Exocrine glands of the caligid copepod Lepeophtheirus salmonis (Kroyer, 1837)

Abstract

A variety of different functions have been attributed to the secretions of copepod exocrine glands. Such secretions have been suggested to possess, amongst other properties, hydrodynamic, predator deterrent, cuticle hardening and antifoulant activities. The nature of the secretion of a selected group of exocrine glands of the caligid copepod Lepeophtheirus salmonis was examined. Firstly, the number and pattern of distribution of the defined glands of L. salmon is were identified in all life-stages. In comparison, several species of parasitic, commensal and freeliving copepods and other crustaceans were examined to determine the extent of the distribution of such glands within the Crustacea. Histochemical techniques and ultrastructural analysis of glandular tissues were utilised to suggest the probable biochemical characteristics of the gland contents and revealed that mucus and protein were components of the gland secretions. TEM analysis revealed a considerable mucus layer covering the body cuticle of L. salmonis. This layer was presumed to be derived from the exocrine glands of this species. To characterise the secretion more precisely specific enzyme assays, selective stammg procedures and high performance thin layer chromatography (HPTLC) were employed. These techniques indicated that the peroxidatic enzyme catalase was present in the glands at significantly higher levels than in the general body tissues. This enzyme was shown to be contained within the secretory vesicles of the glands. Having positively identified an enzymatic component of the gland tissues, acrylamide gel electrophoresis was undertaken to specifically determine the molecular weight and quaternary structure of the enzyme. Further studies using this technique focused on identifying secreted enzymes of L. salmonis and correlated such proteins to those identified in samples of gland tissue. A four subunit, catalase of between 260 and 280kDa was demonstrated to be present in the secretions of L. salmonis. The fmal stage of the work tested the hypothesised functions of the secretions of the identified glands of L. salmon is. The gland secretions of L. salmonis were demonstrated not to possess an antibacterial activity against some common species of marine bacteria whilst the deliberate removal of the external mucus layer significantly affected the hydrodynamic characteristics of L. salmonis.