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Elliott Normal Fish Skin EAFP 2019 Skin Deep: Microscopic Anatomy of Normal Finfish Integument Diane G Elliott Scientist Emeritus Western Fisheries Research Center U.S. Geological Survey, Seattle, Washington USA Fish Integument • Separates and protects fish from its environment – Also provides means through which most contacts with environment are made • Continuous with lining of all body openings – Also covers the fins Fish Integument Has Many Functions publicdomainpictures.net • Some important functions include: – Protection – Communication and sensory perception – Locomotion – Respiration, ion regulation, and excretion publicdomainpictures.net Form Follows Function • More than 33,000 fish species identified • Structure of integument of each species highly adapted to carry out various functions • Adaptations vary widely among species, but some structural similarities publicdomainpictures.net publicdomainpictures.net publicdomainpictures.net General Fish Skin Structure • As in other vertebrates, fish skin consists Idahoof State U two basic layers: epidermis and dermis Drawing by Stewart Alcorn from Elliott 2000b Lamprey skin Epidermis Dermis (scaleless fish) Hypodermis From Elliott 2011b 100 µm Salmonid skin Epidermis wrapped around scales (scales in loose connective tissue of dermis) Dense connective tissue of dermis 100 µm Hypodermis From Elliott 2011b Epidermis Pacific lamprey (Lampetra tridentata) • Unlike land vertebrates, all epidermal layers in Idaho State U most fishes comprised of living cells From Elliott 2011b – Epidermal thickness varies by Goldfish (Carassius auratus) species and body region, and can also vary by age and sex – Surface cells sloughed when dead and replenished from Basement membrane lower cell layers Chinook salmon (Oncorhynchus tshawytscha) – Epidermis separated from dermis by acellular basement membrane (basal lamina) From Elliott 2011b Pacific lamprey (Lampetra tridentata) Epithelial Cell • Basic cellular element of Idaho State U fish epidermis – Only element common in all species From Elliott 2011b – Also known by other Goldfish (Carassius auratus) names. Examples: Surface epithelial cell • Malpighian cell Epithelial cell • Epidermal cell Basal epithelial cell • Filament-containing cell Basement membrane • Principal cell Chinook salmon (Oncorhynchus tshawytscha) • Keratinocyte • Polygonal cell • Mucous cell (jawless fishes) From Elliott 2011b Pacific lamprey (Lampetra tridentata) Epithelial Cell • Metabolically active throughout epidermal Idaho State U layers in most fishes – Capable of mitotic division in From Elliott 2011b all layers in teleosts but not jawless fishes Goldfish (Carassius auratus) Surface epithelial cell – Generally smaller than most other epidermal cell types Epithelial cell Basal epithelial cell – Key element in wound repair Basement membrane via rapid migration from wound edges (Elliott 2000b, Chinook salmon (Oncorhynchus tshawytscha) 2011a) – Capable of phagocytic activity From Elliott 2011b Epithelial Cell • Shape of cell (ec) varies by location Idaho State U – Basal cells (bec) cuboidal to columnar – Surface cells (sec) often squamous (flattened) – Shape of nucleus roughly corresponds to shape of cell Chinook salmon (Oncorhynchus tshawytscha) From Elliott 2011b Epithelial Cell • Microridges or micropapillae on exterior Idaho State U surface of teleost superficial epithelial cells • May help to hold mucous Chinook salmon (Oncorhynchus tshawytscha) secretions on skin surface • May provide some mechanical protection against trauma • Increase absorptive surface area of 10 µm skin From Elliott 2000b Mucous Cuticle • Mucous secretions produced largely by epithelial cells (in most species) form a protective cuticle on skin surfaceIdaho State U – Surface epithelial cell secretions in cuticle mixed with and modified by secretions from other secretory cell types – Avoidance of mechanical damage and special fixation (e.g. glutaraldehyde-alcian blue) often required to preserve cuticle Blue gourami (Trichogaster trichopterus), PAS stain c =cuticle ep = epidermis arrows = scales lct = loose connective tissue ch = chromatophore 100 µm Photo: Elena Catap Photo: Elena Catap 10 µm From Elliott 2000b From Elliott 2000b Mucous Cuticle • Cuticle continuously sloughed and renewed Idaho State U to help keep surface clear of debris and bacteria – Thickness varies (<1-50 µm) by species and area 10 µm on body, and may be affected by other factors such as environment Juvenile Chinook salmon (Oncorhynchus tshawytscha) a) Skin surface without fixation to preserve cuticle b) Skin surface with cuticle preserved (Glutaraldehyde-alcian blue fixative) 10 µm From Elliott 2011b Mucous Goblet Cell • Unicellular exocrine gland Idaho State U common to most animal groups – Reported in most fishes, gc including: • Jawless fishes: hagfish • Selachians (sharks, skates and rays) Goldfish gc epidermis, methylene blue- • Relict bony fishes: dipnoans azure II stain (lungfish) and Polypteriformes (bichirs and reedfish) • Most teleosts Mucous Goblet Cell Idaho State U • Goblet cells reported absent from: • Jawless fishes: lampreys • Relict bony fishes: Polydon (paddlefish) • Teleost fishes: Periophthalmus (mudskipper) Pacific lamprey epidermis From Elliott 2011b In lampreys, mucus is produced by epithelial cells (also called mucous cells) Mucous Goblet Cell • Most frequently recognized in middle to outer layers of epidermis Idaho State U • May differentiate from epithelial cells in lower epidermis • Differentiated goblet cells do not undergo further mitotic division • Goblet cells may enlarge as move toward epidermal surface and numbers of secretory vesicles increase • Nucleus and organelles often become displaced basally • Goblet cell secretions: mucous glycoproteins and other components, depending on species (most weakly basophilic or unstained in routine histological sections) Hagfish (Myxine sp.) Pacific lamprey ec epidermis gc From Elliott 2011b ec gc gc In lampreys,gc mucus is produced by epithelial cells (also called From Elliott 2011bmucous cells) Chinook salmon (Oncorhynchus tshawytscha) From Elliott 2000b Mucous Goblet Cell • At epidermal surface, Idaho State U goblet cell emerges (usually between adjacent epithelial cells) • Apical goblet cell membrane ruptures to release cell contents, and cell dies From Elliott 2011b 10 µm • In some fishes such as Chinook salmon (Oncorhynchus tshawytscha); apical ends of goblet cells at salmonids, greatest epidermal surface (arrows) volume of epidermal secretions from goblet cells Mucous Goblet Cell • Goblet cell mucus has variety of functions Idaho State U – e.g. lubrication, chemical and physical protection, and possible regulatory functions • Goblet cell numbers affected by many factors within a species: – Body region (even specific area of epidermis covering a Goldfish (Carassius auratus) epidermis showing single scale) goblet cells (gc) (Methylene blue-azure II stain) – Fish sex – Season gc – Processes such as larval gc metamorphosis, sexual maturation or adaptation to gc seawater – Environmental changes or gc exposure to irritants or other From Elliott stressors 2000b Club Cell wikimedia.org Idaho State U • Secretory cell characteristic of certain taxa of ray-finned (actinopterygian) fishes. Present in: – Polypteriformes (relict bony fishes) – Anguilliformes (eels) – Fishes of superorder Ostariophysi (Gonorhynchiformes, Cypriniformes, Characiformes, Siluriformes and Gymnotiformes) • Superorder contains nearly 25% of all known fish species and 75% of all freshwater species Club Cell Club cells (cc) in short-fin eel (Anguilla • Usually large and round to oval or wikimedia.orgaustralis)). club-shaped, with 1-2 centrally located nuclei with prominent nucleoli – Generally in middle layers of epidermis (no openings to epidermal surface) – Club cells in eels have cytoplasmic secretory vacuoles (arrows); ostariophysan club cells do not Ostariophysan club cells in goldfish (Carassius auratus) cc cc Photo: Barbara Nowak 10 µm From Elliott (2000b) Ostariophysan club Ostariophysan Club Cells cells in goldfish (Carassius auratus) • Contain alarm pheromone that iswikimedia.org released into water when epidermis cc is damaged cc – Alarm pheromone detected by other fish of same species, which perform H&E stain species-specific anti-predatory defensive behaviour – Club cells may be lost during spawning season in species with abrasive spawning behaviour (e.g. fathead cc minnow Pimephales promelas) cc – Club cell products may have additional functions methylene blue- azure II stain Club cells (cc) in short-fin eel (Anguilla australis) have secretory vacuoles Eel-Type Club Cells (arrows). Other abbreviations: ec = epithelial cell, gc = goblet mucous cell, bl = basal layer epitelial cells, lct = loose wikimedia.orgconnective tissue (dermis), sca = scale • Eel and polypterid club cells do not appear to be involved in alarm reaction • Bioactive substances identified in club cells suggest other functions in ostariophysans and non-ostariophysans: – Toxins – Anti-pathogenic agents – Specific factors that may be involved in epidermal cell regulation Photo: Barbara Nowak 10 µm From Elliott (2000b) Other Epidermal Cells • Serous cells: Secretory cells reported in a variety of fish taxa Idaho State U From Elliott 2011b – Basally located nucleus and Chinook salmon acidophilic staining cytoplasm (Oncorhynchus tshawytscha); epidermal – Two types (serous goblet cells and secretory serous cell (s) that may be a serous sacciform cells); may only be goblet cell or sacciform distinguishable by electron microscopy cell • Serous goblet
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