, Volume 155, Issue 3, pp 357-365

The osmotic response of salmon louse,Lepeophtheirus salmonis (Copepoda: Caligidae), during the transition from sea water to fresh water

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Summary

The osmotic changes in haemolymph and body tissues of the ectoparasitic salmon louse,Lepeophtheirus salmonis, have been studied upon transfer from sea water (SW) to dilute sea water (37% SW), and then to fresh water (FW). The parasite shows osmoconformity in SW but hyperosmotic regulation in 37% SW regardless of whether it is attached to the salmon host or free swimming in the water. The same conclusion is reached by haemolymph Cl measurements. In FW, the osmotic tolerance and response of attached and free swimming parasites differ: Attached animals maintain steady haemolymph osmolality and Cl concentration and survive for at least 1 week, while free swimming parasites quickly become diluted and start to die within 8 h.

Acclimation to 37% SW is accompanied by changes in body tissue water content and in the content of ninhydrin positive substances and specific amino acids which suggest the presence of cell volume regulation. Glycine is the dominating free amino acid in the cephalothorax tissues but alanine, proline and taurine also occur in high amounts. Lysine is found to increase significantly during FW acclimation of attached parasites. A breakdown of cell volume regulation is suggested to limit the survival of attached salmon louse in fresh water.