Sea Lice Report from Chile
Challenges facing Chilean salmon farmers from the Caligus louse
SEA lice is undoubtedly the main threat the salmon farming industry in Chile has faced since the beginning of production at sea. Caligus teres was the first salmon louse reported infecting coho salmon in 1981 (Reyes & Bravo, 1983) and since 1997, Caligus rogercresseyi is the louse affecting the susceptible salmonids species Atlantic salmon and rainbow trout, while coho salmon has been shown to be resistant (Boxshall & Bravo, 2000).
At the beginning, C. rogercresseyi was widely distributed in the Region
X (Los Lagos) where the salmon industry was first developed. However, through the years, salmon production was expanded to the south and so C. rogercresseyi spread together with salmon farming.
Now its distribution in Chile is along the coastline of the regions X (42ºLS); XI (45ºLS) and XII (47ºLS). It has also been recorded in the anadromous brown trout in southern Argentina since 1998 (Bravo et al., 2006) and in northern Peru, infesting tilapias in 2001 (Bravo et al., 2011)
C. rogercresseyi is about 5mm in length with no difference in size between males and females (fig. 1), but there is a difference from Lepheophteirus salmonis where females are larger than males. The lifecycle comprises eight stages: two nauplius, one copepodid, four chalimus stages and adult, with no preadult stages (fig. 2). The lifecycle is completed in about 45 days at 10ºC, while it is completed in around 26 days at 15ºC (Gonzalez & Carvajal, 2003).
The fecundity rate of C. rogercresseyi is 10 to 20 times less than in L. salmonis. The number of eggs per string is around 50, lower than the number of eggs per string reported for L. salmonis. Both louse females produce up to 11 broods after a single mating. The egg strings in gravid C. rogercresseyi females can be produced with a periodicity of between four to six days depending on the water temperature.
Females can survive under laboratory conditions for up to 79 days and males for up to 60 days. However, in the field their life span could be even longer. None of the sexes are able to survive free in seawater without a host for more than seven days under laboratory conditions, the same situation that has been recorded for copepodids (Bravo, 2010).