The role of the skin of early post-hatch turbot (Scophthalmus maximus L.) in osmoregulation

• Main Author: Robinson, Kevin Peter
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Stirling 1996
• Subjects: Psetta maxima; Osmoregulation; Fishes; Skin; Scophthalmus maximus; Turbot
• Online Access: http://hdl.handle.net/1893/21433; http://dspace.stir.ac.uk/bitstream/1893/21433/1/Robinson-thesis.pdf

To date, the structural significance of the skin of fish larvae in osmoregulation has received little attention and the evidence for salt secretion by cutaneous chloride cells is based largely on morphological observations. Thus, in the present study, a combination of microscopical and electrophysiological techniques were utilised to determine the role of the skin of early post-hatch turbot larvae in osmoregulation. A number of specialised structural features were revealed in the skin of the turbot larva with electron microscopy which would appear to provide some protection against the high osmotic and ionic gradients tending to dehydrate and salt load the body tissue and fluids. In the heterogenous epidermis, consisting of both transporting and non-transporting cells, only the shallow junctions between chloride cells and accessory cells were believed to permit ion influx and/or water loss via the paracellular pathway; the extensive junctions between adjacent pavement cells and pavement cells and neighbouring chloride cells effectively occluding the passage of ions and water through the extracellular space. Chloride cells were revealed in the skin and prebranchial epithelium of the turbot larva from hatching, but accessory cells, and thus "leaky" junctions, were only observed in association with the closely juxtaposed chloride cells in the prebranchial epithelium which, although densely packed, represented just a small area of the otherwise "tight" skin. Water and ion permeation through the external plasma membrane of the superficial pavement cells might further be impeded by the extracellular glycocalyx coat observed in TEM. In addition, the large numbers of mucous cells, which were a characteristic feature of the skin of the turbot larva, may produce a protective mucus coating of low permeability. The apparent "tightness" of the skin was reflected by the measurements of diffusional water permeability (Pdiff) from early stage larvae which suggested that the larvae of turbot were relative impermeable to water ...