Both the first (NI) and second (NII) nauplius larvae displayed the same general pattern of DAB-positive staining, although some slight differences were evident. In addition to two large dorsal and ventral ‘median’ glands, both larval stages consistently displayed three pairs of distinct glandular regions arranged in a bilaterally symmetrical pattern (Fig. 1). These gland populations have been named in accordance with their location within the animal.
In addition to these glands, late NII larvae possessed up to 10 small DAB-positive areas, arranged in a symmetrical pattern, in the posterior half of the body between the lateral and posterior glands, position ‘Th’ in Fig. 1. These areas corresponded to the position of glands present in the thoracic limbs of the following copepodid stage. The posterior glands exited via two small pores, one lying close to the ventral side of each balancer.
During the staining process some individual, unhatched eggs of L. salmonis were inadvertently stained along with the hatched nauplius stages. Examination of these eggs showed that pre-hatch nauplii had the same pattern of DAB-positive gland distribution as the NI stage larvae.