The native ichthyofauna of the Baltic Sea is relatively poor, comprising approximately 100 fish species, including about 70 marine species (HELCOM 2009). However, representatives of other species occasionally enter the sea, including large predatory fish, such as the swordfish, Xiphias gladius Linnaeus, 1758 (Xiphiidae). It is a migratory fish, inhabiting mostly oceans within their tropical and temperate zones. Although the swordfish prefers warmer waters, it shows high thermal tolerance, allowing it to move and feed in cooler regions, particularly during summer (Nakamura 1985; Froese & Pauly 2020). It has been mainly observed in the western part of the Baltic Sea. The first such observations from the Polish zone were documented in 1925, near Kuźnica on the Hel Peninsula. However, historical records contain older mentions of large fish with a habit indicating this species. The largest individuals caught include a 3 m specimen caught in Gdynia-Redłowo in 1939 and a slightly shorter (2.9 m) swordfish caught near Kąty Rybackie in 1957 (Skóra 1997; 2000; Bacevičius & Karalius 2005). Recently, i.e. since 2014, swordfish have been regularly observed along the Polish shore of the Baltic Sea. In 2015, for example, fishermen in the Świnoujście area caught a swordfish weighing approx. 60 kg. Large specimens were also found on the beach in Dźwirzyno in August 2016 (current research) and were caught near Jantar in August 2017 (2.7 m, 96 kg). In addition, swordfish were found in fishing nets near Dźwirzyno and Świnoujście even in late autumn, e.g. in November 2017, an approx. 2 m specimen weighing about 60 kg was found entangled in a net. Large individuals were also observed near Rewal in 2018, and an individual longer than 2 m was found on the beach in Stegna in August 2018 (B. Arciszewski, unpublished data).
However, such single, incidental records do not always enable more comprehensive studies, such as parasite fauna analysis. These types of studies are useful when investigating the introduction of parasites into new areas and assessing the possibility of expanding their ranges. Given ongoing climate change, this is a particularly important issue, especially as swordfish are migratory fish, travelling long distances to feed, which can be particularly conducive to parasite expansion. To date, more than 70 parasite species have been documented in X. gladius, most of which are helminths, including species with a wider host range and high zoonotic importance (Palko et al. 1981; Hogans et al. 1983; Dubina 1985; Williams & Bunkley-Williams 1996; Caton et al. 1998; Speare 1999; Castro-Pampillón et al. 2002a,b; Garcia et al. 2008, 2011; Mattiucci et al. 2014; Varghese & Unnikrishnan 2016; De Silva et al. 2017). The present paper describes a preliminary study concerning a unique record of Philichthys xiphiaeSteenstrup, 1862, a rarely observed and poorly studied parasitic copepod from the family Philichthyidae.
Materials and methods
A dead female Xiphias gladius was found on 17 August 2016 on the beach in Dźwirzyno (Poland; Fig. 1). The specimen was large, weighing 96.15 kg and measuring 2.58 m in total length. Two copepods preserved in 70% ethanol were provided for the present study.
Figure 1
Dźwirzyno: sampling locality
The copepods were placed in scientific collections as part of the Collection of Extant Invertebrates at the Department of Invertebrate Zoology and Parasitology, University of Gdańsk, Poland (UGDIZP).
Results and discussion
Two Philichthys xiphiae females were found in the frontal bone of the examined swordfish (Fig. 2). Copepods were identified based on the publications of Kabata (1979) and Boxshall & Helsey (2004). This is the first record of P. xiphiae in the Baltic Sea.
Figure 2
Philichthys xiphiae: A, B – copepods in the frontal bone of the examined swordfish, C, E – dorsal view, D, F – ventral view, G – lateral view
As a marine copepod, P. xiphiae is specific to this host. Members of the family Philichthyidae mainly inhabit the sensory canals of the lateral line and skull bones of marine fish. However, they differ from typical endoparasites in that they maintain contact with the external environment through openings in the host skin (Kabata 1979; Boxshall & Helsey 2004). The Philichthyidae family currently comprises nine genera. However, Philichtys is represented by only one species (Walter & Boxshall 2021). It is distinguished from other genera by the presence of three pairs of lateral processes on the cephalothorax, processes on the swollen region of the thorax located laterally, five pairs of processes on the abdominal section (two ventral and three dorsal), and is characterized by the absence of swimming legs (Kabata 1979; Boxshall & Helsey 2004). Females of these copepods have undergone a clear morphological modification consisting in reduced segmentation and reduction of legs as an adaptation to parasitism. Males, on the other hand, are considerably smaller than females and only slightly differ from a typical cyclopoid copepod, having distinct segmentation and recognizable legs (Kabata 1979; Kazačenko 2001; Boxshall & Halsey 2004).
Although P. xiphiae has mainly been described from swordfish, it has also been reported from other billfish, i.e. Indo-Pacific sailfish, Istiophorus platypterus (Shaw, 1792), and striped marlin, Kajikia audax (Philippi, 1887) (see Speare 1999; Ortega-García & Hernández-Trujillo 2017), classified as a member of closely related Istiophoridae (Froese & Pauly 2020). Due to this small number of records, there are many gaps in the knowledge regarding its distribution, host range, life cycle, biology, and harmfulness to the host. The parasite may not be uncommon, but it is difficult to detect as it is only visible after the dissection of the fish cranium. It is possible that, similarly to other Philichthyidae species, it causes tumors in fish (Kazačenko 2001), the effects of which remain unknown, but so far no such observations have been recorded.
Although the Baltic Sea is not a typical environment for swordfish, their presence there may be associated with strong seasonal storms and intrusions of water from the North Sea, enriching the Baltic with high-salinity waters, or the increased presence of mackerel or other attractive prey that may be followed by large predatory fish. In addition to swordfish, other fish species unusual for the Baltic Sea have also been observed, such as the ocean sunfish, Mola mola (Linnaeus, 1758) (see Grygiel 2010), as well as sharks, e.g. porbeagle, Lamna nasus (Bonnaterre, 1788), piked dogfish, Squalus acanthias Linnaeus, 1758 and lesser spotted dogfish, Scyliorhinus canicula (Linnaeus, 1758), velvet belly lanternshark, Etmopterus spinax (Linnaeus, 1758) (see Zidowitz et al. 2008; Więcaszek et al. 2018). It is now known that climate factors, particularly the progressive global warming, have an increasing influence on local environmental conditions (von Storch et al. 2015), which in turn results in the gradual expansion of the ranges of various species.
The increasingly common occurrence of large, migratory, predatory fish species in the Baltic Sea and other atypical basins represents a potential transmission factor for new, exotic parasites. There is therefore a need for more thorough analyses of their parasitofauna to enable more effective monitoring of potential risks to native fauna.
Bacevičius, E. & Karalius, S. (2005). A survey of the data on swordfish (Xiphias gladius L.) in the southern and southeastern Baltic Sea. Bull. Sea Fish. Inst. 2(165): 63–72.BacevičiusE.KaraliusS.2005A survey of the data on swordfish (Xiphias gladius L.) in the southern and southeastern Baltic SeaBull. Sea Fish. Inst.21656372Search in Google Scholar
Bergsøe, V. (1864). Philichthys xiphiae Stp., monographisk fremstillet. Naturh. Tidsskr. 3(3): 87–103.BergsøeV.1864Philichthys xiphiae Stp., monographisk fremstilletNaturh. Tidsskr.338710310.5962/bhl.title.10397Search in Google Scholar
Boxshall, G.A. & Halsey, S.H. (2004). An introduction to copepod diversity. London: The Ray Society.BoxshallG.A.HalseyS.H.2004An introduction to copepod diversityLondonThe Ray SocietySearch in Google Scholar
Brian, A. (1905). Sui copepodi raccolti nel Golfo di Napoli da Oronzio G. ed Achille Costa. Annuar. Mus. Zool. R. Univ. Napoli (new. ser.) 1(24): 1–11.BrianA.1905Sui copepodi raccolti nel Golfo di Napoli da Oronzio G. ed Achille Costa. AnnuarMus. Zool. R. Univ. Napoli (new. ser.)124111Search in Google Scholar
Brian, A. (1906). Copepodi parassiti dei pesci D'italia. Genova: Stab. Tip-Litograifico R. Istituto Sordomuti.BrianA.1906Copepodi parassiti dei pesci D'italiaGenovaStab. Tip-Litograifico R. Istituto SordomutiSearch in Google Scholar
Castro-Pampillón, J.A., Rodríguez-Domínguez, H., Soto-Búa, M., Mejuto-García, J., Arias-Fernández, C. et al. (2002a). Parasites of swordfish from the Gulf of Guinea. J. Parasitol. 88(1): 188–189. DOI: 10.1645/0022-3395(2002)088[0188:POSFTG]2.0.CO;2.Castro-PampillónJ.A.Rodríguez-DomínguezH.Soto-BúaM.Mejuto-GarcíaJ.Arias-FernándezC.2002aParasites of swordfish from the Gulf of GuineaJ. Parasitol88118818910.1645/0022-3395(2002)088[0188:POSFTG]2.0.CO;2Open DOISearch in Google Scholar
Casto-Pampillón, J.A., Soto-Búa, M., Rodríguez-Domínguez, H., Mejuto-García, J., Arias-Fernández, C. et al. (2002b). Selecting parasites for use in biological tagging of the Atlantic swordfish (Xiphias gladius). Fish. Res. 59(1–2): 259–262. DOI: 10.2307/3285414.Casto-PampillónJ.A.Soto-BúaM.Rodríguez-DomínguezH.Mejuto-GarcíaJ.Arias-FernándezC.2002bSelecting parasites for use in biological tagging of the Atlantic swordfish (Xiphias gladius)Fish. Res.591–225926210.2307/3285414Open DOISearch in Google Scholar
Caton, A., Colgan, K., Sahlqvist, P., Ward, P., Ramirez, C. et al. (1998). Swordfish, Xiphias gladius, and the fisheries for tunas and billfishes in the Australian fishing zone. In I. Barrett, O. Sosa-Nishizaki & N. Bartoo (Eds.), Biology and Fisheries of Swordfish, Xiphias gladius (pp. 11–35). NOAA Technical Report NMFS 142.CatonA.ColganK.SahlqvistP.WardP.RamirezC.1998Swordfish, Xiphias gladius, and the fisheries for tunas and billfishes in the Australian fishing zoneInBarrettI.Sosa-NishizakiO.BartooN.(Eds.),Biology and Fisheries of Swordfish, Xiphias gladius1135NOAA Technical Report NMFS 142.Search in Google Scholar
De Silva, D.P.N., Fernando, H.S.D., Ranatunga, R.R.M.K.P. & De Silva, B.G.D.N.K. (2017). First record of plerocercoid larvae belong to the order Trypanorhyncha (Diesing 1863) isolated from swordfish (Xiphias gladius, Linnaeus 1758) captured off Sri Lanka. Sri Lanka J. Aquat. Sci. 22(1): 67–70.De SilvaD.P.N.FernandoH.S.D.RanatungaR.R.M.K.P.De SilvaB.G.D.N.K.2017First record of plerocercoid larvae belong to the order Trypanorhyncha (Diesing 1863) isolated from swordfish (Xiphias gladius, Linnaeus 1758) captured off Sri LankaSri Lanka J. Aquat. Sci.221677010.4038/sljas.v22i1.7518Search in Google Scholar
Dubina, V.R. (1985). On the parasitofauna of Xiphioidea of the Northwest area of the Indian Ocean. In W.J. Hargis (Ed.), Parasitology and Pathology of marine organisms of the world ocean (pp. 33–34). NOAA Technical Report NMFS 25.DubinaV.R.1985On the parasitofauna of Xiphioidea of the Northwest area of the Indian OceanInHargisW.J.(Ed.),Parasitology and Pathology of marine organisms of the world ocean3334NOAA Technical Report NMFS 25.Search in Google Scholar
Froese, R. & Pauly, D. (2020) FishBase. Retrieved November 08, 2020, from www.fishbase.org.FroeseR.PaulyD.2020FishBaseRetrieved November 08, 2020, from www.fishbase.org.Search in Google Scholar
Garcia, A., Mattiucci, S., Damiano, S., Santos, M.N. & Nascetti, G. (2011). Metazoan parasites of swordfish, Xiphias gladius (Pisces: Xiphiidae) from the Atlantic Ocean: Implications for host stock identification. ICES J. Mar. Sci. 68 (1): 175–182. DOI: 10.1093/icesjms/fsq147.GarciaA.MattiucciS.DamianoS.SantosM.N.NascettiG.2011Metazoan parasites of swordfish, Xiphias gladius (Pisces: Xiphiidae) from the Atlantic Ocean: Implications for host stock identificationICES J. Mar. Sci.68117518210.1093/icesjms/fsq147Open DOISearch in Google Scholar
Garcia, A., Santos, M.N., Damiano, S., Nascetti, G. & Mattiucci, S. (2008). Metazoan parasites of swordfish, Xiphias gladius (Pisces: Xiphiidae) from the Atlantic tropical-equatorial waters. J. Fish Biol. 73(9): 2274–2287. DOI: http://doi.org/10.1111/j.1095-8649.2008.02072.x.GarciaA.SantosM.N.DamianoS.NascettiG.MattiucciS.2008Metazoan parasites of swordfish, Xiphias gladius (Pisces: Xiphiidae) from the Atlantic tropical-equatorial watersJ. Fish Biol.73922742287DOI: http://doi.org/10.1111/j.1095-8649.2008.02072.x10.1111/j.1095-8649.2008.02072.xSearch in Google Scholar
Graeffe, E. (1900). Uebersicht der Fauna des Golfes von Triest nebst Notizen über Vorkommen, Lebensweise, Erscheinungs- und Laichzeit der einzelnen Arten. V. Crustacea. Arb. Zool. Inst. Univ. Wien 13(1): 3–48.GraeffeE.1900Uebersicht der Fauna des Golfes von Triest nebst Notizen über Vorkommen, Lebensweise, Erscheinungs- und Laichzeit der einzelnen Arten. V. CrustaceaArb. Zool. Inst. Univ. Wien131348Search in Google Scholar
Grygiel, W. (2010). Samogłów, nowy przykład bioróżnorodności ichtiofauny Bałtyku. Wiad. Ryb. 11–12(178): 22–25.GrygielW.2010Samogłów, nowy przykład bioróżnorodności ichtiofauny BałtykuWiad. Ryb.11–121782225Search in Google Scholar
Hamond, R. (1969). The copepods parasitic on Norfolk marine fishes. Trans. Norfolk Norwich Nat. Soc. 21(4): 229–234.HamondR.1969The copepods parasitic on Norfolk marine fishesTrans. Norfolk Norwich Nat. Soc.214229234Search in Google Scholar
HELCOM (2009). Biodiversity in the Baltic Sea – An integrated thematic assessment on biodiversity and nature conservation in the Baltic Sea. Baltic Sea Environment Proceedings 116B. Finland: Helsinki Commission.HELCOM2009Biodiversity in the Baltic Sea – An integrated thematic assessment on biodiversity and nature conservation in the Baltic SeaBaltic Sea Environment Proceedings 116B.FinlandHelsinki CommissionSearch in Google Scholar
Hewitt, G.C. & Hine, P.M. (1972). Checklist of parasites of New Zealand fishes and of their hosts. New Zeal. J. Mar. Fresh. Res. 6 (1–2): 69–114, DOI: 10.1080/00288330.1977.9515410.HewittG.C.HineP.M.1972Checklist of parasites of New Zealand fishes and of their hostsNew Zeal. J. Mar. Fresh. Res.61–26911410.1080/00288330.1977.9515410Open DOISearch in Google Scholar
Ho, J-S. (1978). Marine flora and fauna of the Northeastern United States. Copepoda: cyclopoids parasitic on fishes. NOAA Technical Report Circular 409.HoJ-S.1978Marine flora and fauna of the Northeastern United States. Copepoda: cyclopoids parasitic on fishesNOAA Technical Report Circular 409.Search in Google Scholar
Hogans, W.E., Brattey, J., Uhazy, L.S. & Hurley, P.C.F. (1983). Helminth Parasites of Swordfish (Xiphias gladius L.) from the Northwest Atlantic Ocean. J. Parasitol. 69(6): 1178–1179. DOI: 10.2307/3280895.HogansW.E.BratteyJ.UhazyL.S.HurleyP.C.F.1983Helminth Parasites of Swordfish (Xiphias gladius L.) from the Northwest Atlantic OceanJ. Parasitol.6961178117910.2307/3280895Open DOISearch in Google Scholar
Kabata, Z. (1979). Parasitic Copepoda of British fishes. London: The Ray Society.KabataZ.1979Parasitic Copepoda of British fishesLondonThe Ray SocietySearch in Google Scholar
Kazačenko, V.N. (2001). Opredelitel’ semejstv i rodov parazitičeskih copepod (Crustacea: Copepoda) ryb. Vladivostok: Dal’nevostočnyj Gosudarstviennyj Tehničeskij Rybohozâjstvennyj Universitet.KazačenkoV.N.2001Opredelitel’ semejstv i rodov parazitičeskih copepod (Crustacea: Copepoda) rybVladivostokDal’nevostočnyj Gosudarstviennyj Tehničeskij Rybohozâjstvennyj UniversitetSearch in Google Scholar
Mattiucci, S., Garcia, A., Cipriani, P., Santos M.N., Nascetti, G. et al. (2014). Metazoan parasite infection in the swordfish, Xiphias gladius, from the Mediterranean Sea and comparison with Atlantic populations: implications for its stock characterization. Parasite 21, 35. DOI: org/10.1051/parasite/2014036.MattiucciS.GarciaA.CiprianiP.SantosM.N.NascettiG.2014Metazoan parasite infection in the swordfish, Xiphias gladius, from the Mediterranean Sea and comparison with Atlantic populations: implications for its stock characterizationParasite2135DOI: org/10.1051/parasite/2014036.10.1051/parasite/2014036Search in Google Scholar
Nakamura, I. (1985). FAO Species catalogue. Billfishes of the world, vol. 5. An annotated and illustrated catalogue of marlins, sailfishes, spearfishes, and swordfishes known to date. Rome: United Nations Development Programme, Food and Agriculture Organization of the United Nations.NakamuraI.1985FAO Species catalogue. Billfishes of the world, vol. 5. An annotated and illustrated catalogue of marlins, sailfishes, spearfishes, and swordfishes known to dateRomeUnited Nations Development Programme, Food and Agriculture Organization of the United NationsSearch in Google Scholar
Ortega-García, S. & Hernández-Trujillo, S. (2017). First record of Maccallumtrema xiphiados and the Philichthys xiphiae in the striped marlin Kajikia audax (Philippi, 1887) off Cabo San Lucas, Baja California Sur, Mexico. J. Appl. Ichthyol. 33: 804–806. DOI: 10.1111/jai.13364.Ortega-GarcíaS.Hernández-TrujilloS.2017First record of Maccallumtrema xiphiados and the Philichthys xiphiae in the striped marlin Kajikia audax (Philippi, 1887) off Cabo San Lucas, Baja California Sur, MexicoJ. Appl. Ichthyol.3380480610.1111/jai.13364Open DOISearch in Google Scholar
Palko, B.J., Beardsley, G.L. & Richards, W. J. (1981). Synopsis of the Biology of the swordfish, Xiphias gladius Linnaeus. NOAA Technical Report NMFS Circular 441.PalkoB.J.BeardsleyG.L.RichardsW. J.1981Synopsis of the Biology of the swordfish, Xiphias gladius LinnaeusNOAA Technical Report NMFS Circular 441.Search in Google Scholar
Rathbun, M.J. (1905). Fauna of New England. 5. List of the Crustacea. Occas. Pap. Boston Soc. Nat. Hist. 7: 1–117.RathbunM.J.1905Fauna of New England. 5. List of the CrustaceaOccas. Pap. Boston Soc. Nat. Hist.71117Search in Google Scholar
Scott, T. & Scott, A. (1913) The British parasitic Copepoda. Copepoda parasitic on fishes. Vol. 1, 2. London: Ray Society.ScottT.ScottA.1913The British parasitic Copepoda. Copepoda parasitic on fishes1, 2LondonRay Society10.5962/bhl.title.58672Search in Google Scholar
Skóra, K.E. (1997). Włócznik (Xiphias gladius). Helska Bliza 23: 2.SkóraK.E.1997Włócznik (Xiphias gladius)Helska Bliza232Search in Google Scholar
Skóra, K.E. (2000). Zmiany w ichtiofaunie Zatoki Gdańskiej i Puckiej na tle zmian wybranych elementów ekosystemu. Rocz. Helski, 1: 115–146.SkóraK.E.2000Zmiany w ichtiofaunie Zatoki Gdańskiej i Puckiej na tle zmian wybranych elementów ekosystemuRocz. Helski1115146Search in Google Scholar
Speare, P. (1999). Parasites from East-coast Australian billfish. Mem. Queensl. Mus. 43(2): 837–848.SpeareP.1999Parasites from East-coast Australian billfishMem. Queensl. Mus.432837848Search in Google Scholar
Steenstrup, J.D. (1862). Philichthys xiphiae, en ny snylter hos svaerdfisken. Overs. Kongel. Danske Vidensk. Selsk. Forh. Medlemmers Arbeider 1861: 295–305.SteenstrupJ.D.1862Philichthys xiphiae, en ny snylter hos svaerdfiskenOvers. Kongel. Danske Vidensk. Selsk. Forh. Medlemmers Arbeider1861295305Search in Google Scholar
Stossich, M. (1880). Prospetto della fauna del mare Adriatico. Parte 3. Boll. Soc. Adriat. Sci. Nat. 6: 178–271.StossichM.1880Prospetto della fauna del mare Adriatico. Parte 3Boll. Soc. Adriat. Sci. Nat.6178271Search in Google Scholar
Thomson, G.M. (1890). Parasitic Copepoda of New Zealand, with description of new species. Trans. Proc. N. Z. Inst. 22: 353–376.ThomsonG.M.1890Parasitic Copepoda of New Zealand, with description of new speciesTrans. Proc. N. Z. Inst.22353376Search in Google Scholar
Valle, A. (1880). Crostacei parassiti dei pesci del mare Adriatico. Boll. Soc. Adriat. Sci. Nat. 6: 55–90.ValleA.1880Crostacei parassiti dei pesci del mare AdriaticoBoll. Soc. Adriat. Sci. Nat.65590Search in Google Scholar
Varghese, S.P. & Unnikrishnan, N. (2016). Notes on metazoan parasites of Alepisaurus ferox and Xiphias gladius of the eastern Arabian Sea. Mar. Biodiv. 46: 157–161. DOI: 10.1007/s12526-015-0346-4.VargheseS.P.UnnikrishnanN.2016Notes on metazoan parasites of Alepisaurus ferox and Xiphias gladius of the eastern Arabian SeaMar. Biodiv.4615716110.1007/s12526-015-0346-4Open DOISearch in Google Scholar
Vogt, C. (1877). Recherches cotières. Premier mèmorie. De la famille des philichthydes et en particulier du léposphile des labres (Leposphilus labrei Hesse). Mém. Inst. Natn. Genev. 13: 1–41.VogtC.1877Recherches cotières. Premier mèmorie. De la famille des philichthydes et en particulier du léposphile des labres (Leposphilus labrei Hesse)Mém. Inst. Natn. Genev.13141Search in Google Scholar
von Storch, H., Omstedt, A., Pawlak, J. & Reckermann, M. (2015). Introduction and Summary. In H.-J. Bolle, M. Menenti, S.S. al Vesuvio & S. I. Rasool (Eds.), Second assessment of climate change for the Baltic Sea Basin. Regional climate studies (pp. 1–22). Germany: Springer Open. DOI: 10.1007/978-3-319-16006-1_1.von StorchH.OmstedtA.PawlakJ.ReckermannM.2015Introduction and SummaryInBolleH.-J.MenentiM.al VesuvioS.S.RasoolS. I.(Eds.),Second assessment of climate change for the Baltic Sea Basin. Regional climate studies122GermanySpringer Open10.1007/978-3-319-16006-1_1Open DOISearch in Google Scholar
Walter, T.C. & Boxshall, G. (2021). World of copepods database. Philichthys Steenstrup, 1862. Retrieved January 10, 2021 from World Register of Marine Species from http://www.marinespecies.org/aphia.php?p=taxdetails&id=128697 on 2020-11-29.WalterT.C.BoxshallG.2021World of copepods database. Philichthys Steenstrup, 1862Retrieved January 10, 2021 from World Register of Marine Species from http://www.marinespecies.org/aphia.php?p=taxdetails&id=128697 on 2020-11-29.Search in Google Scholar
Więcaszek, B., Sobecka, E., Panicz, R., Keszka, S., Górecka, K. et al. (2018). First record of the deep-water shark Etmopterus spinax (Chondrichthyes: Etmopteridae) from the southern Baltic Sea (Pomeranian Bay). Oceanologia 60(3): 426–430.WięcaszekB.SobeckaE.PaniczR.KeszkaS.GóreckaK.2018First record of the deep-water shark Etmopterus spinax (Chondrichthyes: Etmopteridae) from the southern Baltic Sea (Pomeranian Bay)Oceanologia60342643010.1016/j.oceano.2018.02.001Search in Google Scholar
Williams, E.H. & Bunkley-Williams, L. (1996). Parasites of offshore big game fishes of Puerto Rico and the Western Atlantic. Puerto Rico: Antillean College Press, Mayaguez.WilliamsE.H.Bunkley-WilliamsL.1996Parasites of offshore big game fishes of Puerto Rico and the Western AtlanticPuerto RicoAntillean College Press, MayaguezSearch in Google Scholar
Wilson, C.B. (1932). The copepods of the woods Hole Region Massachusetts. Washington: Smithsonian Institution United States National Museum. Bulletin 158: 1–635.WilsonC.B.1932The copepods of the woods Hole Region Massachusetts. Washington: Smithsonian Institution United States National MuseumBulletin1581635Search in Google Scholar
Zidowitz, H., George, G., Fordham, S., Kullander, S.O. & Pelczarski, W. (2008). Sharks in the Baltic. Distribution, use and conservation of cartilaginous fishes in the Baltic Sea. The Shark Alliance. (Report May).ZidowitzH.GeorgeG.FordhamS.KullanderS.O.PelczarskiW.2008Sharks in the Baltic. Distribution, use and conservation of cartilaginous fishes in the Baltic SeaThe Shark Alliance(Report May).Search in Google Scholar
