, and marine environs with four different fish species, with results showing broad homology between samples, demonstrating the robustness of the approach. Evidence presented is widely applicable to samples similar in composition, such as sputum or mucus, or those that are challenging due to the inherent inclusion of inhibitors. IMPORTANCE The interaction between the fish gill and surrounding bacteria-rich water provides an intriguing model for examining the interaction between the fish, free-floating bacteria, and the bacterial microbiome on the gill surface. Samples that are inherently low in bacteria, or that have components that inhibit the ability to produce libraries that identify the components of microbial communities, present significant challenges. Gill samples present both of these types of challenges. We developed methods for quantifying both the bacterial and host DNA material and established a sampling method which both reduced inhibitor content and maximized bacterial diversity. By quantifying and normalizing bacteria prior to library construction, we showed significant improvements with regards to the fidelity of the final data. Our results support wide-ranging applications for analyzing samples of similar composition, such as mucus and sputum, in other microbiological spheres.

Positive feedback promotes terrestrial emergence behaviour in an amphibious fish.

Major ecological transitions such as the invasion of land by aquatic vertebrates may be facilitated by positive feedback between habitat choice and phenotypic plasticity. We used the amphibious fish Kryptolebias marmoratus to test the hypothesis that aquatic hypoxia, emergence behaviour and respiratory plasticity create this type of positive feedback loop that causes fish to spend increasing amounts of time on land. Terrestrially acclimated fish were more sensitive to aquatic hypoxia (emergence at higher PO2) and were less hypoxia tolerant (shorter time to loss of equilibrium) relative to water-acclimated fish, which are necessary conditions for positive feedback. Next, we tested the prediction that exposure to aquatic hypoxia causes fish to emerge frequently, reduce gill surface area, and become less hypoxia tolerant. Indeed, fish exposed to severe aquatic hypoxia spent almost 50% of the time out of water and coverage of the gill lamellae by an inter-lamellar cell mass almost doubled. Fish exposed to aquatic hypoxia that could emerge from water were also more sensitive to subsequent acute aquatic hypoxia and were less hypoxia tolerant than normoxia-exposed controls. These results are opposite those of fish that cannot escape from aquatic hypoxia and presumably arise owing to plastic changes that occur during air exposure. Together, these results indicate that emergence behaviour begets further emergence behaviour, driven by gill remodelling which reduces aquatic respiratory function. This type of positive feedback may explain how amphibious behaviour has repeatedly evolved in fishes that occupy hypoxic aquatic habitats despite the associated challenges of life on land.

Novel development of cationic surfactant-based mucoadhesive nanovaccine for direct immersion vaccination against Francisella noatunensis subsp. orientalis in red tilapia (Oreochromis sp.)

Francisella noatunensis subsp. orientalis (Fno) is one of the infectious diseases that causes economic losses associated with tilapia mortality. Even though direct immersion administration of vaccines is more practicable for small fish and fry compared with oral and injection vaccination in the fields, the efficacy is still insufficient due to lower potency of antigen uptake. Herein, we accomplished the development of a mucoadhesive nanovaccine platform using cetyltrimethylammonium bromide (CTAB), a cationic surfactant, to improve the efficiency of immersion vaccination against Fno in tilapia. Cationic Fno nanovaccine (CAT-Fno-NV) was prepared though emulsification using an ultrasonic method. In our investigation, the CAT-Fno-NV increased the opportunity of Fno vaccine uptake by extending the contact time between vaccine and mucosal surface of fish gills and enhancing the protective efficacy against Fno infection. Fish were vaccinated with the CAT-Fno-NV by a direct immersion protocol. The challenge trial by Fno injection revealed that CAT-Fno-NV at the concentration 1:100 ratio (approximately 1 × 106 cfu/mL) had the highest efficacy to protect fish from Fno infection at day 30 after post challenge period according to the total number of Fno detected in head kidney, spleen and liver. A significant upregulation of IgM gene was observed in gills, skin, head kidney, serum and peripheral blood lymphocytes (PBLs) and spleen tissues treated with WC and CAT-Fno-NV (1:100) vaccines, while IgT gene was highly expressed in only gills and skin tissues for treated WC and CAT-Fno-NV (1:100) groups. We anticipate that the cationic surfactant-based nanovaccine developed in this study could become an efficient alternative for direct immersion vaccination to induce humoral immune responses against Fno in vaccinated tilapia.

Comparative morphology of gill apparatus of common carp (&lt;em&gt;Cyprinus carpio&lt;/em&gt;) and African catfish (&lt;em&gt;Clarias gariepinus&lt;/em&gt;)

Common carp and African catfish belong to the Cyprinidae (Cypriniformes) and Catfish (Siluriformes) orders, respectively. They are characterized by a different habitat, as a result of which the structure of the gill apparatus has a number of features [3]. The article describes the macroscopic and microscopic morphology of the gills of the represented fish species. Each of them had four complete pairs of gills, and the fifth was rudimentary without gill filaments. The gill rakers of carp tended to be short and widely spaced compared to the long and thin rakers of catfish. The gill filaments of the carp were longer than those of the African catfish, indicating a larger area of the gill surface in the former species. All gill regions, as seen from light microscopy, are covered with mucous epithelium.

Morphological characteristics and abundance of prokaryotes associated with gills in mangrove brachyuran crabs living along a tidal gradient.

Due to the chemico-physical differences between air and water, the transition from aquatic life to the land poses several challenges for animal evolution, necessitating morphological, physiological and behavioural adaptations. Microbial symbiosis is known to have played an important role in eukaryote evolution, favouring host adaptation under changing environmental conditions. We selected mangrove brachyuran crabs as a model group to investigate the prokaryotes associated with the gill of crabs dwelling at different tidal levels (subtidal, intertidal and supratidal). In these animals, the gill undergoes a high selective pressure, finely regulating multiple physiological functions during both animal submersion under and emersion from the periodical tidal events. We hypothesize that similarly to other marine animals, the gills of tidal crabs are consistently colonized by prokaryotes that may quantitatively change along the environmental gradient driven by the tides. Using electron microscopy techniques, we found a thick layer of prokaryotes over the gill surfaces of all of 12 crab species from the mangrove forests of Saudi Arabia, Kenya and South Africa. We consistently observed two distinct morphotypes (rod- and spherical-shaped), positioned horizontally and/or perpendicularly to the gill surface. The presence of replicating cells indicated that the prokaryote layer is actively growing on the gill surface. Quantitative analysis of scanning electron microscopy images and the quantification of the bacterial 16S rRNA gene by qPCR revealed a higher specific abundance of prokaryote cells per gill surface area in the subtidal species than those living in the supratidal zone. Our results revealed a correlation between prokaryote colonization of the gill surfaces and the host lifestyle. This finding indicates a possible role of prokaryote partnership within the crab gills, with potential effects on animal adaptation to different levels of the intertidal gradient present in the mangrove ecosystem.

Linking environmental salinity to respiratory phenotypes and metabolic rate in fishes: a data mining and modelling approach.

The gill is the primary site of ionoregulation and gas exchange in adult teleost fishes. However, those characteristics that benefit diffusive gas exchange (large, thin gills) may also enhance the passive equilibration of ions and water that threaten osmotic homeostasis. Our literature review revealed that gill surface area and thickness were similar in freshwater (FW) and seawater (SW) species; however, the diffusive oxygen (O2) conductance (Gd) of the gill was lower in FW species. While a lower Gd may reduce ion losses, it also limits O2 uptake capacity and possibly aerobic performance in situations of high O2 demand (e.g. exercise) or low O2 availability (e.g. environmental hypoxia). We also found that FW fishes had significantly higher haemoglobin (Hb)-O2 binding affinities than SW species, which will increase the O2 diffusion gradient across the gills. Therefore, we hypothesized that the higher Hb-O2 affinity of FW fishes compensates, in part, for their lower Gd. Using a combined literature review and modelling approach, our results show that a higher Hb-O2 affinity in FW fishes increases the flux of O2 across their low-Gd gills. In addition, FW and SW teleosts can achieve similar maximal rates of O2 consumption (ṀO2,max) and hypoxia tolerance (Pcrit) through different combinations of Hb-O2 affinity and Gd. Our combined data identified novel patterns in gill and Hb characteristics between FW and SW fishes and our modelling approach provides mechanistic insight into the relationship between aerobic performance and species distribution ranges, generating novel hypotheses at the intersection of cardiorespiratory and ionoregulatory fish physiology.

Generation of Reactive Oxygen Species (ROS) by Harmful Algal Bloom (HAB)-Forming Phytoplankton and Their Potential Impact on Surrounding Living Organisms.

Most marine phytoplankton with relatively high ROS generation rates are categorized as harmful algal bloom (HAB)-forming species, among which Chattonella genera is the highest ROS-producing phytoplankton. In this review, we examined marine microalgae with ROS-producing activities, with focus on Chattonella genera. Several studies suggest that Chattonella produces superoxide via the activities of an enzyme similar to NADPH oxidase located on glycocalyx, a cell surface structure, while hydrogen peroxide is generated inside the cell by different pathways. Additionally, hydroxyl radical has been detected in Chattonella cell suspension. By the physical stimulation, such as passing through between the gill lamellas of fish, the glycocalyx is easily discharged from the flagellate cells and attached on the gill surface, where ROS are continuously produced, which might cause gill tissue damage and fish death. Comparative studies using several strains of Chattonella showed that ROS production rate and ichthyotoxicity of Chattonella is well correlated. Furthermore, significant levels of ROS have been reported in other raphidophytes and dinoflagellates, such as Cochlodinium polykrikoides and Karenia mikimotoi. Chattonella is the most extensively studied phytoplankton in terms of ROS production and its biological functions. Therefore, this review examined the potential ecophysiological roles of extracellular ROS production by marine microalgae in aquatic environment.

The ratio of length at first maturity to maximum length across marine and freshwater fishes

The prevailing determinant of maturation in fishes is thought to be a redirection of energy from growth to reproduction. Instead, the Gill Oxygen Limitation Theory predicts that maturation, and thus reproduction, is induced when a fish reaches a critical ratio of oxygen supply to demand (Qm /Qmaint ). The consistency of this critical ratio has been previously documented in many fishes, but a broader test was lacking. In this study, the authors assess if this critical ratio is consistent across 132 unique fish species, as measured by the slope of the relationship between Lmax D and Lm D , where Lmax is the maximum length reached in a given population, Lm is the mean size at first maturity in that population and D is a gill-related exponent which renders the Lmax D /Lm D ratio equivalent to the Qm /Qmaint ratio. The authors found that across all species, the Lmax D /Lm D ratio was 1.40 (95% c.i. 1.38-1.42), which was not significantly different from that previously estimated across other species groups (1.35, 95% c.i. 1.22-1.53), especially when phylogenetic relationships were considered (1.25, 95% Bayesian credible interval 1.09-1.40). The consistency of the Lmax D /Lm D ratio across taxa, which expresses the difference in metabolic rate at maturity and maximum size, suggests that the scaling of gill surface area is the factor that underlies this ratio, and which triggers the maturation in fishes.

Gill Transcriptomic Responses to Toxin-producing Alga Prymnesium parvum in Rainbow Trout.

The gill of teleost fish is a multifunctional organ involved in many physiological processes, including protection of the mucosal gill surface against pathogens and other environmental antigens by the gill-associated lymphoid tissue (GIALT). Climate change associated phenomena, such as increasing frequency and magnitude of harmful algal blooms (HABs) put extra strain on gill function, contributing to enhanced fish mortality and fish kills. However, the molecular basis of the HAB-induced gill injury remains largely unknown due to the lack of high-throughput transcriptomic studies performed on teleost fish in laboratory conditions. We used juvenile rainbow trout (Oncorhynchus mykiss) to investigate the transcriptomic responses of the gill tissue to two (high and low) sublethal densities of the toxin-producing alga Prymnesium parvum, in relation to non-exposed control fish. The exposure time to P. parvum (4–5 h) was sufficient to identify three different phenotypic responses among the exposed fish, enabling us to focus on the common gill transcriptomic responses to P. parvum that were independent of dose and phenotype. The inspection of common differentially expressed genes (DEGs), canonical pathways, upstream regulators and downstream effects pointed towards P. parvum-induced inflammatory response and gill inflammation driven by alterations of Acute Phase Response Signalling, IL-6 Signalling, IL-10 Signalling, Role of PKR in Interferon Induction and Antiviral Response, IL-8 Signalling and IL-17 Signalling pathways. While we could not determine if the inferred gill inflammation was progressing or resolving, our study clearly suggests that P. parvum blooms may contribute to the serious gill disorders in fish. By providing insights into the gill transcriptomic responses to toxin-producing P. parvum in teleost fish, our research opens new avenues for investigating how to monitor and mitigate toxicity of HABs before they become lethal.

Correlation between Metabolic Rate and Salinity Tolerance and Metabolic Response to Salinity in Grass Carp (Ctenopharyngodon idella).

Simple SummaryThe association between the metabolic rate and salinity tolerance in stenohaline freshwater fish could affect how fish adapt to changes in environmental salinity. In Experiment I, the metabolic rates and upper salinity tolerance limit of the grass carp were determined individually, and we aimed to test whether an association existed between the salinity tolerance capacity and both the resting metabolic rate and maximum metabolic rate. In Experiment II, the effects of increasing salinity on metabolic rates, gill histology, and Na+-K+-ATPase activities were determined in grass carp. The results suggest that a lower metabolic rate may not necessarily allow for a better salinity tolerance capacity of grass carp. Salinity-induced changes in the gill surface contribute more to ion exchange capacity than to oxygen uptake capacity.The metabolic rate could be one of the factors affecting the salinity tolerance capacity of fish. Experiment I tested whether metabolic rates correlate with the upper salinity tolerance limit among individual grass carp by daily increasing salinity (1 g kg−1 day−1). The feeding dropped sharply as the salinity reached 10 g kg−1 and ceased when salinities exceeded 11 g kg−1. The ventilation frequency decreased weakly as salinity increased from 0 to 12 g kg−1 and then increased rapidly as salinity reached 14 g kg−1. The fish survived at salinities lower than 14 g kg−1, and all fish died when salinity reached 17 g kg−1. The upper salinity tolerance limit was not correlated with metabolic rates. Therefore, a lower metabolic rate may not necessarily allow for better salinity tolerance capacity. Experiment II tested how different salinities (0, 0.375, 0.75, 1.5, 3, and 6 g kg−1 for 2 weeks) affect the metabolic parameters of grass carp. The changes in the resting metabolic rate with increasing salinity could be explained by the relative changes in interlamellar cell mass and protruding lamellae. The maximum metabolic rate remained constant, suggesting that the salinity-induced changes in the gill surface had a minor effect on oxygen uptake capacity.