Genetic homogeneity coupled with morphometric variability suggests high phenotypic plasticity in the sea louse Caligus rogercresseyi (Boxshall and Bravo, 2000), infecting farmed salmon (Salmo salar) along a wide latitudinal range in southern Chile.

The sea louse Caligus rogercresseyi is the most important pathogen causing "caligidosis" in the Chilean salmon industry. In this study, using cox1 gene, we evaluate the genetic variation of C. rogercresseyi from farmed Salmo salar along a latitudinal range (40°-52°S) in south Chile to determine whether morphological differences are explained by genetic or environmental factors. Female parasites were randomly collected from S. salar at five farms. Body variation was examined using multivariate analyses and genetic heterogeneity was explored with AMOVA. C. rogercresseyi exhibited significant morphometric variability among sites and parasites collected from >54°S were the longest ones. Parasites did not show genetic structure among farms. Thus, C. rogercresseyi infesting salmons is panmictic along an extensive latitudinal range in south Chile. The same genetic pattern can be explained by the frequent movement of parasitized S. salar among farms in that region. Phenotypic plasticity in parasites could be explained by natural or aquaculture-mediated environment variability. C. rogercreseyi from 54°S could favor the local spread of this disease, suggesting an immediate health risk for the recent salmon industry in that region. Further research is required to confirm genetic homogeneity of this parasite along its geographical distribution using more powerful markers (e.g. SNPs).

First report of an egg-predator nemertean worm in crabs from the south-eastern Pacific coast: Carcinonemertes camanchaco sp. nov.

Nemertean worms belonging to the genus Carcinonemertes have been tied to the collapse of crab fisheries in the northeastern Pacific Ocean. A new species is described from egg masses of two commercial crabs, Cancer porteri and Romaleon setosum, inhabiting the central-north Chilean coast. This is the first species of Carcinonemertes described from the southeastern Pacific Ocean. Total body length of Carcinonemertes camanchaco sp. nov. ranged from 2.38 to 4.93 and from 4.29 to 8.92 mm, in males and females, respectively. Among others, traits that distinguish this new species from other previously described congeneric species include: presence of two gonad rows on each side of the intestine, a simple (not decorated) mucus sheath, and a relatively wide stylet basis. Maximum likelihood and Bayesian inference phylogenetic analyses distinguished this new species from all other species of Carcinonemertes with available cox1 sequences in GenBank. Prevalence and mean (± SD) intensity of C. camanchaco sp. nov. was 24% and 2.6 (± 2.07) worms per egg mass in C. porteri and 38.1% and 3.8 (± 2.4) worms per egg mass in R. setosum. The formal description of this new species represents the first step towards the understanding of this worm's impact on the health of crab fisheries in the southeastern Pacific Ocean.

Determining Intermediate Hosts for Opecoelidae and Microphallidae Species (Platyhelminthes: Trematoda) in the Southeastern Pacific Coast, Using Molecular Markers.

Metacercarial stages of digeneans were collected from decapod crustaceans inhabiting intertidal rocky zones in central Chile. The digeneans were identified through a molecular analysis based on the V4 region of the 18S ribosomal RNA gene. We analyzed 356 crustaceans belonging to 10 species, 115 intertidal fish belonging to 6 species, and 4 specimens of 1 coastal bird species. In total, 74.1% of crustaceans were parasitized with metacercariae. We found 1 species of Opecoelidae. This species showed low genetic divergence (0% and 0.1%) with adult digeneans found in intertidal fish and with the species Helicometrina labrisomi infesting a subtidal fish from northern Chile (Labrisomus philippii). Additionally, we found 2 species of Microphallidae, 1 closely related to Maritrema (1.3% genetic distance) and the other related to Microphallus (5% genetic distance). Therefore, our findings showed that the decapod crustaceans are relevant hosts in food webs from the southeastern Pacific coast. Furthermore, we found 5 species of crustaceans as second intermediate hosts for H. labrisomi and 2 species as secondary intermediate hosts for 2 Microphallidae, which contribute to elucidate parts of their life cycles through molecular markers and extended the host distribution of H. labrisomi in the southeastern Pacific coast.