Review of lumpfish biology
Adam Powell,1 Craig Pooley,2 Maria Scolamacchia2 and
1University of Gothenburg – Kristineberg, Department of Biological and
Environmental Sciences, Sweden
2Centre for Sustainable Aquatic Research, Department of Biosciences,
Swansea University, UK
e lumpsh, Cyclopterus lumpus, occupies diering habitats depending on life stage. Adults are
generally solitary and spend much of the year far from land, and at up to several hundred metres
depth (Kudryavtseva and Karamushko, 2002; Parin et al., 2002). e following distribution
describes hatchlings, juveniles and adults during the breeding season, which takes place gener-
ally closer to shore, in shallow coastal water (after Davenport, 1985; Stein, 1986; Aquamaps,
Lumpsh may be regarded as abundant, potentially inhabiting c. 32,000 km of coast across both
sides of the Atlantic Ocean (see Davenport, 1985 for a summary of archive studies). Lumpsh
are distributed in the boreal region of the east and west North Atlantic coasts (Figure 6.1). For
the western Atlantic, the most northerly occurrence has been found on the island of Disko o
north-western Greenland; lumpsh are distributed from there southwards to Chesapeake Bay
(range: 70° – 37°N). is distribution incorporates most of eastern Canada, including Nunavut,
Hudson Bay, James Bay, Labrador, Newfoundland (Stephenson and Baird, 1988), Gulf of St
Lawrence, New Brunswick and Nova Scotia.
On the western side of the Atlantic Ocean, the species has been recorded over a wider range
of latitudes than the European coast (see Davenport, 1985). However, in Europe, recent records
of the species have been recently reported from lower latitudes o Spain, southern Portugal
(36°N) and a probable vagrant in the Mediterranean Sea (Banon et al., 2008; Vasconcelos et
al., 2004; Dulčić and Golani, 2006). e most northerly occurrences in Europe include Jan
Mayen (north of Iceland), Svalbard, and the White and Barents Seas including Novaya Zemlya
(Kudryavtseva and Karamushko, 2002), with populations found easterly into the Baltic Sea.
e species is commonly found o Iceland, the southerly tip of Greenland and the Faroes,
Norway (Holst, 1993) and countries bordering the North Sea, particularly France, the UK and
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6.2 Description of the appearance of sh and taxonomy
e lumpsh or lumpsucker was formally named and initially characterised by Linnaeus (1758)
as Cyclopterus lumpus (‘round n’). Other common names in current usage across Europe (in
direct translation to English) include stone biter, sea chicken and fatsh, with names occasionally
diering for each sex due to pronounced sexual dimorphism (Davenport, 1985). e species is
a bony sh (class: Osteichthyes, infraclass: Teleostei) belonging to the Order Scorpaeniformes,
family Cyclopteridae. C. lumpus is unique and morphologically distinct, and is the only species
of the genus Cyclopterus. Related taxa include the less common Eumicrotremus spinosus (Atlantic
spiny lumpsh, found in the western Atlantic Ocean) and Aptocyclus ventricosus (Smooth lump-
sh, northern Pacic Ocean; Froese and Pauly, 2017). ese other species have no recorded
commercial value and have not been investigated for use as cleaner sh to our knowledge.
Davenport (1985) and Bigelow and Schroeder (2002) provide a detailed generic and specic
description of adult C. lumpus. Briey, in prole the body is about twice as long as it is deep, and
it is compressed anteriorly and posteriorly. e rst dorsal n forms a high crest with large com-
pressed tubercles, which increase in size with age, although these may be reduced in specimens
inhabiting particularly cold or low salinity habitats, such as the Baltic Sea. ere are three longi-
tudinal ridges along the length of the body marked by a line of pointed tubercles, with the most
obvious as a dorsal crest. e head is short with lateral moderate-sized eyes, while the opercula
have slit-like openings. e snout is blunt with a terminal, slightly upturned mouth containing
small teeth. In cross section, the body is vaguely triangular with a attened ventral surface (with
the exception of gravid females, when distended with roe), with a round, broad, muscular suck-
ing disc (Davenport and orsteinsson, 1991) that gives the species its generic name. e disc
constitutes approximately 20% of the body length and is a specialised organ that descends from
the pectoral ns. e vivid skin colouring in adults and associated sexually dimorphic character-
istics (see section 6.12) and skin texture (rubbery, tough and scaleless) are also diagnostic features
Fig. 6.1 Map showing coastal
distribution Cyclopterus lumpus
(shaded areas showing probable
extent of adult spawning grounds
and habitat of hatchlings and
substrate associated juveniles).
Credit: Redrawn by the authors
(after Davenport, 1985)
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6.3 The lumpsh shery: vulnerability to shing and sources of
Historically, the lumpsh shery has entered three distinct phases. Prior to the 1940s, there
was a small-scale artisanal shery for males that were sold smoked, salted or dried. is was
then largely replaced by a commercial shery emerging in the late 1940s, focusing on roe from
females (as a cheap alternative to caviar from sturgeon; see Davenport, 1985). is has continued
to the present day at scales of many thousand tonnes per year (Figure 6.3; Johannesson, 2006).
More recently, the shery has diversied somewhat to include male and female broodstock for
the emerging cleaner sh industry. Aquaculture production of the species currently depends on
the capture of wild broodstock, which together with current sheries may impact on natural
e species has a trophic level of 3.9, typical of secondary consumers, and a low resilience to
shing pressure, with an estimated time for doubling of population size of 4.5 to 14 years. It
also has a moderate to high vulnerability to shing (47 of 100; Cheung et al., 2005; Friese and
Pauly, 2017). Although the conservation status of the species has not been assessed by the IUCN
(International Union for Conservation of Nature), the characteristics outlined above suggest a
species vulnerable to overexploitation. A signicant decrease in some spawning stocks has been
recorded in recent decades, suggesting that some stocks may already be overexploited (Pampoulie
et al., 2014). Global lumpsh production from sheries is seasonably variable (Johannesson,
2006; FAO, 2017), potentially inuenced by the combined impacts of exploitation, with emerg-
ing problems such as invasive species that feed on lumpsh eggs (Mikkelsen and Pedersen, 2012),
climate change (e.g. Perry et al., 2005) and emerging diseases (e.g. Freeman et al., 2013).
e reported catch of lumpsh has steadily increased from a few hundreds of tonnes per year
in the early 1950s to 20,365 tonnes in 2013 (FAO 2017, Figure 6.3). Mean catch since the year
2000 has been 15,997 tonnes (SE = 1,002) with unreported catches probably varying between
1,600 and 4,600 tonnes (i.e. 9–22% of the total). However, historical catch records are proba-
bly misleading because most of the former catch was unreported, mostly due to discards on the
Fig. 6.2 Caption: Cyclopterus lumpus adult male
and female a. Lateral view. b. Ventral view. Credit:
Photograph by Craig Pooley and Maria Scolamacchia,
CSAR, Swansea University
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east coast of Canada. Data reconstruction indicates that unreported catches may have reached c.
124,000 tonnes (98% of total) by 1965, when the declared catch was only 2,400 tonnes (Pauly
and Zeller, 2015).
Nowadays, the most important lumpsh sheries operate in the Canadian eastern Atlantic–
west Greenland (c. 70% of catch) and Iceland (c. 23% of catch), which are exploited by the
Greenlandic and Icelandic eets. Data from 2010 indicate that these are mostly mixed artisanal
(57% of catch) and commercial sheries (43% of catch), with only 30 tonnes being classied as
subsistence (0.1% of catch; Pauly and Zeller, 2015).
e artisanal sheries consist of small boats, shing close to shore in up to ~30 m depth, and
which are typically manned by one to three people. Gears vary among locations (Johannesson,
2006). In Norway, nets with 252 mm mesh size are used, these typically being c. 47 m wide
with a 3.4 m drop (Bertelsen, 1994). Mesh size in Iceland varies between 267 and 286 mm
(orsteinsson, 1996). Monolament nets with a 256–281 mm mesh size are used in Canada
to catch lumpsh, nets being 100m long (Benson et al., 1998). eir round shape and short ns
means that lumpsh do not entangle in the nets to the same extent that other species do, and
this is the reason lumpsh nets have as much ‘bag’ as possible, as this is thought to increase catch
eciency. Typically, nets are set up on 45 m oat and foot lines, with 90–125 cm verticals to
maintain the bags and prevent lumpsh escape (Johannesson, 2006).
Traditionally, lumpsh have been harvested for their roe, which can be processed into an alter-
native to caviar (Johannesson, 2006). No reliable data are available for the number of females
removed from the wild for the caviar industry, but this probably amounts to several million sh
annually; eorts to harvest lumpsh eggs non-destructively have met with limited success (Grant,
2001). e number of adult lumpsh taken by the incipient cleaner sh industry (c. 300 tonnes
in the UK in 2014, personal observation) is currently small compared with the commercial and
artisanal sheries (20,365 tonnes in 2013, FAO 2017), but there is a growing concern from some
conservation bodies regarding the sustainability of the catch (Anon, 2013a). Maximum lumpsh
Fig. 6.3 Reported global catch for
lumpsh (tonnes), 1950–2013 (FAO
FishStat). Credit: FAO Fishstat
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102 ♦ Biology and rearing of wrasse and lumpsh
production is attained when males reach 20 cm and females reach 32 cm (equivalent to two and
three years of age, respectively (Hedeholm et al., 2014), and that means that removing brood-
stock older than two to three years of age may have a disproportionately high impact on wild
populations. Both Iceland and Greenland have adopted strict shing regulations (Stevenson and
Baird, 1988) and their lumpsh sheries have recently been awarded MSC certication (Anon,
2013b; Lassen et al., 2015).
While it is possible to use means other than gillnets to capture lumpsh, for example by
scuba diving (Killen et al., 2007a), these tend to be more labour intensive and much less e-
cient. Lumpsh lack a swim bladder, and adults hauled quickly to the surface may experience
barotrauma, even using static gear. is can be rectied by returning animals to depth in a cage,
followed by gradual decompression.
6.4 Commercial uses of lumpsh
Up until the 20th century lumpsh had little economic value. Small sheries existed on both
sides of the North Atlantic for local consumption, but sh caught as bycatch were often used
as animal feed or bait (Stevenson and Baird, 1988). A dedicated shery targeting lumpsh roe
started in the late 20th century. Ripe females yield 15–36% of roe by weight (Davenport, 1985,
Stevenson and Baird, 1988, Mitamura et al., 2007, Hedeholm et al., 2014) and were rapidly
targeted by the shery. us, in Newfoundland, roe production grew from 21 tonnes in 1970
to 3,000 tonnes by 1989 (Stevenson and Baird, 1988). Similarly in Norway, 100 tonnes of roe
were taken annually in the 1950s, compared with 500 tonnes of roe by the middle of the 1980s
(c. 2,500 tonnes of sh).
Lumpsh eggs are marketed in two ways: either as whole roe, which is then dried, salted, or
smoked, or as processed eggs, which are separated from the ovaries and then further elaborated
into lumpsh caviar. Annual production of lumpsh caviar is about 4 million kg and has a
market value of about $ 60 million, with Canada (35%), Iceland (31%) and Norway (15%) as
the main producers (Johannesson, 2006). e price of lumpsh caviar uctuates depending on
supply, but is currently sold in supermarkets at $36–72 per kg.
Excluding the sale of caviar, the shery has a low value (always below $5 million since 2000),
and the species is classed as a ‘low value’ sh in the prize category of FishBase (Sumaila et al.,
2007; FishBase, 2017). is is in stark contrast to the situation during 1950–1970, when the
value of the shery peaked at c. $200 million in 1961, mostly generated by the European eet
(Spain, Portugal, Germany) operating in eastern Canada. However, in some places such as
Iceland, the UK and Norway, this situation has changed in recent years, with the development
of the cleaner sh industry. Fishermen are currently paid US $87 (GBP £60) for ripe females in
some parts of the UK, and a kilogram of fertilised eggs for export to the cleaner sh industry may
cost several hundred US dollars in Iceland personal observation), which may put new pressures
on wild stocks.
Currently, all lumpsh used as cleaner sh are culled at the end of the salmon production
cycle, when they reach about 500 g. Although this is done on biocontainment grounds, to pre-
vent transmission of diseases between salmon and cleaner sh, some have considered this prac-
tice as wasteful and have urged the industry to nd alternative uses for farmed lumpsh (Anon
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Review of lumpsh biology ♦ 103
2013a; Powell et al., 2017). is has prompted research into new markets and a consideration
of possibilities for nutrient recycling, either as animal feed or into more valuable products, par-
ticularly in the lucrative Asian markets, where the species could perhaps nd a market niche as a
delicacy (Nøstvold, 2017). Another alternative to culling would be to recondition large juveniles
in captivity and use them as broodstock for the production of eggs, either for caviar or for the
cleaner sh industry (Powell et al., 2017), although such animals would need to be certied free
Lumpsh occupy a wide distribution, and have been recorded in 24 countries in Europe and
North America. Animal distribution also varies according to life history stage and season, with
many historic reports unaware of the semi-pelagic adult phase outside the spawning season.
Davenport (1985) summarised this as a fundamental problem with assessments of the total area
occupied by the species. A recent study of stocks in the Barents Sea (Eriksen et al., 2014) sug-
gested a mean annual biomass (48 000–143 000 t) and mean annual abundance (53 –132 mil-
lion individuals) since 1980. Some data on stock assessment are available for the Icelandic and
Greenland sheries that were recently awarded MSC certication, but not for other areas. On
the other hand, reliance on catch data (Figure 6.3) to infer trends in abundance is fraught with
diculties, as the majority of lumpsh caught during 1950–1970 went unreported.
e diet of lumpsh was summarised by Davenport (1985), who concluded that the overall
impression was of a species that subsisted mainly on large planktonic organisms living in surface/
mid waters, but which sometimes browsed upon benthic organisms, particularly those dwelling
upon weed. For adults, historic studies found a high proportion (c. 70–80%) of adults with
empty stomachs in sampled populations. A similarly high proportion of empty stomachs has also
been reported in juveniles (Ingólfsson and Kristjánsson, 2002). e intestine is long, being more
than twice the length of the body in adult sh, with many bends and numerous pyloric caecae
(Davenport, 1985) suggesting ecient digestion and absorption of food. Gut contents of adults
are variable across all studies, with small crustaceans (mysids, amphipods, euphausids, isopods,
decapod zoeae), ctenophores, polychaetes, seagrass, insects, small sh and sh eggs recorded
(Davenport, 1985; Davenport and Rees, 1993).
Juvenile lumpsh (c. 5–55 mm length) are apparently year-round seaweed specialists, inhabit-
ing and feeding on surface plankton after hatching, and weed-associated invertebrate fauna when
larger (Daborn and Gregory, 1983; Vandendriessche et al., 2007). Motile crustaceans larger than
0.5 mm dominate diet, with the natural abundance of these prey items on seaweed correlating
with their abundance in the gut of juvenile lumpsuckers (Ingólfsson and Kristjánsson 2002).
Furthermore, as hatchlings increased in size and yolk reserves became exhausted, the proportion
of larvae with full guts increased. Hatchlings tend to consume harpacticoid copepods or halac-
rid mites, with older juveniles switching to physically bigger and more active crustacean prey
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104 ♦ Biology and rearing of wrasse and lumpsh
such as amphipods or decapod larvae (Daborn and Gregory, 1983; Tully and Ó Ceidigh, 1989;
Ingólfsson and Kristjánsson 2002). Since cannibalism has been observed between individuals
of similar age and size, mouth gape is probably not a limiting factor to the size of prey that is
consumed. Rather, a change in behaviour corresponding to age and feed density may allow them
to enter a dierent trophic group (See section 6.15; Brown, 1986; Tully and Ó Ceidigh, 1989;
Killen 2007a, b).
More recently, interest has switched to the gut contents of lumpsuckers deployed in salmon
pens. Large lumpsh juveniles 54 g in weight deployed in sea pens are seemingly highly oppor-
tunistic, not limiting themselves to one food item (Imsland et al., 2015a). Over a 77-day trial,
the most common food items observed were salmon pellets, although crustaceans, hydrozoans,
mussels and, as the study progressed, sea lice, became an increasing part of the diet. Further
research suggests that food preference in pens may also depend on genetic provenance, and dier
between juveniles originating from distinct families (Imsland et al., 2016a), size and co-existence
with other species during deployment (Imsland et al., 2016b, 2016c).
Lumpsh anatomy is unusual, with most studies focusing on the skeleton, skin and ventral
sucker, tissue composition and buoyancy, and reproduction.
Although the species has no swim bladder and contains large quantities of dense eggs, gravid
females have a body density very similar to seawater (Davenport and Kjörsvik, 1986). e low
density is achieved by extensive subcutaneous jelly, low osmolarity ovarian uid, and a dorsal
musculature, which is loose-bred and has high water content. Males do not present these char-
acteristics to such an extent, but have a higher lipid composition. is enables adult lumpsh to
reside in the open ocean for long durations. However, during the breeding season, they return to
shallow, rocky waters that experience strong wave surge. e low body density, large surface area
and limited swimming power demands an extremely powerful and ecient muscular, cartilagi-
nous sucker (or disc), which enables lumpsuckers to attach themselves to substrate, and to rest
without being swept away (Davenport and Kjorsvik, 1986; Davenport and orsteinsson, 1990).
Lumpsuckers can also colour-match their skin to local substrates within minutes (Davenport and
Bradshaw, 1995). Suitable resting places and substrates have also been recommended during
deployment in salmon pens, to promote sh welfare (Imsland et al., 2015b).
Unfertilised eggs in the large ovaries are bathed and protected in copious ovarian uid, which
has a low divalent ion concentration. As portions of ripened eggs are released during spawning
events, they harden and clump together in seawater due to the presence of divalent ions, particu-
larly calcium and magnesium. Copious uid and a strong sphincter muscle reduces the risk of
seawater reux into the oviduct, hardening remaining eggs inside the sh and blocking further
egg release. e kidney likely removes divalent ions, while female sh have large urinary blad-
ders that may assist with urine storage and water reabsorption (Davenport and Lönning, 1983;
Lönning et al., 1984).
Sperm extracted from males was found to remain viable for several days after removal of the
sh, although Davenport (1983) suggested that stripping eggs or milt from adults was not pos-
sible and euthanasia was required to extract gametes for articial fertilisation. Powell et al. (2017)
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found that it was possible to strip eggs from very ripe females, while recently caught males often
release milt upon handling (although this was never achieved a few days later, in aquaria) requir-
ing culling and manipulation of male gonadal tissue. However, with well-considered logistics, it
may be possible to store sperm from wild ‘running’ males and, using enhancers or cryopreserva-
tion techniques (Norðberg et al., 2015), to reduce the necessity for maintaining or euthanising
6.8 Environmental requirements and ecotoxicology
Overall, C. lumpus is regarded as ‘hardy’ (i.e. robust); with the southern and northern limits of
distributional range approximating to the 20°C and 0°C August surface water isotherms, indicat-
ing that the lumpsucker is eurythermal but capable of inhabiting very cold water (overview by
Davenport, 1985). Adults are generally not found in low salinities within their latitudinal range,
although populations exist in the Baltic Sea and Hudson Bay that have permanently low salini-
ties; these populations also show some dierences in skin, body shape and smaller comparative
size (Davenport, 1985), suggesting a discrete race or even subspecies inside a particular oceano-
graphic area that experiences low salinity.
Hatchlings are precocious with a functional sucker, allowing immediate attachment to rock
or weed substrate, or even momentarily to the tending male shortly after hatching (Davenport,
1985). Hatchlings and juveniles appear to be almost obligate inhabitants of seaweed, living and
feeding on and around weed beds (Vandendriessche et al., 2007), although young juveniles are
also commonly found in parts of the intertidal zone such as rockpools (Moring, 2001).
Few ecotoxicological studies have been made on the species, although very low concentra-
tions of mercury have been found in the esh of wild adult lumpsuckers (Freeman, 1974).
Juveniles proved relatively resilient to experimental oil exposures designed to simulate oil spills
(Frantzen et al., 2015). An antifoulant candidate (medetomidine) has been tested on lump-
sh larvae; sub-lethal eects (a reduction respiration rate and skin colour adaptation rate) were
found when exposed at nanomolar concentrations for 72–98 hours. However, larvae returned to
baseline levels after 48 hours in untreated seawater (Bellas et al., 2005). is nding may have
implications for deployment near antifoulant-treated structures.
6.9 Movements and migrations
e species is benthopelagic and can be found at depths <868 m (Parin et al., 2002), although
they usually live in waters between 50 and 150 m deep (Stein, 1986). e semi-pelagic status of
adult females has been conrmed with a recent tagging study (Kennedy et al., 2016). Lumpsh
may undertake extensive annual migrations between their feeding grounds found in deeper waters
in the winter and the shallower waters preferred for spawning in spring and summer (Blacker,
1983; Davenport, 1985; Kaspar et al., 2014). Tagging studies indicate that the species displays
homing behaviour and may return to breed in the same areas more than once (Davenport, 1985,
Stevenson and Baird, 1988, Kennedy et al., 2014). Tagged females were found to reside in a ord
for up to a week and then disappeared, possibly returning oshore after spawning (Mitamura
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et al., 2012). Following spawning, females can travel up 49 km per day (Kennedy et al., 2014),
unlike males, which remain in the same location for several weeks to tend the eggs (Davenport,
6.10 Genetic diversity and genetic stock differentiation
Lumpsh have 25 haploid chromosomes (n) and 50:50 diploid chromosomes (2n; Li and
Clyburne, 1977; Klinkhardt et al., 1995), but little is known about its genetic diversity or extent
of population dierentiation. Twenty-two novel microsatellite DNA loci were characterised
recently for the species (Skirnisdottir et al., 2013) and these have revealed three distinct genetic
groups in the North Atlantic: Maine–Canada–Greenland; Iceland–Norway, and the Baltic Sea
(Pampoulie et al., 2014; Garcia-Mayoral et al., 2016) with little evidence of gene ow among
these zones. However, data for other parts of the range are currently lacking. Preliminary results
from populations in the English Channel suggest that lumpsh there have low to moderate levels
of genetic diversity and low genetic dierentiation (Expected Heterozygosity, He = 0.53–0.61;
Pooley et al., 2015). is initial data suggests indistinct genetic populations in this particular
geographic area. is demands further investigation to inform a sustainable shing strategy, and
potential end uses after deployment as cleaner sh.
Adult lumpsh are typically solitary in the wild, though hatchlings tend to aggregate in clumps
in tanks during captivity (personal observation). Adult spawning behaviour has been described
by Goulet et al. (1986), Goulet and Green (1988) and is summarised in section 6.13. At spawn-
ing, the male exhibits parental care and tends the eggs, which are kept oxygenated through
fanning and air pung.
Unlike most other Actinopterygians (ray-nned sh), lumpsh lack Mauthner neurons that
are involved in the startle response and escape behaviour (Hale et al., 2000). ey have a longer
startle response latency than other shes, but are nevertheless capable of performing a fast anti-
predatory response, albeit not as eective. ey appear to have a relatively small brain for their
size (encephalisation coecient = 0.07–0.21; Albert et al., 1999), though this may be due to
the unusual shape and large body mass of the species. e species is apparently an intelligent,
inquisitive sh that can be entrained to accept feed (personal observation) and can change colour
rapidly for camouage (Davenport, 1989; Davenport, 1995).
e ventral sucking disc enables lumpsh to forage dierently from most other shes. ey
can cling and feed passively, or forage actively in pursuit of prey. e larvae become more active
a few weeks post-hatch (Brown, 1986) and their foraging mode appears to depend on prey abun-
dance. us, they adopt a ‘passive cling’ foraging mode when food is abundant, and switch to a
more ‘active swim’ mode when food is more scarce (Killen et al., 2007a).
Little is known about the welfare requirements for the species. Some information is avail-
able on the substrate and colour preferences following deployment in salmon pens (Imsland et
al., 2014a, 2015b), but studies are also needed during the juvenile phase. In the wild, lumpsh
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match the colour of seaweed, suggesting that light intensity, photoperiod and tank colour may
also aect juvenile growth, since these factors have been observed to alter melanin concentrations
under experimental conditions (Davenport and Bradshaw, 1995). In salmon pens at night, they
prefer to aggregate together on smooth plastic and concrete substrates (thought to be similar to
seaweed), rather than on stones or car tyres (Imsland et al., 2015b). In comparison with Ballan
wrasse, Labrus bergylta (Helland et al., 2014), availability of suitable substrates appears to be
important for health and welfare.
e behaviour of lumpsh in cages has been studied via underwater cameras (Imsland et al.,
2015b,), and an ethogram has been constructed that identied a range of dierent behavioural
elements, which varied with the presence of Atlantic salmon (Imsland et al., 2014a). When
salmon were present, lumpsh were more active and spent less time resting, but little antagonis-
tic behaviour was observed between the two species. However, lumpsh did show some aggres-
sion to co-deployed goldsinny wrasse (Ctenolabrus rupestris), particularly across disparate size
grades between the two species (Imsland et al., 2016b).
Lumpsh are opportunistic omnivores in salmon cages, eating not only sea lice, but also
salmon pellets and organisms attached to the cages (Imsland et al., 2015a, 2016b. Signicant
variation appears to exist among families in the ecacy of sea lice grazing (Imsland et al., 2016a),
and this may provide the basis for the selective breeding of lumpsh with improved delousing
6.12 Sexual dimorphism and sex ratio
Lumpsh display pronounced sexual dimorphism, allowing straightforward dierentiation of
sexually mature specimens. Males are typically smaller (30 ±10 cm length) and during the spawn-
ing season attain startling red, orange or purple coloration of the ns, eyes and ventral surfaces
(e.g. Davenport and orrsteinsson, 1989). Females are larger (42 ± 10 cm length), less colourful
and usually grey or blue-green, and are markedly rotund, likely due to increased subcutaneous
gelatinous tissue, urinary bladder and copious ovarian tissue, eggs and uid; they also have a
larger vent (Davenport and Lonning 1983; Davenport, 1985; Goulet et al., 1986; Figure 6.2).
Although the available data on sex ratio is scant, it is clear that the species deviates from the
Fisherian 1:1 ratio, the extent of which is likely to dier in space and time. e apparent itin-
erant, oceanic and solitary nature of sexually mature lumpsh outside spawning seasons, and
contrasting habitat favoured by juveniles (and diculty to assign gender) makes an accurate and
meaningful estimation of the sex ratio somewhat challenging. It is also likely that dierent arrival
and residence times between sexes during the spawning period (females arrive later and for only
a few days; Davenport, 1985; Mitamura et al., 2007) would further complicate the description
since sex ratio would change during the season. For instance, the reported sex ratio of 1:1.57
(F:M; n=54; Gregory and Daborn, 1982) is likely to be specic for the sample taken in shallow
water, in the Bay of Fundy, in early summer.
Furthermore, some have speculated that males outnumber females since they are apparently
capable of guarding more than one egg mass at a time; however, females may spawn their eggs
in a number of batches at dierent locations (Mochek, 1973; Davenport, 1985; Davenport and
Kjvosvik, 1986). In addition, it has yet to be conrmed if sexually mature females spawn annually,
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108 ♦ Biology and rearing of wrasse and lumpsh
at greater intervals or if they are eectively semelparous due to potentially low recovery rates
after spawning (which becomes progressively more expensive with increasing size; orsteinsson,
1983; Kaspar et al., 2014). An added complication is that males mature one to two years earlier
than females, however females appear to experience greater longevity (Davenport, 1985; Albert
et al., 2002; Hedeholm et al. 2014). erefore, it seems the operational sex ratio (i.e., the local
ratio of fertilisable females to sexually active males at any given time) for lumpsh is apparently
In areas of their range where a roe shery is signicant, there may be further bias toward
recorded numbers due to the dierence in size and behaviour between genders, and stronger
swimming ability of males. Males are likely to be underestimated in the gillnet shery since
they may be able to evade capture or are unlikely to move signicant distances while guarding
eggs (Davenport, 1985). Furthermore, the very presence of a shery that targets gravid female
sh will bias the sex ratio. Landing data is often expressed by biomass or tonnage rather than by
number (e.g. Marine Research Institute, 2015) although analysis of long-term survey data from
Newfoundland found that the sex ratio has decreased progressively from approximately 2.24:1
to 1.09:1 (F:M) between 1985–1994, despite an increase in Catch per Unit Eort (CPUE;
Stansbury, 1995; Hoenig and Hewitt, 2005). However, human activity may not be the sole
reason for female mortality. Emerging diseases such as Nucleospora cyclopteri were more prevalent
in females in a recent survey of the species o Iceland (Freeman et al., 2013).
6.13 Reproduction, spawning and geographical patterns
Early in the breeding season, males establish territories in shallow water on rocky and/or sea-
weed-covered substrate, prior to the arrival of females; females arrive asynchronously, allowing
more than one pairing and breeding event to occur per animal. is process occurs in spring and
early summer (Davenport, 1985) with a likely latitudinal variation. In Iceland, northern Norway
and Newfoundland, females start to move inshore during March and April, with evidence for
spawning occurring in early July and hatching until late August (Brown et al., 1992; Kennedy
et al., 2014; Mitamura et al., 2012) whereas in the English Channel gravid females have been
caught from early January until early May only (personal observation).
Davenport (1985) and Goulet et al. (1986) provide accounts of courtship, which appears to
be extended and of several hours’ duration. is includes showing anks to one another, pectoral
n brushing, quivering, and long periods of sucker attachment in close proximity; there was also
evidence for olfactory (perhaps pheromone) communication. In the wild, this included cleaning
a nest site (which may be a simple crevice or depression in bedrock, boulders and/or vegetation).
Mating appears to correlate with night (or darkness in aquaria) and potentially with high tide.
Fertilisation is external, with females releasing eggs freely into the water on to the surface of
a nest (or in the aquaria, near to any shallow depression or tank structure, personal observation)
with attendant males immediately fertilising the eggs, with the overall act lasting only ve to ten
seconds (Goulet, 1986). Females are thought to lay two to three batches of eggs over c. one to
two weeks (Davenport et al., 1985), and in one study actively moved in and out of a ord within
days of spawning (Mitamura et al., 2012). On contact with sea water, the eggs adhere to one
another to form large ovoid masses, which are fertilised by the male. Before the mass hardens, the
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male may mould the eggs into the nest. Males also create funnel-like depressions that likely assist
gaseous exchange and removal of nitrogenous waste from the centre of the egg mass.
e eggs undergo paternal care throughout the incubation, with the females expending no
time in egg care after fertilisation. e most frequent behaviour includes water circulation by
fanning with the pectoral, but also dorsal and caudal ns (for a few seconds to hours in dura-
tion), and pung (expelling water from the mouth). is appears to occur more frequently for
a few hours after fertilisation, and also near the end of the incubation period when the embryos
are more developed, and to disseminate emergent larvae (Davenport, 1985; Goulet et al., 1986).
If eggs are exposed by low tides, males have been observed to spout water from the mouth to
maintain them (Davenport et al., 1984; Davenport, 1985). e male also becomes aggressive
and removes or defends the egg mass from conspecics and predators, including sea urchins,
periwinkles and even large predatory sh, although this is more challenging against schools of
ocean pout Zoarces americanus, cunners Tautogolabrus adspersus (Davenport, 1985 Goulet et
al., 1986) or large crabs such as the invasive red king crabParalithodes camtschaticus (Mikkelsen
and Pedersen, 2012). Males expend much eort in guarding egg masses, apparently not eating
during this period, potentially guarding more than one mass at a time or guarding successive
masses over the spawning season. e amount of time spent in parental care, or number of eggs
guarded, is independent of male size, while nest characteristics such as depth, distance from
shore, and topography do not correlate with hatching success (Davenport, 1985; Goulet et al.,
1986; Goulet and Green, 1988).
6.14 Egg stages and environmental preferences
Lumpsh eggs are relatively uniform in size (2.0–2.6 mm diameter) across their range (see
Davenport, 1985; Benfrey and Methven, 1986; Brown et al., 1992) and after extrusion undergo a
colour change from pink to a variety of colours that are homogenous within a particular egg mass.
Colour is lost with time as the pigments move from the yolk into the chromatophores of the
developing embryo. e hardening process occurs via a transparent adhesive material, secreted
by the ovary to coat the eggs. is becomes viscous and elastic on exposure to seawater and con-
denses within an hour at 5°C to form a dense layer around the eggs. Within 48 hours the eggs
themselves harden and become dense (Zhitenev, 1970; Lonning et al., 1984; Davenport, 1985).
Embryonic development has been pictorially described for the related smooth lumpsucker
Aptocyclus ventricosus (Kyûshin, 1975) and for C. lumpus in this chapter (Figure 6.4). With the
naked eye, the initial egg colour fades three to four days after fertilisation, and eggs ‘eye-up’ after
10–12 days, with full embryo pigmentation and a darker egg mass existing from about day 16
onwards. Infertile or undeveloped eggs remain unpigmented and opaque. Initial development
can be slow and variable in the egg mass (Davenport, 1983). In our studies, the following stages
were observed post-fertilisation at 10°C: morula (one to two days); blastula and blastodisc (two
to four days); gastrulation; initial somites visible (ve to six days); otic capsule visible, continued
segmentation (seven days); eye pigmentation and heart beat (eight to ten days); yolk vascularisa-
tion and head pigmentation (11–12 days); development of eyes, head and extensive vascularisa-
tion (15 days); uniform pigmentation, regular heart beats, mouth opening, movement (16–19
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110 ♦ Biology and rearing of wrasse and lumpsh
Early observations showed that eggs develop more rapidly as temperature rises (Davenport,
1985), with studies showing a temperature of greater than 3.8°C is required for development,
with hatching after 40, 31 and 25 days at 5°C, 6.4°C and 9.8°C respectively (Collins, 1978;
Davenport, 1983) with hatching occurring mainly at night (Benfrey and Methven, 1986).
Studies at Swansea University have found a time to hatch of 20–30 days at 10°C (i.e. 200–300
degree days C) with hatching occurring over a seven- to ten-day period. Egg masses manipulated
into attened layers 5–10 mm thick immediately after fertilisation (but prior to hardening)
have generally led to better hatching success and more even development rate, perhaps due to
improved water circulation. is is in agreement with Brown et al. (1992), who had better suc-
cess with ‘monolayers’ rather than fragmented egg masses, and which developed at 28.5 days at
10°C. Lumpsh embryos at early developmental stages are capable of extracting oxygen at low
oxygen tensions (c. 40% of air saturation), or even withstand 30 minutes of anoxia, although sen-
sitivity is increased in more developed embryos nearing hatching (Davenport, 1983). Correct egg
development also demands salinities between c. 20–34 ppt (Kjorsovik et al., 1984). Little appears
to be known regarding optimal photoperiod or pH. Further details on lumpsh broodstock,
hatchery and deployment are reviewed by Powell et al. (2017) and are considered in Chapters
7, 8 and 9.
Juvenile lumpsh hatchlings are c. 5–6 mm length and 2–3 mg weight (Benfey and Methven,
1986; Brown et al., 1992). e sucker is present at hatching and allows immediate attachment to
surfaces, although in other respects newly hatched lumpsh do not resemble adults. A posterior,
protocercal n is present dorsally and ventrally that terminates at the tail. e median n breaks
up into separate ns by the length of about 8–9 mm. e rst dorsal n is gradually overgrown
Fig. 6.4 Overview of embryogenesis of C.
lumpus at 10°C. A. Morula stage, c. two days
post-fertilisation. B. Blastula stage, c. four days
post-fertilisation. C. Eye pigmentation, c. ten
days post-fertilisation. D. Full pigmentation and
development at hatch. Scale bar = 1mm. E. Part
of egg mass, corresponding to Blastula stage; eye
pigmentation has not developed but mass has
lost initial colour. F. Part of egg mass, just before
hatch. Note dark colour of eggs and occasional
light eggs denoting undeveloped embryos. Scale
bar = 10mm. Credit: Description and images
courtesy of Maria Scolomacchia
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Review of lumpsh biology ♦ 111
by the characteristic dorsal ‘hump’, and a 32 mm specimen is essentially a miniature of the adult
sh (Figure 6.5; Davenport, 1985). Feminisation of lumpsucker hatchlings has been demon-
strated, either by immersion in oestradiol or via enrichment in live feeds, which could promote
production of monosex populations (Martin-Robichaud et al.,1994).
Wild juveniles feed on plankton, and substrate-associated small invertebrates, and have been
oered Artemia and/or small dry feed pellets in hatcheries (e.g. Benfey and Methven, 1986;
Brown, 1986; Nytro et al., 2014, Powell et al., 2017). Juvenile lumpsh show limited aerobic
scope compared with other sh species (Killen, 2007a, b) and thus feed and behave dierently
from most other cultured sh due to the ventral sucker. is enables hatchlings to choose a
‘passive cling’ mode or a more costly ‘active swim’, with the latter change in behaviour induced
at low prey densities. Higher prey densities allow scope for other physiologically demanding
processes such as growth and digestion (Killen 2007a, b). However, lumpsh larvae grew faster
when food was administered in short pulses than when it was administered continuously (Brown
et al., 1997).
A few weeks post-hatch, hatchlings become more active (Brown, 1986), and also have redu-
ced yolk stores (Ingólfsson and Kristjánsson, 2002) allowing the start of weaning. Immobile dry
feed pellets <800 µm have been oered after 21 days, and hatchlings are maintained in shallow
raceways (Nytro et al., 2014), or circular tanks (Powell et al., 2017). e use of live feeds early
in the ontogeny of lumpsh larvae seems crucial, although the use of preserved or dry feeds in
older hatchlings switched on genes responsible for lipid metabolism and in some cases yielded
improved growth and survival (Belova, 2015). A strategy for species-specic improvement of
live feed enrichments or dry feeds is to match their composition with that of early life stages of
the species. Indeed, vitellogenin amino acid composition has been described for lumpsh eggs
(Yao and Crim, 1996) and proximate carcass analysis for juveniles (Sayer et al., 2000). Further
research eort could yield a range of specic feeds for lumpsh hatcheries, particularly as the
sector increases in scale.
Fig. 6.5 C. lumpus. Larval hatchlings and juveniles (not to
scale). Credit: Davenport, 1985 after Cox, 1920
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112 ♦ Biology and rearing of wrasse and lumpsh
Davenport (1985) provides an overview on the length–weight relationship of lumpsh (Fig. 6.6)
and age of sexual maturity. Historic studies suggest that spawning lumpsh are at least four years
of age but most common at ve to seven years up to nine to ten years, while males in the North
Sea may attain sexual maturity one or two years earlier. More recent studies (using updated oto-
lith readings, age estimates and length frequencies) suggest that males may actually spawn for the
rst time at age two to three, and females at age three to four in the North Sea, Norway, Iceland
and Greenland (Albert et al., 2002; Hedeholm et al., 2014).
O Greenland, the maximum total production rate (somatic and gonadal tissue) for males
and females was 0.47 and 0.92 kg wet weight per year, attained at 20 and 32 cm total length
respectively. For both sexes, somatic production declined steeply after the onset of matura-
tion (Hedeholm et al., 2014; Kasper et al., 2014). e anatomy of the gonads is described by
Davenport and Lönning (1983). In mature, ripe females, up to two-thirds of the visceral cavity
contains pink roe. e ovaries and oviducts are fused to form a single sac that is strongly bifur-
cated anteriorly, although the left horn is reduced to allow space for other organs. e dorsal
and dorso–lateral portions of the ovary-oviduct are lined by a thick, viscous layer that contains
whiteish opaque, unripe eggs in most females. Ripe eggs, which are clear and rose pink, fall from
this layer into the lumen of the structure, which is lled with 200–500 ml protective ovarian
uid. Egg numbers (100,000 to 400,000 per female) vary with the overall size of the sh, and
geographic population. e gonads of the male lumpsucker are simple and unremarkable white
Mortality appears to be size dependent. In Icelandic populations orsteinsson (1983) showed
that mean length increased with age until a certain length interval (c. 42–44 cm in Icelandic
females). ereafter, mean length decreased with age, indicating death of larger sh. Other than
shing pressure, adults are predated upon by dierent animals depending on their location.
During pelagic stages there is evidence of predation by sharks, seals and sperm whales. In shal-
low water during spawning season, males (which have a longer residency), are taken by gulls, sh
eagles and otters (see Davenport, 1985 for an overview). orsteinsson (1983) also suggested
that reproduction becomes progressively more expensive with increasing size, and that eventually
Fig. 6.6 C. lumpus. Length–weíght relationship of adult
lumpsuckers from Newfoundland waters. Credit: Davenport,
1985 after Cox, 1920
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Review of lumpsh biology ♦ 113
large sh do not recover from spawning (i.e. gonad production, spawning migration and the
associated period of prolonged starvation). Davenport and Kjörsvik (1986) suggested that spent
female sh might be positively buoyant (because the eggs are much denser than seawater) and
more vulnerable to predation. is is probably more likely for larger females following spawning.
6.17 Growth rate in the wild and hatcheries
e itinerant nature of adult lumpsh outside the breeding season makes growth assessments
challenging, with tagging experiments highlighting some limitations of this approach in the
species (e.g. Kaspar et al., 2014). Archive data on tagging, summarised by Davenport (1985)
suggests that large adults show a very small linear growth increment of a few centimetres after
about one year between tagging and recapture. Juveniles, however, are thought to possess rapid
allometric growth prior to leaving surface waters and follow a LW relationship of W = 8.7L3.36
x 10-6, (Newfoundland) and W = 2.309L3.053 (Norway; L in mm) with 55 mm length juveniles
thought to be about one year old (Myrseth, 1971; Daborn and Gregory, 1983). A long-term
study of wild juveniles found in summer rockpools by Moring (2001) reported that average
lengths increased by 23–43% and wet weight by 280–342% per month. Studies of both wild
and cultured larval and juvenile lumpsh show a rapid increase in growth rate from mid-July
to August, before decreasing in August–September (Benfey and Methven, 1986; Moring, 2001;
Ingolfsson and Kristjansson, 2002).
For adults, the largest reported lumpsh was an individual of body mass 9.5 kg, (maximum
total length 70 cm, maximum age of 14 years). However, the bulk of spawning females caught
in commercial gillnets are between 35 and 50 cm in length (roughly 2–5 kg) with slow growth
after maturity (Bagge, 1964; orsteinsson, 1983; Davenport, 1985).
Rearing studies started in the mid-1980s and attempted to culture larvae from the egg, oer-
ing dry (Benfey and Methven, 1986) and live (Brown, 1986) Artemia spp. to hatchlings. After
experimental periods of approximately one month, larvae reached a standard length of c. 12
mm on live feed, compared to 7 mm on dry feed. Brown et al. (1992) grew lumpsh from eggs
and reported a growth of 29 g after one year, and 510 g after two years at ambient temperatures
(between -1.8 and 14°C), although survival had declined to 0.5% after the rst year. Lumpsh
cultured in the laboratory became sexually mature at the end of their second year.
Sayer et al. (2000) attempted on-growing of wild caught juveniles, most success being achieved
by use of a low lipid diet formulated specically for the species (higher lipid diets allowed rapid
growth, but fat accumulated in brain and liver, causing early mortality). For sh under 350 g in
weight, a SGR of up to 3.8% per day was recorded, although the temperature varied between
6.1°C and 15.4°C during the on-growing period. e most recent studies of juvenile growth
have been derived from juveniles originating from eggs reared in-house and weaned on to appro-
priate dry feeds (Nytro, 2013; Nytro et al., 2014). e highest growth rates were comparable to
those reported by Sayer et al. (2000), and were observed for juveniles under 120g in warmer 13
and 16°C treatments, which resulted in an SGR of 3.65 and 3.60% per day. However, the eect
of rearing temperature on juvenile growth was reduced in size grades over 120 g. For lumpsh
deployed in sh pens at sea, a recent study has shown dierences in growth rate between juveniles
originating from dierent families (c. 1.2–2.1%/day; Imsland et al., 2016a).
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114 ♦ Biology and rearing of wrasse and lumpsh
Although there is likely genetic variation between families (Imsland et al., 2016a), given opti-
mal temperature, there is a high growth potential for juveniles (i.e. potentially increasing their
weight by an order of magnitude in under 80 days), thus allowing animals to reach deployable
size (10–15 g) within months, and achieving some annual synchrony with commercial salmon
6.18 Diseases and health implications
Maintaining high health status of all life stages of lumpsh is key during hatchery operations
to promote welfare and to attain numbers of deployable juveniles, and is particularly important
given the goal of closing the life cycle in captivity. Furthermore, understanding the susceptibility
of lumpsh to notiable diseases (or the potential to act as ‘carriers’) and thus onward transfer
to salmonid species during deployment, is also of clear importance to understand and manage
potential risks (Murray, 2016).
Lumpsh are a relatively novel candidate for aquaculture, with diseases and parasite records
found in academic literature (summarised in Powell et al., 2017), but also increasingly from ‘grey’
literature (such as veterinary reports) as cultured stock present with symptoms. e knowledge
of lumpsh diseases has increased in recent years, alongside research into the species immune
system that may foster vaccine development (e.g. Rønneseth et al., 2015). e topic will be con-
sidered in further detail in Chapter 13.
Briey, general (and treatable or preventable) pathogenic and non-pathogenic diseases in
hatcheries include ciliates (Trichodinia sp.), ukes (Gyrodactylus sp.), fungi (Exophiala sp), cata-
racts and post-capture stress (physical handling, transport, barotrauma, fatty deposits around
organs with high lipid diets) have been recorded in adults and reared juveniles (Scyborska, 1948;
Dawit, 2000; Sayer et al., 2000; personal observation).
Whilst parasitic worms (Rolbiecki and Rokicki, 2008) and myxosporeans (Cavin et al., 2012;
Kristmundsson and Freeman, 2014) have been recorded in wild lumpsh, endemic diseases are
likely more damaging. e fungal microsporidian Nucleospora cyclopteri (Mullins et al., 1994)
has been found at high (c. 25%) prevalence in wild adults (Freeman et al., 2013) although there
is currently no conrmed route of transmission or eective treatment. Lumpsh also appear to
suer from a high prevalence (61–100%) of sea lice such as Caligus elongatus (Boxshall, 1974;
Heuch et al., 2007). More recently, amoebic gill disease (Perry and Treasurer, 2015), pasteurel-
losis and other bacterial infections (e.g. Alarcon et al., 2015; Smage et al., 2016), and viral dis-
eases (Towers, 2015) have been detected.
6.19 Summing up: gaps in knowledge and research needs
Knowledge of the biology of lumpsh has advanced greatly over the last few years in response to
the needs of the new cleaner sh industry, but information on many critical areas is still missing.
A detailed gap analysis is provided in Powell et al. (2017) but in brief, the ultimate objective is to
produce disease-free juveniles that adapt well in captivity, do not pose a risk to salmon or other
shes, and are ecient at delousing.
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To work toward this goal, the production of lumpsh needs to be closed in captivity, without
dependence on wild broodstock. is will require better knowledge of articial reproduction,
particularly with respect to control of maturation, gamete collection and storage. Commercial
production will need to be derived entirely from farmed strains, and this will require the devel-
opment of a genetic breeding programme, one that can produce elite lines with superior perfor-
mance and desirable traits, including disease resistance and delousing eciency. Targeting slow
growing lumpsh strains may be advantageous in order to prolong the time lumpsh can graze
on sea lice. Larval production also needs to be optimised, along with improved diets to help
reduce high post-weaning mortality. Vaccines, as well as more eective therapeutants, are also
required to combat emerging infectious diseases. Finally, reuse of deployed lumpsh needs to be
considered, perhaps through their use as broodstock, in animal feeds, or for human consumption.
e authors would like to thank an anonymous reviewer for constructive comments during the
preparation of this chapter.
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