Skin toxins in coral-associated Gobiodon species (Teleostei: Gobiidae) affect predator preference and prey survival

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.

Trophic separation in planktivorous reef fishes: a new role for mucus?

The feeding apparatus directly influences a species' trophic ecology. In fishes, our understanding of feeding modes is largely derived from studies of rigid structures (i.e. bones, teeth, gill rakers). A recently described lip innovation, however, highlighted the role of soft anatomy in enabling specialized feeding modes. In this study, we explore whether similar diversification may also occur in the soft anatomy of the buccal cavity. Using four key anatomical traits to classify 19 species (14 genera) of wrasses, we evaluated the relationship between anatomical specialization of the buccal cavity and diet. Our data revealed a previously undocumented anatomical adaptation in the mouths of fairy wrasses (Cirrhilabrus): the mucosa throughout the buccal cavity (i.e. anterior to the pharynx) is packed with goblet cells, enabling it to secrete large quantities of mucus in this region; a new trait that, until now, had not been documented in wrasses. This disparity reflects diet differences, with mucus secretion found only in planktivorous Cirrhilabrus that feed predominantly on amorphous organic material (potentially gelatinous organisms). This suggests a cryptic mucus-based resource partitioning in planktivorous wrasses.

Evolutionary Ecology of Fish Venom: Adaptations and Consequences of Evolving a Venom System

Research on venomous animals has mainly focused on the molecular, biochemical, and pharmacological aspects of venom toxins. However, it is the relatively neglected broader study of evolutionary ecology that is crucial for understanding the biological relevance of venom systems. As fish have convergently evolved venom systems multiple times, it makes them ideal organisms to investigate the evolutionary ecology of venom on a broader scale. This review outlines what is known about how fish venom systems evolved as a result of natural enemy interactions and about the ecological consequences of evolving a venom system. This review will show how research on the evolutionary ecology of venom in fish can aid in understanding the evolutionary ecology of animal venoms more generally. Further, understanding these broad ecological questions can shed more light on the other areas of toxinology, with applications across multiple disciplinary fields.

Biological and Ecological Roles of External Fish Mucus: A Review

Fish mucus layers are the main surface of exchange between fish and the environment, and they possess important biological and ecological functions. Fish mucus research is increasing rapidly, along with the development of high-throughput techniques, which allow the simultaneous study of numerous genes and molecules, enabling a deeper understanding of the fish mucus composition and its functions. Fish mucus plays a major role against fish infections, and research has mostly focused on the study of fish mucus bioactive molecules (e.g., antimicrobial peptides and immune-related molecules) and associated microbiota due to their potential in aquaculture and human medicine. However, external fish mucus surfaces also play important roles in social relationships between conspecifics (fish shoaling, spawning synchronisation, suitable habitat finding, or alarm signals) and in interspecific interactions such as prey-predator relationships, parasite–host interactions, and symbiosis. This article reviews the biological and ecological roles of external (gills and skin) fish mucus, discussing its importance in fish protection against pathogens and in intra and interspecific interactions. We also discuss the advances that “omics” sciences are bringing into the fish mucus research and their importance in studying the fish mucus composition and functions.

The hidden half: ecology and evolution of cryptobenthic fishes on coral reefs

Teleost fishes are the most diverse group of vertebrates on Earth. On tropical coral reefs, their species richness exceeds 6000 species; one tenth of total vertebrate biodiversity. A large proportion of this diversity is composed of cryptobenthic reef fishes (CRFs): bottom-dwelling, morphologically or behaviourally cryptic species typically less than 50 mm in length. Yet, despite their diversity and abundance, these fishes are both poorly defined and understood. Herein we provide a new quantitative definition and synthesise current knowledge on the diversity, distribution and life history of CRFs. First, we use size distributions within families to define 17 core CRF families as characterised by the high prevalence (>10%) of small-bodied species (<50 mm). This stands in strong contrast to 42 families of large reef fishes, in which virtually no small-bodied species have evolved. We posit that small body size has allowed CRFs to diversify at extremely high rates, primarily by allowing for fine partitioning of microhabitats and facilitation of allopatric reproductive isolation; yet, we are far from understanding and documenting the biodiversity of CRFs. Using rates of description since 1758, we predict that approximately 30 new species of cryptobenthic species will be described per year until 2050 (approximately twice the annual rate compared to large fishes). Furthermore, we predict that by the year 2031, more than half of the described coral reef fish biodiversity will consist of CRFs. These fishes are the 'hidden half' of vertebrate biodiversity on coral reefs. Notably, global geographic coverage and spatial resolution of quantitative data on CRF communities is uniformly poor, which further emphasises the remarkable reservoir of biodiversity that is yet to be discovered. Although small body size may have enabled extensive diversification within CRF families, small size also comes with a suite of ecological challenges that affect fishes' capacities to feed, survive and reproduce; we identify a range of life-history adaptations that have enabled CRFs to overcome these limitations. In turn, these adaptations bestow a unique socio-ecological role on CRFs, which includes a key role in coral reef trophodynamics by cycling trophic energy provided by microscopic prey to larger consumers. Although small in body size, the ecology and evolutionary history of CRFs may make them a critical component of coral-reef food webs; yet our review also shows that these fishes are highly susceptible to a variety of anthropogenic disturbances. Understanding the consequences of these changes for CRFs and coral reef ecosystems will require us to shed more light on this frequently overlooked but highly diverse and abundant guild of coral reef fishes.

Quantitative shotgun proteomics distinguishes wound-healing biomarker signatures in common carp skin mucus in response to Ichthyophthirius multifiliis

Ichthyophthirius multifiliis is a ciliated protozoan parasite recognized as one of the most pathogenic diseases of wild and cultured freshwater fish. Fish skin mucus plays a significant role against invading pathogens. However, the protein-based modulation against infection with I. multifiliis, of host fish at this barrier is unknown. Thus, we investigated the skin mucus proteome of common carp using a shotgun proteomic approach at days 1 and 9 after I. multifiliis exposure. We identified 25 differentially expressed proteins in infected carp skin mucus. Upregulated proteins were mainly involved in metabolism, whereas downregulated proteins were mainly structural. This is the first proteomic analysis of infected common carp skin mucus, and it provides novel information about proteome alteration caused by I. multifiliis. Furthermore, we identified novel proteins with yet unknown function in common carp following penetrating injuries such as olfactomedin 4, lumican, dermatopontin, papilin and I cytoskeletal 18. This analysis, therefore, represents a key for the search for potential biomarkers, which can help in a better understanding and monitoring of interactions between carp and I. multifiliis. This proteomic study not only provides information on the protein-level pathways involved in fish-ciliate interactions but also could represent a complementary system for studying tissue repair.

Biliary Tract-Infecting Myxosporeans from Estuarine and Reef Stonefish (Scorpaeniformes: Synanceiidae) Off Eastern Australia, with Descriptions of Sphaeromyxa horrida n. sp. and Myxidium lapipiscis n. sp. (Myxosporea: Bivalvulida)

Two new species of myxosporeans are described from the gallbladders of estuarine stonefish, Synanceia horrida, and reef stonefish, Synanceia verrucosa, from localities off Cairns, in tropical north Queensland and in Moreton Bay in southern Queensland, Australia. Sphaeromyxa horrida n. sp. can be distinguished from congeners in the morphologically distinct "balbianii" species group within Sphaeromyxa on the basis of morphometric differences in length and width of mature spores, length and width of polar capsules, and unique small-subunit (SSU) ribosomal (rDNA) sequence composition relative to other taxa. Replicate SSU rDNA sequences generated from Sph. horrida n. sp. collected from Sy. horrida and Sy. verrucosa in tropical north Queensland and from Sy. horrida in Moreton Bay were identical, suggesting that this species is widely distributed along the east coast of Australia. Myxidium lapipiscis n. sp. can be distinguished from the majority of described Myxidium species on the basis of its relatively small mature spore size (6.1-7.9 μm long × 3.1-3.9 μm wide), and its unique SSU rDNA sequence. Specimens putatively identified as M. lapipiscis n. sp. were found in Sy. horrida from both tropical north Queensland and Moreton Bay, suggesting that this taxon is also widely distributed along the east coast of Australia. However, no molecular data were available for the specimens from tropical north Queensland for comparative genetic analyses. Bayesian inference and maximum likelihood analysis of the SSU rDNA sequences for these 2 new species revealed that Sph. horrida n. sp. formed a strongly supported clade with Sphaeromyxa zaharoni Diamant, Whipps, and Kent, 2004, which was described from the scorpaeniform, Pterois miles, from the Red Sea. This is the first report of myxozoans infecting stonefish (Synanceiidae).