The distribution of exocrine glands in Lepeophtheirus salmonis and Caligus elongatus (Copepoda: Caligidae)

The morphology, function and distribution of exocrine glands of copepods have rarely been studied in detail and almost nothing is known about them in the sea lice species L. salmonis and C. elongatus. This study utilised a novel application of a light-microscopy staining technique to reveal a variety of glands in nauplius, copepodid, chalimus, preadult and adult stages. The stain, 3',3-diaminobenzidine tetrahydrochloride (DAB), applied to fresh material, differentiated a population of exocrine glands and enabled a study of their distribution. The stain was successful in highlighting the ducts and pores associated with the larger glands. The locations of gland sub-populations were conserved in all life-stages, although glands in the swimming legs were found to be better represented in mobile and free-swimming stages i.e. copepodids, preadults and adults. Glands associated with the mouth-tube were also located. Other, nonglandular, peroxidase-positive regions were also highlighted by the stain. These regions were found mainly in preadult and adult stages where they formed characteristic bi-symmetrical patterns on the cuticle of the dorsal surface. A study of some calanoid copepods suggested that peroxidase-positive glands are a feature peculiar to caligid copepods. This staining technique has proven useful for elucidating the ontogeny of gland populations in caligids.