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

Abstract

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 m 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, non-glandular, 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.

Exocrine glands of Lepeophtheirus salmonis (Copepoda: Caligidae): Distribution, developmental appearance, and site of secretion

“…As previously reported (Bell et al, ), numerous glands were found within the salmon louse cephalothorax, and some in the genital segment, abdomen and the thoracic legs. A bilateral symmetry in the gland distribution was noticed.…”

“…The teg 2 glands and some teg 1 glands have identical location to glands identified after DAB staining (Fig. , Bell et al, ). This indicates that these glands express peroxidases, supported by the expression of LsPxt1 in teg 2 glands.…”

“…Teg 2 glands are present at the nauplius I stage (Fig. 3D), corresponding to the medial, anterior, lateral and posterior glands named by Bell et al (2000). In the copepodid stage, teg 2 glands are also found within the thoracic legs 1 and 2, while the medial gland directly overlays the mouth tube and the posterior glands are situated in the abdomen near the caudal rami.…”

“…DAB‐staining of adult female lice was done according to Bell et al (). In short, live adult female lice were put into Tris buffered DAB (0.66% w/v) (Sigma Aldrich) with 0.026% H 2 O 2 , and incubated for 16 h before the reaction was stopped with 70% ethanol.…”

“…Bron et al () suggested that mucus producing glands are connected to the mouth tube of the copepodid via large ducts, and two labral pores have been identified in the copepodid and preadult salmon louse (Fast, ). A general 3′,3‐diaminobenzidine tetrahydrochloride (DAB) staining applied to visualize the distribution of exocrine glands in all lice life stages also revealed possible glands around the area of the mouth tube in addition to numerous glands within the rest of the cephalothorax, genital segment and abdomen (Bell et al, ). The whole‐mount DAB staining indicated that exocrine glands of salmon lice have peroxidase activity, but their morphology and function still remains unknown despite some effort to identify salmon lice glandular products.…”