Stonefish (Synanceia spp.) Ichthyocrinotoxins: An ecological review and prospectus for future research and biodiscovery

Marine organisms possess a diverse array of unique substances, many with wide ranging potential for applications in medicine, industry, and other sectors. Stonefish (Synanceia spp.), a bottom-dwelling fish that inhabit shallow and intertidal waters throughout the Indo-Pacific, harbour two distinct substances, a venom, and an ichthyocrinotoxin. Stonefish are well-known for the potent venom associated with their dorsal spines as it poses a significant risk to public health. Consequently, much of the research on stonefish focusses on the venom, with the aim of improving outcomes in cases of envenomation. However, there has been a notable lack of research on stonefish ichthyocrinotoxins, a class of toxin that is synthesised within specialised epithelial cells (i.e., tubercles) and exuded onto the skin. This has resulted in a substantial knowledge gap in our understanding of these animals. This review aims to bridge this gap by consolidating literature on the ecological functions and biochemical attributes of ichthyocrinotoxins present in various fish species and juxtaposing it with the current state of knowledge of stonefish ecology. We highlight the roles of ichthyocrinotoxins in predator defence, bolstering innate immunity, and mitigating integumentary interactions with parasites and detrimental fouling organisms. The objective of this review is to identify promising research avenues that could shed light on the ecological functions of stonefish ichthyocrinotoxins and their potential practical applications as therapeutics and/or industrial products.

Suspected stonefish envenomation in Queensland over eight years: a retrospective series

INTRODUCTION

Stonefish envenomation results in localized severe pain and swelling and systemic features, including vomiting, arrhythmia, pulmonary oedema, and possibly death. There are limited data regarding the effectiveness of the available antivenom. The aim of this series is to characterize presentations of patients with suspected stonefish envenomation and investigate treatment, including antivenom.

METHODS

This is a retrospective observational series of suspected stonefish envenomation as reported to the Queensland Poisons Information Centre or Princess Alexandra Hospital Clinical Toxicology Unit from July 2015 to January 2023. Patients were identified through the databases held by both the Centre and Unit, and data on clinical features and investigations were collected from the patient's electronic medical record.

RESULTS

There were 87 suspected stonefish envenomations from July 2015 to January 2023. The median age was 26 (range: 5-69) years, and 69 (79 per cent) patients were male. Pain was reported in 85 (98 per cent) with a median peak pain score of 10 (range 4-12; three rated their pain greater than 10/10). A clear wound was documented in 64 (74 per cent), with local swelling in 63 (72 per cent). A foreign body was retained in eight (9 per cent) presentations. Systemic symptoms were rare, with vomiting in four (5 per cent) and dizziness in two (2 per cent) presentations. There were no instances of hypotension, arrhythmia, or pulmonary oedema. Hot water was administered in 72 (83 per cent) presentations. Oral analgesia was given in 55 (63 per cent). Parenteral analgesia was given in 53 (61 per cent), most commonly opioids. Local anaesthetic block was performed in 19 presentations (22 per cent), with effectiveness documented in 16/19 (84 per cent). Five patients received antivenom for intractable pain, and all received subsequent parenteral analgesia or local anaesthetic block.

CONCLUSIONS

Stonefish envenomation is characterized by severe pain. Systemic symptoms were rare and not severe in this series. Local anaesthetic block appeared to be the most effective intervention for severe pain when performed. Antivenom appeared to be ineffective in managing pain.

Getting stoned: Characterisation of the coagulotoxic and neurotoxic effects of reef stonefish (Synanceia verrucosa) venom

The reef stonefish (Synanceia verrucosa) is a venomous fish which causes excruciatingly painful envenomations. While some research on the pathophysiology and functions of the venom have been conducted, there are still some gaps in the understanding of the venom effects due to the extreme lability of fish venom toxins and the lack of available testing platforms. Here we set out to assess new functions of the venom whilst also attempting to address some unclear pathophysiological effects from previous literature. Utilising a biolayer interferometry assay, our results highlight that the venom binds to the orthosteric site of the α-1 nicotinic acetylcholine receptor as well as the domain IV of voltage-gated Ca²⁺ (Ca_V1.2) channel mimotopes. Both these results add some clarity to the previously ambiguous literature. We further assessed the coagulotoxic effects of the venom using thromboelastography and Stago STA-R Max coagulation analyser assays. We reveal that the venom produced anticoagulant activity and significantly delayed time until clot formation of recalcified human plasma which is likely through the degradation of phospholipids. There was a difference between fresh and lyophilised venom activity toward the nicotinic acetylcholine receptor mimotopes and coagulation assays, whilst no difference was observed in the activity toward the domain IV of Ca_V1.2 mimotopes. This research adds further insights into the neglected area of fish venom whilst also highlighting the extreme labile nature of fish venom toxins.

Is stonefish Synanceia verrucosa envenomation potentially lethal?

Stonefish sting lethality in man has been scarcely documented since the middle of the 20th century. We report three clinical cases, including one fatality, emphasizing the cardiovascular toxicity of the Synanceia verrucosa venom, and its potentially lethal effects. All clinical data have been recently collected in New Caledonia and French Polynesia.

Investigation of the estuarine stonefish (Synanceia horrida) venom composition

The Estuarine stonefish (Synanceia horrida) is recognised as one of the most venomous fish species in the world but the overall venom composition has yet to be investigated using in-depth transcriptomic and proteomic methods. To date, known venom components are restricted to a hyaluronidase and a large, pore-forming toxin known as Stonustoxin (SNTX). Transcriptomic sequencing of the venom gland resulted in over 170,000 contigs with only 0.4% that were homologous to putative venom proteins. Integration of the transcriptomic data with proteomic data from the S. horrida venom confirmed the hyaluronidase and SNTX to be present, together with several other protein families including major contributions from C-type lectins. Other protein families observed included peroxiredoxin and several minor protein families such as Golgi-associated plant pathogenesis related proteins, tissue pathway factor inhibitors, and Kazal-type serine protease inhibitors that, although not putative venom proteins, may contribute to the venom's adverse effects. BIOLOGICAL SIGNIFICANCE: Proteomic analysis of milked Synanceia horrida venom, paired with transcriptomic analysis of the venom gland tissue revealed for the first time the composition of one of the world's most dangerous fish venoms. The results demonstrate that the venom is relatively less complex compared to other well-studied venomous animals with a number of unique proteins not previously found in animal venoms.

Relationship between food and venom production in the estuarine stonefish Synanceia horrida

BACKGROUND

The potential costs of venom production may be significant to many marine venomous taxa. In general, the parameters that influence the rate of venom production are poorly understood, but seem to be related to feeding frequency.

METHODS

This study examines the effects of starvation on venom profile and venom yield on the estuarine stonefish (Synanceia horrida). In total, the venom of eight stonefishes was tested under two feeding regimes. Over a four week period, one of the two groups underwent an episode of suspended feeding, while the other was fed on a daily basis. The effect of time on venom replacement was determined by a paired T-test. ANOVA was performed to analyze differences in venom weight between fed and unfed treatments.

RESULTS

Nutritional suspension was found to have a significant effect on the quantity of venom produced. SDS-PAGE gel and FPLC revealed that the components of the venom collected from both groups were similar, indicating that four weeks is an adequate time to regenerate key venom components but not replenish initial venom quantities.

CONCLUSIONS

Venom production was found to be affected by starvation.

Stonefish envenomation of hand with impending compartment syndrome

Background

Marine stings and envenomation are fairly common in Malaysia. Possible contact to various marine life occurs during diving, fishing and food handling. Even though majority of fish stings are benign, there are several venomous species such as puffer fish, scorpion fish, lionfish, stingray and stonefish that require urgent medical treatment. Stonefish is one of the most venomous fish in the world with potential fatal local and systemic toxicity effects to human.

Case Presentation

We reported a case of stonefish sting complicated with impending compartment syndrome.

Conclusions

Medical staff should be alert about the possibility of this potential emergency in standard management of stonefish stings.