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Aquaculture 183 2000 13–23 www.elsevier.nlrlocateraqua-online
Differential infectivity of Caligus flexispina ž
Copepoda, Caligidae in three farmed salmonids in Chile
Laura Gonzalez
a,
, Juan Carvajal
a
, Mario George-Nascimento
b
´
a
Dept. de Recursos Naturales y Medio Ambiente, UniÕersidad de Los Lagos, Casilla 557, Puerto Montt, Chile
b
UniÕersidad Catolica de la Santısima Concepcion, Casilla 297, Concepcion, Chile
´ ´
´ ´
Accepted 4 August 1999
Abstract
The ectoparasitic copepod, Caligus flexispina, is causing increasing problems in farmed salmonids in southern Chile. Field and experimental approaches were used to assess whether any
of the three host species, rainbow trout Oncorhynchus mykiss, atlantic salmon Salmo salar and coho salmon Oncorhynchus kisutch, is preferentially colonized. Prevalence, abundance, density
and developmental stages attained by the parasite in three host species were compared. Results clearly revealed that rainbow trout is the most susceptible species: under field conditions, C.
flexispina is more prevalent and abundant and there is a higher proportion of adult stages. No ovigerous females were found in coho salmon. In experimental infestations, rainbow trout were
more heavily colonized by infective copepodids, and these were more likely to reach the adult stage. A mixture of factors inherent to each host-parasite relationship is considered to play a role
in these observations because coho salmon is also colonized by copepodids but a low proportion of the parasites reach the adult stage. However, atlantic salmon is less suitable for colonizing
larva. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Sea lice; Caligus flexispina; Farmed salmonids; Host susceptibility; Copepodid settlement
1. Introduction
Chilean sea lice, Caligus flexispina, ectoparasitic copepods belonging to the Caligi- dae family, have a life cycle consisting of the following stages: two nauplius, one
Ž infectious copepodid, four attached chalimus stages, one pre-adult and the adult unpub-
Corresponding author. Tel.: q56-65-255744; fax: q56-65-254788; e-mail: lgonzaleecored.cl 0044-8486r00r - see front matter q 2000 Elsevier Science B.V. All rights reserved.
Ž .
PII: S 0 0 4 4 - 8 4 8 6 9 9 0 0 2 8 2 - 3
. lished data . With the exception of the naupliar stages, sea lice feed on host mucus, skin
and blood. Sea lice have been reported to reduced productivity and cause disease Ž
outbreaks in a variety of farmed fish species Pike, 1989; Berland, 1993; Grimnes and .
Jakobsen, 1996 . Large scale aquaculture of introduced salmonids began in the early 1980’s in
southern Chile. The first report of sea lice on farmed salmonids in Chile was Caligus Ž
. teres found on coho salmon Reyes, 1983; Bravo, 1987 . Then Gonzalez and Carvajal
´
Ž .
Ž .
1994 and Gonzalez et al. 1997 reported for the first time the presence of C.
´
flexispina on rainbow trout from sea pens. The latter was soon recognized to be a major Ž
. problem on rainbow trout and atlantic salmon on sea sites Carvajal et al., 1998 .
Fig. 1. Map of the south of Chile, indicating the location where seapen reared salmonids were collected.
However, infections with this sea louse have not been reported as a problem on farms Ž
raising coho salmon Associacion Chilena de Productores de Salmon y Trucha, pers.
´ ´
. com. .
C. teres and C. flexispina have low host specificity and are found on several species Ž
. of wild hosts commonly present around salmon farms Carvajal et al., 1998 . In addition
to both species, seven other species of Caligus have been reported from Chilean wild Ž
. fish Fernandez and Villalba, 1986 . Seven of these species have been found in coastal
´
Ž .
waters and others in offshore areas. Nevertheless, Gonzalez and Carvajal 1994 first
´
reported the presence of C. flexispina on farmed salmonids in 1992, even though the species had been previously reported in offshore areas such as the Juan Fernandez
´
Ž .
archipelago and Easter Island, as parasites of non-salmonid fish Carvajal et al., 1998 . The aim of this study was to determine whether there are differences in the
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Ž .
susceptibility of rainbow trout Oncorhynchus mykiss , atlantic salmon Salmo salar Ž
. and coho salmon O. kisutch to C. flexispina infection under both field and controlled
laboratory conditions. The development rate of the parasite in the three hosts was assessed to determine host preference.
2. Materials and methods
