Infective Copepodid Research Articles

Using sentinel cages to estimate infestation pressure on salmonids from sea lice in Loch Shieldaig, Scotland

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 5:49-59 (2014) - DOI: https://doi.org/10.3354/aei00094 Using sentinel cages to estimate infestation pressure on salmonids from sea lice in Loch Shieldaig, Scotland Campbell C. Pert1,*, Rob J. Fryer1, Paul Cook1, Rachel Kilburn1, Sonia McBeath1, Alastair McBeath1, Iveta Matejusova1, Katy Urquhart1, Sarah J. Weir1, Una McCarthy1, Catherine Collins1, Trish Amundrud1, Ian R. Bricknell1,2 1Marine Scotland Science, Marine Laboratory, PO Box 101, 375 Victoria Road, Aberdeen, Scotland AB11 9DB, UK 2School of Marine Sciences, University of Maine, 5735 Hitchner Hall, Orono, Maine 04469-5735, USA *Corresponding author: campbell.pert@scotland.gsi.gov.uk ABSTRACT: Sentinel Atlantic salmon, held in cages, were used to estimate the monthly infestation pressure of sea lice at 3 locations along a salmonid migration route in Loch Shieldaig, a Scottish west coast sea loch. The study lasted 30 mo, covering an entire production cycle and fallow period at nearby fish farms. A total of 5007 sea lice were sampled from 3097 sentinel fish, with over 99% of these being Lepeophtheirus salmonis. Infestation pressure was higher in cages nearer the head of the loch and the River Shieldaig estuary. Copepodids were the main infective life cycle stage, but a few (0.5% of total lice sampled) mobile pre-adult and adult stages were also found on the sentinel fish. Infestation pressure on the sentinel fish was correlated with gravid L. salmonis counts from nearby farms. However, there was no evidence that particular events, such as treatments, at the farms led directly to changes in infestation pressure. These findings suggest that, although aquaculture is a contributor of sea lice larvae into the Torridon system, further work is required to determine factors influencing the relationship between farm sea lice levels and infestation pressure in the wider environment. KEY WORDS: Lepeophtheirus salmonis · Sea lice · Infestation pressure · Sentinel cages · Aquaculture · Sea loch · Infectious copepodid Full text in pdf format PreviousNextCite this article as: Pert CC, Fryer RJ, Cook P, Kilburn R and others (2014) Using sentinel cages to estimate infestation pressure on salmonids from sea lice in Loch Shieldaig, Scotland. Aquacult Environ Interact 5:49-59. https://doi.org/10.3354/aei00094 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 5, No. 1. Online publication date: March 20, 2014 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2014 Inter-Research.

The Life Cycle of the Parasitic Crustacean, Lernanthropus latis Yamaguti, 1954 (Copepoda: Lernanthropidae), on Marine-Cultured Fish, Lates calcarifer, from Setiu Wetland, Terengganu.

Parasitic crustaceans of Lernanthropus latis were isolated from the host, the seabass, Lates calcarifer, obtained from a cage culture in Setiu Wetland, Terengganu. The adult females with egg were kept alive in vials containing 20 mL of filtered seawater and incubated at 30°C. The eggs were monitored every hour and the hatching periods were recorded. Three developmental stages were observed, namely, nauplii I, nauplii II, and infective copepodid. The infective copepodids were then transferred into a tank containing 60 litres of seawater with 150 fingerlings for infection purpose. One fish was sacrificed every 24 hr to inspect the next developmental stage. As a result, six more stages were obtained within 298 hrs starting from the infection day. The stages were known as fixed copepodid I, fixed copepodid II, fixed copepodid III, fixed copepodid IV, preadult, and adult. Parasitic L. latis takes a 483 hr period to complete a life cycle.

Free-living stages of the parasitic copepod Lernanthropinus labracoglossae Izawa, 2014 (Siphonostomatoida, Lernanthropidae), reared from eggs

Free-living stages, comprising two naupliar stages and the infective copepodid I, of the parasitic copepod Lernanthropinus labracoglossae Izawa, 2014 are described. The larvae were reared from eggs detached from an ovigerous female, recovered from the branchial lamellae of the Japanese actinopterygian fish Labracoglossa argentiventris Peter, 1866 (Kyphosidae). The number of naupliar stages prior to copepodopid I in the Lernanthropidae is the same as in the Caligidae, Pseudohatschekidae and Trebiidae. The copepodid I of the species has a frontal filament, as do representatives of the Caligidae, Pandaridae and Trebiidae. However, this is regarded as a vestigial feature in the last two families. Copepodid I of L. labracoglossae has a 6-segmented antennule, including the naked first segment, as do the first copepodids of eudactylinid copepods.

Complete life cycle of a pennellidPeniculus minuticaudaeShiino, 1956 (Copepoda: Siphonostomatoida) infecting cultured threadsail filefish,Stephanolepis cirrhifer

The complete life cycle of a pennellid copepod Peniculus minuticaudae Shiino, 1956 is proposed based on the discovery of all post-embryonic stages together with the post-metamorphic adult females infecting the fins of threadsail filefish Stephanolepis cirrhifer (Monacanthidae) cultured in a fish farm at Ehime Prefecture, Japan. The hatching stage was the infective copepodid. The life cycle of P. minuticaudae consists of six stages separated by moults: the copepodid, four chalimi and adult. In this study, the adult males were observed frequently in precopulatory amplexus with various stages of females however, copulation occurs only between adults. Fertilized pre-metamorphic adult females carrying spermatophores may detach from the host and settle again before undergoing massive differential growth into the post-metamorphic adult female. Comparison of the life cycle of P. minuticaudae has been made with three known pennellids: Lernaeocera branchialis (Linnaeus, 1767), Cardiodectes medusaeus (Wilson, 1908) and Lernaeenicus sprattae (Sowerby, 1806). Among the compared species, P. minuticaudae is the first ectoparasitic pennellid to be discovered to complete its life cycle on a single host without any change in infection site preferences between infective copepodid and fertilized pre-metamorphic female.

Free-living stages of three species of parasitic copepods (Siphonostomatoida, Eudactylinidae) reared from eggs, with discussion on the ontogenetic features in the Siphonostomatoida

Five naupliar stages and the infective copopodid stage of Eudactylina dasiati Izawa, 2011, Dangoka japonica Izawa, 2011, and an unidentified eudactylinid species are described based on free-living larvae reared from eggs detached from ovigerous females, which were recovered from the branchial lamellae of Japanese elasmobranchs, Dasyatis akajei (Muller & Henle, 1841) (Dasyatidae), Rhinobatos schlegelii Muller & Henle, 1841 (Rhinobatidae), and Alopias vulpine (Bonnaterre, 1788) (Alopiidae), respectively. These species of Eudactylinidae, along with Gangliopus pyriformis Gerstaecker, 1854 (Pandaridae) are the only Siphonostomatoida known to have five naupliar stages prior to the infective copepodid I. Naupliar morphology and the antennular segmentation in the Siphonostomatoida are discussed. Siphonostomatoid nauplii may possess six caudal elements and limb buds of the maxillae, maxillipeds, and two legs, but not maxillules. In the Siphonostomatoida, the naked first antennular segment of the nauplius may be retained to the adult stage.

Experimental challenges of Atlantic salmonSalmo salarwith incremental levels of copepodids of sea louseCaligus rogercresseyi: effects on infestation and early development

Aquaculture ResearchVolume 43, Issue 12 p. 1904-1908 Short Communication Experimental challenges of Atlantic salmon Salmo salar with incremental levels of copepodids of sea louse Caligus rogercresseyi: effects on infestation and early development Angélica Araya, Angélica Araya Escuela de Ciencias del Mar, Pontificia Universidad Católica de Valparaíso, Valparaíso, ChileSearch for more papers by this authorMelinka Mancilla, Melinka Mancilla Departamento de Producción Animal, Facultad de Ciencias Agronómicas, Universidad de Chile, Santiago, Chile Aquainnovo S.A., Puerto Montt, ChileSearch for more papers by this authorJean Paul Lhorente, Jean Paul Lhorente Aquainnovo S.A., Puerto Montt, ChileSearch for more papers by this authorRoberto Neira, Roberto Neira Departamento de Producción Animal, Facultad de Ciencias Agronómicas, Universidad de Chile, Santiago, Chile Aquainnovo S.A., Puerto Montt, ChileSearch for more papers by this authorJosé Andrés Gallardo, Corresponding Author José Andrés Gallardo Escuela de Ciencias del Mar, Pontificia Universidad Católica de Valparaíso, Valparaíso, ChileCorrespondence: José Andrés Gallardo, Pontificia Universidad Católica de Valparaíso, Avenida Altamirano Nº1480, Valparaíso, Chile. E-mail: [email protected]Search for more papers by this author Angélica Araya, Angélica Araya Escuela de Ciencias del Mar, Pontificia Universidad Católica de Valparaíso, Valparaíso, ChileSearch for more papers by this authorMelinka Mancilla, Melinka Mancilla Departamento de Producción Animal, Facultad de Ciencias Agronómicas, Universidad de Chile, Santiago, Chile Aquainnovo S.A., Puerto Montt, ChileSearch for more papers by this authorJean Paul Lhorente, Jean Paul Lhorente Aquainnovo S.A., Puerto Montt, ChileSearch for more papers by this authorRoberto Neira, Roberto Neira Departamento de Producción Animal, Facultad de Ciencias Agronómicas, Universidad de Chile, Santiago, Chile Aquainnovo S.A., Puerto Montt, ChileSearch for more papers by this authorJosé Andrés Gallardo, Corresponding Author José Andrés Gallardo Escuela de Ciencias del Mar, Pontificia Universidad Católica de Valparaíso, Valparaíso, ChileCorrespondence: José Andrés Gallardo, Pontificia Universidad Católica de Valparaíso, Avenida Altamirano Nº1480, Valparaíso, Chile. E-mail: [email protected]Search for more papers by this author First published: 10 October 2011 https://doi.org/10.1111/j.1365-2109.2011.02991.xCitations: 9Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume43, Issue12November 2012Pages 1904-1908 RelatedInformation

The settlement and reproductive success of Lepeophtheirus salmonis (Krøyer 1837; Copepoda: Caligidae) on atypical hosts

The reproductive success of Lepeophtheirus salmonis settled on host and non-host fish has been compared. Triplicate single species tanks of Atlantic salmon, marine three-spined sticklebacks, saithe and Atlantic cod were exposed to 10 adult female L. salmonis per tank (n=30 lice per species). Adult female L. salmonis settlement and egg string production occurred only on salmon and cod, with no egg production occurring on saithe and three-spined sticklebacks. The number of eggs in egg strings, hatching success of eggs and the survival of all larval stages to the copepodid stage were severely affected by the species of fish on which female L. salmonis had settled. L. salmonis settled on cod produced significantly fewer eggs, lower hatching rates and lower survival rates of larvae than females on Atlantic salmon. The production of egg strings by L. salmonis females infecting cod, which successfully hatch and moult through to the infective copepodid stage, albeit in small numbers, is discussed in terms of the implications to aquaculture and salmon and cod farming scenarios.

Densities of planktonic Lepeophtheirus salmonis before and after an Atlantic salmon farm relocation

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 1:225-232 (2011) - DOI: https://doi.org/10.3354/aei00022 Densities of planktonic Lepeophtheirus salmonis before and after an Atlantic salmon farm relocation Michael J. Penston*, Alastair J. A. McBeath, Colin P. Millar Marine Scotland Science, Marine Laboratory, PO Box 101, 375 Victoria Road, Aberdeen AB11 9DB, UK *Email: m.penston@marlab.ac.uk ABSTRACT: Relocating Atlantic salmon Salmo salar L. farms away from important salmonid rivers is possibly a means to reduce Lepeophtheirus salmonis (Krøyer, 1837) interactions between farmed Atlantic salmon and wild salmonids. However, to date, no data have been presented on the consequences of salmon farm relocation in terms of densities of planktonic L. salmonis. Near-surface plankton were sampled at 5 stations during 2 full farming production cycles; 1 before and 1 after a salmon farm relocation within a sea loch/fjord. The relocation comprised the removal of a salmon farm and the reallocation of its fish biomass to a different farm within the same management area. Over 85% of the larval sea lice we identified in sub-samples were L. salmonis; we therefore assumed that the majority of the larvae found were of that species. Densities of L. salmonis larvae increased significantly at all stations post relocation, except at the station near the vacated farm site where mean densities of nauplii were significantly lower and mean densities of copepodids were lower without statistical ­significance. The removal/relocation of the salmon farm significantly reduced the production of L. salmonis larvae, but did not significantly reduce the infection pressure, as represented by densities of the infectious copepodid stage, at the vacated farm site. This finding indicates that planktonic L. salmonis were transported to the vacated farm site from sources at a minimum of 5 to 8 km distant. KEY WORDS: Scotland · Sea lice · Relocation · Management · Salmon aquaculture · Sea trout Full text in pdf format PreviousNextCite this article as: Penston MJ, McBeath AJA, Millar CP (2011) Densities of planktonic Lepeophtheirus salmonis before and after an Atlantic salmon farm relocation. Aquacult Environ Interact 1:225-232. https://doi.org/10.3354/aei00022 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 1, No. 3. Online publication date: April 15, 2011 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2011 Inter-Research.

Chalimus Stages of Caligus latigenitalis (Copepoda: Caligidae) Parasitic on Blackhead Seabream from Japanese Waters, with Discussion of Terminology Used for Developmental Stages of Caligids

The first and third chalimus stages and chalimus adult (previously known as young adult) of Caligus latigenitalis are described based on new material collected from the body surface of a heavily infected wild blackhead seabream Acanthopagrus schlegelii schlegelii from Hiroshima Bay, Japan. The second and fourth chalimus stages of the same species are redescribed. Adults of C. latigenitalis are characterized by possessing 2 stout marginally indented processes at the base of 2 terminal spines at distal exopodal segment of leg 4. The chalimi were identified to stage based on the structure of the frontal filament and the discrete ranges in body length. Sexual dimorphism is first observed at the third chalimus stage in the shape of the distal segment of the antenna. The total number of postnaupliar stages of C. latigenitalis is 6, including 4 semaphoronts, i.e., 1 copepodid stage consisting of 1 infective copepodid and the chalimus copepodid, 4 chalimus stages, and 1 adult stage with 1 chalimus adult and 1 mobile adult. New terminology for the developmental stages of caligid copepods is proposed herein by amending the definition of chalimus as the postnaupliar stages, as well as semaphoronts having a frontal filament for host attachment.

Pseudohatschekiidae, a new family for Pseudohatschekia branchiostegi Yamaguti, 1939 (Crustacea: Copepoda: Siphonostomatoida) from Branchiostegus spp. (Teleostei: Perciformes: Malacanthidae) in Japanese waters, with descriptions of the early developmental stages of P. branchiostegi

The siphonostomatoid copepod Pseudohatschekia branchiostegi Yamaguti, 1939 is redescribed in detail based on specimens of both sexes collected from the gill filaments of three species of Branchiostegus Rafinesque (Teleostei: Malacanthidae) captured in Japanese waters. Descriptions of two naupliar stages and the infective copepodid stage of P. branchiostegi are also provided for the first time, and P. mebaru Yamaguti, 1939 is recognised herein as a junior synonym of P. branchiostegi. The latter copepod species represents a new family, the Pseudohatschekiidae fam. nov., of the Siphonostomatoida characterised by the following apomorphies: (a) two free pedigerous somites present between the cephalothorax and the genital complex; (b) a chelate antenna bearing two digitate processes and a thin cuticular covering; (c) a unilobate maxillule, with the palp completely fused to the endite and represented by a surface seta; (d) a rounded process furnished with pectinate membranes on the apex of the maxillary basis; (e) 2-segmented rami on legs 1-3; and (f) the absence of leg 4. It is also now evident that P. branchiostegi is a relatively common and abundant parasite of Branchiostegus spp. in the Far East.

Distribution of Kroeyerina elongata (Kroyeriidae: Siphonostomatoida, Copepoda) in the Olfactory Sacs of the Blue Shark, Prionace glauca

The infection pattern of Kroeyerina elongata (Kroyeriidae, Copepoda) in the olfactory sacs of the blue shark, Prionace glauca, was investigated using 4,722 copepods from 54 olfactory sacs. Copepod prevalence and mean intensity of infection per olfactory sac were 94.0 and 91.1%, respectively, and the most intensely infected olfactory sac and shark hosted 218 and 409 copepods, respectively. There were significant linear relationships between the number of female and total copepods per left olfactory sac and shark fork length as well as between the numbers of female, male, and total copepods per shark and mean olfactory sac width and cumulative olfactory sac width. Female copepods typically outnumbered males within olfactory sacs (mean intensity = 65.7 and 26.3, respectively), and no statistical differences were detected between the numbers of copepods inhabiting the left and right olfactory sacs. Copepods were not evenly distributed within olfactory sacs. Typically, female copepods occupied olfactory chambers located centrally along the length of the olfactory sac, while males infected lateral olfactory chambers nearest the naris. The orientation of most copepods (84.6%) suggested positive rheotaxis relative to the path of water through the olfactory sac. Within olfactory chambers, most mature females (68.2%) infected the first third of the peripheral excurrent channel and the adjacent fringe of olfactory lamellae, while most males (91.7%) infected the olfactory lamellae, and the 4 larval females collected were attached within the lamellar field and grasped by males. Based on the observed infection patterns and the pattern of water flow throughout the olfactory sac, a hypothesis regarding the life cycle of K. elongata is advanced wherein infective copepodids are swept into the olfactory sac from the surrounding sea and initially colonize the olfactory lamellae. Copepodids feed and mature among the olfactory lamellae, and adult males search for mates and copulate with young females among the olfactory lamellae. Inseminated females move to the peripheral excurrent channels to mature and produce ovisacs. Hatching ovisacs release free-swimming nauplii into the excurrent water flow to be swept into the milieu, where they can molt into infective copepodids that may infect new hosts.

Lipid and fatty acid composition of parasitic caligid copepods belonging to the genus Lepeophtheirus

Sea lice are copepod ectoparasites that constitute a major barrier to the sustainability and economic viability of marine finfish aquaculture operations worldwide. In particular, the salmon louse, Lepeophtheirus salmonis, poses a considerable problem for salmoniculture in the northern hemisphere. The free-swimming nauplii and infective copepodids of L. salmonis are lecithotrophic, subsisting principally on maternally-derived lipid reserves. However, the lipids and fatty acids of sea lice have been sparsely studied and therefore the present project aimed to investigate the lipid and fatty acid composition of sea lice of the genus Lepeophtheirus obtained from a variety of fish hosts. Total lipid was extracted from eggs and adult female L. salmonis obtained from both wild and farmed Atlantic salmon (Salmo salar L.) sampled at two time points, in the mid 1990s and in 2009. In addition, L. salmonis from wild sea trout (Salmo trutta L.) and L. hippoglossi from wild Atlantic halibut (Hippoglossus hippoglossus L.) were sampled and analyzed. The lipids of both females and egg strings of Lepeophtheirus were characterized by triacylglycerol (TAG) as the major neutral (storage) lipid with phosphatidylcholine and phosphatidylethanolamine as the major polar (membrane) lipids. The major fatty acids were 22:6n-3 (DHA), 18:1n-9 and 16:0, with lesser amounts of 20:5n-3, 22:5n-3 and 18:0. L. salmonis sourced from farmed salmon was characterized by higher levels of 18:2n-6 and 18:3n-3 than lice from wild salmon. Egg strings had higher levels of TAG and lower DHA compared to females, whereas L. hippoglossi had lower levels of TAG and higher DHA than L. salmonis. The results demonstrate that the fatty acid compositions of lice obtained from wild and farmed salmon differ and that changes to the lipid and fatty acid composition of feeds for farmed salmon influence the louse compositions.

Developmental stages and growth of Pseudocaligus fugu Yamaguti, 1936 (Copepoda: Siphonostomatoida: Caligidae) host-specific to Puffer

The post-embryonic development of the copepod Pseudocaligus fugu is described. This sea louse only parasitizes toxic pufferfish, and causes commercial loss of cultured Takifugu rubripes in Japan. Two naupliar, one copepodid and four chalimus stages preceding the adult are recognized in the species. The development pattern is similar to that of Caligus except for the suppression of leg 4 in the early chalimus phase. Pseudocaligus fugu lacks any preadult stage, as in Caligus, but contrasts with Lepeophtheirus species in which two preadult stages are reported. The nature of the metamorphic changes in size and even in degree of expression of articulations can occur without moulting. The validity of some chalimus stages recognized in Lepeophtheirus species is questioned. Growth and egg production in P. fugu were obtained in the laboratory. Pseudocaligus fugu attained adulthood 9 days after the infective copepodid attached to the host.

Considerations in developing an integrated pest management programme for control of sea lice on farmed salmon in Pacific Canada

In the development of integrated pest management (IPM) plans for the control of sea lice there are some components that are common to many areas. However, effective plans must be tailored to regionally varying environmental and biological factors affecting the severity of sea lice infections. This paper describes factors that would be involved in the development of an IPM plan for sea lice in the Broughton Archipelago, British Columbia. Temperature, salinity and currents affect the production, dispersion and competence of larvae of sea lice, Lepeophtheirus salmonis (Krøyer), as they develop to the infective copepodid stage. This information can be coupled with oceanographic conditions in the Broughton Archipelago and emerging computer models to define zones of infection where infections of new hosts are most likely. Salinity and temperature depend, in part, on river discharge in estuarine systems. River discharge depends on precipitation, snow pack and ambient temperatures, which can be monitored to help forecast the intensity of sea lice infections associated with both farmed and wild hosts. One of the goals of IPM planning is to reduce reliance on pesticides to avoid development of resistance in targeted parasites and to minimize environmental residues. Recommendations for developing an IPM plan specific to the Broughton Archipelago are provided along with a discussion of the additional information needed to refine IPM plans in this and other areas.

Temporal partitioning: dynamics of alternating occupancy of a host microhabitat by two different crustacean parasites

Double infection by 2 crustacean parasites was found on the mysid Siriella okadai collected from the Seto Inland Sea, Japan. An epicaridean isopod, Prodajus curviabdominalis, and a siphonostom- atoid copepod, Neomysidion rahotsu, both occupied the lumen of the host marsupium, and fed vora- ciously upon host eggs. Interestingly, adult females of these 2 parasites occurred alternately on the host, with almost no overlap: the copepod occurred from mid-winter to summer when water temperatures were <20°C (with mean prevalence of 7.2%), whereas the isopod occurred exclusively from mid- summer to late autumn when water temperatures exceeded 20°C (with mean prevalence of 9.1%). Pos- sible factors responsible for generating and maintaining this alternation of microhabitat occupancy on the host are discussed on the basis of the life cycles and host-specificities of the 2 parasites. In addition, we explored the possible means by which these obligate parasites survive during the periods when they are not on the mysid host. In the case of the isopod, we hypothesise that survival away from the mysid host involves the utilisation of an intermediate host by an as yet undiscovered microniscus larva, as in other epicarideans. For the copepod, we considered the available evidence in support of a number of hy- potheses. A new pattern of behaviour, unique within the copepod family Nicothoidae, was discovered in N. rahotsu. After the infective female copepodid stage attached to the host, it moulted into an imma- ture female and penetrated the host tissue. It then migrated internally, typically through the dorsal trunk musculature of the host, finally emerging into the host marsupium. This behaviour was observed exclu- sively during the season when copepods occurred within the marsupium. We inferred that this internal migration behaviour in some ways facilitates the synchronisation of the parasite life cycle with the oviposition by the host into the marsupium. It remains uncertain how and where N. rahotsu passes the exclusive occurence of P. curviabdominalis.

Effect of environmental salinity on sea lice Lepeophtheirus salmonis settlement success

The sea louse Lepeophtheirus salmonis (Krøyer, 1837) (Copepoda: Caligidae) is an ectoparasite of salmonid fish. It has earlier been proposed that the free-swimming infectious copepodid stage of L. salmonis gather at river mouths to infect wild Atlantic salmon Salmo salar L. and sea trout S. trutta L. smolts during their seaward migration. This study used aquarium-based methods to investigate the survival, infective ability and behaviour of L. salmonis copepodids exposed to short periods of low salinity levels, such as those encountered at river mouths. Survival of free-swimming copepodids was found to be severely compromised at salinity levels below 29 parts per thousand (ppt). Attachment to an S. salar host did not aid copepodid survival during post-infection exposure to low salinity environment, and a reduction in salinity appears to reduce the ability of copepodids to remain attached to S. salar smolts. Pre-infection exposure of copepodids to reduced salinity levels reduced infection of S. salar. Infection levels at reduced salinity were lower than predicted from the free-swimming survival experiment, suggesting that low salinity compromises the copepodids' ability to sense or respond to the presence of a host. In salinity gradients, copepodids demonstrated avoidance of salinities below 27 ppt, by both altering their swimming behaviour and changing the orientation of passive sinking. Avoidance of low salinity levels may be due to their adverse effects on copepodid physiology, as suggested by the reduction in survival. Sinking rates were also faster in reduced salinity, suggesting that remaining in the water column would be more energetically demanding for the copepodids at reduced salinity. These results show that both survival and host infectivity of L. salmonis are severely compromised by short-term exposure to reduced salinity levels.

The Effects of Water Temperature, Salinity and Currents on the Survival and Distribution of the Infective Copepodid Stage of the Salmon Louse ( Lepeophtheirus salmonis ) Originating on Atlantic Salmon Farms in the Broughton Archipelago of British Columbia, Canada (Brooks, 2005)—A Response to the Rebuttal of Krkošek et al. (2005a)

The following comments are offered in response to the rebuttal of Krkosek et al. (2005a) to Brooks (2005). The response has required a closer look at the model of Krkosek et al. (2005b) in order to...

The Effects of Water Temperature, Salinity, and Currents on the Survival and Distribution of the Infective Copepodid Stage of Sea Lice (Lepeophtheirus Salmonis) Originating on Atlantic Salmon Farms in the Broughton Archipelago of British Columbia, Canada

Recent reports claim that pink salmon fry are heavily infected by Lepeoptheirus salmonis as they pass salmon farms in the Broughton Archipelago. Hydrodynamic studies reveal that the top 25 to 40 m of water generally flows seaward through the archipelago under the influence of freshwater, reducing surface salinity from 15–25% from June through November of most years. Sea lice larvae do not consistently develop to an infectious stage at salinities < 30‰—providing a natural control in the archipelago. The larvae require 4.2–5.8 days to develop to the infective stage at the temperatures typical during the time that pink salmon fry are migrating. Net current speeds measured at 15 salmon farms are predicted to carry most sea lice nauplii 7.3–10.0 km downcurrent and out of the archipelago before they become infective. A particle-tracking model predicts that nauplii released in the vicinity of two farms located deep in the archipelago are carried 10–40 km from the farms before they become infective. These predictions are consistent with the European experience and suggest little potential for salmon farms to be self-infecting or to infect migrating wild fish in their immediate vicinity, except where net current vectors are zero. A clearer picture of sea lice epizootics requires detailed knowledge of site-specific oceanographic characteristics and the affects these have on sea lice survival and dispersal during development to the infectious copepodid stage.

An evaluation of three potential methods for preventing the spread of larval Lepeophtheirus salmonis (Kroyer, 1837)

Within the State of Maine, only a portion of the farm sites experience sea lice (Lepeophtheirus salmonis) infections on an annual basis. There has been concern about the further spread of lice by farming activities to unaffected areas despite routine disinfection of equipment with sodium hypochlorite or iodophors. We examined the effects of Povidone-iodine, sodium hypochlorite and desiccation on egg strings of L. salmonis and the potential of these methods for preventing hatching of nauplii or development to the copepodid stage. L. salmonis egg strings were exposed to one of eight treatments: 200 ppm of sodium hypochlorite or Povidone-iodine solutions for 1 min, 500 ppm of either disinfectant for one minute or 10 min, or desiccation for either 4 or 24 h. The egg strings were then incubated and the hatched copepods were kept for 6 days in filtered natural seawater at 32 ppt salinity at 12°C. Desiccation for 4 or 24 h were the only methods that prevented L. salmonis nauplii from hatching or developing to the infective copepodid stage. Common disinfection procedures against pathogenic bacteria and virus were not found to be effective against L. salmonis eggs.

Differential infectivity of Caligus flexispina (Copepoda, Caligidae) in three farmed salmonids in Chile

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.