the fish. The second pair of antennae is also used by males to grasp the female during copulation. The adult females are always significantly larger than males and develop a very large genital complex, which in many species makes up the majority of the body mass. Two egg strings of 500 to 1000 eggs (L. salmonis), which darken with maturation, are roughly the same length as the female's body. One female can produce 6-11 pairs of egg strings in a lifetime around 7 months. Development Sea lice have both free-swimming (planktonic) and parasitic life stages, all separated by moults. The development rate for L. salmonis from egg to adult varies from 17 to 72 days depending on temperature. The lifecycle of L. salmonis is shown in the figure; the sketches of the stages are from Schram. Eggs hatch into nauplii I, which moult to a second naupliar stage; both naupliar stages are nonfeeding, depending on yolk reserves for energy, and adapted for swimming. The copepodid stage is the infectious stage and it searches for an appropriate host, likely by chemo- and mechanosensory clues. Currents, salinity, light, and other factors also assist copepodids in finding a host. Preferred settlement on the fish occurs in areas with the least hydrodynamic disturbance, particularly the fins and other protected areas. Copepodids once attached to a suitable host feed for a period of time prior to moulting to the chalimus I stage. Sea lice continue their development through three additional chalimus stages each separated by a moult. A characteristic feature of all four chalimus stages is that they are physically attached to the host by a structure referred to as the frontal filament. Differences in the timing, method of production, and the physical structure of the frontal filament are seen between different species of sea lice. With exception of a short period during the moult, the preadult and adult stages are mobile on the fish, and in some cases, can move between host fish. Adult females, being larger, occupy relatively flat body surfaces on the posterior ventral and dorsal midlines and may actually outcompete preadults and males at these sites. Feeding habits The naupliar and copepodid stages until they locate a host are nonfeeding and live on endogenous food stores. Once attached to the host, the copepodid stage begins feeding and begins to develop into the first chalimus stage. Copepods and chalimus stages have a