Life history of the caligid copepod Lepeophtheirus hospitalis Fraser, 1920 (Crustacea:Caligoida)

Abstract

Specimens of the starry flounder, Platichthys stellatus (Pallas, 1811) Girard, 1854, were collected in Yaquina Bay near Newport, Oregon, from July, 1970, to August, 1971. Fish infected with Lepeophtheirus hospitalis Fraser, 1920, were transported to Corvallis, Oregon, and maintained in a sea water system at 15°C. Isolated copepods were studied in finger bowls in non-aerated sea water. which was changed several times daily. The morphology and behavior of the ten life history stages of the parasitic copepod L. hospitalis have been described. Measurements and figures for all stages were included. Adults are motile ectoparasites on the ventral surface of the starry flounder. They adhere with prehensile second antennae, maxillipeds, and a suction cup action produced by the arched cephalothorax. The primary food was slime, but if an abrasion or cut was present, blood was sometimes ingested. Seasonal abundance of the parasite in Yaquina Bay seemed to be correlated with the amount of fresh water flowing through the bay. Ovulation and egg string formation occurred simultaneously at night. At 20°C, 64 hours elapsed between ovulation and hatching. The major features of ovulation, egg string formation, embryology, and hatching have been described. The two unsegmented naupliar stages were free-swimxning, positively phototropic, and possessed three pairs of appendages: first antennae, second antennae, and mandibles all of which were used in swimming. The duration of the first naupliar stage at 20°C was seven and a half hours and at 15°C about 24 hours. For the second nauplius these times were 11 and 40 hours respectively. Mortality on the molts following each of these two stages was less than five percent and five to ten percent. The segmented body of the copepodite possessed those appendages present on the naupliar stages, and added the post oral processes, maxillae, maxillipeds, the first two pairs of thoracic legs, and the caudal rami. This stage was free-swimming, but died in three to eight days, at 20°c, if a host was not located. Copepodites held onto the flounder with their prehensile second antennae for four to six days, at 15°c, at which time they formed attaching filaments. This process began with a series of rapid jabs to the host substrate by the anterior cephalothorax. A droplet of frontal organ secretion appeared between copepodite and host and was pulled out into a filament which hardened immediately. At 15°C the molt to the first chalimus stage took place 36 to 48 hours after filament formation. Laboratory mortality from copepodite to first chalimus was over 95 percent. The six chalimus stages at 20°C lasted 6½, 5, 4½, 2½, 2, and 1 days respectively. The first four stages were attached by a frontal filament, the fifth was usually unattached, and the sixth was always unattached. Sexual differentiation became evident in the fifth chalimus: males possessed a sixth pair of legs, females did not. Sixth chalimus males were usually found coupled to adult females or mobile chalimus stages of either sex. The third and fourth pairs of legs appeared in the first chalimus stage. The post antennal processes and fifth pair of legs were new structures in the third chalimus, and the sternal furca was new to the fourth chalimus. The above mentioned times, changes, and behavior were compared to that of other caligids. Possible functions for all appendages and processes previously proposed were given and it was herein suggested that the post oral process serves to protect the mouth cone.