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This paper provides the first description of the cellular composition of the gill epithelium of feeding adults of Ichthyomyzon unicuspis Hubbs and Trautman, 1937 (silver lamprey), a parasitic species of lamprey that is confined to fresh water. The surface layer of this epithelium consists solely of pavement cells and intercalated mitochondria-rich cells, which are the only cell types found in all freshwater stages of lampreys and thus considered responsible for the uptake of [Na.sup.+] and [Cl.sup.-] in hypotonic environments. This epithelium does not contain, however, the chloride cells present during the marine parasitic phase of anadromous lamprey species, such as Petromyzon marinus L., 1758 (sea lamprey), and which are responsible for secreting excess [Na.sup.+] and [Cl.sup.-]. The absence of this cell type in parasitic adults of I. unicuspis also differs from its presence in parasitic adults of landlocked P. marinus and metamorphosing individuals of the exclusively freshwater nonparasitic species Lethenteron appendix (DeKay, 1842) (American brook lamprey), and which thus reflects the retention of a cell type that was crucial for osmoregulation during the marine phase of their respective anadromous parasitic ancestors. The absence of chloride cells in I. unicuspis is consistent with the hypothesis that Ichthyomyzon, which is at or close to the base of the phylogenetic tree for Northern Hemisphere lampreys (Petromyzontidae), evolved in fresh water or has been confined to fresh water for a very long period. Key words: freshwater parasitic lamprey, silver lamprey (Ichthyomyzon unicuspis), gills, chloride cells, osmoregulation, evolution. Le present article fournit la premiere description de la composition cellulaire de l'epithelium branchial d'adultes en quete de nourriture d'Ichthyomyzon unicuspis Hubbs et Trautman, 1937 (la lamproie argentee), une espece parasitique de lamproies confinee aux milieux d eau douce. La couche superficielle de l'epithelium est constituee uniquement de cellules pavimenteuses et de cellules intercalees riches en mitochondries, qui sont les seuls types de cellules observes dans les stades d eau douce des lamproies et qui sont donc consideres comme etant responsables de l'apport de [Na.sup.+] et de [Cl.sup.-] en milieux hypotoniques. Cet epithelium ne contient toutefois pas de cellules a chlorure presentes durant le stade parasitique marin des especes de lamproies anadromes, comme Petromyzon marinus L., 1758 (la lamproie marine), et responsables de la secretion de [Na.sup.+] et de [Cl.sup.-] excedentaires. L'absence de ce type de cellules chez les adultes parasitiques d'I. unicuspis contraste egalement avec sa presence chez des adultes parasitiques confines aux eaux interieures de P. marinus et chez les individus en metamorphose de l'espece non parasitique exclusivement d eau douce Lethenteron appendix (DeKay, 1842) (la lamproie de l'Est). Ces observations refletent donc la retention d un type de cellules essentielles a l'osmoregulation durant le stade marin des ancetres parasitiques anadromes respectifs de ces especes. L'absence de cellules a chlorure chez I. unicuspis concorde avec l'hypothese voulant qu Ichthyomyzon, qui se situe a la base ou pres de la base de l'arbre phylogenetique des lamproies de l'hemisphere Nord (Petromyzontides), ait evolue en eau douce ou ait ete confine a des milieux d eau douce durant une tres longue periode. Mots-cles: lamproie parasitique d'eau douce, lamproie argentee (Ichthyomyzon unicuspis), branchies, cellules a chlorure, osmoregulation, evolution. [Traduit par la Redaction], Introduction The lampreys, one of the two surviving groups of jawless (agnathan) fishes (Hardisty 2006; Janvier 2008), comprise 41 species. These species all have a freshwater microphagous larval (ammocoete) phase [...]

Abstract--The hypothesis that heavy fishing pressure has led to changes in the biological characteristics of the estuary cobbler (Cnidoglanis macrocephalus) was tested in a large seasonally open estuary in southwestern [...]

Several lamprey species form pairs, comprising an anadromous parasitic species and a derivative nonparasitic species that neither leaves fresh water nor feeds as an adult. This paper provides the first description of the radical changes undergone by the cellular composition of the gill epithelium during the major phases in the life cycle of a nonparasitic lamprey (American brook lamprey, Lethenteron appendix (DeKay, 1842) (= Lampetra appendix (DeKay, 1842)) and discusses their potential functional and evolutionary significance. The gill epithelium of the larva of L. appendix contains ammocoete mitochondrion-rich cells (AMRCs), intercalated mitochondrion-rich cells, and pavement cells, as does that of the larva of anadromous parasitic species which likewise lives in fresh water. By the completion of metamorphosis, the AMRCs have disappeared and well-developed chloride cells have been produced, the latter cell type being essential for osmoregulation by its closely related anadromous species in hypertonic environments. By the attainment of sexual maturity, the chloride cells have been lost. Such changes in the timing of chloride cell representation could help account for the ability of some metamorphosing, but not mature individuals of another nonparasitic species (Lampetra planeri (Bloch, 1784)), to osmoregulate in up to 70% of seawater. The well-developed chloride cells in the nonparasitic L. appendix represent the retention of an ancestral character. Plusieurs especes de lamproies forment des paires, formees d'une espece parasite anadrome et une espece non parasite derivee qui ne quitte pas les eaux douces et qui ne nourrit pas au stade adulte. Notre travail decrit pour la premiere fois les changements radicaux operes dans la composition cellulaire de l' epithelium branchial durant les phases principales du cycle biologique d'une lamproie non parasite (lamproie de l'est, Lethenteron appendix (DeKay, 1842) (= Lampetra appendix (DeKay, 1842)) et discute de leur importance fonctionnelle et evolutive potentielle. L'epithelium branchial de la larve de L. appendix contient des cellules riches en mitochondries d' ammocete (AMRC), des cellules riches en mitochondries et pavimenteuses intercalees, comme chez la larve de l'espece parasite anadrome qui vit aussi en eau douce. Une fois la metamorphose completee, les AMRC disparaissent et des cellules a chlorures bien developpees se developpent; ce second type de cellule est essentiel pour l'osmoregulation chez l'espece parasite fortement apparentee dans les milieux hypertoniques. Au moment de l' atteinte de la maturite sexuelle, les cellules a chlorures sont perdues. De tels changements dans le calendrier de presence des cellules a chlorures pourraient aider a expliquer la capacite de certains individus qui se metamorphosent mais qui ne sont pas matures d'une autre espece non parasite (Lampetra planeri (Bloch, 1784)) de faire de l'osmoregulation jusque dans 70 % d'eau de mer. Les cellules a chlorures bien developpees chez L. appendix qui est non parasite representent la retention d'un caractere ancestral. [Traduit par la Redaction], Introduction The lampreys, which are one of the only two extant groups of agnathan (jawless) vertebrates (Hardisty 2006), contain the 38 species listed by Potter and Gill (2003), and three [...]

Abstract--Commercial catches taken in southwestern Australian waters by trawl fisheries targeting prawns and scallops and from gillnet and longline fisheries targeting sharks were sampled at different times of the year [...]

Abstract--The western blue groper (Achoerodus gouldii) is shown to be a temperate protogynous hermaphrodite, which spawns between early winter and mid-spring. Because A. gouldii changes body color at about the [...]

ABSTRACT The reproductive biology of females of Hypothalassia acerba and Chaceon bicolor off the lower west coast of Australia, and of the former species off the southern coast of Western [...]

We have studied the reproductive biology of the goldlined seabream (Rhabdosargus sarba) in the lower Swan River Estuary in Western Australia, focusing particularly on elucidating the factors influencing the duration, [...]