International Council for the
Exploration of the Sea
ICES CM 2005/K:17
1
*Ken MacKenzie,
2
Pablo Abaunza and
1
Neil Campbell
1
School of Biological Sciences (Zoology), The University of Aberdeen, Tillydrone
Avenue, Aberdeen AB24 2TZ, UK [tel: +44 1224 272861, fax: +44 1224 272396, emails: k.mackenzie@abdn.ac.uk
, neil.campbell@abdn.ac.uk.
2
Instituto Español de Oceanografía (IEO), PO Box 240, 39080 Santander, Spain [+34
942 291060, fax: +34 942 275072, email: pablo.abaunza@st.ieo.es.
*Contact author.
Abstract
Parasites have been used as biological tags in a number of studies of stock structure in small pelagic fish. Here we review these studies and discuss the particular features of the parasite fauna of small pelagic fish, the advantages and limitations of biological tagging compared with other methods, and the methodology of using parasites as biological tags. While a multidisciplinary study has the major advantage of permitting comparisons to be made between results from different methods of stock identification, compromises usually have to be made with regard to the methods of preservation and processing to suit the requirements of all the methods involved, and these may not be ideal for one or more of the disciplines involved, including the preservation and identification of parasites. Based largely on our experience of the EC-funded HOMSIR and WESTHER projects, we propose guidelines for the use of parasites in multidisciplinary studies of small pelagics.
Keywords: parasite tags, small pelagic fish, stock identification.

Introduction
MacKenzie and Abaunza (2005) described the general principles of using parasites as biological tags in the stock identification of marine fish in general, and proposed guidelines for the use of parasites in such studies. In the present paper we focus on small pelagics and discuss how these principles and guidelines apply in studies of their stock identification. We also review publications on stock identification of small pelagics using parasites as biological tags and compare studies in which parasites were the sole method used with multidisciplinary studies in which parasite tags have been one of a number of methods used.
General principles
The basic principles of using parasites as tags for small pelagics are the same as for any other group of fish. This is that fish can become infected with a particular parasite only when they come within the endemic area of that parasite, the endemic area being the geographic region in which transmission of the parasite can take place. If infected fish are found outside the endemic area, we can infer that these fish had been within that area at some time in its past history.
Advantages and limitations of parasite tagging
In any multidisciplinary study of stock identification, each method will have its own strengths and weaknesses compared to other methods.
•
Parasite tagging is recognized as being more appropriate than artificial tagging for studies of small delicate species of fish which have poor survival rates following the stressful processes of capture, handling and tagging. This applies particularly to small pelagic species.
•
In parasite tagging each specimen sampled represents a valid observation, whereas with artificial tags each individual must be sampled, tagged and recaptured to obtain a valid observation.
•
Parasite tagging is less expensive because samples can be obtained from routine sampling programmes and research vessel surveys.
•
The use of parasite tags eliminates doubts concerning the possible abnormal behaviour of artificially tag hosts.
•
Parasites can have some advantage over genetic studies in that they can be used to identify host subpopulations distinguished by behavioural differences, but between which there is still a considerable amount of gene flow. For example, a gene flow rate of only 1% will give genetic homogeneity among samples (Ward, 2000).
On the other hand, lack of information on the complex biology and ecology of many marine parasites can limit their value as tags. However, as research adds to our knowledge, the use of parasites in stock identification is becoming more efficient. The specific identification of closely related parasite species may be also difficult. The recent application of molecular biology techniques to parasite taxonomy has resulted in the identification of two or more “sibling” or “cryptic” species in parasite groups which had previously been assumed to be a single species. Conversely, the same techniques have occasionally shown that parasites that had previously been regarded as separate species may in fact be conspecific.

Features of the parasite fauna of small pelagics
Small pelagics are generally infected with fewer parasite species than demersal fish
(Polyanski, 1966). Within the group, piscivorous species and those with relatively diverse diets have richer parasite faunas than planktophagous species. The parasite fauna of small pelagics tends to be dominated by larval forms, particularly helminths, which mature in the predatory species that prey on them.
Methodology and selection of tag parasites
Two different approaches to the use of parasites as biological tags in general are recognized.
1) A small number of parasite species are selected according to selection criteria that have been described by a number of authors and have changed and evolved over the past 42 years (Kabata, 1963; Sindermann, 1983, MacKenzie, 1983, 1987;
Williams et al.
, 1992). A large number of host individuals are then examined specifically for these parasites. The selection criteria for the most appropriate tag parasites can be summarized as follows.
•
They should have significantly different levels of infection in the target host in different parts of the study area.
•
They should persist in the target host for more than one year.
•
Parasites with single-host life cycles, such as monogenetic trematodes and most parasitic crustaceans, are the simplest to use. However, parasites with complex life cycles involving developmental stages in different hosts can also be used effectively, given sufficient information on their life cycles and ecology.
•
The level of infection should remain relatively constant from year to year. The effects of annual variations can, however, be taken into account by following infection levels in single year-classes of the target host over several years.
•
They should be easily detected and identified, Examination of the host should involve the minimum of dissection, otherwise time can become a limiting factor.
•
Parasites that are serious pathogens should be avoided.
This first approach is the one that has been used most frequently in stock identification studies of small pelagics.
2) In the second approach, entire parasite assemblages are analyzed using multivariate statistical techniques such as discriminant analysis or multiple logistic regression. This approach is more appropriate for large valuable host species with rich and varied parasite faunas. It use for small pelagics is limited by the relative paucity of the parasite faunas of most small pelagic species, but there are exceptions to this general rule (e.g., George-Nascimento, 2000; Timi, 2003).
For both approaches, summary statistics of levels of infection in terms of prevalence, mean intensity and/or abundance should be expressed by the mean value plus and minus the standard deviation, and the range. The biological interpretations of the statistical parameters should be clearly described and understood to avoid misleading interpretations concerning the true nature of the infection (Rózsa et al.
,
2000). For full descriptions of the statistical methods appropriate for application to parasite data in stock identification studies, see MacKenzie and Abaunza (2005).

Review of publications on parasites as tags in the stock identification of small pelagics
Tables 1, 2 and 3 list the publications in which parasites have been used as biological tags in stock identification studies of small pelagics. They show that the most frequently used tag parasites have been larval nematodes, particularly those of the genus Anisakis, while digenean metacercariae, cestode plerocercoids (Figure 1), juvenile acanthocephalans and parasitic crustaceans have also been used to good effect. All of the publications listed used parasite tags as the only method of stock identification, with the exception of those by George-Nascimento and Arancibia
(1992), who used host morphometrics in addition to parasites, and Campbell et al.
(2002), which was based on the multidisciplinary HOMSIR project. Our own experience of the EC-funded HOMSIR and WESTHER projects has shown that the most useful parasite tags for Atlantic horse mackerel Trachurus trachurus and
Atlantic herring Clupea harengus have been digenean metacercariae (Figure 2) anisakid nematode larvae (Figure 3), monogeneans, and juvenile acanthocephalans
(Campbell et al.
, 2002 and unpublished results). Horse mackerel have a much richer parasite fauna than herring, reflecting the more diverse diet of the former.
While multidisciplinary studies have the major advantage of permitting comparisons to be made between results from different methods, planning the sampling and examination protocols must be done with great care so that the requirements of all the disciplines involved are taken fully into account. Compromises will inevitably have to be made and, in the case of the parasite studies, this can mean that the methods of preservation of the parasite material may not be ideal, with obvious implications for precise identification.

Table 1. Studies using parasites as biological tags for stock identification of small clupeoid species.
Host species Study area Parasites used Reference
Atlantic herring
Clupea harengus harengus
Pacific herring
Clupea harengus pallasi
Sprat Sprattus sprattus
Sardine Sardina pilchardus
Anchovy Engraulis anchoita
British
Columbia
White Sea
Northeast
Pacific
California
North Sea
Northeast
Atlantic
Argentina
Northwest
Atlantic
Northwest
Atlantic
Baltic Sea
Baltic Sea
Northeast
Atlantic
Northwest
Atlantic
Baltic Sea
Anisakid nematode larvae, cestode plerocercoids, myxosporean
Anisakis
Anisakis
Anisakis sp. larvae, cestode plerocercoid, adult digeneans
Digenean larvae, cestode plerocercoid
Anisakis sp. larvae
Anisakis sp. larvae
Anisakis sp. larvae
(Nematoda)
Gyrodactylidae
(Monogenea)
Digenean larvae,
Anisakid nematode larvae
sp. larvae
sp. larvae
Anisakid nematode larvae, cestode plerocercoid, adult digenean
Monogenea
General parasite community
General parasite community
Sindermann (1957)
Parsons & Hodder
(1971)
Grabda (1974)
Gaevskaya & Shapiro
(1981)
MacKenzie (1985)
Chenoweth et al.
(1986)
Lang et al. (1990)
Bishop & Margolis
(1955)
Kulachkova (1977)
Arthur & Arai (1980)
Moser & Hsieh (1992)
Reimer (1978)
Shukhgalter (1998)
Timi (2003)

Table 2. Studies using parasites as biological tags for stock identification of small carangid species.
Host species Study area Parasites used Reference
Black Sea horse mackerel
Trachurus mediterraneus ponticus
Atlantic horse mackerel
Trachurus trachurus
Horse mackerels
Trachurus spp.
Jack mackerel Trachurus symmetricus murphyi
Round scad russelli
Decapterus
Black Sea
North & Northwest
Spain
Northeast Atlantic and Mediterranean
Sea
Eastern Atlantic
Chile
Pacific Ocean
Chile
Chile, Peru
Java Sea
Helminth fauna
Anisakis sp. larvae
General parasite community
General parasite community
Anisakid nematode larvae, juvenile acanthocephalan, parasitic isopod
Parasitic isopods
Parasitic isopods
General parasite community
Anisakis larvae
sp.
Kovaleva (1965)
Abaunza et al.
(1995)
Campbell et al.
(2002)
Gaevskaya & Kovaleva
(1980)
George-Nascimento &
Arancibia (1992)
Avdeev (1992)
Aldana et al. (1995)
George-Nascimento
(2000)
Burhanuddin & Djamali
(1978)

Table 3. Studies using parasites as biological tags for stock identification of other small pelagics.
Host species Study area Parasites used Reference
Atlantic mackerel
Scomber scombrus
Japanese mackerel
Scomber japonicus
Pacific saury saira
Garfish
Capelin
Cololabis
Belone belone
Mallotus villosus
Blue whiting
Micromesistius poutassou
North &
Northwest Spain
Northeast Atlantic
Northwest Pacific
Pacific Ocean
Baltic Sea
Barents Sea
Atlantic Canada
Celtic Sea and adjacent waters
Anisakis
Cestode
Anisakis
sp. larvae plerocercoids
General parasite community
Parasitic copepods
sp. larvae, cestode plerocercoid
Adult cestode
Anisakid nematode larvae, protozoan
Myxosporean
Abaunza et al.
(1995)
MacKenzie (1990)
Pozdnyakov &
Vasilenko (1994)
Sokolovsky (1969)
Grabda (1981)
Kennedy (1979)
Arthur & Albert (1996)
Karasev (1988)

Figure 2. Cestode plerocercoid. Figure 3. Digenean metacercariae.
Figure 1. Anisakis larvae in the visceral cavity of a herring

Guidelines for the use of parasites as biological tags for small pelagics
The selection of tag parasites should initially follow the criteria listed above, but we further offer the following guidelines for the use of parasites in multidisciplinary studies of the stock identification of small pelagics, based largely on our own experience of the HOMSIR and WESTHER projects.
•
Those doing the parasite study must receive the material to be examined in a form that allows for accurate identification of any parasites found. If whole fish are to be deep-frozen, as was the case in HOMSIR, they should be frozen as soon after capture as possible. Many parasites begin to deteriorate very quickly after death, especially in warm temperatures. Where material is preserved in alcohol, as was the case in WESTHER, the strength and volume of the alcohol used must be sufficient for adequate preservation and should take account of any dilution due to liquids present in the material itself.
•
If whole deep-frozen fish are supplied, they should be frozen individually and preferably in individual plastic bags or other suitable containers. Defrosting large blocks of fish can lead to loss of, and damage to, parasites.
•
Deep-frozen fish must be labelled in such a way that the labels are not easily lost and do not damage fish tissues or organs. For example, plastic ties around the gills can result in bleeding and damage which can make examination difficult and may result in loss of, or damage to, ectoparasites.
•
If the material to be examined is liquid-preserved, the type of container must be selected with great care so that it will not crack or leak and so that numbers of them can be easily packed for transport.
•
The labelling system for identifying individual samples should be as simple and concise as possible. The brain most readily processes information that is either the first or last in a string of numbers, so the most important information, such as the sampling position and individual sample number, should be at the beginning and end of the label. The system used in HOMSIR had the sampling position at the beginning and the individual fish number at the end, with the sampling year in the middle – for example 09-01-001 refers to fish no. 1 of sampling position 09 in year 2001.
•
If the requirements of other disciplines mean that it is not possible to obtain whole fish for parasitological examinations, those organs and tissues that are the sites of infection of the most potentially useful tag parasites should be identified. For example, in WESTHER we received only the visceral organs of herring preserved in alcohol, because we had previously identified the most likely tag parasites as helminths infecting the visceral cavity and associated organs.
References
Abaunza, P., Villamor, B. and Pérez, J.R. 1995. Infestation by larvae of Anisakis simplex (Nematoda: Ascaridata) in horse mackerel, Trachurus trachurus , and
Atlantic mackerel, Scomber scombrus , in ICES Divisions VIIIb, VIIIc and Ixa (N-
NW of Spain. Scientia Marina 59: 223-233.
Aldana, M., Oyarzun, J. and George-Nascimento, M. 1995. Parasitic isopods as population indicators in the horse mackerel Trachurus symmetricus murphyi
Nichols, 1920 (Pisces: Carangidae) off the Chilean coast. Biologia Pesquera 24:
23-32.
Arthur, J.R. and Albert, E. 1996. Parasites as potential biological tags for capelin
( Mallotus villosus ) in the St. Lawrence estuary and gulf. Canadian Technical

Report of Fisheries and Aquatic Sciences No. 2112: 1-9.
Arthur, J.R. and Arai, H.P. 1980. Studies on the parasites of Pacific herring ( Clupea harengus pallasi Valenciennes): a preliminary evaluation of parasites as indicators of geographical origin for spawning herring. Canadian Journal of
Zoology 58: 521-527.
Avdeev, V.V. 1992. On a possible use of parasitic isopods as bioindicators of migration routes of horse mackerels in the Pacific Ocean. Journal of Ichthyology
32: 14-21.
Bishop, Y.M.M. and Margolis, L. 1955. A statistical examination of Anisakis larvae
(Nematoda) in herring ( Clupea pallasi ) of the British Columbia coast. Journal of the Fisheries Research Board of Canada 12: 571-592.
Burhanuddin and Djamali, A. 1978. Anisakis parasite as an indicator for identification of discrete populations of round scad ( Decapterus russelli Ruppell) in the Java
Sea. (In Bahosa Indonesia, English abstract). Oseanologi di Indonesia 9: 1-11.
Campbell, N., MacKenzie, K., Mattiucci, S., Ramos, P., Pereira, A., and Abaunza, P.
2002. Parasites as biological tags in a population study of horse mackerel
Trachurus trachurus.
In Proceedings of the 10 th
International Congress of
Parasitology – ICOPA X: Symposia, Workshops and Contributed papers.
Vancouver (Canada), August 4–9, 2002, pp. 217-222. Monduzzi Editore,
International Proceedings Division, Bologna, Italy.
Chenoweth, J.F., McGladdery, S.E., Sindermann, C.J., Sawyer, T.K. and Bier, J.W.
1986. An investigation into the usefulness of parasites as tags for herring ( Clupea harengus ) stocks in the western North Atlantic, with emphasis on use of the larval nematode Anisakis simplex.
Journal of Northwest Atlantic Fisheries Science 7:
25-34.
Gaevskaya, A.V. and Kovaleva, A.A. 1980. The use of parasitological data in population studies of Atlantic mackerel from the genus Trachurus (Abstract, in
Russian). In IX Konferentsiya Ukrainskogo Parazitologicheskogo Obsch-chestva
Tezisy dokladov, pp. 132-133. Chast’l. ‘Naukova Dumka’, Kiev, USSR
Gaevskaya, A.V. and Shapiro, L.S. 1981. The question of the local nature of Baltic herring ( Clupea harengus membras L.) in the Vistula lagoon of the Baltic Sea (In
Russian). In Stock State and Principles of the Rational Fishery in the Atlantic.
Trudy AtlantNIRO, Kaliningrad: 11-19
George-Nascimento, M. 2000. Geographical variations in the jack mackerel
Trachurus symmetricus murphyi populations in the southeastern Pacific Ocean as evidenced from the associated parasite communities. Journal of Parasitology
86: 929-932.
George-Nascimento, M. and Arancibia , H.F. 1992. Ecological stocks of the jack mackerel ( Trachurus symmetricus murphyi Nichols) in three fishing areas off
Chile, detected through comparison of the parasite fauna and morphometry.
Revista Chilena de Historia Natural 65: 453-470.
Grabda, J. 1974. The dynamics of the nematode larvae, Anisakis simplex (Rud.) invasion in the south-eastern Baltic herring ( Clupea harengus L.). Acta
Ichthyologica et Piscatoria 4: 3-21.
Grabda, J. 1981. Parasitic fauna of garfish Belone belone (L.) from the Pomeramian
Bay (southern Baltic) and its origin. Acta Ichthyologica et Piscatoria 11: 75-85.
Kabata, Z. 1963. Parasites as biological tags. ICNAF Special Publication No. 4: 31-
37.
Karasev, A.B. 1988. Myxosporidian Myxobolus aeglefini (Cnidospora: Myxosporea) – blue whiting biological tag from the Celtic Sea and adjacent waters. ICES
C.M.1988/H:27: 1-16.
Kennedy, C.R. 1979. The distribution and biology of the cestode Eubothrium parvum in capelin, Mallotus villosus (Pallas) in the Barents Sea, and its use as a biological tag. Journal of Fish Biology 15: 223-236.

Kovaleva, A.A. 1965. The helminth fauna of local shoals of Carangidae in the Black
Sea. Materiali k nauchnoi Konferentsii vsesoysnogo Obshchestva
Gelmintologov, 1965, Part II, 121-126.
Kulachkova, V.G. 1977. Gyrodactylidae as indicators of local herring ( Clupea harengus pallasi marisalbi ) shoals in the White Sea (In Russian).
Parazitologicheskii Sbornik, Leningrad, No 27: 27-34.
Lang, T., Damm, U., Weber, W., Neudecker, T. and Kuhlmorgen-Hille, G. 1990.
Infestation of herring ( Clupea harengus L.) with Anisakis sp. larvae in the western
Baltic. Archiv für Fischereiwissenschaft 40: 101-117.
MacKenzie, K. 1983. Parasites as biological tags in fish population studies.
Advances in Applied Biology 7: 251-331.
MacKenzie, K. 1985. The use of parasites in population studies of herring, Clupea harengus L., in the North Sea and to the north and west of Scotland. Journal du
Conseil International pour l’exploration de la Mer 42: 33-64.
MacKenzie, K. 1987. Parasites as indicators of host populations. International
Journal for Parasitology 17: 345-352.
MacKenzie, K. 1990. Cestode parasites as biological tags for mackerel in the Northeast Atlantic. Journal du Conseil International pour l’exploration de la Mer 46:
155-166.
MacKenzie, K. and Abaunza, P. 2005. Parasites as biological tags. In Stock
Identification Methods. Applications in Fisheries Science (eds S.X. Cadrin, K.D.
Friedland & J.R. Waldman), pp. 211-226. Elsevier Academic Press, San Diego,
USA.
Moser, M. and Hsieh, J. 1992. Biological tags for stock separation in Pacific herring
Clupea harengus pallasi in California. Journal of Parasitology 78: 54-60.
Parsons, L.S. and Hodder, V.M. 1971. Variation in the incidence of larval nematodes in herring from Canadian Atlantic waters. International Commission for Northwest
Atlantic Fisheries Research Bulletin 8: 5-14.
Pozdnyakov, S.E. and Vasilenko, A.V. 1994. Distribution, migration, and the helminth fauna of the Japanese mackerel, Scomber japonicus , in the Northwestern Pacific
Ocean.
Reimer, L.W. 1978. Monogenean trematodes as biological tags for sprat in the North
Sea. ICOPAIV, Short Communications, Section H, Warsaw, 6-7.
Rózsa, L., Reiczigal, J. and Majoros, G. 2000. Quantifying parasites in samples of hosts. Journal of Parasitology 86: 228-232.
Shukhgalter, O.A. 1998. General characteristics of the parasitofauna of the European sardine ( Sardina pilchardus Walb.) and some aspects of its geographical variability. Fishery Biological Researches by AtlantNIRO in 1996-1997, pp. 170-
180. Trudy AtlantNIRO, Kaliningrad.
Sindermann, C.J. 1957. Diseases of fishes of the western North Atlantic. V. Parasites as indicators of herring movements. Maine Department of Sea and Shore
Fisheries Research Bulletin No. 27, pp. 30.
Sindermann, C.J. 1983. Parasites as natural tags for marine fish: a review. NAFO
Scientific Council Studies 6: 63-71.
Sokolovsky, A.S. 1969. On the investiagtion of stocks of saury in the Pacific Ocean.
Izvestia TINRO 68: 203-208.
Timi, J.T. 2003. Parasites of Argentine anchovy in the south-west Atlantic: latitudinal patterns and their use for discrimination of host populations. Journal of Fish
Biology 63: 90-107.
Ward, R.D. 2000. Genetics in fisheries management. In Marine Genetics (eds A.M.
Solé-Cava, C.A.M. Russo and J.P Thorpe), Hydrobiologia 420: 191-201.
Williams, H.H., MacKenzie, K. and McCarthy, A.M. 1992. Parasites as biological indicators of the population biology, migrations, diet and phylogenetics of fish.
Reviews in Fish Biology and Fisheries 2: 144-176.