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Cytat
Do celu tam się wysiada. Lec Stanisław Jerzy (pierw. de Tusch-Letz, 1909-1966)
A bogowie grają w kości i nie pytają wcale czy chcesz przyłączyć się do gry (. . . ) Bogowie kpią sobie z twojego poukładanego życia (. . . ) nie przejmują się zbytnio ani naszymi planami na przyszłość ani oczekiwaniami. Gdzieś we wszechświecie rzucają kości i przypadkiem wypada twoja kolej. I odtąd zwyciężyć lub przegrać - to tylko kwestia szczęścia. Borys Pasternak
Idąc po kurzych jajach nie podskakuj. Przysłowie szkockie
I Herkules nie poradzi przeciwko wielu.
Dialog półinteligentów równa się monologowi ćwierćinteligenta. Stanisław Jerzy Lec (pierw. de Tusch - Letz, 1909-1966)
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., 1996).(Reproduced with permissionfrom Academic Press.) Toxic responses of the skin 171Figure 3.3 Scanning electron micrograph of theepidermal surface of a rainbow trout.Individual filament-containing cells havemicroridges on their surface, and theirboundaries are delineated by a continuouscircumferential microridge.The tops ofthe mucous glands (arrows) squeezebetween the filament-containing cells togain access to the surface (2500×, fromHawkes, 1983).(US Governmentpublication.)DermisThe dermis of fish skin lies between the epidermis and the underlying muscle (Figures3.1 and 3.2).It is made up of two layers.The outer layer or stratum spongiosum consistsof collagen, fibroblasts and pigment cells.The lower layer, the stratum compactum, is anon-cellular layer of orthogonal bands of collagen required for structural rigidity andattachment of the skin to the underlying muscle (Hawkes, 1974a; Whitear, 1986b).Collagen fibers in sheets are attached at right angles, which allows them to bend andmove horizontally during swimming without wrinkling the skin surface (Figures 3.1 and3.2).The dermis contains the primary vasculature of the skin, composed of an extensivenetwork of blood vessels concentrated in the upper stratum spongiosum of the dermis(Figure 3.5A) just below the epidermis with branches reaching upward into the epidermisthat covers the scales (Figure 3.5B) (Jakubowski, 1982).On the distal part of the scale(covered with epidermis), shown in Figure 3.5B, the topography of the capillary networkfollows closely the sculpture of the scale. Target organ toxicity in marine and freshwater teleosts 172Scales are flexible, translucent, calcified plates that provide further surface protectionand are located in pockets obliquely inserted within the superficial dermis or stratumspongiosum (Van Oosten, 1957).The outermost edges of the scales are covered withepidermis and a fold of dermal tissue, as shown in Figure 3.6.For a more in depthaccount of the development and regeneration of scales, the reader is referred to a recentreview by Bereiter-Hahn and Zylberberg (1993).Trout possess scales originating fromthe stratum spongiosum of the dermis, whereas the catfish are scaleless and have manytaste bud papillae emanating from the stratum spongiosum (Figures 3.1 and 3.2).Theepidermis of the catfishFigure 3.4 Electron micrograph of a mucous cellfrom an adult rainbow trout.Themembrane-bound packets of mucin breakdown as the contents of the cell areemptied (6400×, from Hawkes, 1983).(USGovernment publication.)at the point where taste bud papillae near the surface is only 0.08 mm thick, but is 0.50mm thick where there are no taste buds.The rather uneven surface of the catfish skin inFigure 3.2 is probably caused by the large number of taste buds forming pits on the Toxic responses of the skin 173epidermal surface.In those fish that are scaleless, the epidermis is thicker than in scaledspecies and often has a more abundant supply of mucous and alarm substance cells.Figure 3.5 Subepidermal capillary network in theskin on the scaleless head of the Amur(Ctenopharyngodon idella) (A), and on thescales (B).Vessels are stained with anindia ink injection (from Jakubowski,1982).(Reproduced with permission fromPolish Academy of Science.) Target organ toxicity in marine and freshwater teleosts 174The color of fish skin comes from an interaction between three major types of pigmentcells (melanophores, xanthophores, and iridophores) that are located within the dermisforming a chromatophore unit (Hawks, 1974b).The melanophores contain melaningranules which absorb light in the visible range and appear black.The xanthophores havedrosopterin and carotenoid granules, which are yellow.Iridophores contain platelets ofguanine or hypoxanthine, which reflect light and give fish a shiny appearance.Thexanophores lie above the melanophores and are surrounded by cytoplasmic extensions ofthe melanophores.Environmental or physiologic stimuli can cause melanin to move inand out of the cytoplasmic extensions of the melanophores, thereby darkening orlightening the fish color as required for its camouflage protection (Hawks, 1974b).The layer beneath the dermis, the subcutis or hypodermis, is mostly loose connectivetissue.Pigment cells, fat cells, small blood vessels, and nerves are also numerous withinthe hypodermis, which rests on the muscle layer beneath (Figures 3.1 and 3.2) (Hawkes,1974a).FunctionThe function of fish skin is unique in that it must provide an effective protective barrieragainst physical abrasion, parasites, disease organisms and environmental chemicals,while simultaneously acting as a sensitive, interactive, exchange surface between theinternal and external environments of the fish.To perform this task successfully, fish skinmust rely on a number of capabilities that involve morphologic (structural), physiologic,biochemical, and sensory processes.Figure 3.6 Longitudinal section perpendicular to theskin of a typical teleost fish showing thescales in their pockets obliquely insertedin the superficial dermis.The inner surfaceof the scale pocket is lined by the SPL(scale-pocket lining)
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