Morphology and pathology of the ectoparasitic copepod,
Nicothoë astaci (‘lobster louse’) in the European lobster,
Homarus gammarus
EMMA C. WOOTTON1, EDWARD C. POPE1, CLAIRE L. VOGAN2, EMILY C. ROBERTS1,
CHARLOTTE E. DAVIES1 and ANDREW F. ROWLEY1*
1Department of Biosciences, College of Science, Swansea University, Singleton Park, Swansea SA2 8PP, UK
2College of Medicine, Swansea University, Singleton Park, Swansea SA2 8PP, UK
(Received 6 January 2011; revised 18 March and 21 April 2011; accepted 10 May 2011; first published online 15 July 2011)
SUMMARY
Ectoparasitic copepods have been reported in a wide range of aquatic animals, including crustacean shellfish. However, with
the exception of the salmon louse, Lepeophtheirus salmonis, our knowledge of such parasites in commercial species is
rudimentary. The current study examines the morphology and pathology of the parasitic copepod, Nicothoë astaci (the
‘lobster louse’) in its host, the European lobster, Homarus gammarus. Lobsters were sampled from waters surrounding
Lundy Island (Bristol Channel, UK) and all individuals collected were found to harbour female adultN. astaci in their gills,
with a mean of 47·3 parasites/lobster. The majority of N. astaci were found in the basal region of pleurobranch gills. The
parasite was found to attach to gill filaments via its oral sucker, maxillae and maxillipeds, and to feed on host haemolymph
(blood) through a funnel-like feeding channel. It caused varying degrees of damage to the host gill, including occlusion of
gill filaments and disruption to the vascular system in the central axis. Although there was evidence of extensive host
response (haemocytic infiltration) to the parasite, it was displaced from the parasite attachment site and thus was observed in
the central gill axis below. The region of gill filament immediately underlying the parasite feeding channel was devoid of
such activity suggesting that the parasite interferes with the cellular defence and haemostatic mechanisms of the lobster in
order to maintain invasion of the host.
Key words: Homarus gammarus, European lobster, Nicothoë astaci, parasitic copepod, pathology, host defence.
INTRODUCTION
Copepods are a group of ca. 12000 planktonic species
of the phylum Crustacea (Brusca and Brusca, 2003).
Approximately 50% of these species are considered to
live in symbiotic associations (including parasitism)
with a broad spectrum of aquatic animals, ranging
from sponges to marine mammals (Boxshall, 2005).
To date, the majority of research has concentrated on
ectoparasitic copepods of fish, such as the salmon
louse,Lepeophtheirus salmonis. Over the past 30 years,
L. salmonis has become a major worldwide problem
of salmonid aquaculture, costing ca. US$480 million
p.a. in terms of loss of production and parasite control
(Costello, 2009a). There is also evidence suggesting
that salmon farms may be responsible for declines in
wild populations of salmonids as a result of parasitic
sea lice transfer (e.g. Krkošek et al. 2007; Costello,
2009b), but this idea remains controversial (e.g.
Riddell et al. 2008). Furthermore, sea lice are thought
to act as reservoirs of infection and vectors of
transmission for various viral (Nylund et al. 1994),
bacterial (Cusack and Cone, 1986), and other
parasitic (Nowak et al. 2010) diseases.
Our knowledge of ectoparasitic copepods in
commercially important shellfish is far more limited.
For example, lobsters harbour various species of
copepod (Shields et al. 2006), but research into their
effect on lobsters, in terms of health and survival, is
very limited. One parasitic copepod species, Nicothoë
astaci (‘lobster louse’), has been recorded in
European lobsters, Homarus gammarus, from a wide
variety of locations, including the UK, Ireland,
Sweden, Norway, Germany, Netherlands, Portugal,
France and Morocco (e.g. Gotto, 1954; Faure, 1958;
Mason, 1959; Sindermann and Rosenfield, 1967;
Holmes et al., 1997; ICES 2007; GBIF Data Portal,
data.gbif.org, accessed 23-11-10). However, very
little is known about its pathology and subsequent
effect on lobster populations. Even the full life cycle,
including the male copepod, remain elusive. Early
studies, however, have revealed that the copepod
attaches to lobster gill filaments via a suctorial mouth
in order to feed on host haemolymph (blood) (Leigh-
Sharpe, 1926; Gurney, 1930; Mason, 1959). Since
lobster fisheries in the UK are worth an estimated
£26 million p.a. (Marine Management Organisation,
2009) and the fact that this parasite could provoke
* Corresponding author: Department of Biosciences,
College of Science, Swansea University, Singleton Park,
Swansea SA2 8PP, UK. Tel: +1792 295455. E-mail: a.f.
rowley@swansea.ac.uk
1285
Parasitology (2011), 138, 1285–1295. © Cambridge University Press 2011
doi:10.1017/S003118201100093X

severe detrimental effects on its host, there is a need to
improve our understanding of N. astaci infections at
both the host and ecosystem level.
The current study is an assessment of N. astaci
infection in the European lobster, H. gammarus
collected from Lundy Island, Bristol Channel, UK.
Particular emphasis was placed on the intensity of
the N. astaci infection, together with the nature of
the host-parasite interaction, and subsequent tissue
damage and host response.
MATERIALS AND METHODS
Lobster collection
European lobsters (H. gammarus) were collected
using baited commercial pots from waters surround-
ing Lundy Island, Bristol Channel, UK, during July
and September 2010. In total, 23 lobsters (16 males
and 7 females) were processed for histopathology. All
lobsters were transported back to SwanseaUniversity
for analysis. Lobsters collected in July were sampled
immediately while those collected in September were
maintained under aquarium conditions (<7 days)
with fish and shellfish feed, prior to sampling.
Parasite prevalence and intensity
Gross external characteristics of each lobster includ-
ing size, sex and condition (berried, epibiont
shell fouling, limb loss, injury, shell erosion/disease)
were recorded. Lobsters were then sacrificed after
ca. 10 min at−20 °Cwith either an intra-haemocoelic
injection of 30–40ml of absolute ethanol chilled
to −20 °C or by injection of the same volume of
Davidson’s fixative (30% distilled water, 30% ethanol,
20% formaldehyde (37% stock), 10% glycerol, 10%
glacial acetic acid). The animals were fully dissected
and tissue samples (gills, hepatopancreas, gonad and
muscle) routinely taken for histology. During dis-
section, the outer carapace (branchiostegite) of both
gill chambers was removed and the gills excised. The
presence or absence of adult Nicothoë astaci parasites
was noted, and both parasitized and un-parasitized
gills taken for detailed histological analysis. Intensity
of infection was assessed in lobsters by recording the
number and location of parasites within each gill
filament.
Parasite morphology and pathology
Samples of excised gills (parasitized and un-
parasitized) were fixed in either Davidson’s fixative
(exchanged for 70% ethanol after 18 h) or Bouin’s
seawater fixative (71% seawater saturated picric acid,
24% formaldehyde (37% stock), 5% glacial acetic acid)
for histological analysis. Tissues were then dehy-
drated, embedded in histological wax, and 6–7 μm
thick sections cut and stained with Cole’s
haematoxylin and eosin. In an attempt to improve
parasite embedding and wax infiltration, a subset of
samples were either; (i) double embedded in 1%
necoloidine solution, (ii) tips of parasite egg sacs
and lateral wings excised prior to wax embedding, or
(iii) wax blocks soaked in Mollifex tissue softener for
ca. 30 min at 4 °C to soften the tissues for sectioning
(Wynnchuk, 1992).
In addition, laser scanning confocal microscopy
(LSCM) was employed to reveal further detail
on N. astaci morphology. An adapted protocol
of Michels (2007) allowed autofluorescence of
Davidson’s fixed adult and cyclopid larvae (excised
from adult egg sacs) to be captured using a Carl Zeiss
LSM 710 laser scanning confocal microscope. The
488 nm and 543 nm lasers were used for excitation,
and green and red autofluorescence was observed
using band-pass filters 493–538 nm and 548–685 nm,
respectively.
Data analysis
Statistical analyses were performed using GraphPad
Prism 5.00 for Windows (GraphPad software).
RESULTS
Parasite prevalence and intensity
Lobsters collected in July (9 males, 1 female) had
a mean size (i.e. carapace length; CL) of
126·8±5·8mm (mean±S.E.) while those collected
in September (7 males, 6 females) had a mean CL of
115·8±3·3mm (mean±S.E.). Lobsters included
visually healthy individuals, as well as those exhibit-
ing epibiont shell fouling, chelae damage or loss, and
low severity shell disease (a bacterial condition that
damages the cuticle and can result in intra-
haemocoelic secondary infections; Vogan et al.
2008). All individuals collected in both July and
September (N=23) were found to harbour adult
N. astaci in their gills (Fig. 1A–C). The intensity of
N. astaci infection in lobsters was highly variable,
ranging from 4 to 137 copepods/lobster (47·3±10·1,
mean±S.E.). Significantly more parasites were
found in the basal region of the gill (Fig. 2A)
compared with either the middle (P<0·01) or tip
(P<0·001), with no significant difference between
the latter two regions (repeated measures one-way
ANOVA with Bonferroni’s multiple comparison
post-test, Fig. 2A). Within each gill, parasites were
found attached towards the base of individual gill
filaments, with their egg sacs and wings protruding
(Figs. 1A–C). The specific parasite attachment point
on the gill filament was not recorded. Pleurobranch
gills harboured significantly greater numbers of
parasites than podobranch or arthrobranch gills
(P<0·001 for both, repeated measures one-way
ANOVA with Bonferroni’s multiple comparison
1286Emma C. Wootton and others