Swim Bladder Research Articles

Studies on organogenesis of Cyprinus carpio var. koi with reference to histological perspectives

The objective of the current study was to investigate the histological characteristics of larval organogenesis in Cyprinus carpio var. koi. The eggs and several developmental stages of C. carpio var. koi larvae were preserved in Bouin's fluid. Histological examinations were conducted daily from the first day after fertilisation (DAF) to the 12th DAF and the 16th, 24th, 32nd, and 40th DAF. Histological examinations of C. carpio var. koi eggs revealed the development of an embryonic disc, followed by the formation of the neural tube and embryonic eyes on the second day after fertilisation (DAF). The just-emerged larvae have distinct eyes and a neural tube that has undergone differentiation into the brain. Following that, an examination was conducted on the development of the digestive system, swim bladder, gills, skin, and fins. The ontogeny developments were categorised into five distinct stages. During larval development, the initial two stages have exhibited variations in their organogenesis. The larvae head was aligned and devoid of the yolk, but their body was connected to the yolk sac and gill arches, which were visible between the 3rd and 5th days after fertilisation (DAF), and their total length range was 4.35-6.83mm. The digestive system had a linear configuration, with an enlargement in both the dorsal and ventral regions of the body on the ninth day after fertilisation (DAF). During the 10th to 17th developmental stages, larvae have a total length range of 11.23-14.35mm. The operculum, gill lamella, and dorsal fin were developed in this stage. Between the 24th and 40th days after fertilisation (DAF), the larvae acquired a fin, a coiled gut, and well-developed accessory glands and their total length was measured between 15.01 and 23.68mm.

Amelioration of arsenic-induced hepatic injury via sulfated glycosaminoglycan from swim bladder: Modulation of Nrf2 pathway and amino acid metabolism.

Arsenic, a known environmental pollutant with a carcinogenic risk, is associated with chronic liver toxicity. Prebiotic regulation represents an emerging dietary strategy to alleviate arsenic-induced hepatotoxicity; however, research in this area remains limited. This study employed sulfated swim bladder glycosaminoglycan (SBSG), a potential prebiotic, to assess its efficacy in mitigating arsenic-induced liver injury. In basic indicators, SBSG resisted oxidative stress by down-regulating AST, ALT, MDA, and MPO, up-regulating antioxidants (T-SOD, GSH, and GSH-px), and ameliorating histopathological damage. RT-qPCR analysis revealed that SBSG could regulate the Nrf2 signaling pathway and affect the expression of o genes related to ferroptosis and detoxification. The expression of protein further verified that SBSG could play an antioxidant and detoxifying role as an Nrf2 activator. Non-targeted metabolomics results demonstrated that SBSG primarily addresses metabolic disorders by up-regulating D-amino acid metabolism, ABC transporter, and alanine, aspartate and glutamate metabolism. Correlation analysis suggests that SBSG alleviates arsenic-induced liver oxidative damage through mechanisms linked to the Nrf2 pathway and amino acid metabolism. This study provided a research basis for expanding the dietary strategy to reduce arsenic induced toxicity.

Impacts of Hexafluoropropylene Oxide Tetrameric Acid (HFPO-TeA) on Neurodevelopment and GABAergic Signaling in Zebrafish Larvae

Hexafluoropropylene oxide oligomer acids (HFPOs), an emerging environmental pollutant, are increasingly utilized in the manufacture of fluorinated synthetic materials as a substitute for traditional perfluorooctanoic acid (PFOA), resulting in a corresponding rise in detection rates in aquatic environments, which may present inherent safety hazards to ecosystems and public health. However, few data are available on the issue of their toxicity and mechanism. This study aimed to investigate the potential toxic effects of hexafluoroepoxypropane tetrameric acid (HFPO-TeA), a typical HFPO, on the early developmental stages of zebrafish larvae. It revealed that HFPO-TeA exposure resulted in significant detrimental effects, including adverse impacts on general morphological characteristics, such as eye area, heart rate, and swimming bladder, in zebrafish embryos and larvae. Targeted metabolomics and transcriptomics inquiries clarified that HFPO-TeA exposure reduced the levels of the neurotransmitter gamma-aminobutyric acid (GABA) and downregulated the expression of genes related to the GABA pathway. Simultaneously, transgenic zebrafish exhibited that exposure to HFPO-TeA impedes the growth of GABAergic neurons. Moreover, the molecular docking analysis indicated that GABAA receptors might be the potential targets of HFPO-TeA. Taken together, the current data highlights that the HFPO-TeA might not be safe alternatives to PFOA. This study presented a model for HFPO-TeA-induced neurotoxicity in developing zebrafish that can aid in ecological risk assessments.

Saccular potentials of the male round goby, Neogobius melanostomus, a hearing non-specialist.

The round goby (Neogobius melanostomus) is a benthic fish species native to Central Eurasia but has colonized much of the waterways in the Laurentian Great Lakes in North America. While they are known to produce acoustic signals that aid in conspecific agonistic and reproductive interactions, the species does not possess a swim bladder and thus does not have any hearing specializations that would allow for sound pressure detection. Here, the auditory evoked potentials from saccular hair cells were characterized to determine the frequency response and auditory sensitivity of the saccule. Saccular potentials were recorded from the medial region of the saccular maculae during playback of single frequency acoustic stimuli (105-605 Hz). Auditory tuning curves based on both sound pressure (dB re: 1 μPa.) and particle acceleration (dB re: 1 ms-2) suggest that the saccule is most sensitive to 105 and 125 Hz and that the highest thresholds occurred at frequencies ≥205 Hz.

Extended Photoperiod Facilitated the Restoration of the Expression of GH-IGF Axis Genes in Submerged Rainbow Trout (Oncorhynchus mykiss).

Salmonids, classified as physostomous fish, maintain buoyancy by ingesting air to inflate their swim bladders. Long-term submergence has been shown to cause body imbalance and reduced growth performance in these fish. Previous studies have demonstrated that extended photoperiod can promote growth in salmonids. This study aimed to investigate the regulatory effects of prolonged lighting on the growth of submerged rainbow trout (Oncorhynchus mykiss) by examining the transcriptional expression of genes in the growth hormone (GH)-insulin-like growth factor (IGF) axis. Rainbow trout were individually reared in one of the six environments, defined by the combination of three photoperiods (0L:24D, 12L:12D, and 24L:0D) and two spatial rearing modes (routine and submerged), for 16 weeks. We compared the growth performance of rainbow trout in different environments and further analyzed the transcription profiles and correlations of GH-IGF axis genes in the brain, liver, and muscle. The findings of this study were as follows: growth performance of rainbow trout gradually increased with photoperiod duration. Specifically, final body weight (FBW) and specific growth rate (SGR) increased, while feed conversion ratio (FCR) decreased. Extended photoperiod partially mitigated the adverse effects of long-term submergence on rainbow trout growth. Under 24L:0D photoperiod conditions, growth performance (FBW, SGR, and FCR) in submerged and routine rainbow trout was more closely aligned compared to 0L:24D and 12L:12D photoperiod conditions. In response to variations in the photoperiod, GH-IGF axis genes of rainbow trout exhibited significant transcriptional differences, particularly between treatments with 0L:24D and 24L:0D light exposure. An extended photoperiod facilitated the restoration of the expression of GH-IGF axis genes in submerged rainbow trout towards routine levels, including the up-regulation of sst and sstr2 genes in the brain. Correlation analysis implied differentiation of physiological functions of ghr and igfbp paralogs. This study provided insights into the feasibility of enhancing the growth performance of submerged salmonids through photoperiod manipulation.

Free Falling: Fizzing Wild‐Caught Smallmouth Bass Results in the Inability to Control Buoyancy in Deep Water

ABSTRACTFizzing, a somewhat controversial technique for mitigating barotrauma, uses hollow hypodermic needles to release gas from the swim bladder of fish. To isolate effects of fizzing, 106 smallmouth bass (Micropterus dolomieu) were caught from shallow water without barotrauma and tested to determine if they could effectively control their buoyancy after having their swim bladder fizzed or punctured by releasing them over shallow (10 m) or unsuitably deep (55 m) habitat. Depth and behavior were monitored with biologgers. Most fizzed (57%) and punctured (61%) fish were unable to regulate their buoyancy in deepwater, sinking to the bottom and appearing moribund. In shallow water, punctured smallmouth bass stayed higher in the water column (like controls), while many fizzed fish stayed on the bottom. Our results suggest that if smallmouth bass are fizzed and immediately released, precautions should be taken to ensure they are released in areas of appropriate water depths (< 10 m).

Age and growth of American Eel in lower St. Johns River in northeast Florida

AbstractObjectiveLittle is known about American Eel Anguilla rostrata populations across much of the species' large geographic range. This study aimed to collect important information on the life history and population biology of American Eel in a northeast Florida river.MethodsDuring two 12‐week periods, from August to November 2021 and September to December 2022, American Eel were collected from a ~90‐km stretch of the lower St. Johns River via boat electrofishing. Data on length, weight, age, Anguillicoloides crassus parasite infection, and swim bladder condition were recorded for American Eel collected in both years, and additional data on sex, sexual maturity, and fin and eye morphology were recorded for American Eel collected in 2022.ResultOverall, biologists spent more than 63.5 h of effort over 42 sampling days to collect 297 American Eel, ranging in size from 150 to 705 mm total length (TL) with a continental age ranging from 0 to 8 years. American Eel catches were low and varied by section of river and over time; however, no differences in the length–weight relationship or size structure were observed between river sections. Adult parasites were observed in swim bladders of 36% of American Eel, and 57% of eel exhibited some level of swim bladder damage. Although length–weight relationships were similar regardless of swim bladder condition, relative swim bladder length was lower for fish with severe damage. Histological examination of gonads from 160 American Eel in 2022 revealed that the male : female sex ratio was 0.9:1 and nearly all eel were sexually immature. The majority of fish were 2–4 years of age; average growth was modeled with a von Bertalanffy curve for American Eel aged 1–8: TL = 740 × [1 – e−0.12(age + 1.98)].ConclusionGiven the paucity of information about American Eel in this region, the data provided in this study will be critical to informing future decisions on the management of the American Eel stock.

From hatching to juvenile: Larval development of Vieja fenestrata (Teleostei: Cichlidae).

This study delves into the early development of Vieja fenestrata (Cichlidae), with a specific focus on the description of external morphological and morphometric changes, and growth patterns from hatching to the loss of larval characters under controlled laboratory conditions at a temperature of 28°C. Asynchronous hatching was observed between 58 and 60 h postfertilization, with the posterior body emerging first. Over 14 days, significant morphological, physiological, and behavioral changes were observed, revealing a complex developmental trajectory. The initial developmental phases were characterized by rapid vascularization, fin differentiation, and heightened activity, and the subsequent days witnessed the flexion of the notochord, emergence of swim bladder functionality, and transition to exogenous feeding. Maturation progressed with the absorption of the yolk sac, regression of cement glands, and fin ray development, culminating in metamorphosis by 14 days post-hatching. Throughout this period, evolving pigmentation patterns and structural adaptations highlight the species' adaptive strategies. During the larval period of V. fenestrata, substantial changes in morphological proportions were observed. Before the inflection, tail length, trunk length, and body depth had negative allometric growth, and head length, eye diameter, and snout length had positive allometric growth. After the inflection, body depth and snout length showed positive allometric growth; head length and trunk length exhibited isometric growth, whereas tail length and eye diameter demonstrated negative allometric growth. These findings contribute insights into the intricate developmental dynamics of V. fenestrata. Moreover, further research may explore these developmental dynamics' ecological and evolutionary implications.

Elucidating the molecular mechanism of angiogenic activity of sulfate glycosaminoglycan derived from fish swim bladder in human umbilical vein endothelial cells

Fish swim bladders are considered a traditional marine aquatic food that has medicinal and nutritional properties. Sulfate glycosaminoglycans (SBSG) obtained from fish swim bladders may have anti-angiogenic activity. However, the anti-angiogenic activity of SBSG and its mechanism has not been reported. Therefore, the present study investigated the effect of SBSG on angiogenesis and examined molecular pathways in human umbilical vein endothelial cells (HUVECs) using cell viability, chicken chorioallantoic membrane (CAM) assay, tube formation assay, and proteomic analyses. The results demonstrated that the SBSG significantly (P < 0.05) suppressed tube formation in the HUVECs while decreasing vascular density in CAM. Quantitative proteome analysis identified 1474 differentially expressed proteins (DEPs) involved in different molecular pathways. In the bladder cancer pathway, 10 proteins were significantly downregulated [matrix metalloproteinase-9 (MMP-9), epidermal growth factor receptor (EGFR), cyclin-dependent kinase 4 (CDK4), fibroblast growth factor receptor 3 (FGFR3), harvey rat sarcoma (H-Ras), rat sarcoma (Ras), mitogen-activated extracellular signal-regulated kinase (MEK), extracellular regulated protein kinases (ERK), receptor tyrosine-protein kinase erbB-2 (ERBB2), and E-Cadherin (E-cad)], whereas 2 proteins were significantly upregulated [thrombospondin-1 (TSP-1) and E-cad]. Notably, SBSG was effectively bound to the active sites of EGFR, MMP-9, and TSP-1, which led to reduced EGFR and MMP-9 protein expression (p < 0.05), and increased TSP-1 (P < 0.05), thereby inhibiting angiogenesis. These findings suggest that SBSG is a potential candidate for the nutraceuticals industry for angiogenesis management.

An expert system for species discrimination and grade identification of fish maw

Fish maw, derived from dried swim bladders of fish, is valued for its nutritional and medicinal properties, which has led to an increased market demand. However, price variability based on species and grades has results in unethical practices such as counterfeiting and mislabeling, highlighting the need for reliable quality authentication. To address this, an expert system using MATLAB software has been developed. This system employs nuclear magnetic resonance (NMR) technology and pattern recognition methods to identify fish maw species and classify their grade. The study analyzed ten species across three grades of fish maw, identifying 43 nutritional components from NMR spectra, including sugars, amino acids, fatty acids, organic acids, and vitamins. Univariate statistical analysis was integrated with multivariate statistical analyses, including principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA), and orthogonal partial least squares (OPLS-DA) using SIMCA software, to develop models for species and grades identification. A four-dimensional volcano map was constructed to highlight characteristic components of various fish maws, resulting in an NMR database for common fish maws. The expert system’s accuracy was validated with new samples, achieving 92.6% for species identification and 90.0% for grade classification. This study provides a valuable tool for the quality evaluation of fish maw and a scientific basis for market regulation.

Assessment of toxicity and endocrine-disrupting activity of bisphenol analogues during ozone and UV treatments in zebrafish eleutheroembryos

In recent decades, increased regulations on the use of bisphenol A (BPA) have prompted a surge in the use of BPA alternatives. Consequently, a widespread occurrence of BPA substitutes in aquatic environments is currently being detected. While some evidence exists about the degradation of these compounds through various water treatment technologies, the evolution of the resulting toxicity and endocrine-disrupting activity during these processes remains scarcely evaluated. In this study, the acute toxicity and transcriptomic responses in zebrafish eleutheroembryos exposed to selected bisphenols (BPA, bisphenol AF (BPAF) and bisphenol CCl (BPC-Cl)) were assessed during their oxidation by ozone. In addition, the response of zebrafish eleutheroembryos exposed to BPC-Cl treated with UV radiation was also investigated. Results showed that both ozonation and UV treatment effectively reduced the intrinsic toxicity of the studied bisphenols. This was observed with the increase of the survival and swim bladder inflation rates of zebrafish eleutheroembryos, reaching control levels. In concordance with these results, the initially altered mRNA levels in genes related to xenobiotic stimulus (cyp2k18); lipid homeostasis and transport (apoa1a); retinoid metabolism (aldh1a2); neutrophil differentiation (alas1); and oxygen transport (hbae3) in zebrafish eleutheroembryos were generally mitigated during the ozonation and UV treatment of bisphenols. Similarly, the high estrogenicity of these bisphenols, observed by elevated mRNA levels of cyp19a1b, decreased significantly during the ozonation treatment, reaching control levels. On the contrary, an increase in mRNA levels of fads2 and cyp19a1b was observed in animals exposed to BPC-Cl treated with UV radiation. These results suggest that the photolysis products of BPC-Cl may induce disruption of the lipid biosynthesis and estrogenicity. This was further confirmed with RNA-sequencing analysis, which revealed that embryos exposed to BPC-Cl treated with UV radiation presented alterations in mRNA levels of genes specifically related to estrogenic stimulus.

Collagen (peptide) extracted from sturgeon swim bladder: Physicochemical characterization and protective effects on cyclophosphamide-induced premature ovarian failure in mice

Premature ovarian failure (POF) is a common female reproductive disorder, with oxidative damage playing a significant role in its development. Studies had demonstrated the beneficial antioxidant, anti-aging, and other biological properties of swim bladder collagen (peptide). In this study, acid extraction, water extraction, and enzymatic hydrolysis methods were used to extract collagen (peptide) from sturgeon (Acipenser sinensis) swim bladder, all of which exhibited significant antioxidant activity. Moreover, the effects observed in POF mice were enhanced, including an increasing in the number of growing ovarian follicles, regulation of serum hormone levels, and alterations in signaling pathways, as evidenced by the up-regulation of Phosphatidylinositol 3-kinase/Protein Kinase B (PI3K/Akt) and B cell lymphoma-2/ Bcl-associated x protein (Bcl-2/Bax) pathways, alongside the down-regulation of the mitogen-activated protein kinases (MAPK) signaling pathway. Sturgeon swim bladder collagen (peptide) could protect against cyclophosphamide-induced POF in mice, which could be very beneficial in the future advancement of health products.

Physical constraints on the positions and dimensions of the zebrafish swim bladder by surrounding bones

AbstractPrecise regulation of organ size and position is crucial for optimal organ function. Since the swim bladder is primarily responsible for buoyancy in teleosts, early development and subsequent inflation of the swim bladder should be appropriately controlled with the body growth. However, the underlying mechanism remains unclear. In this study, we show that the size and position of the swim bladder are physically constrained by the surrounding bones in zebrafish. Non‐invasive micro‐CT scanning revealed that the anterior edge of the swim bladder is largely attached to the os suspensorium, which is an ossicle extending medioventrally from the 4th centrum. Additionally, we observed that hoxc6a mutants, which lack the os suspensorium, exhibited an anterior projection of the swim bladder beyond the 4th vertebra. During the swim bladder development, we found that the counterclockwise rotation of the os suspensorium correlates with posterior regression of the swim bladder, suggesting that the os suspensorium pushes the swim bladder posteriorly into its proper position. Furthermore, our results revealed a close association between the posterior region of the swim bladder and the pleural ribs. In hoxaa cluster mutants with additional ribs, the swim bladder expanded posteriorly, accompanied by an enlarged body cavity. Taken together, our results demonstrate the importance of the surrounding bones in the robust regulation of swim bladder size and position in zebrafish.

The overlooked first intercostal ligament: Does it help to stabilize the Weberian apparatus?

The Weberian apparatus is a novel hearing adaptation that facilitates increased hearing sensitivity in otophysan fishes. The apparatus is a complex system composed of modifications to anterior vertebral elements, the inner ear, and the swim bladder. A critical piece of the system that often receives minor attention are the various ligaments that bridge these three regions. The most famous of the ligaments is the interossicular ligament, which connects the Weberian ossicle chain (scaphium-intercalarium-tripus). Several other ligaments are present, including the suspensor (tripus to parapophysis 4) and the triple ligament (tripus-os suspensorium-tunica externa). Here, by combining diffusible iodine-based contrast enhancement (DICE) and propagation phase-contrast synchrotron radiation micro-computed tomography (PPC-SRμCT) with classic histological methods, we shine new light on the first intercostal ligament (ICL1) and discuss its potential function in relation to the Weberian apparatus. ICL1 is nearly absent from the cypriniform literature, typically only mentioned in a general discussion together with other intercostal ligaments. This study examines the development and structure of ICL1 comparatively with the other definitive Weberian ligaments in the zebrafish (Danio rerio). We provide a comprehensive view of three-dimensional shape, development, and composition to generate hypotheses regarding potential functions of ICL1 within the greater Weberian apparatus. Given new detail presented herein regarding the structure of ICL1, modifications to rib 5 and parapophysis 4 for ICL1 attachment, and the alignment of ICL1 with the os suspensorium, we propose a supportive (anchoring) role of ICL1 to aid in minimizing non-optimal movement of the structures of the fourth vertebra. This addition would focus vibrations anteriorly through the ossicle chain with minimal signal loss in zebrafish and other species with similar Weberian apparatus morphologies. We conclude that ICL1 should be included in future analyses of Weberian apparatus function where ligaments are addressed.

Baseline Raman Spectral Fingerprints of Zebrafish Embryos and Larvae.

As a highly sensitive vibrational technique, Raman spectroscopy (RS) can provide valuable chemical and molecular data useful to characterise animal cell types, tissues and organs. As a label-free, rapid detection method, RS has been considered a valuable asset in forensics, biology and medicine. The technique has been applied to zebrafish for various purposes, including physiological, biochemical or bioaccumulation analyses. The available data point out its potential for the early diagnosis of detrimental effects elicited by toxicant exposure. Nevertheless, no baseline spectra are available for zebrafish embryos and larvae that could allow for suitable planning of toxicological assessments, comparison with toxicant-elicited spectra or mechanistic understanding of biochemical and physiological responses to the exposures. With this in mind, this work carried out a baseline characterisation of Raman spectra of zebrafish embryos and larvae throughout early development. Raman spectra were recorded from the iris, forebrain, melanocytes, heart, muscle and swim bladder between 24 and 168 h post-fertilisation. A chemometrics approach, based on partial least-squares discriminant analysis (PLS-DA), was used to obtain a Raman characterisation of each tissue or organ. In total, 117 Raman bands were identified, of which 24 were well represented and, thus, retained in the data analysed. Only three bands were found to be common to all organs and tissues. The PLS-DA provided a tentative Raman spectral fingerprint typical of each tissue or organ, reflecting the ongoing developmental dynamics. The bands showed frequencies previously assigned to collagen, cholesterol, various essential amino acids, carbohydrates and nucleic acids.

Effects of fish meal replacement with composite proteins source on growth performance, antioxidant capacity and swim bladder quality of chu’s croaker (Nibea coibor)

Collagen, as a commercial functional protein, is widely applied in food, cosmetics, biomedicine and other industries, and swim bladder is regarded as an ideal source of raw materials due to its rich collagen content. Chu’s croaker (Nibea coibor), as an economical fish that can produce high-grade swim bladder, is popularly farmed, however, its high fishmeal demand limits the development of the feed industry. Therefore, it is worth thinking about how to reduce the use of fish meal without affecting the swim bladder quality. Given that, an 8-week feeding trial was conducted to investigate the effects of fish meal partially replaced (0.0%, 5.0%, 10.0%, 15.0%, 20.0%) with composite proteins (CPs, consisted of corn protein meal and hydrolyzed feather meal) on growth, antioxidant capacity and swim bladder quality (texture and collagen deposition) of chu’s croaker. Results showed that although growth performance decrease with the increase of CPs’ replacement level, it did not compromise the swim bladder quality. Specifically, 5% - 10% CPs did not affect the growth significantly, but can improve antioxidant capacity, protein content, collagen synthesis and texture quality of swim bladder. The enhancement of swim bladder texture, including hardness, chewiness, springiness, and adhesiveness may be caused by changes in the expression of related genes, such as colga1t1, col12a1, cyp27a1, etc. These results indicated that appropriate fish meal replaced by CPs could be applied during aquaculture practice after comprehensive consideration of feed cost, growth rate and quality of swim bladder. This study provides support for the development of cost-effective feed formulations that improve the sustainability and economic viability of chu’s croaker culture.

An adverse outcome pathway approach linking retinoid signaling disruption to teratogenicity and population-level outcomes

Recent research efforts in endocrine disruption have focused on evaluating non-EATS (estrogen, androgen, thyroid, and steroidogenesis) pathways. Retinoid signaling disruption is noteworthy because of its teratogenic effects and environmental relevance. However, current environmental risk assessments are limited in their ability to evaluate impacts on individuals and populations. This study characterizes an Adverse Outcome Pathway (AOP) network linking retinoid signaling disruption to teratogenicity and survival in zebrafish. We identified Retinoic Acid Receptor (RAR) overactivation as the molecular initiating event leading to key events including craniofacial (CFM) and tail (TM) malformations, posterior swim bladder (SB) non-inflation, impaired swimming performance, and reduced feeding, ultimately resulting in decreased survival. Our study (1) determines critical sensitivity windows for CFM, posterior SB non-inflation, and TM, (2) provides quantitative measurements for CFM and TM, and (3) defines impacts on higher biological levels including food ingestion, swimming, and survival. Results show that all-trans retinoic acid (ATRA) induces strong teratogenic effects with sensitivity windows between 4 and 48 h post fertilization (hpf) for CFM, TM, and posterior SB non-inflation. TM is the most sensitive indicator, with EC50 of 0.2 - 0.26 µg/L across exposure windows 4–48, 4–72, 4–96, and 4–120 hpf. Besides inducing known malformations, ATRA impaired posterior SB inflation with EC50 of 1 - 1.21 µg/L across the same exposure windows. ATRA exposure (1 µg/L) resulted in 50 % food ingestion inhibition at 7 days post fertilization (dpf) and 10 % survival at 14 dpf. This study provides a regulatory-relevant framework linking developmental effects to population outcomes, highlighting ecological risks and needs for improved risk assessments.

Developmental Toxicity and Teratogenic Effects of Dicarboximide Fungicide Iprodione on Zebrafish (Danio rerio) Embryos

Iprodione (IDN) is a broad-spectrum fungicide used to treat various fungal infections in plants. Despite its extensive use, assessment of its toxicity in aquatic organisms remains incomplete. This study investigated the deleterious effects of IDN using zebrafish (ZF) as a model organism. ZF embryos, beginning at 2 h post-fertilization (hpf), were exposed to IDN (3.75–40 mg/L), and both mortality and deformities were assessed. The impact of IDN on mortality was concentration-dependent and significant from 14 mg/L. Importantly, IDN induced several deformities at sublethal concentrations, including abnormal somites, reduced retinal pigment accumulation, yolk sac edema, hatching failure, abnormal swim bladders, and spinal curvature. The EC50 values for IDN-induced deformities were 3.44 ± 0.74 to 21.42 ± 6.00 mg/L. The calculated teratogenic index values for all deformities were above 1, indicating that IDN is teratogenic to ZF. IDN-exposed ZF also displayed abnormalities in touch-evoked escape responses. IDN significantly affected heart rate and blood flow, and induced pericardial edema and hyperemia in a concentration-dependent manner, suggesting its influence on cardiac development and the function of ZF. In conclusion, these results suggest that IDN exerts toxic effects on ZF embryos, affecting mortality, development, and behavior.

Can air nanobubbles improve the swim bladder inflation in developing European perch? A pilot study of advanced water treatment.

Swim bladder inflation (SBI) is a fundamental step in larval development for both physostome and physoclist fish species. Failure of the SBI triggers higher energy expenditures of the individual, which negatively affects swimming ability, growth rate, feeding efficiency, susceptibility to predation, and survival rate. In aquaculture, the SBI failure is caused by different factors including: (a) water contamination with oil increasing the surface water tension and preventing the larvae from gulping air bubbles for inflation, and (b) bacterial aerocystitis of the swim bladder caused by gulped organic debris. Hence, novel and effective water treatment technologies such as nanobubbles can be employed in aquaculture to reduce the risk of low SBI. In the present study, we compared conventional water treatment, i.e. surface spray combined with skimmers with air nanobubbles either alone or in combination, on the SBI of European perch larvae. In the control, no water treatment technology was employed. All treatments showed higher SBI efficiency compared to the control. The control group showed the lowest percentage of swim bladder-inflated individuals associated with low body weight (BW). The highest BW and SBI efficiency was recorded with the combination of surface skimmer, spray, and nanobubbles. The current study offers the first investigation of the nanobubbles' effect on SBI promotion in larvae of European perch and gives motivation for future optimizations.

Embryonic and larval development of black jewfish, Protonibea diacanthus: A new candidate for aquaculture in northern Australia

Black jewfish Protonibea diacanthus is a large, commercially important fish distributed across the tropical Indo-Pacific. In Australia, there is an established commercial wild fishery for the species but it’s aquaculture potential has not been investigated. This research presents hatchery production of native P. diacanthus in Darwin, Australia and documents ontogeny of early life stages of this species over three trial runs. Wild P. diacanthus were induced to spawn with luteinizing hormone-releasing hormone analog (LHRHa) and eggs were released approximately 25–28 h after injection (0.88 ± 0.01 mm in diameter with oil globule 0.24 ± 0.01 mm). Larvae hatched 12 h after spawning. At one day post hatch (dph) larvae were 2.68 ± 0.01 mm standard length with 0.15 ± 0.01 mm oil globule diameter. Larvae mouths opened at 31 h post hatch (hph) and first feeding was seen at 57 hph. Swim bladder inflation (92 %) occurred between 40 and 62 hph. Larvae were progressively fed rotifers, Artemia and Otohime microdiet, and metamorphosis occurred between 20 and 25 dph, completing as they reached over 13 mm standard length. Tail biting cannibalism began with the onset of metamorphosis and caused significant mortality until approximately 24 dph when metamorphosed juveniles could be handled and moved to low stocking density systems. This study demonstrates that northern Australian P. diacanthus is amenable to hatchery production and provides important foundational knowledge for this emerging aquaculture species.