Mucosal epithelial homeostasis: Reference intervals for skin, gill lamellae and filament for Atlantic salmon and other fish species.

Mucosal barriers are gatekeepers of health and exhibit homeostatic variation in relation to habitat and disease. Mucosal Mapping technology provides an in-depth examination of the dynamic mucous cells (MCs) in fish mucosal barriers on tangential sections, about 90° from the view of traditional histology. The method was originally developed and standardized in academia prior to the establishment of QuantiDoc AS to apply mucosal mapping, now trademarked as Veribarr™ for the analysis of skin, gills and gastrointestinal tracts. Veribarr™ uses design-based stereology for the selection and measurement of cell area (size) (µm2), the volumetric density of MCs in the epithelium (MCD, amount of the epithelia occupied by MCs, in %) and the calculated abundance of the MCs (barrier status or defence activity). MC production was mapped across the skin and gill epithelia in 12 species, discovering that gills consistently have two distinct groups of MCs, one on the lamellae where MCs are few and small and one on the filament where MCs are larger and more abundant. MCs were usually much larger in the skin than in the gills, with the latter requiring fewer and smaller cells for adequate respiration. The difference observed between MCs in gill lamella and gill filament is likely a result of functional demands. In addition, our findings also highlight a variation in the mucosal parameters between the species skin, which cannot be explained by the weight differences, and a potential link between MC distribution and species-specific lifestyles in the gill lamella. This diversity necessitates the development of species and tissue site-specific reference intervals for mucosal health evaluation. Mucosal bivariate reference intervals were developed for MC production, including size (trophy) and calculated defence activity (plasia) in the skin and gills of Atlantic salmon, to contrast new measurements against historical data patterns. The application of mucosal reference intervals demonstrates that stress from parasites and treatments can manifest as changes in mucosal architecture, as evidenced by MC hypertrophy and hyperplasia within the gill lamellae. These reference intervals also facilitate comparisons with wild Atlantic salmon, revealing a somewhat higher MC level in farmed salmon gill lamellae. These findings suggest that MC hyperplasia and hypertrophy in the gills are stress/environmental responses in aquaculture. They also advocate for developing specific mucosal bivariate homeostatic reference intervals in aquaculture to improve fish health and welfare across all farmed species.

Unveiling osmoregulation and immunological adaptations in Eleutheronema tetradactylum gills through high-throughput single-cell transcriptome sequencing.

The fourfinger threadfin fish (Eleutheronema tetradactylum) is an economically significant species renowned for its ability to adapt to varying salinity environments, with gills serving as their primary organs for osmoregulation and immune defense. Previous studies focused on tissue and morphological levels, whereas ignored the cellular heterogeneity and the crucial gene information related to core cell subsets within E. tetradactylum gills. In this study, we utilized high-throughput single-cell RNA sequencing (scRNA-seq) to analyze the gills of E. tetradactylum, characterizing 16 distinct cell types and identifying unique gene markers and enriched functions associated within each cell type. Additionally, we subdivided ionocyte cells into four distinct subpopulations for the first time in E. tetradactylum gills. By employing weighted gene co-expression network analysis (WGCNA), we further investigated the cellular heterogeneity and specific response mechanisms to salinity fluctuant. Our findings revealed the intricate osmoregulation and immune functions of gill cells, highlighting their crucial roles in maintaining homeostasis and adapting to fluctuating salinity levels. This comprehensive cell-type atlas provides valuable insights into the species adaptive strategies, contributing to the conservation and management of this commercially significant fish as well as other euryhaline species.

Species-specific differences and temperature-dependence of Na+/K+-ATPase in freshwater mussels Anodonta anatina and Unio tumidus (Bivalvia: Unionidae).

The predicted global warming of surface waters can be challenging to aquatic ectotherms like freshwater mussels. Especially animals in northern temperate latitudes may face and physiologically acclimate to significant stress from seasonal temperature fluctuations. Na+/K+-ATPase enzyme is one of the key mechanisms that allow mussels to cope with changing water temperatures. This enzyme plays a major role in osmoregulation, energy control, ion balance, metabolite transport and electrical excitability. Here, we experimentally studied the effects of temperature on Na+/K+-ATPase activity of gills in two freshwater mussel species, Anodonta anatina and Unio tumidus. The study animals were acclimated to three ambient temperatures (+4, +14, +24 °C) and Na+/K+-ATPase activity was measured at those temperatures for each acclimation group. Both species had their highest gill Na+/K+-ATPase activity at the highest acclimation temperature. Na+/K+-ATPase activity of gills exhibited species-specific differences, and was higher in A. anatina than U. tumidus in all test groups at all test temperatures. Temperature dependence of Na+/K+-ATPase was confirmed in both species, being highest at temperatures between +4 and + 14 °C when Q10 values in the acclimation groups varied between 5.06 and 6.71. Our results underline the importance of Na+/K+-ATPase of gills for the freshwater mussels in warming waters. Because Na+/K+-ATPase is the driving force behind ciliary motion, our results also suggest that in warming waters A. anatina may be more tolerant at sustaining vigorous ciliary action (associated with elevated respiration rates and filter-feeding) than U. tumidus. Overall, our results indicate great flexibility of the mussel's ecophysiological characteristics as response to changing conditions.

Increased ingestion and toxicity of polyamide microplastics in Nile tilapia with increase of salinity.

Microplastics pollution and salinity intrusion in freshwater ecosystem is one of the worldwide climate change consequences those have negative impacts on the physiology of aquatic organisms. Hence, a 15-day experiment was carried out where Nile tilapia (Oreochromis niloticus) was exposed to different salinity gradients i.e. 0 ‰, 3 ‰, 6 ‰, 9 ‰, and 12 ‰ alone and along with 10 mg/L polyamide microplastics (PA-MP) in order to measure its effects on the hematology, gill, and intestinal morphology. The results exhibited that all the fish treated with PA-MP ingested microplastics and the quantity of accumulation was significantly greater in higher salinity gradients (9 ‰ and 12 ‰). In addition, the PA-MP treated fish showed increased glucose level and at the same time reduced hemoglobin concentration with the increase of salinity. The percentages of abnormalities in erythrocytes both cellular (twin, teardrop and spindle shaped) and nuclear (notched nuclei, nuclear bridge and karyopyknosis) significantly enhanced with PA-MP exposure again in higher salinity treatments (9 ‰ and 12 ‰). The principal component analysis (PCA) exhibited that the addition of 10 mg/L PA-MP negatively affected the hematology of Nile tilapia than that of salinity treatments alone. Besides, the exposure of PA-MP in 9 ‰ and 12 ‰ salinity gradients escalated the severity of histological damages in gills and intestine. Overall, this experiment affirms that the increase of salinity enhanced the microplastics ingestion and toxicity in Nile tilapia, therefore, PA-MP possibly is addressed as additional physiological stressors along with increased salinity gradients in environment.

From Personal Care to Coastal Concerns: Investigating Polyethylene Glycol Impact on Mussel's Antioxidant, Physiological, and Cellular Responses.

Pharmaceutical and personal care products (PPCPs) containing persistent and potentially hazardous substances have garnered attention for their ubiquitous presence in natural environments. This study investigated the impact of polyethylene glycol (PEG), a common PPCP component, on Mytilus galloprovincialis. Mussels were subjected to two PEG concentrations (E1: 0.1 mg/L and E2: 10 mg/L) over 14 days. Oxidative stress markers in both gills and digestive glands were evaluated; cytotoxicity assays were performed on haemolymph and digestive gland cells. Additionally, cell volume regulation (RVD assay) was investigated to assess physiological PEG-induced alterations. In the gills, PEG reduced superoxide dismutase (SOD) activity and increased lipid peroxidation (LPO) at E1. In the digestive gland, only LPO was influenced, while SOD activity and oxidatively modified proteins (OMPs) were unaltered. A significant decrease in cell viability was observed, particularly at E2. Additionally, the RVD assay revealed disruptions in the cells subjected to E2. These findings underscore the effects of PEG exposure on M. galloprovincialis. They are open to further investigations to clarify the environmental implications of PPCPs and the possibility of exploring safer alternatives.

Hypoxia in the Blue Mussel Mytilus chilensis Induces a Transcriptome Shift Associated with Endoplasmic Reticulum Stress, Metabolism, and Immune Response.

The increase in hypoxia events, a result of climate change in coastal and fjord ecosystems, impacts the health and survival of mussels. These organisms deploy physiological and molecular responses as an adaptive mechanism to maintain cellular homeostasis under environmental stress. However, the specific effects of hypoxia on mussels of socioeconomic interest, such as Mytilus chilensis, are unknown. Using RNA-seq, we investigated the transcriptomic profiles of the gills, digestive gland, and adductor muscle of M. chilensis under hypoxia (10 days at 2 mg L-1) and reoxygenation (10 days at 6 mg L-1). There were 15,056 differentially expressed transcripts identified in gills, 11,864 in the digestive gland, and 9862 in the adductor muscle. The response varied among tissues, showing chromosomal changes in Chr1, Chr9, and Chr10 during hypoxia. Hypoxia regulated signaling genes in the Toll-like, mTOR, citrate cycle, and apoptosis pathways in gills, indicating metabolic and immunological alterations. These changes suggest that hypoxia induced a metabolic shift in mussels, reducing reliance on aerobic respiration and increasing reliance on anaerobic metabolism. Furthermore, hypoxia appeared to suppress the immune response, potentially increasing disease susceptibility, with negative implications for the mussel culture industry and natural bed populations. This study provides pivotal insights into metabolic and immunological adaptations to hypoxia in M. chilensis, offering candidate genes for adaptive traits.

Mangrovimonas cancribranchiae sp. nov., a novel bacterial species associated with the gills of the fiddler crab Cranuca inversa (Brachyura, Ocypodidae) from Red Sea mangroves.

Two bacteria, UG2_1T and UG2_2, were isolated from the gill tissues of the mangrove fiddler crab Cranuca inversa collected on the east coast of the Red Sea (Thuwal, Saudi Arabia). The cells are Gram-negative, rod-shaped, orange-pigmented, motile by gliding with no flagella, strictly aerobic, and grow at 20-37 °C (optimum, 28-35 °C), at pH 5.0-9.0 (optimum, pH 6.0-7.0), and with 1-11 % (w/v) NaCl (optimum, 2-4 %). They were positive for oxidase and catalase activity. Phylogenetic analysis based on 16S rRNA gene sequences indicated that isolates UG2_1T and UG2_2 belong to the genus Mangrovimonas, showing the highest similarity to Mangrovimonas spongiae HN-E26T (99.4 %). Phylogenomic analysis based on the whole genomes, independently using 49 and 120 concatenated genes, showed that strains UG2_1T and UG2_2 formed a monophyletic lineage in a different cluster from other type strain species within the genus Mangrovimonas. The genome sizes were 3.08 and 3.07 Mbp for UG2_1T and UG2_2, respectively, with a G+C content of 33.8 mol% for both strains. Values of average nucleotide identity and digital DNA-DNA hybridization between the strains and closely related species were 91.0 and 43.5 %, respectively. Chemotaxonomic analysis indicated that both strains had iso-C15 : 0 and iso-C15 : 1 G as dominant fatty acids, and the primary respiratory quinone was identified as MK-6. The major polar lipids comprised phosphatidylethanolamine, one unidentified glycolipid, one unidentified phospholipid, two unidentified aminolipids, and four unidentified lipids. Based on phylogenetic, phylogenomic, genome relatedness, phenotypic, and chemotaxonomical data, the two isolates represent a novel species within the genus Mangrovimonas, with the proposed name Mangrovimonas cancribranchiae sp. nov., and the type strain UG2_1T (=KCTC 102158T=DSM 117025T).

Transcriptomic and histologic analyses preliminarily reveal the immune-metabolic response mechanism to saline-alkaline in large yellow croaker (Larimichthys crocea).

There are large areas of saline-alkaline waters worldwide, the utilization of which would greatly enhance the development of aquaculture productivity. To elucidate the regulatory mechanisms underlying the adaptation of large yellow croaker (Larimichthys crocea) to saline-alkaline water, this study analyzed the growth performance, tissue histology, and gills transcriptome profiles of L. crocea in both seawater (CK) and saline-alkaline water (EX) groups. Growth indices statistics revealed that L. crocea can adapt to saline-alkaline water, with growth performance comparable to that of the CK group. Histological examination revealed partial cellular detachment and structural relaxation in the gills tissue of the EX group, while liver and kidney tissues appeared normal. Transcriptome analysis revealed 3821 differentially expressed genes (DEGs), with 1541 DEGs up-regulated and 2280 DEGs down-regulated. GO enrichment analysis indicated that up-regulated DEGs were enriched in terms related to metabolite production during biological activities, while down-regulated DEGs were associated with terms related to maintaining cellular activities. KEGG enrichment analysis revealed that up-regulated DEGs were enriched in pathways related to the synthesis and metabolism of amino acids and lipids, such as the PPAR signaling pathway and glutathione metabolism. The down-regulated DEGs were predominantly enriched in immune-related signaling pathways, including the Toll-like receptor signaling pathway and NOD-like receptor signaling pathway. Further analysis revealed that genes such as lipoprotein lipase A (lpla), branched-chain amino acid aminotransferase 2 (bcat2), interleukin 8 (il8), interleukin 10 (il10), and interferon regulatory factor 7 (irf7) were involved in the adaptation of L. crocea to saline-alkaline water culture conditions. This study provides a basis for understanding the adaptability of large yellow croaker to saline-alkaline water and lays the foundation for the rational utilization of fishery water resources.

The Tilapia Cyst Tissue Enclosing the Proliferating Myxobolus bejeranoi Parasite Exhibits Cornified Structure and Immune Barrier Function.

Myxozoa, a unique group of obligate endoparasites within the phylum Cnidaria, can cause emerging diseases in wild and cultured fish populations. Recently, the myxozoan Myxobolus bejeranoi has been identified as a prevalent pathogen infecting the gills of cultured hybrid tilapia, leading to systemic immune suppression and considerable mortality. Here, we employed a proteomic approach to examine the impact of M. bejeranoi infection on fish gills, focusing on the structure of the granulomata, or cyst, formed around the proliferating parasite to prevent its spread to surrounding tissue. Enrichment analysis showed increased immune response and oxidative stress in infected gill tissue, most markedly in the cyst's wall. The intense immune reaction included a consortium of endopeptidase inhibitors, potentially combating the myxozoan arsenal of secreted proteases. Analysis of the cyst's proteome and histology staining indicated that keratin intermediate filaments contribute to its structural rigidity. Moreover, we uncovered skin-specific proteins, including a grainyhead-like transcription factor and a teleost-specific S100 calcium-binding protein that may play a role in epithelial morphogenesis and cysts formation. These findings deepen our understanding of the proteomic elements that grant the cyst its distinctive nature at the critical interface between the fish host and myxozoan parasite.

Marteilia pararefringens infections are more frequent than revealed by the Norwegian surveillance programme, highlighting the need for its improvement.

Norway had historically been considered free of marteiliosis in bivalves since the disease surveillance programme began in 1995. However, in 2016, Marteilia pararefringens, a protistan parasite of mussels Mytilus spp., was described in a heliothermic lagoon-a poll-previously used to produce flat oyster spat. To study whether the parasite was introduced, and possibly spread, via the historical flat oyster networks on the south and west coast, we sampled aquaculture polls that were part of different networks of farmers and wild, natural polls with no aquaculture activity. Additionally, we sampled mussel banks influenced by polls and sheltered bays that could have a similar environment to that of polls. We identified 7 sites with M. pararefringens-infected mussel populations: 5 were polls used in flat oyster production and 2 were in fjord areas with no known connection to any bivalve aquaculture. Prevalence ranged between 2 and 88%. At one site, Trysfjorden, we found M. pararefringens in atypical organs, including the gills, mantle, and intestine. Marteilia-like cells were also observed in the epithelium, lumen, and surrounding connective tissue of metanephridia and in the sinus of the anterior retractor muscle. Our results demonstrate that the parasite is more widespread than previously thought and is neither isolated to polls nor connected directly to aquaculture activity. Lastly, our findings highlight the need for an improved sampling strategy in surveillance programmes to detect marteiliosis in mussels.

Hypoxia stress alters gene expression in the gills and spleen of greater amberjack (Serioladumerili).

Greater amberjack (Seriola dumerili) is a fish species that has significant economic and cultural value. It has a large size and grows rapidly. However, the intolerance to hypoxia poses a major obstacle to the growth of its aquaculture industry. This study focuses on the gills and spleen, two organs closely associated with the response to acute hypoxic stress. By simulating the acute hypoxic environment and using Illumina RNA-Seq technology, we explored the gills and spleen transcriptome changes in the acute hypoxia intolerant and tolerant groups of greater amberjack. It was discovered that gill tissues in the tolerant group may maintain a stable intracellular energy supply by promoting glycolysis and ß-oxidation compared to the intolerant group. Additionally, it promotes angiogenesis, enhances the ability to absorb dissolved oxygen, and accelerates oxygen transport to the mitochondria, adapting to the hypoxic environment. Anti-apoptotic genes were up-regulated in gill tissues in the tolerant group compared to the intolerant group, thereby minimizing the damage of acute hypoxia. On the other hand, the spleen inhibited the TCA and energy-consuming lipid synthesis pathways to supply energy under acute hypoxic stress. Pro-angiogenic genes were down-regulated in the spleen of individuals in the tolerant group compared to the intolerant group, which may be related to organ function. The suppressed reactive oxygen species (ROS) production and the impaired immune response function of the spleen were also found. The study explored the acute hypoxic stress response in greater amberjack and the molecular mechanisms underlying its tolerance to acute hypoxia.

Protective effect of feed additive ferulic acid on respiratory depression and oxidation imbalance of carp induced by pesticide difenoconazole via ROS/NF-κB/NLRP3 axis.

Difenoconazole (DFZ), classified as a "low-toxicity pesticide," has seen widespread application in recent years. Nevertheless, the non-target toxicity of the substance, particularly towards aquatic creatures, has generated considerable apprehension. The anti-inflammatory and antioxidant effects of Ferulic Acid (FA) have attracted considerable study in this particular setting. This study established a chronic exposure model to DFZ and investigated the protective effects of FA on chronic respiratory inhibition leading to gill damage in freshwater carp. Histological analyses via HE staining indicated that FA effectively alleviated gill tissue damage induced by chronic DFZ exposure. The qRT-PCR results showed that the addition of FA reduced the expression of IL-1ß, IL-6 and TNF-α while boosting the expression of IL-10 and TGF-ß1. Biochemical analyses and DHE staining revealed that FA reduced MDA levels and increased CAT and GSH activities, along with T-AOC, decreased ROS accumulation in response to chronic DFZ exposure. The results obtained from Western blotting analysis demonstrated that the addition of FA effectively suppressed the activation of the NF-κB signalling pathway and the NLRP3 inflammasome pathway in the gills subjected to prolonged exposure to DFZ. In summary, FA ameliorated gill tissue inflammation and blocked ROS accumulation in carp exposed to chronic DFZ, mitigating tissue inflammation and restoring redox homeostasis through the NF-κB-NLRP3 signaling pathway. Hence, the application of FA has been found to be efficacious for improving respiratory inhibition and mitigating gill tissue inflammation and oxidative stress resulting from DFZ pollution in aquatic habitats.

Coping with salinity extremes: Gill transcriptome profiling in the black-chinned tilapia (Sarotherodon melanotheron).

Steeper and sometimes extreme salinity gradients increasingly affect aquatic organisms because of climate change. Hypersalinity habitats demand powerful physiological adaptive strategies. Few teleost species have the capacity to spend their whole life cycle in salinities way over seawater levels. Focusing on the multifunctional gill, we unraveled the tilapia S. melanotheron key strategies to cope with different environmental conditions, ranging from freshwater up to hypersaline habitats. De novo transcriptome assembly based on RNAseq allowed for the analysis of 40,967 annotated transcripts among samples collected in three wild populations at 0, 40 and 80 ‰. A trend analysis of the expression patterns revealed responses across the salinity gradient with different gene pathways involved. Genes linked to ion transport, pH regulation and cell surface receptor signaling were mainly upregulated in the high salinity habitat. We identified tight junction proteins that were critical in high salinity habitats and that were different from the well-known tightening junctional proteins identified and expressed in fresh water. Expression profiles also suggest a change in the vascular tone that could be linked to an osmorespiratory compromise not only in fresh water, but also in high salinity environments. A striking downregulation of genes linked to the immune system and to the heat shock response was observed suggesting an energetic trade-off between immunity and acclimation/adaptation in the hypersaline habitat. The high expression of transcripts coding for immune and heat shock response in the freshwater habitat suggests the establishment of powerful mechanisms to protect gills from environmental threats and to maintain protein integrity. Non-directional expression trends were also detected with an upregulation of genes only in the hypersaline habitat (80 ‰) or only in the marine habitat (40 ‰). Unravel physiological strategies in S. melanotheron populations will help to better understand the molecular basis of fish euryhalinity in salinity-contrasted environments.

Incidence of microplastics in Indian anchovy Stolephorus indicus from Tuticorin, Southeast coast of India.

In the present study, the occurrence of microplastics (MPs) in the gut, gill, and muscle of edible fish Stolephorus indicus sampled from Tuticorin coastal regions of Tamilnadu, India was investigated. We recorded a total of 689 MPs which includes 510 and 179 MPs from males and females respectively. The total abundance of MPs was significantly (P < 0.05) higher in the gut followed by gills and muscle. The sex-wise distribution of average MPs showed high in the females' gut and compared to that in males. Further, the length wise distribution of MPs was higher in the muscle in both male and female fish, followed by other organs. The predominance of MPs in tissues were transparent and blue colour with fibers and fragments in both males and females. Besides, polyethylene terephthalate and nylon were evidenced by the Fourier-transform infrared spectroscopy spectrum in all organs of fishes.

The evolution of larvae in temnospondyls and the stepwise origin of amphibian metamorphosis.

The question of what the ancient life cycle of tetrapods was like forms a key component in understanding the origin of land vertebrates. The existence of distinct larval forms, as exemplified by many lissamphibians, and their transformation into adults is an important aspect in this field. The temnospondyls, the largest clade of Palaeozoic-Mesozoic non-amniote tetrapods, covered a wide ecomorphological range from fully aquatic to terrestrial taxa. In various species, rich ontogenetic data have accumulated over the past 130 years, permitting the study of early phases of temnospondyl development. In temnospondyls, eight ontogenetic phases have been identified in which the skeleton formed. In branchiosaurids and the eryopiform Sclerocephalus, large parts of the ossification sequence are now known. Most taxa in which small specimens are preserved had aquatic larvae with external gills that superficially resemble larval salamanders. In the edopoids, dvinosaurs, and eryopiforms, the larvae developed slowly, with incompletely ossified axial and appendicular skeletons, but possessed a fast-developing dermal skull with strong teeth. Irrespective of adult terrestriality or a fully aquatic life, there was no drastic transformation during later ontogeny, but a slow and steady acquisition of adult features. In dissorophoids, the limbs developed at a much faster pace, whereas skull formation was slowed down, especially in the amphibamiforms, and culminating in the neotenic Branchiosauridae. In the zatracheid Acanthostomatops, slow but profound transformation led to a fully terrestrial adult. The basal dissorophoid Stegops retained rapid development of dermal skull bones and established a fully dentigerous, strongly ossified palate early. In Micromelerpeton, formation of the last skull bones was slightly delayed and metamorphosis remained a long and steady phase of morphological transformations. In amphibamiforms, metamorphosis became more drastic, with an increasing number of events packed into a short phase of ontogeny. This is exemplified by Apateon, Platyrhinops, and Amphibamus in which this condensation was maximised. We distinguish three different types of metamorphosis (morphological, ecological and drastic) that evolved cumulatively in early tetrapods and within temnospondyls.

Toxicity of Ammonia Stress on the Physiological Homeostasis in the Gills of Litopenaeus vannamei under Seawater and Low-Salinity Conditions.

Ammonia is a major water quality factor influencing the survival and health of shrimp, among which the gill is the main effector organ for ammonia toxicity. In this study, we chose two types of Litopenaeus vannamei that were cultured in 30‱ seawater and domesticated in 3‱ low salinity, respectively, and then separately subjected to ammonia stress for 14 days under seawater and low-salinity conditions, of which the 3‱ low salinity-cultured shrimp were domesticated from the shrimp cultured in 30‱ seawater after 27 days of gradual salinity desalination. In detail, this study included four groups, namely the SC group (ammonia-N 0 mg/L, salinity 30‱), SAN group (ammonia-N 10 mg/L, salinity 30‱), LC group (ammonia-N 0 mg/L, salinity 3‱), and LAN group (ammonia-N 10 mg/L, salinity 3‱). The ammonia stress lasted for 14 days, and then the changes in the morphological structure and physiological function of the gills were explored. The results show that ammonia stress caused the severe contraction of gill filaments and the deformation or even rupture of gill vessels. Biochemical indicators of oxidative stress, including LPO and MDA contents, as well as T-AOC and GST activities, were increased in the SAN and LAN groups, while the activities of CAT and POD and the mRNA expression levels of antioxidant-related genes (nrf2, cat, gpx, hsp70, and trx) were decreased. In addition, the mRNA expression levels of the genes involved in ER stress (ire1 and xbp1), apoptosis (casp-3, casp-9, and jnk), detoxification (gst, ugt, and sult), glucose metabolism (pdh, hk, pk, and ldh), and the tricarboxylic acid cycle (mdh, cs, idh, and odh) were decreased in the SAN and LAN groups; the levels of electron-transport chain-related genes (ndh, cco, and coi), and the bip and sdh genes were decreased in the SAN group but increased in the LAN group; and the level of the ATPase gene was decreased but the cytc gene was increased in the SAN and LAN groups. The mRNA expression levels of osmotic regulation-related genes (nka-ß, ca, aqp and clc) were decreased in the SAN group, while the level of the ca gene was increased in the LAN group; the nka-α gene was decreased in both two groups. The results demonstrate that ammonia stress could influence the physiological homeostasis of the shrimp gills, possibly by damaging the tissue morphology, and affecting the redox, ER function, apoptosis, detoxification, energy metabolism, and osmoregulation.

The origins of gas exchange and ion regulation in fish gills: evidence from structure and function.

Gill function in gas exchange and ion regulation has played key roles in the evolution of fishes. In this review, we summarize data from the fields of palaeontology, developmental biology and comparative physiology for when and how the gills first acquired these functions. Data from across disciplines strongly supports a stem vertebrate origin for gas exchange structures and function at the gills with the emergence of larger, more active fishes. However, the recent discovery of putative ionocytes in extant cephalochordates and hemichordates suggests that ion regulation at gills might have originated much earlier than gas exchange, perhaps in the ciliated pharyngeal arches in the last common ancestor of deuterostomes. We hypothesize that the ancestral form of ion regulation served a filter-feeding function in the ciliated pharyngeal arches, and was later coopted in vertebrates to regulate extracellular ion and acid-base balance. We propose that future research should explore ionocyte homology and function across extant deuterostomes to test this hypothesis and others in order to determine the ancestral origins of ion regulation in fish gills.

Effects of Ferulic Acid on Respiratory Metabolism, Oxidative Lesions, and Apoptotic Parameters in Gills and Red Blood Cells of Carp (Cyprinus carpio Var. Jian) Response to Copper.

In sustainable aquaculture systems, copper sulfate (CuSO4) is widely applied as a disinfectant to control parasitic infections and algal growth. However, aquatic organisms may suffer from exposure to excessive concentrations of Cu. Elevated Cu concentrations could activate damage to the respiratory functions of aquatic animals. Thus, this study explored the effects exerted by ferulic acid (FA) on respiratory metabolism, oxidation-related lesions, and the apoptosis parameters of the gills and red blood cells in copper sulfate pentahydrate (CuSO4·5H2O)-treated carp (Cyprinus carpio var. Jian). When the 30-day feeding experiment was completed, the carp were exposed to 12.5 µM of Cu for 4 days. The results indicated that the Cu decreased the oxygen consumption and ammonia excretion rates in the carp, reduced the metabolic- and antioxidant-related enzyme activities and glutathione levels in the carp, and enhanced the caspase activities and reactive oxygen species and malondialdehyde levels in the gills of the carp. Moreover, in addition to the changes in the above parameters, the Cu decreased the cell numbers and hemoglobin concentrations and increased the phosphatidylserine exposure and cytochrome c levels in the red blood cells of the carp. These results demonstrate that Cu is capable of decreasing respiratory metabolism and increasing oxidation-related lesions and apoptosis inside the gills and red blood cells of the fish. However, dietary FA quenched the Cu-induced apoptosis and oxidative lesions by reversing the same biomarker indicators, thereby suppressing the Cu-induced decrease in respiratory metabolism. Thus, FA can be used as a suppressor of Cu stress in fish.

Pesticide-induced alterations in zebrafish (Danio rerio) behavior, histology, DNA damage and mRNA expression: An integrated approach.

To assess the impact of glyphosate and 2,4-D herbicides, as well as the insecticide imidacloprid, both individually and in combination, the gills of adult zebrafish were used due to their intimate interaction with chemicals diluted in water. Bioassays were performed exposing the animals to the different pesticides and their mixture for 96 h. The behavior of the fish was analyzed, a histological examination of the gills was carried out, and the genotoxic effects were also analyzed by means of the comet assay (CA) and the change in the expression profiles of genes involved in the pathways of the oxidative stress and cellular apoptosis. The length traveled and the average speed of the control fish, compared to those exposed to the pesticides and mainly those exposed to the mixture, were significantly greater. All the groups exposed individually exhibited a decrease in thigmotaxis time, indicating a reduction in the behavior of protecting themselves from predators. Histological analysis revealed significant differences in the structures of the gill tissues. The quantification of the histological lesions showed mild lesions in the fish exposed to imidacloprid, moderate to severe lesions for glyphosate, and severe lesions in the case of 2,4-D and the mixture of pesticides. The CA revealed the sensitivity of gill cells to DNA damage following exposure to glyphosate, 2,4-D, imidacloprid and the mixture. Finally, both genes involved in the oxidative stress pathway and those related to the cell apoptosis pathway were overexpressed, while the ogg1 gene, involved in DNA repair, was downregulated.

Brobdingnagians and Goliaths: two forms of gigantism in fish.

Two forms of gigantism are differentiated in fish, Brobdingnagian and Goliathan gigantism, the former applying to populations whose individuals are all larger than is typical for the taxon, the latter to single individuals within a population. While Brobdingnagian gigantism is largely explained by various ecological and evolutionary rules, Goliathan gigantism is not. A mechanistic hypothesis is proposed which explains Goliathan gigantism in terms of the reduction of oxygen requirements of individual fish via moving to cooler temperatures and/or acquiring larger, more energy-dense prey, which enable them to get bigger, and, in the process, sometimes generate bimodal size distributions that may qualify as gradual forms between Goliathan and Brobdingnagian gigantism. This mechanism, which relies on the manner in which their gill surface area grows, is more likely to operate in fish that can get big in the first place than in fish that remain small.