Toxic effects of freshwater grouper (Acrossocheilus fasciatus) eggs on poultry: Morphological and transcriptomic insights into hepatic toxicity.

Fish egg poisoning is a serious and neglected public menace that kills hundreds of people and numerous poultry each year. Freshwater groupers (Acrossocheilus fasciatus) are common food fish in the southeastern regions of China. Their toxic eggs are regarded as a significant public health concern. The molecular mechanisms of egg-toxin toxicity in freshwater grouper to poisoned organisms are elusive. In this study, black-boned chicks were exposed to toxic eggs from freshwater grouper at a lethal dose. The hepatic morphology of the intoxicated chick was assessed. An analysis of the liver gene expression profile was conducted by comparing samples exposed to toxic eggs with control samples using RNA-Seq. The result revealed that an increase in vacuolation and congestion was observed in chicks with toxic eggs exposure. The transcriptome analysis revealed 5421 genes with differential expression, comprising 2810 up-regulated and 2611 down-regulated genes. The genes were primarily linked to energy metabolism, cell apoptosis, cell adhesion, exogenous microbial infection, and cell junction. The most strongly upregulated genes were cholecystokinin (CCK), cholecystokinin A receptor (CCKAR), and unc-80 homolog, NALCN activator (UNC80), and the most downregulated genes were glycine amidinotransferase (GATM), fatty acid desaturase 2 (FADS2), and hexokinase 2 (HKDC1). GO term with the highest enrichment of DEGs is nucleosome assembly. According to KEGG pathways, the three most significant metabolic pathways in the liver are DNA replication, retinol metabolism, and steroid biosynthesis. The results could be crucial for comprehending the negative biological impacts of egg-toxin and its toxic mechanisms. The outcome could provide potential biomarkers of egg-toxin exposure in hepatic, which might be useful for manufacturing an antidote to egg-toxin and providing valuable insights for ecotoxicity studies.

Epidermal oxysterols function as alarm substances in zebrafish.

Alarm substances signal imminent predation thread and enable anti-predation strategies. In shoaling fish, alarm cues diffuse from injured skins that induce intense fear and anti-predation behaviors in other members. While these "fear substances" are shown to be present in numerous fishes and thought to exist in roughly 8,000 Ostariophysan species, their chemical nature remains largely unknown. We posited that fish alarm cues comprise small compounds and induce specific behaviors characteristic of fish exposed to skin extracts. Using the behaviors as bioassays, we tracked the alarm function of zebrafish skin extract to two compounds, 24-methyl-5α-cholestane-3α,7α,12α,24,28-pentahydroxy 28-sulfate, an oxysterol sulfate, and 5α-cyprinol sulfate. At concentrations of less than one nanomolar, each compound induced anti-predator behaviors and increased cortisol levels in zebrafish. Their mixture, at the natural ratio, replicated the skin extract in eliciting the full suite of anti-predator behavior patterns. Our findings reveal a molecular mechanism whereby fish escape predation danger.

Sea Cucumber Viscera Contains Novel Non-Holostane-Type Glycoside Toxins that Possess a Putative Chemical Defense Function.

Sea cucumbers frequently expel their guts in response to predators and an aversive environment, a behavior perceived as releasing repellents involved in chemical defense mechanisms. To investigate the chemical nature of the repellent, the viscera of stressed sea cucumbers (Apostichopus japonicus) in the Yellow Sea of China were collected and chemically analyzed. Two novel non-holostane triterpene glycosides were isolated, and the chemical structures were elucidated as 3ꞵ-O-[ꞵ-D-glucopyranosyl-(1→2)-ꞵ-D-xylopyranosyl]-(20S)-hydroxylanosta-7,25-diene-18(16)-lactone (1) and 3ꞵ-O-[ꞵ-D-quinovopyranosyl-(1→2)-ꞵ-D-xylopyranosyl]-(20S)-hydroxylanosta-7,25-diene-18(16)-lactone (2) by spectroscopic and mass-spectrometric analyses, exemplifying a triterpene glycoside constituent of an oligosaccharide containing two sugar-units and a non-holostane aglycone. Zebrafish embryos were exposed to various doses of 1 and 2 from 4 to 96 hpf. Compound 1 exposure showed 96 h-LC50 41.5 µM and an increased zebrafish mortality rates in roughly in a dose- and time-dependent manner. Compound 2, with different sugar substitution, exhibited no mortality and moderate teratogenic toxicity with a 96 h-EC50 of 173.5 µM. Zebrafish embryos exhibited teratogenic effects, such as reduced hatchability and total body length. The study found that triterpene saponin from A. japonicus viscera had acute toxicity in zebrafish embryos, indicating a potential chemical defense role in the marine ecosystem.

Development of a trace quantitative method to investigate caffeine distribution in the Yellow and Bohai Seas, China, and assessment of its potential neurotoxic effect on fish larvae.

Caffeine is an emerging contaminant in aquatic environments. The study utilized a validated method to investigate the presence and distribution of caffeine in the surface water of the Yellow and Bohai Seas, urban rivers, and the Yantai estuary area. The analytical method conforms to EPA guidelines and exhibits a limit of quantification that is 200 times lower than that of prior investigations. The study revealed that the highest concentration of 1436.4 ng/L was found in convergence of ocean currents in the Yellow and Bohai Seas. The presence of larger populations and the process of urban industrialization have been observed to result in elevated levels of caffeine in offshore regions, confirming that caffeine can serve as a potential indicator of anthropogenic contamination. Fish larvae exhibited hypoactivity in response to caffeine exposure at environmentally relevant concentrations. The study revealed that caffeine pollution can have adverse effects on marine and offshore ecosystems. This emphasizes the importance of decreasing neurotoxic pollution in the aquatic environment.

Embryotoxicity and Teratogenicity of Steroidal Saponin Isolated from Ophiopholis mirabilis.

Benthic invertebrates produce secondary metabolites that serve as defenses against consumers and promote their fitness. To explore the chemical defense in marine benthic echinoderms, the chemical constituents of Ophiopholis mirabilis were investigated. A steroidal monoglycoside, asterosaponin P1, was isolated from O. mirabilis for the first-time using column chromatography. The chemical structure was characterized by spectroscopic and spectrometric methods. The embryotoxicity and teratogenicity of the isolated compound were assessed using the zebrafish embryo assay, a powerful vertebrate animal model system to study mechanisms of toxicity. When applied at high concentrations, asterosaponin P1 causes a significant increase in embryo mortality. A moderate LC50 of asterosaponin P1 appeared to be time- and concentration-dependent in its toxicity to zebrafish embryos. Teratogenicity in zebrafish embryos also included morphological defects, decreased hatchability, and a reduced heart rate. These findings revealed that steroidal saponin extracted from O. mirabilis exhibited acute toxic effects on zebrafish embryos, suggesting a potential chemical defense function in marine habitats.