Swim Bladder Inflation Research Articles

Swim bladder as a primary site of mycobacterial infection in Nothobranchius 'belly sliders'.

The swim bladder inflates early after fish hatching via its interconnection with the digestive tract (ductus pneumaticus). This interconnection may serve as a portal to foreign particles, including bacteria, causing deficiencies in primary swim bladder inflation. We histologically examined 134 African annual killifish (genus Nothobranchius) with secondary loss of swim bladder function ('belly sliders'). We demonstrate that these fish lost the ability of air regulation in their swim bladders likely due to Mycobacterium spp. infection at an individual-specific age. Nearly all examined belly sliders had thickened swim bladder walls, and their swim bladder was filled with material containing mycobacteria, cell debris, young monocytic cells and phagocyting macrophages. Mycobacterial infection was restricted to the swim bladder in juveniles, where mycobacteria likely enter the host through the ductus pneumaticus. Infection in adults was systemic and mycobacteria were present in all examined organs. Presence of mycobacteria in the epithelial lining and submucosal layers of the digestive tract of adults suggests that it may also serve as the entrance site of infection. We suspect 2 sources of Mycobacterium contamination: dietary (with bloodworms) and/or contaminated hatching substrate. These sources of contamination may be eliminated by use of laboratory dry feed and egg disinfection prior to hatching.

Perfluorooctanesulfonic Acid-Induced Toxicity on Zebrafish Embryos in the Presence or Absence of the Chorion.

Perfluorooctanesulfonic acid (PFOS) is a perfluorinated compound used in many industrial and consumer products. It has been linked to a broad range of adverse effects in several species, including zebrafish (Danio rerio). The zebrafish embryo is a widely used vertebrate model to elucidate potential adverse effects of chemicals because it is amenable to medium and high throughput. However, there is limited research on the full extent of the impact the chorion has on those effects. Results from the present study indicate that the presence of the chorion affected the timing and incidence of mortality as well as morphometric endpoints such as spinal curvature and swim bladder inflation in zebrafish embryos exposed to PFOS. Furthermore, removal of the chorion prior to exposure resulted in a lower threshold of sensitivity to PFOS for effects on transcriptional expression within the peroxisome proliferator–activated receptor (PPAR) nuclear signaling pathway. Perturbation of PPAR pathway gene expression can result in disruption of metabolic signaling and regulation, which can adversely affect development, energy availability, and survival. It can be concluded that removal of the chorion has significant effects on the timing and incidence of impacts associated with PFOS exposure, and more research is warranted to fully elucidate the protective role of the chorion and the critical timing of these events. Environ Toxicol Chem 2021;40:780–791. Published 2020. This article is a US Government work and is in the public domain in the USA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Evaluation and comparison of the mitochondrial and developmental toxicity of three strobilurins in zebrafish embryo/larvae.

Strobilurin fungicides have been frequently detected in aquatic environments and can induce mitochondrial toxicity to non-target aquatic organisms. However, the derived toxicity and subsequent mechanisms related to their adverse effects are not fully elucidated. In the present study, we compared the mitochondrial and developmental toxicity of azoxystrobin, pyraclostrobin, and trifloxystrobin using zebrafish embryo/larvae. The results showed that all three strobilurins inhibited mitochondrial and non-mitochondrial respiration (the potency is pyraclostrobin≈trifloxystrobin>azoxystrobin). Behavioral changes indicated that sublethal doses of pyraclostrobin and azoxystrobin caused hyperactivity of zebrafish larvae in dark cycles, whereas trifloxystrobin resulted in hypoactivity of zebrafish larvae. In addition, pyraclostrobin exposure impaired the inflation of swim bladder, and caused down-regulation of annexin A5 (anxa5) mRNA levels, and up-regulated transcript levels of pre-B-cell leukemia homeobox 1a (pbx1a); conversely, azoxystrobin and trifloxystrobin did not cause detectable effects with swim bladder inflation. Molecular docking results indicated that azoxystrobin had higher interacting potency with iodotyrosine deiodinase (IYD), prolactin receptor (PRLR), antagonistic conformation of thyroid hormone receptor β (TRβ) and glucocorticoid receptor (GR) compared to pyraclostrobin and trifloxystrobin; pyraclostrobin and azoxystrobin were more likely to interact with the antagonistic conformation of TRβ and GR, respectively. These results may partially explain the different effects observed in behavior and swim bladder inflation, and also point to potential endocrine disruption induced by these strobilurins. Taken together, our study revealed that all three strobilurins alter mitochondrial bioenergetics and cause developmental toxicity. However, the toxic phenotypes and underlying mechanisms of each chemical may differ, and this requires further investigation. Pyraclostrobin showed higher mitochondrial toxicity at lethal doses and higher developmental toxicity at sublethal doses compared to the two other strobilurins tested. These results provide novel information for toxicological study as well as risk assessment of strobilurin fungicides.

A comparison of developmental toxicity of brominated and halogen-free flame retardant on zebrafish

Brominated diphenyl ethers (BDEs) are halogenated flame retardants. Several concerns related to persistence and toxicity of BDEs have been resulted in a growing need of BDEs replacement. The use of halogen-free flame retardants (HFFR) has increased as a safer alternative, but little information is available on their toxic potential for environmental health and for developing organisms. Therefore, the aim of this study was to evaluate and compare the toxicity of three congeners of BDEs (BDE-47, BDE-99 and BDE-154) with an HFFR (aluminum diethylphosphinate, ALPI) on zebrafish (Danio rerio) by assessing endpoints of lethality, sub-lethality and teratogenicity at the earlier stages of development. The highest tested concentration of BDE-47 (12.1 mg/L) induced pericardium and yolk sac edemas that first appeared at 48 h post-fertilization (hpf) and then were mostly reabsorbed until 144 hpf. BDE-47 also showed a slight but non-significant tendency to affect swim bladder inflation. The rate of edemas increased in a concentration-dependent manner after exposure to BDE-99, but there were no significant differences. In addition, the congener BDE-99 also presented a slight and non-significant effect on swim bladder inflation, but only at the highest concentration tested. Regarding BDE-154 exposure, the rate of edemas and swim bladder inflation were not affected. Finally, in all ALPI exposure concentrations (0.003 up to 30 mg/L), no sub-lethal or teratogenic effects were observed on developing organisms until 96 hpf. Although further studies are needed, our results demonstrate that when comparing the developmental toxicity induced by flame retardants in zebrafish, the HFFR ALPI may be considered a more suitable alternative to BDE-47.

MORPHO-FUNCTIONAL AND DEVELOPMENTAL STUDY OF SWIM BLADDER IN PRE TO POST FLEXION STAGES LARVAE OF HIMALAYAN SNOW TROUT SCHIZOTHORAX PLAGIOSTOMUS (HECKEL) REARED IN ARTIFICIAL AND NATURAL CONDITIONS

Present study deals with histology, gross morphology of the larvae and its behavioural aspects to describe the progression of the development of swim bladder in pre to post flexion stages larvae of the Himalayan Snow Trout Schizothorax plagiostomus (Heckel) reared in laboratory as well as in natural site. It reveals a very significant information in respect to derivation, tissue differentiation, initial inflation as well as factors responsible for noninflation of swim bladder especially among laboratory reared larvae. At hatching (108-110 and 124-130 hours after fertilization in laboratory and natural site respectively), larvae measured 9.00 mm and 10.5 mm in laboratory and natural site respectively, and their body cavity was mostly occupied with a huge amount of yolk. The mouth, pharynx and esophagus were impervious till 3rd day post hatching (dph). Primordial swim bladder appeared on 3rd.dph as a cluster of mesenchymal cells evaginating from the posterior dorsal surface of the differentiating esophagus. Later on it grows toward the caudal direction below the differentiating vertebral column and kidney. Initial swim bladder inflation occurred by 6-dph when larvae attained 12.50–13.50 mm length, with the onset of first exogenous feeding. During this phase a mucous like substance was also observed in the pneumatic duct as well as lumen of swim bladder of some laboratory reared larvae and later on they got mortality. By 8-dph well differentiated and inflated swim bladder becomes externally visible and pneumatic duct extended to join the dorsal wall of esophagus. A number of biotic and abiotic factors were found associated with preventing swim bladder inflation during Pre flexion to Post flexion stages.

The agrochemical S-metolachlor disrupts molecular mediators and morphology of the swim bladder: Implications for locomotor activity in zebrafish (Danio rerio)

Metolachlor herbicides are derived from the chloroacetamide chemical family of which there are the S- and R-metolachlor isomers. S-metolachlor is a selective herbicide that inhibits cell division and mitosis via enzyme interference. The herbicide is used globally in agriculture and studies report adverse effects in aquatic organisms; however, there are no studies investigating sub-lethal effects of S-metolachlor on swim bladder formation, mitochondrial ATP production, nor light–dark preference behaviors in fish. These endpoints are relevant for larval locomotor activity and metabolism. To address these knowledge gaps, we exposed zebrafish embryos/larvae to various concentrations of S-metolachlor (0.5–50 µM) over early development. S-metolachlor affected survival, hatching percentage, and increased developmental deformities at concentrations of 50 µM and above. Exposure levels as high as 200 µM for 24 and 48 h did not alter oxygen consumption rates in zebrafish, and there were no changes detected in endpoints related to mitochondrial oxidative phosphorylation. We observed impairment of swim bladder inflation at 50 µM in 6 dpf larvae. To elucidate mechanisms related to this, we measured relative transcript abundance for genes associated with the swim bladder (smooth muscle alpha (α)-2 actin, annexin A5, pre-B-cell leukemia homeobox 1a). Smooth muscle alpha (α)-2 actin mRNA levels were reduced in fish exposed to 50 µM while annexin A5 mRNA levels were increased in abundance, corresponding to reduced swim bladder size in larvae. A visual motor response test revealed that larval zebrafish exhibited some hyperactivity in the light with exposure to the herbicide and only the highest dose tested (50 µM) resulted in hypoactivity in the dark cycle. Regression analysis indicated that there was a positive relationship between surface area of the swim bladder and distance traveled, and the size of the swim bladder explained ~10–14% in the variation for total distance moved. Lastly, we tested larvae in a light dark preference test, and we did not detect any altered behavioral response to any concentration tested. Here we present new data on sublethal endpoints associated with exposure to the herbicide S-metolachlor and demonstrate that this chemical may disrupt transcripts associated with swim bladder formation and morphology, which could ultimately affect larval zebrafish activity. These data are expected to contribute to further risk assessment guidelines for S-metolachlor in aquatic ecosystems.

Effects of tank shapes and aerations on survival, growth and swim bladder inflation of red seabream Pagrus major larvae

This study aimed to seek for the optimal condition for small-scale larviculture of red seabream Pagrus major larvae. We examined the effects of tank shapes and aerations, which were assumed to influence the larval survival, growth and swim bladder inflation of P. major larvae. Seawater (50-l) was filled into three cylindrical (CT: 1.7 × 103 cm2 water surface area, 30 cm deep) and six rectangular (RT: 1.8 × 103 cm2 water surface area, 28 cm deep) tanks. One air stone with 100 ml/min aeration rate was set at the bottom center of three CT and RT (RT1AS), and two air stones with 50 ml/min aeration rate were set at the half bottom center of three RT (RT2AS). Five hundred eggs were distributed into each experimental tank. Rotifers were fed to larvae at 10 individuals/mL on 3 days post hatching (dph) and their distribution in tanks were measured. Survival rate at 14 dph in CT (54.7 ± 11.0 %) and RT1AS (55.3 ± 6.0 %) were significantly higher than that in RT2AS (29.6 ± 9.3 %, p < 0.05). However, the growth of larvae was not significantly different between tank shapes and aerators. Swimbladder inflation rates were not different between tank shapes and aerations, however, CT (58.9±28.3 %) showed lower trend (RT1AS 94.4±6.9 %, RT2AS 92.2±10.7 %). Rotifer distribution in tanks was higher at tank bottom (p < 0.05). Low flow regions were observed along the side walls of the tanks and bottom areas in CT and RT1AS due to a single-pair vortex system and formed at the center (between air stones) and from the air stone to the tank walls in RT2AS due to two single-pair vortex systems. These low-flow areas were coincided with higher rotifer distribution areas at the tank bottom indicating that measuring rotifer density can estimate the flow in a tank. We recommend the rectangular tank with one air stone system for red seabream larvae.

Finding a rare gem: Identification of a wild biological unit with high potential for European perch larviculture

Potential for aquaculture can differ among allopatric wild populations of a species of interest. This makes relevant to seek best candidates for fish farming at the intraspecific level. Here, we compare the aquaculture potential among allopatric population groups of the European perch, a species of interest for fish farming. More specifically, we aim at finding population groups with the best performance in larviculture through an integrative approach that allows considering geographic differentiation in domestication processes. A multi-function/trait assessment was performed on three genetically differentiated groups of European perch populations: (i) Danube, (ii) Eastern Europe, and (iii) European Plain. A geographic differentiation was highlighted for six important traits for perch larviculture: survival rate, swim bladder inflation rate, deformity rate, length at hatching, mean of interindividual distances, and change in activity following a stress event. Along with fish farmer-advice-based weighting of the traits, the calculation of an aquaculture potential score allowed identifying the populations from the Danube region as the most interesting to potentially overcome current bottlenecks in European perch larviculture.

Folic acid reduces the ethanol-induced morphological and behavioral defects in embryonic and larval zebrafish (Danio rerio) as a model for fetal alcohol spectrum disorder (FASD)

The objective of this work was to determine whether folic acid (FA) reduces the embryonic ethanol (EtOH) exposure induced behavioral and morphological defects in our zebrafish fetal alcohol spectrum disorder (FASD) model. Teratogenic effects, mortality, the excitatory light-dark locomotion (ELD), sleep (SL), thigmotaxis (TH), touch sensitivity (TS), and optomotor response (OMR) tests were evaluated in larvae (6–7 days post-fertilization) using four treatment conditions: Untreated, FA, EtOH and EtOH + FA. FA reduced morphological defects on heart, eyes and swim bladder inflation seen in EtOH exposed fish. The larvae were more active in the dark than in light conditions, and EtOH reduced the swimming activity in the ELD test. EtOH affected the sleep pattern, inducing several arousal periods and increasing inactivity in zebrafish. FA reduces these toxic effects and produced more consistent inactivity during the night, reducing the arousal periods. FA also prevented the EtOH-induced defects in thigmotaxis and optomotor response of the larvae. We conclude that in this FASD model, EtOH exposure produced several teratogenic and behavioral defects, FA reduced, but did not totally prevent, these defects. Understanding of EtOH-induced behavioral defects could help to identify new therapeutic or prevention strategies for FASD.

Improving pikeperch larviculture by combining environmental, feeding and populational factors

Pikeperch (Sander lucioperca) has a high potential for inland aquaculture diversification in Europe. Bottlenecks (i.e. low survival, cannibalism and deformity rates) hamper further expansion of pikeperch culture, because of the weak production performances at the nursery level. To improve the production of pikeperch juveniles under recirculation system we used a pilot scale larval rearing system (700 L tanks) and multifactorial designs. Three successive larval rearing trials (duration: 35-49 days) were conducted to identify the best combination of environmental, feeding and population factors. Considering the main significant effects observed on survival, growth, swim bladder inflation rates and biomass gain, a favourable combination of twelve factor (F) modalities was proposed (F1- initial density: 100 larvae.L-1, F2- no sorting of fish jumper, F3- no sibling population, F4- eggs from large females, F5- discontinuous feeding, F6- no co-feeding, F7- light intensity: 50 lx, F8- beginning of the weaning at 16 dph (days post-hatching), F9- weaning duration: 9 days, F10- water renewal rate of 100 % per hour, F11- tank cleaning during morning and F12- tank bottom-up water current). A final validation step was realized over a last trial (seven replicates, duration: 49 days), and validated with the best productive results obtained over the global experimental period (2015-2018). These results were: a final body weight of 815.64 ± 95.34 mg, a survival rate of 16.9 ± 1.7 %, a specific growth rate of 15.1 ± 5.9 %.d-1, a final fish biomass of 9.55 ± 0.23 kg, a swim bladder inflation rate of 92.6 ± 3.2 % and a food conversion rate of 0.65 ± 0.02 (dry food). The final stocking density was 13.6 kg.m-3 of rearing volume. Authors were able to validate and provide a reliable basic protocol for pikeperch larval rearing using recirculating units.

Effect of Thyroperoxidase and Deiodinase Inhibition on Anterior Swim Bladder Inflation in the Zebrafish.

A set of adverse outcome pathways (AOPs) linking inhibition of thyroperoxidase and deiodinase to impaired swim bladder inflation in fish has recently been developed. These AOPs help to establish links between these thyroid hormone (TH) disrupting molecular events and adverse outcomes relevant to aquatic ecological risk assessment. Until now, very little data on the effects of TH disruption on inflation of the anterior chamber (AC) of the swim bladder were available. The present study used zebrafish exposure experiments with three model compounds with distinct thyroperoxidase and deiodinase inhibition potencies (methimazole, iopanoic acid, and propylthiouracil) to evaluate this linkage. Exposure to all three chemicals decreased whole body triiodothyronine (T3) concentrations, either through inhibition of thyroxine (T4) synthesis or through inhibition of Dio mediated conversion of T4 to T3. A quantitative relationship between reduced T3 and reduced AC inflation was established, a critical key event relationship linking impaired swim bladder inflation to TH disruption. Reduced inflation of the AC was directly linked to reductions in swimming distance compared to controls as well as to chemical-exposed fish whose ACs inflated. Together the data provide compelling support for AOPs linking TH disruption to impaired AC inflation in fish.

PRPS polymerization influences lens fiber organization in zebrafish.

The self-assembly of metabolic enzymes into filaments or foci highlights an intriguing mechanism for the regulation of metabolic activity. Recently, we identified the conserved polymerization of phosphoribosyl pyrophosphate synthetase (PRPS), which catalyzes the first step in purine nucleotide synthesis, in yeast and cultured mammalian cells. While previous work has revealed that loss of PRPS activity regulates retinal development in zebrafish, the extent to which PRPS filament formation affects tissue development remains unknown. By generating novel alleles in the zebrafish PRPS paralogs, prps1a and prps1b, we gained new insight into the role of PRPS filaments during eye development. We found that mutations in prps1a alone are sufficient to generate abnormally small eyes along with defects in head size, pigmentation, and swim bladder inflation. Furthermore, a loss-of-function mutation that truncates the Prps1a protein resulted in the failure of PRPS filament assembly. Lastly, in mutants that fail to assemble PRPS filaments, we observed disorganization of the actin network in the lens fibers. The truncation of Prps1a blocked PRPS filament formation and resulted in a disorganized lens fiber actin network. Altogether, these findings highlight a potential role for PRPS filaments during lens fiber organization in zebrafish.

Evaluation of Developmental Toxicity, Developmental Neurotoxicity, and Tissue Dose in Zebrafish Exposed to GenX and Other PFAS.

Background:Per- and polyfluoroalkyl substances (PFAS) are a diverse class of industrial chemicals with widespread environmental occurrence. Exposure to long-chain PFAS is associated with developmental toxicity, prompting their replacement with short-chain and fluoroether compounds. There is growing public concern over the safety of replacement PFAS.Objective:We aimed to group PFAS based on shared toxicity phenotypes.Methods:Zebrafish were developmentally exposed to 4,8-dioxa-3H-perfluorononanoate (ADONA), perfluoro-2-propoxypropanoic acid (GenX Free Acid), perfluoro-3,6-dioxa-4-methyl-7-octene-1-sulfonic acid (PFESA1), perfluorohexanesulfonic acid (PFHxS), perfluorohexanoic acid (PFHxA), perfluoro-n-octanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), or 0.4% dimethyl sulfoxide (DMSO) daily from 0–5 d post fertilization (dpf). At 6 dpf, developmental toxicity and developmental neurotoxicity assays were performed, and targeted analytical chemistry was used to measure media and tissue doses. To test whether aliphatic sulfonic acid PFAS cause the same toxicity phenotypes, perfluorobutanesulfonic acid (PFBS; 4-carbon), perfluoropentanesulfonic acid (PFPeS; 5-carbon), PFHxS (6-carbon), perfluoroheptanesulfonic acid (PFHpS; 7-carbon), and PFOS (8-carbon) were evaluated.Results:PFHxS or PFOS exposure caused failed swim bladder inflation, abnormal ventroflexion of the tail, and hyperactivity at nonteratogenic concentrations. Exposure to PFHxA resulted in a unique hyperactivity signature. ADONA, PFESA1, or PFOA exposure resulted in detectable levels of parent compound in larval tissue but yielded negative toxicity results. GenX was unstable in DMSO, but stable and negative for toxicity when diluted in deionized water. Exposure to PFPeS, PFHxS, PFHpS, or PFOS resulted in a shared toxicity phenotype characterized by body axis and swim bladder defects and hyperactivity.Conclusions:All emerging fluoroether PFAS tested were negative for evaluated outcomes. Two unique toxicity signatures were identified arising from structurally dissimilar PFAS. Among sulfonic acid aliphatic PFAS, chemical potencies were correlated with increasing carbon chain length for developmental neurotoxicity, but not developmental toxicity. This study identified relationships between chemical structures and in vivo phenotypes that may arise from shared mechanisms of PFAS toxicity. These data suggest that developmental neurotoxicity is an important end point to consider for this class of widely occurring environmental chemicals. https://doi.org/10.1289/EHP5843

Effect of tank shape on survival and growth of Pacific bluefin tuna Thunnus orientalis larvae

We examined the effect of rearing tank shape on survival and growth of Pacific bluefin tuna Thunnus orientalis larvae. Cylindrical (1.7 × 103 cm2 water surface area; 30 cm deep) and rectangular (1.8 × 103 cm2 water surface area; 28 cm deep) tanks (n = 3 each) were filled with 50 l of seawater. One air stone with a 100 ml/min aeration rate was set at the bottom center of each tank. Light intensity at the water surface was 2000 lx with a photoperiod of 24 L:0D. Larvae were introduced into each tank at a rate of 10 individuals/l at 2 days post-hatching (dph). Rotifers were fed at 10 individuals/ml and their distribution in tanks was measured. Survival of larvae in cylindrical tanks (CT; 52.7 ± 5.1%) at 8 dph was higher than that in rectangular tanks (RT; 0.8 ± 0.7%, p < .01). Meanwhile, larvae growth was not significantly different between tank shapes either in body length (CT: 4.23 ± 0.26 mm; RT: 4.09 ± 0.20 mm) or dry weights (CT: 95.1 ± 17.6 μg; RT: 67.7 ± 10.9 μg). The swimbladder inflation rate of larvae also did not differ significantly between tank shapes (CT: 16.5 ± 14.5%; RT: 56.9 ± 3.47%). Rotifer distribution was higher at tank bottom in both shapes (p < .05). Two-phase bubbly flow simulations in the tanks revealed that the low-flow area was larger in the RT. The low-flow area at tank bottom varied by tank shape, occurring at the edge of the tank wall on the bottom in the CT, and from the center of the tank (air stone) to the tank wall in the RT. These low-flow areas at tank bottom coincided with areas of higher rotifer distribution, which may be a cause of sinking syndrome in fish larvae. Our results indicate that small-scale (50-l) PBT larviculture experiments can be conducted using a CT with the present aeration system, and that an RT requires an improved aerator in place of the single air stone.

Domestication process modifies digestion ability in larvae of Eurasian perch (Perca fluviatilis), a freshwater Teleostei

To date, a comparative analysis of larval performance and digestion abilities between wild and domesticated Eurasian perch has not yet been performed. Eurasian perch larvae from wild and domesticated spawners were reared in the same conditions and at different development stages, growth performance variables, the expression of genes encoding digestive enzymes and specific enzymatic activity were analysed. No significant differences in hatching rate, deformity rate or swim bladder inflation effectiveness between wild and domesticated larvae were found. Specific growth rate, final total length and wet body weight were significantly lower in wild larvae, whereas higher mortality in wild larvae was observed compared to domesticated larvae. The data obtained in this study clearly indicate that during domestication, significant modification of digestion ability occurs at the very beginning of ontogeny, where domesticated fish are characterised by lower enzymatic activity and lower expression of genes encoding digestive enzymes. This probably results from the low diversity of the food offered in culture conditions, which significantly modified digestion capability. The obtained data provide an understanding of how domestication affects fish in aquaculture and may improve the planning of selective breeding programs of Eurasian perch and other freshwater Teleosts.

Embryonic exposure to pentabromobenzene inhibited the inflation of posterior swim bladder in zebrafish larvae

The emerging flame retardants pentabromobenzene (PBB) has been frequently detected in recent years and may pose exposure risks to wild animals and human beings. In this study, the inflation of posterior swim bladder of zebrafish larvae was used as an endpoint to study the developmental toxicity and putative mechanisms associated with PBB toxicity. Our results showed that embryonic exposure to PBB could significantly inhibit the inflation of posterior swim bladders. Reduced T3 levels and transcriptional changes of crh and pomc were observed in PBB treated zebrafish larvae at 120 hpf. However, key regulators of thyroid and adrenocortical system involved in the synthesis (tsh), biological conversion (ugt1ab, dio2) and functional regulation (trα, trβ, gr) showed no significant changes. Further data revealed that prlra was the only gene that was altered among the detected genes at 96 h post fertilization (hpf). At 120 hpf, the morphology of swim bladder indicated deflation in treatments at 0.25 μM and higher. In addition, the mRNA levels of anxa5, prlra, prlrb, atp1b2 and slc12a10 were all significantly changed at 120 hpf. Taken together, we suppose that embryonic exposure to PBB inhibited the inflation of swim bladder in zebrafish probably via prlra mediated pathways. The observed changes of thyroid and adrenocortical parameters might be indirect effects evoked by PBB exposure. Overall, our results provide important data and indications for future toxicological study and risk assessment of the emerging flame retardants PBB.

The synthetic pyrethroid deltamethrin impairs zebrafish (Danio rerio) swim bladder development

Deltamethrin (DM) is a widely used insecticide and reveals neural, cardiovascular and reproductive toxicity to various aquatic organisms. It has been known that DM negatively affects motion of zebrafish (Danio rerio). However, little is known in relation to the impacts of DM on development of swim bladder, which is a key organ for motion. In the present study, zebrafish embryos were exposed to 20 and 40 µg/L DM. The changes of swim bladder morphology were observed and transcription levels of key genes were compared between DM treatments and the control. The results showed that DM treatments significantly blocked the formation of progenitor and tissue layers in swim bladder of zebrafish embryos, leading to failed inflation of swim bladder. Compared with the control, the key genes (pbx1, foxA3, mnx1, has2, anxa5b, hprt1l and elovl1a) responsible for swim bladder development also showed decreased levels in response to DM treatments, suggesting that DM might specifically affect swim bladder development. Moreover, transcription levels of genes in the Wnt (wnt5b, tcf3a, wnt1, wnt9b, fzd1, fzd3 and fzd5) and Hedgehog (ihhb, ptc1 and ptc2) signaling pathways all decreased significantly in response to DM treatments, compared with the control. Considering the importance of Wnt and Hedgehog pathways in development of swim bladder, these results suggested that DM might affect swim bladder development through inhibiting the Wnt and Hedgehog pathways. Overall, the present study reported that swim bladder might be a potential target organ of DM toxicity in zebrafish, which contributed more information to the evaluation of DM’s environmental risks.

Health Impact Assessment of Sulfolane on Embryonic Development of Zebrafish (Danio rerio).

Sulfolane is a widely used polar, aprotic solvent that has been detected by chemical analysis in groundwater and creeks around the world including Alberta, Canada (800 µg/mL), Louisiana, USA (2900 µg/mL) and Brisbane, Australia (4344 µg/mL). Previous research provided information on adverse effects of sulfolane on mammals, but relatively little information is available on aquatic organisms. This study tested the effects of sulfolane (0–5000 µg/mL) on early development of zebrafish larvae, using various morphometric (survival, hatching, yolk sac and pericardial oedema, haemorrhaging, spinal malformations, swim bladder inflation), growth (larval length, eye volume, yolk sac utilisation), behavioural (touch response, locomotor activity and transcript abundance parameters (ahr1a, cyp1a, thraa, dio1, dio2, dio3, 11βhsd2, gr, aqp3a, cyp19a1b, ddc, gria2b and hsp70) for 120 h. Embryos were chronically exposed to sulfolane throughout the experimental period. For locomotor activity, however, we also investigated acute response to 2-h sulfolane treatment. Sulfolane sensitivity causing significant impairment in the observed parameters were different depending on parameters measured, including survival (concentrations greater than 800 µg/mL), morphometric and growth (800–1000 µg/mL), behaviour (500–800 µg/mL) and transcript abundance (10 µg/mL). The overall results provide novel information on the adverse health impacts of sulfolane on an aquatic vertebrate species, and an insight into developmental impairments following exposure to environmental levels of sulfolane in fish embryos.

Exposure to water-accommodated fractions of two different crude oils alters morphology, cardiac function and swim bladder development in early-life stages of zebrafish

The present study investigated the developmental toxicity of water-accommodated fractions (WAFs) of Oman crude oil (OCO) and Merey crude oil (MCO) on zebrafish (Danio rerio) in early-life stages (ELS). Based on total petroleum hydrocarbons (TPH), LC50 values manifested that OCO WAF was 1.2-fold more lethal to zebrafish embryos than MCO WAF. As for hatching rate, EC50 value for OCO WAF was 5.7-fold lower than that for MCO WAF. To evaluate the sublethal morphological effects, semi-quantitative extended general morphological score (GMS) and general teratogenic score (GTS) systems were adopted. The GMS and GTS scores indicated that the WAFs caused remarkable developmental delay and high frequencies of malformation in a dose-dependent manner. Additionally, OCO and MCO WAFs exposure exhibited severe bradycardia (reduced heart rate) and overt reduction of stroke volume, with a concomitant decrease in the cardiac output. Meanwhile, the WAFs also induced dose-dependent down-regulated expressions of several key functional genes of excitation-contraction coupling in cardiomyocytes, including ryr2, atp2a2a, atp2a2b, ncx1h, and kcnh2. For key gene markers of swim bladder development, results showed that high dose of TPH induced significant down-regulation of hb9 and anxa5 with no obvious change of acta2, suggesting that the WAFs could affect the specification and development of epithelium and outer mesothelium of swim bladder in zebrafish ELS. A strong negative relationship between the failure of swim bladder inflation and cardiac dysfunction via cardiac output was found. All these findings provide novel insights into the complicated mechanisms of the developmental toxicity of crude oil on fish in ELS.

Swim bladder inflation failure in pikeperch (Sander lucioperca) larvae in pond culture

Environmental conditions have a major impact on swim bladder inflation (SBI) in intensively cultured pikeperch Sander lucioperca, but there is currently no evidence of SBI inflation failure under natural conditions. The goals of this study were to quantify SBI failure in pond-cultured pikeperch larvae and to investigate whether pond conditions and characteristics including surface area, average depth, submerged and littoral vegetation, or bottom substrate play a significant role in its occurrence. Pikeperch larvae (n = 5700) in 19 ponds were examined for SBI at 16 days post-hatching. The swim bladder (SB) failed to inflate in 243 (4.2%) of the larvae with incidence of non-inflation ranging from 0 to 17.6% in individual ponds. No significant differences were found in total length (P > 0.27) or weight (P > 0.14) of larvae with and without inflated SB. The proportion of larvae with successfully inflated SB was significantly influenced by the presence of littoral vegetation and by interaction of presence of littoral vegetation with pond surface area and with pond average depth. Fish in ponds lacking littoral vegetation with water depth < 0.9 m showed higher rates of SB inflation failure.