Reviews in Fish Biology and Fisheries

, Volume 15, Issue 1–2, pp 37–52 | Cite as

Sex Determination in Freshwater Eels and Management Options for Manipulation of Sex

  • Andrew J. H. Davey
  • Donald J. Jellyman


Catadromous eels enter fresh water as sexually undifferentiated glass eels and develop into males and females before migrating back to sea as silver eels. Females develop ovaries directly from the ambiguous primordial gonad whereas males pass through a transitional intersexual stage before developing testes. Eels have sex-specific life-history strategies. Males may grow faster than females initially, but this difference is soon reversed and females attain a greater age- and size-at-metamorphosis than males. Male fitness is maximized by maturing at the smallest size that allows a successful spawning migration (a time-minimizing strategy) whereas females adopt a more flexible size-maximizing strategy that trades off pre-reproductive mortality against fecundity. Although heteromorphic sex chromosomes have been identified in some species, the sex of developing gonads is labile and gender is determined principally by environmental factors. Individuals experiencing rapid growth prior to gonad differentiation tend to develop as males, whereas eels that grow slowly initially are more likely to develop as females. Paradoxically, males tend to predominate under conditions of high density, which may be because a male “grow quickly, mature early” strategy increases an individual’s chances of survival during periods of intraspecific competition. High temperatures and saline conditions have also been proposed to favor development as males but experimental studies have failed to demonstrate a clear effect of either on sex determination. High proportions of female silver eels migrating from some upstream areas, lakes and large rivers may be due to low population density or poor conditions for growth in these habitats. Manipulating sex ratios in favor of females has the potential to increase eel production in aquaculture and to buffer natural populations against fishing pressure. Sex steroids (oestrogens and phytoestrogens) have a strong feminizing effect on undifferentiated individuals and are most effective when targeted at younger eels and administered at high doses for prolonged periods. Modifying local environmental conditions, in particular reducing eel density and limiting interference and social stress, may also promote the development of females. Further research into the timing and mechanisms of sex determination in eels is required to effectively and efficiently manipulate sex for conservation and/or economic benefit.


Anguillidae life history strategy metagamic sex sex differentiation 


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  1. Amin, E.M. 1997Gonad differentiation and early gonadal development of the European eel Anguilla anguilla L. in Egyptian watersArab Gulf J. Sci. Res.15175186Google Scholar
  2. Anderson, D., Boëtius, I., Olesen Larsen, L., Hjulmann Seidler, P. 1996Effects of oestradiol-enriched diet and of feeding with porcine testicular tissue on macroscopic gonadal sex in European eelsJ. Fish. Biol.48484494Google Scholar
  3. Avise, J., Nelson, W.S., Arnold, J., Koehn, R.K., Williams, G.G., Thorsteinsson, W. 1990The evolutionary genetic status of Icelandic eelsEvolution4412541262Google Scholar
  4. Barbin, G.P., McCleave, J.D. 1997Fecundity of the American eel Anguilla rostrata at 45°N in Maine U.S.AJ. Fish Biol.51840847Google Scholar
  5. Beentjes, M.P. (1999) Size, age, and species composition of commercial eel catches from South Island market sampling, 1997–98. NIWA Technical Report, 51, National Institute of Water and Atmospheric Research, Wellington, New ZealandGoogle Scholar
  6. Beentjes, M.P., Jellyman, D.J. 2003Enhanced growth of longfin eels, Anguilla dieffenbachii, transplanted into Lake Hawea, a high country lake in South Island, New ZealandNZ J. Mar. Freshw. Res.37111Google Scholar
  7. Bertin, L. 1956Eels – A Biology StudyCleaver-HumeLondon192Google Scholar
  8. Beullins, K., Eding, E.H., Ollevier, F., Komen, J., Richter, C.J.J. 1997aSex differentiation, changes in length, weight and eye size before and after metamorphosis of European eel (Anguilla anguilla L.) maintained in captivityAquaculture153151162Google Scholar
  9. Beullins, K., Eding, E.H., Gilson, P., Ollevier, F., Komen, J., Richter, C.J.J. 1997bGonadal differentiation, intersexuality and sex ratios of European eel (Anguilla anguilla L.) maintained in captivityAquaculture153135150Google Scholar
  10. Bienarz, K., Epler, P.B.M., Passakas, T. 1981Development of European eel (Anguilla anguilla L.) gonads in artificial conditionsAquaculture225366Google Scholar
  11. Boëtius, I., Boëtius, J. 1980Experimental maturation of female silver eels, Anguilla anguilla. Estimates of fecundity and energy reserves for migration and spawningDana1128Google Scholar
  12. Cau, A.E.C., Deiana, A.M., Pichiri, G., Roissino, R., Salvadori, S., Mezzanotte, R. 1992Chromosomes and DNA of Anguilla anguilla: a study with restriction endonucleasesGenome35838843Google Scholar
  13. Chiba, H., Iwatsuki, K., Hayami, K., Yamauchi, K. 1993Effects of dietary estradiol-17 beta on feminization, growth and body composition in the Japanese eel (Anguilla japonica)Comp. Biochem. Physiol. A.106367371Google Scholar
  14. Colombo, G., Grandi, G. 1995Sex differentiation in the European eel: histological analysis of the effects of sex steroids on the gonadJ. Fish Biol.47394413CrossRefGoogle Scholar
  15. Colombo, G., Grandi, G. 1996Histological study of the development and sex differentiation of the gonad in the European eelJ. Fish Biol.48493512CrossRefGoogle Scholar
  16. Colombo, G., Grandi, G., Rossi, R. 1984Gonad differentiation and body growth in Anguilla anguilla LJ. Fish Biol.24215228Google Scholar
  17. Leo, G.A., Gatto, M. 1996Trends in vital rates of the European eel: evidence for density dependence?Ecol. Appl.612811294Google Scholar
  18. Degani, G. 1986aEffect of dietary 17-ß-estradiol and 17-α-methyltestosterone on growth and body composition of slow-growing elvers (Anguilla anguilla L.)Comp. Biochem. Physiol. A.85243247CrossRefGoogle Scholar
  19. Degani, G. 1986bEffect of combined dietary 17-ß-estradiol and 17-α-methyltestosterone on growth and body composition of European eels (Anguilla anguilla L.)Aquaculture59169175CrossRefGoogle Scholar
  20. Degani, G., Kushnirov, D. 1992Effects of 17-ß-estradiol and grouping on sex determination of European eelsProg. Fish Cult.548891CrossRefGoogle Scholar
  21. Degani, G., Tzchori, I., Yom-Din, S., Goldberg, D., Jackson, K. 2003Growth differences and growth hormone expression in male and female European eels Anguilla anguilla (L.)Gen. Comp. Endocrinol.1348893PubMedCrossRefGoogle Scholar
  22. Dekker, W. 2003Did lack of spawners cause the collapse of the European eel, Anguilla anguilla?Fish. Manag. Ecol.10365376Google Scholar
  23. Egusa, S. 1979Notes on the culture of the European eel (Anguilla anguilla L.) in Japanese eel-farming pondsRapp. Proc.-Verb. Reun. Cons. Int. Expl. Mer1745158Google Scholar
  24. Glova, G.J. 2002Density effects on juvenile shortfinned eel (Anguilla australis) cover preferences in replicate channelsNZ J. Mar. Freshw. Res.36483490Google Scholar
  25. Grandi, G., Poerio, F., Colombo, G., Chicca, M. 2000Effects of diet supplementation with carp ovary on gonad differentiation and growth of the European eelJ. Fish Biol.5715051525CrossRefGoogle Scholar
  26. Hansen, R.A., Eversole, A.G. 1984Age, growth and sex ratio of American eels in brackish-water portions of a South Carolina riverTrans. Am. Fish. Soc.113744749CrossRefGoogle Scholar
  27. Harries, D.H.A. 1974Sex, growth and distribution of the long finned eel, Anguilla dieffenbachiiUniversity of OtagoDunedinM.Sc. ThesisGoogle Scholar
  28. Helfman, G.S., Bozeman, E.L., Brothers, E.B. 1984Size, age, and sex of American eels in a Georgia riverTrans. Am. Fish. Soc.113132141CrossRefGoogle Scholar
  29. Helfman, G.S., Facey, D.E., Stanton Hales, L., Bozeman, E.L. 1987Reproductive ecology of the American eelAm. Fish. Soc. Symp.14256Google Scholar
  30. Holmgren, K. 1996Effect of water temperature and growth variation on the sex ratio of experimentally reared eelsEcol. Freshw. Fish5203212Google Scholar
  31. Holmgren, K., Mosegaard, H. 1996Implications of individual growth status on the future sex of the European eelJ. Fish Biol.49910925CrossRefGoogle Scholar
  32. Holmgren, K., Wickström, H., Clevestam, P. 1997Sex-related growth of European eel, Anguilla anguilla, with focus on median silver eel ageCan. J. Fish. Aquat. Sci.5427752781CrossRefGoogle Scholar
  33. Horn, P.L. (1996) A review of the age and growth data for New Zealand freshwater eels (Anguilla spp.). New Zealand Fisheries Assessment Research Document 96/6 Ministry of Fisheries, Wellington, NZ, 26 ppGoogle Scholar
  34. Hoyle, S.D., Jellyman, D.J. 2002Longfin eels need reserves: modeling the effects of commercial harvest on stocks of New Zealand eelsMar. Freshw. Res.53887895CrossRefGoogle Scholar
  35. Ibbotson, A., Smith, J., Scarlett, P., Aprhamian, M. 2002Colonization of freshwater habitats by the European eel Anguilla anguilla Freshw. Biol.4716961706CrossRefGoogle Scholar
  36. Imre, I., Grant, J.W.A., Keeley, E.R. 2002The effect of visual isolation on territory size and population density of juvenile rainbow trout (Oncorhynchus mykiss)Can. J. Fish. Aquat. Sci.59303309CrossRefGoogle Scholar
  37. Jellyman, D.J. 2001The influence of growth rate on the size of migrating female eels in Lake Ellesmere, New ZealandJ. Fish. Biol.58725736CrossRefGoogle Scholar
  38. Kamstra, A. 1993The effect of size-grading on individual growth in eel, Anguilla anguilla, measured by individual markingAquaculture1126777CrossRefGoogle Scholar
  39. Knights, B. 1987Agonistic behaviour and growth in the European eel, Anguilla anguilla L., in relation to warm water aquacultureJ. Fish Biol.31265276Google Scholar
  40. Krueger, W.H., Oliveira, K. 1999Evidence for environmental sex determination in the American eel, Anguilla rostrata Env. Biol. Fish.55381389Google Scholar
  41. Kuhlmann, H. 1975Der Einfluss von Temperatur, Futter, Grösse und Herkunft auf die sexuelle Differentierung von Glassaalen (Anguilla anguilla)Helgoländer wissenschaftliche Meeresuntersuchungen27139155Google Scholar
  42. Larsson, P., Hamrin, S., Okla, L. 1990Fat content as a factor inducing migratory behaviour in the eel (Anguilla anguilla L) to the Sargasso SeaNaturwissenschaften77488490CrossRefGoogle Scholar
  43. Lokman, P.M., Young, G. 1998An intersexual migratory (silver) longfinned New Zealand eel and its gonadal response to treatment with salmon pituitary homogenateJ. Fish Biol.52547555CrossRefGoogle Scholar
  44. McCleave, J.D., Jellyman, D.J. 2004Male dominance in the New Zealand longfin eel population of a New Zealand river: probable causes and implications for managementN. Am. J. Fish. Mgmt.24490505Google Scholar
  45. Miles, S.G. 1968Rheotaxis of elvers of the American eel (Anguilla rostrata) in the laboratory to water from different streams in Nova ScotiaJ. Fish. Res. Board Can.2515911602Google Scholar
  46. Naismith, I.A., Knights, B. 1990Modeling of unexploited and exploited populations of eels, Anguilla anguilla (L.), in the Thames estuaryJ. Fish Biol.37975986Google Scholar
  47. Ohno, S., Christian, L., Romero, M., Dofuku, R., Ivey, C. 1973On the question of American eels, Anguilla rostrata, versus European eels, Anguilla anguilla Experientia29891CrossRefGoogle Scholar
  48. Oliveira, K. 1997Movements and growth rates of yellow-phase American eels in the Annaquatucket River, Rhode IslandTrans. Am. Fish. Soc.126638646CrossRefGoogle Scholar
  49. Oliveira, K. 1999Life history characteristics and strategies of the American eel, Anguilla rostrata Can. J. Fish. Aquat. Sci.56795802CrossRefGoogle Scholar
  50. Oliveira, K., McCleave, J.D. 2000Variation in population and life history traits of the American eel, Anguilla rostrata, in four rivers in MaineEnv. Biol. Fish.59141151Google Scholar
  51. Oliveira, K., McCleave, J.D. 2002Sexually different growth histories of the American eel in four rivers in MaineTrans. Am. Fish. Soc.131203211CrossRefGoogle Scholar
  52. Oliveira, K., McCleave, J.D., Wipplehauser, G.S. 2001Regional variation and the effect of lake:river area on sex distribution of American eelsJ. Fish Biol.58943952Google Scholar
  53. Park, E.H., Kang, Y.S. 1979Karyological conformation of conspicuous ZW sex chromosomes in two species of Pacific anguilloid fishes (Teleostomi, Anguilliformes)Cytogenet. Cell Genet.233338PubMedGoogle Scholar
  54. Parsons, J., Vickers, K.U., Warden, Y. 1977Relationship between elver recruitment and changes in the sex ratio of silver eels Anguilla anguilla L migrating from Lough Neagh, Northern IrelandJ. Fish Biol.10211229Google Scholar
  55. Passakas, T. 1976Further investigations on the chromosomes of Anguilla anguilla Folia Biol.24239244Google Scholar
  56. Passakas, T., Klekowski, R.Z. 1973Chromosomes of European eel (Anguilla anguilla) as related to in vivo sex determinationPol. Arch. Hydrobiol.20517519Google Scholar
  57. Paulovits, G., Biró, P. 1986Age determination and growth of eel, Anguilla anguilla (L) in Lake Fertö, HungaryFish. Res.4101110CrossRefGoogle Scholar
  58. Pesaro, M., Balsamo, M., Gandolfi, G., Tongiorgi, P. 1981Discrimination among different kinds of water in juvenile eels Anguilla anguilla (L.). Ital J. Zool.15183191Google Scholar
  59. Peters, G., Delventhal, H., Klinger, H. 1980Physiological and morphological effects of social stress in the eel, (Anguilla anguilla L.). Arch Fishchereiwiss30157180Google Scholar
  60. Poole, W.R., Reynolds, J. 1996Growth rate and age at migration of Anguilla anguilla J. Fish Biol.48633642Google Scholar
  61. Poole, W.R., Reynolds, J.D., Moriarty, C. 1990Observations on the silver eel migration of the Burrishoole River system, Ireland, 1959 to 1988Int. Rev. Ges. Hydrobiol.75807815Google Scholar
  62. Roncarati, A., Melotti, P., Mordenti, O., Gennari, L. 1997Influence of stocking density of European eel (Anguilla anguilla L.) elvers on sex differentiation and zootechnical performancesJ. Appl. Ichthyol.13131136Google Scholar
  63. Rossi, R., Colombo, G. 1976Sex ratio, age and growth of silver eels in two brackish lagoons in the northern Adriatic Valle of Comacchio and Valle NuovaArch. Oceanogr. Limnol.18327341Google Scholar
  64. Rossi, R., Villani, P. 1980A biological analysis of eel catches, Anguilla anguilla L., from the lagoons of Lesina and Varano, ItalyJ. Fish Biol.16413423Google Scholar
  65. Sadler, K. 1979Effects of temperature on the growth and survival of the European eel, Anguilla anguilla LJ. Fish Biol.15499507Google Scholar
  66. Satoh, H., Nimura, Y., Hibiya, T. 1992Sex control of the Japanese eel by estrogen (DES-Na) in feedBull. Jpn. Soc. Scient. Fish.5812111218Google Scholar
  67. Seymour, E.A. 1984High stocking rates and moving water solve the grading problemFish Farmer71214Google Scholar
  68. Sinha, V.R.P., Jones, J.W. 1966On the sex and distribution of the freshwater eel (Anguilla anguilla)J. Zool.150371385Google Scholar
  69. Sinha, V.R.P., Jones, J.W. 1967On the age and growth of the freshwater eel (Anguilla anguilla)J. Zool.153119137Google Scholar
  70. Smith, P.J., Benson, P.G., Stanger, C., Chisnall, B.L., Jellyman, D.J. 2001Genetic structure of New Zealand eels Anguilla dieffenbachii and A. australis with allozyme markersEcol. Freshw. Fish10132137Google Scholar
  71. Sola, C., Tosi, L. 1993Bile salts and taurine as chemical stimuli for glass eels, Anguilla anguilla: a behavioural studyEnv. Biol. Fish.37197204Google Scholar
  72. Sola, L., Camerini, B., Cataudella, S. 1984Cytogenetics of Atlantic eels: C- and G-banding, nucleolus organizer regions and DNA content CytogenetCell Genet.38206210CrossRefGoogle Scholar
  73. Sorensen, P.W. 1986Origins of the fresh water attractant(s) of migrating elvers of the American eel Anguilla rostrata Env. Biol. Fish.17185200Google Scholar
  74. Stearns, S.C. 1976Life -history tactics: a review of ideasQ. Rev. Biol.51347PubMedCrossRefGoogle Scholar
  75. Svendäng, H., Wickström, H. 1997Low fat content in female silver eels: indications of insufficient energetic stores for migrational and gonadal developmentJ. Fish Biol.50475786Google Scholar
  76. Svendäng, H., Neuman, E., Wickström, H. 1996Maturation patterns in female European eel: age and size at the silver eel stageJ. Anim. Ecol.48342351Google Scholar
  77. Tesch, F.-W. 2003The EelBlackwell ScienceOxford, UK408Google Scholar
  78. Todd, P.R. 1980Size and age of migrating New Zealand freshwater eels (Anguilla spp.)NZ. J. Mar. Freshw. Res.14283293Google Scholar
  79. Tzchori, I., Degani, G., Elisha, R., Eliyahu, R., Hurvitz, A., Vaya, J., Moav, B. 2002The influence of phytoestrogens and estradiol-17 beta on growth rates and sex determination in the European eel (Anguilla anguilla)Israeli. J. Aquac.545354Google Scholar
  80. Tzeng, W.N., Lin, H.R., Wang, C.H., Xu, S.N. 2000Differences in size and growth rates of male and female migrating Japanese eels in Pearl River, ChinaJ. Fish Biol.5712451253CrossRefGoogle Scholar
  81. Valdimarsson, S.K., Metcalfe, N.B. 2001Is the level of aggression and dispersion in territorial fish dependent on light intensity?Anim. Behav.6111431149CrossRefGoogle Scholar
  82. Vladykov, V.D. 1966Remarks on the American eel (Anguilla rostrata LeSueur)Internationale Vereinigung für Theoretische und Angewandte Limnologie Verhandlungen1610071017Google Scholar
  83. Vøllestad, L.A. 1992Geographic variation in age and length at metamorphosis of maturing European eel: environmental effects and phenotypic plasticityJ. Anim. Ecol.614148Google Scholar
  84. Vøllestad, L.A., Jonsson, B. 1986Life-history characteristics of the European eel, Anguilla anguilla, in the Isma River, NorwayTrans. Am. Fish. Soc.115864871Google Scholar
  85. Vøllestad, L.A., Jonsson, B. 1988A 13-year study of the population dynamics and growth of the European eel Anguilla anguilla in a Norwegian river: evidence for density-dependent mortality, and development of a model for predicting yieldJ. Anim. Ecol.57983997Google Scholar
  86. Walsh, C.T., Pease, B.C. 2003Sexual dimorphism and gonadal development of the Australian longfinned river eelJ. Fish Biol.63137152CrossRefGoogle Scholar
  87. Walsh, C.T., Pease, B.C., Booth, D.J. 2004Variation in the sex ratio, size and age of longfinned eels within and among coastal catchments of south-eastern AustraliaJ. Fish Biol.6412971312CrossRefGoogle Scholar
  88. Wenner, C.A., Musick, J.A. 1974Fecundity and gonad observations of the American eel, Anguilla rostrata, migrating from Chesapeake Bay, VirginiaJ. Fish. Res. Board Can.3113871391Google Scholar
  89. Wiberg, U. 1983Sex determination in the European eel (Anguilla anguilla L.) A hypothesis based on cytogenetic results correlated with the finding of skewed sex ratios in eel culture pondsCytogenet. Cell Genet.36589598PubMedGoogle Scholar
  90. Wickins, J.F. 1985Growth variability in individually confined elvers, Anguilla anguilla (L.)J. Fish Biol.27469478Google Scholar
  91. Wickins, J.F. 1987Effects of size, culling and social history on growth of cultured elvers, Anguilla anguilla (L.)J. Fish Biol.317182Google Scholar
  92. Wickström, H., Westin, L., Clevestam, P. 1996The biological and economic yield from a long-term eel-stocking programmeEcol. Freshw. Fish5140147Google Scholar
  93. Wirth, T., Bernatchez, L. 2001Genetic evidence against panmixia in the European eelNature40910371040PubMedCrossRefGoogle Scholar

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© Springer 2005

Authors and Affiliations

  1. 1.National Institute of Water and Atmospheric ResearchChristchurchNew Zealand

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