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Sea lice in Chilean salmon farms

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Sandra Bravo at Universidad Austral de Chile
Sandra Bravo
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Sea lice infestation is one of the biggest problems for the Chilean salmon farming-industry. Initially, Caligus teres was the most common species and the most susceptible fish were rainbow trout (Oncorhynchus mykiss) and coho salmon (Oncorhynchus kisutch). However in 1997, a new species of sea lice, Caligus rogercresseyi (Boxshall & Bravo, 2000), appeared which has become the most dangerous ectoparasite affecting Atlantic salmon (Salmo salar) in net pens. To obtain more information about the behavior of C. rogercresseyi on the salmonid species reared in Chile, a survey was conducted over one year at a farm located in Puerto Montt, Region X. Every two weeks, 10 fish were randomly sampled from cages containing stocks of Atlantic salmon, coho salmon and rainbow trout. Results clearly showed that the most susceptible species were Atlantic salmon and rainbow trout which showed the same level of infestation, while coho salmon did not show susceptibility under the same conditions of rearing.
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Bull. Eur. Ass. Fish Pathol., 23(4) 2003, 197
Notes
Sea lice in Chilean salmon farms
Sandra Bravo
Instituto de Acuicultura, Universidad Austral de Chile. Casilla 1327, Puerto Montt, Chile.
sbravo@uach.cl
Abstract
Sea lice infestation is one of the biggest problems for the Chilean salmon farming industry.
Initially, Caligus teres was the most common species and the most susceptible fish were rainbow
trout (Oncorhynchus mykiss) and coho salmon (Oncorhynchus kisutch). However in 1997, a new
species of sea lice, Caligus rogercresseyi (Boxshall & Bravo, 2000), appeared which has become the
most dangerous ectoparasite affecting Atlantic salmon (Salmo salar) in net pens. To obtain more
information about the behavior of C. rogercresseyi on the salmonid species reared in Chile, a
survey was conducted over one year at a farm located in Puerto Montt, Region X. Every two
weeks, 10 fish were randomly sampled from cages containing stocks of Atlantic salmon, coho
salmon and rainbow trout. Results clearly showed that the most susceptible species were Atlan-
tic salmon and rainbow trout which showed the same level of infestation, while coho salmon
did not show susceptibility under the same conditions of rearing.
In Chile a wide variety of caligid copepods
has been reported from a wide variety of wild
fish since 1840, when the first descriptions of
Caligus ornatus were made by Milne-Edwards.
In 1905, Wilson described for the first time
Caligus teres on wild fishes but many years
later this caligid was described as parasite of
coho salmon (Oncorhynchus kisutch) in net
pens (Reyes and Bravo, 1983). According to
Fagetti and Stuardo (1961), most of the caligid
copepods reported for Chile are cosmopoli-
tan and not exclusive to Chilean wild fish.
Since the beginning of the 1980´s, Caligus teres
has always been regarded as the most impor-
tant parasite for salmonids in Chile even
though in 1985, Reyes reported three new spe-
cies of caligid copepods (Caligus serratus,
Caligus amplifurcus and Lepeoptheirus sp.) as
parasites of coho salmon. However Caligus
teres was the predominant species in the sur-
veys carried out at the different farms of the
X Region.
In 1987 the commercial scale production of
rainbow trout (Oncorhynchus mykiss) in ma-
rine waters started in Chile. This species was
found to be highly susceptibility to C. teres,
mainly in sites located in closed bays and shal-
low water, with high productivity and poor
water circulation. Trout severely infested with
caligus showed dark color and high mucus
production on the body surface, as the main
signs of the stressful condition caused by the
high number of parasites on the skin. In se-
vere cases, over 100 parasites were counted
on some individual fish.
In the spring of 1997 a new species of caligus
was recorded, which at the beginning was
Bull. Eur. Ass. Fish Pathol., 23(4) 2003, 198
described as Caligus flexispina (Carvajal et
al.,1998), now formerly named as C.
royercresseyi (Boxshall and Bravo, 2000). This
new species, which has been found to be more
aggressive than Caligus teres, has been present
in the salmon farms since that date. The most
susceptible host species has been the Atlantic
salmon (Salmo salar) on which over 200 para-
sites have been recorded on individual fish
in the most severe cases of infestation. In ad-
dition, rainbow trout have also showed a high
level of susceptibility in recent years.
The aim of this study was to obtain informa-
tion about the behavior of Caligus rogercresseyi
in the three main species of salmon reared in
Chile in order to adopt best strategies to re-
duce the level of parasite on the fish and to
make the use of drugs for its control more ef-
fective.
Surveys were conducted during one year in
order to evaluate the level of infestation of
caligus over the three different stocks of fish
reared in a farm located in Puerto Montt, X
Region. Atlantic salmon were introduced into
seawater in April of 2000 with a weight of 156
g and rainbow trout were introduced one
month later at 167g.
To collect the information, every two weeks
from April 2000 to February 2001, 10 fish were
randomly sampled from one cage of each
stock of Atlantic salmon, rainbow trout and
coho salmon. The stock in each cage was con-
stant during the entire period of sampling,
due to the fact that the fish were being reared
at the sea site until ready for harvest.
For each individual fish, the weight and
number of parasites were recorded, as well
as the developmental stage of the parasite.
The specimens were classified according to
the sex and stage of development (female,
male and chalimus).
etaD nomlaScitnaltAtuorTwobniaR
)rg(thgieWelameFelaMsumilahClatoT)rg(thgieWelameFelaMsumilahClatoT
00/40/02651
00/50/52761
00/60/4101522 4
00/70/0246733173142215
00/80/8044195218
00/80/51 4419 641 11
00/90/70120,1 4206 3263216
00/90/32073,111139681113
00/01/91727,11113541,11124
00/11/513520147451
00/11/12701,2215 4 12874,154871
00/21/2141319634131853
00/21/71055,24213459,154101
10/10/02888,21113941,2 3003
10/20/12095,31113657,23216
Table 1: Data collected from Atlantic salmon and rainbow trout.
Bull. Eur. Ass. Fish Pathol., 23(4) 2003, 199
Daily records were taken of temperature, dis-
solved oxygen, salinity and turbidity through
a Secchi disc, to determine their relationship
to the level of infestation of caligus and the
success of the two treatments used for the two
susceptible species. For both treatments
ivermectin was used via feed at a dosage of
0.21 mg /kg of body weight, administered at
weekly intervals for three times, in doses of
0.07 mg /kg. The first treatment was carried
out in August 2000 and the second in Decem-
ber 2000.
Table 1 shows the data collected from April
2000 to February 2001 for Atlantic salmon and
rainbow trout. Data were not recorded for
coho salmon because they were not found to
be infected during the study.
Results in Figure 1 show no significant dif-
ferences between the susceptibilities of Atlan-
tic salmon and rainbow trout. Both species
showed the same level of infestation and simi-
lar responses to the treatments used for the
control of the sea lice (Mann-Whitney test).
Of the environmental parameters collected
every day, water temperature was the most
relevant factor affecting the abundance of the
parasite. The highest abundance was recorded
in the spring-summer period when the tem-
perature was increasing. (Table 2).
The results obtained in this study revealed no
differences between the susceptibilities of
Atlantic salmon and rainbow trout to caligus,
in that both species were parasitised by both
adult and juvenile copepods during the en-
tire period of sampling. No caligus parasites
were recorded on coho salmon, which is con-
sistent with the information reported by Chil-
ean farmers during recent years (Carvajal et
al. , 1998). Also there were no significant dif-
ferences in abundance of the different devel-
opmental stages on the infected fish.
As the survey in this study was carried out at
a newly established site with a first salmon
production of 4.000 tonnes and located in an
open and deep water with high water circu-
lation, it was concluded that the infestation
of the fish by caligus was mainly due to the
presence of infested wild fish, the suscepti-
bility of the farmed species and the environ-
mental conditions. C. rogercresseyi has shown
high preference for Atlantic salmon and rain-
bow trout and not for coho salmon. Around
the cages a wide variety of non salmonids
marine fish were recorded which have previ-
ously been shown to act as vectors of sea lice
(Carvajal et al., 1998)
There was no mortality associated with the
caligus because infested fishes were treated
before the number of parasites began to be
harmful. The economic losses caused by sea
lice result from the cost of treatments, man-
agement strategies, low growth rates and car-
cass downgrading at harvest, besides the in-
creased susceptibility to other infectious dis-
eases. In this situation, the cost of delousing
Figure 1: Abundance of C. rogercresseyi on rainbow
trout and Atlantic salmon. Arrows show the end of
both treatment with ivermectin.
Bull. Eur. Ass. Fish Pathol., 23(4) 2003, 200
with ivermectin was about US$ 0.004/ kilo of
fish produced, however in sites where the
conditions are more favorable for sea lice, the
number of treatments per year are usually
three or more depending on the environmen-
tal conditions, and consequently the costs are
much higher to the farmer. Because of the
absence of a withdrawal period for the
emamectin benzoate, it is the only drug al-
lowed for control of sea lice in Chile at the
present time, with a cost of delousing about
US$ 0.022/kilo of fish produced.
Acknowledgement
Thanks to Dr. Barry Hill for revision of the
manuscript.
References
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of common Caligus (Copepoda:
Siphonostomatoida: Caligidaer) from
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Carvajal J, Gonzalez L, George- Nascimento
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htnoM)m(psnarTCºTO
2
l/gmcitnaltA/]1R[sugilacºNtuort/]2R[sugilaCºN
00-nuJ3,013,111,84 0
00-luJ3,015,013,87 5
00-guA6,86,018,89 8
00-peS0,117,016,83 3
00-tcO1,64,113,93 4
00-voN9,73,211,91271
00-ceD5,53,310,96353
10-naJ4,80,315,83 01
10-beF0,65,317,93 6
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Gonzalez L, Carvajal J.1994. Parásitos en los
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Gonzalez L., Carvajal J., George-Nascimento
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Table 2: Environmental parameters data
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  • Mar 2000
  • AQUACULTURE
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.
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Native sea lice (Copepoda: Caligidae) infestation of salmonids reared in netpen systems in southern Chile
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  • Jul 1998
  • AQUACULTURE
A survey of parasitic copepods carried out in three introduced salmonid species in Southern Chile and 5 native fish species commonly found in the vicinity of the fish farm cages yielded 5 caligid species. Caligus flexispina, formerly found in the oceanic islands of the Pacific ocean, is currently the dominant species found in continental waters on native fish species (Eleginops maclovinus and Odonthestes regia) as well as on cultured trout Oncorhynchus mykiss from the south of Chile. Coho salmon O. kisutch and Atlantic salmon Salmo salar are more resistant to this parasite. Among the native fish species associated with netpen aquaculture, E. maclovinus harbours 4 caligid copepods, namely Lepeophtheirus mugiloidis, C. flexispina, C. teres and C. cheilodactylus (in the same order of ranked abundance). Odonthestes regia only harbours C. flexispina, whereas Paralichthys microps is a host of Lepeophtheirus edwardsi and C. flexispina. It is highly likely that the transfer of C. flexispina to salmonids is mediated by the presence of these native fish species.
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