Observations on skin structure and sloughing in the stone fish Synanceja verrucosa and related fish species as a functional adaptation to their mode of life

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.

Composition and formation of flame cell caps: A substratum for the attachment of micro-organisms to sea horse epidermis

The epidermis of the sea horseHippocampus kudais characterised by flame cone cells, each of which protrudes 20-40 μm above the surface and is covered by a prominent mucous cap. Unlike normal surface cells, the mucoid caps can support epiphytic microbial growth.

Histochemically the mucous cap is a neutral mucopolysaccharide-protein complex possessing 1,2 glycol groups and SH-groups; acid mucopolysaccharides are absent. The acid mucopolysaccharide glycocalyx of unmodified surface cells is absent from the mucous cap surface.

Ultrastructurally two types of vesicle can be distinguished in flame cells. Type I is oval (0·3 × 0·6 um) with contents of medium electron density and occurs principally in mature flame cells. Type II, seen only in developing cells, is spherical (0·4 μm) and contains rod-like subunits characteristic of the cap mucous. Secretion is mediated by channels formed by smooth endoplasmic reticulum. Unmodified surface cells also secrete their vesicular contents, which resemble the Type I vesicles of flame cells and are similar to the goblet mucous vesicles of other fish, through similar channels.

Flame cell mucous caps, by virtue of their histochemistry, possible provide a suitable substratum for the adhesion and growth of epiphytes which in turn may afford protection against cnidarian nematocysts.

Cutaneous biology and diseases of fish

The normal structure and function of the piscine integument reflects the adaptation of the organism to the physical, chemical, and biological properties of the aquatic environment, and the natural history of the organism. Because of the intimate contact of fish with the environment, cutaneous disease is relatively more common in fish than in terrestrial vertebrates and is one of the primary disease conditions presented to the aquatic animal practitioner. However, cutaneous lesions are generally nonspecific and may be indicative of disease that is restricted to the integument or a manifestation of systemic disease. Regardless, a gross and microscopic examination of the integument is simple to perform, but is highly diagnostic and should always be included in the routine diagnostic effort of the aquatic animal practitioner, especially since various ancillary diagnostic procedures are either not practical or lack predictive value in fish. The purpose of this article is to provide an overview of normal cutaneous biology prior to consideration of specific cutaneous diseases in fish.

Mucosaccharide histochemistry and histoenzymorphologic observations on the epidermis of Ariosoma balearicum de la Roche (Anguilliformes, Pisces)

The epidermis of Ariosoma balearicum consists of three layers - the basal layer, the middle layer and the outer layer. In between the basal cells are found clusters of small lymphocytes which show a moderat acid phosphatase activity. The middle layer and the outer layer are composed of three types of cells - the polygonal cells, the mucous cells and the club cells. The mucosubstances within the mucous cells exhibit the properties of neuraminic acid containing mucosaccharides with vicinal hydroxyl, sulfate esters and carboxyl groupings. The superficial cells of the outermost layer are capable of secreting sulphated and carboxylated mucosubstances to form an extracellular mucous coating which in fish epidermis seems to be necessary for the accumulation of electrolytes. The club cells are generally provided with one nucleus or double nuclei which appear displaced from the center and constitute the main histological component of the middle layer. The contents of these cells, in addition to a strong protein uptake visualized by the positive reactions exhibited in the coupled tetrazonium and mercuric bromophenol blue preparations, gave positive response to neutral mucosubstances which appear to be a glycoprotein involved in the slime secretions. Alkaline phosphatase and TPP-hydrolysing enzyme which could be detectable in the basal layer and the basement membrane were correlated with the probable role that they could play in the transportation of various chemicals and nutriments through the cell membranes.