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Insight into fish annual reproductive dynamics (including spawn timing) can elucidate key determinants of recruitment. However, few methods, if any, are available to directly index individual spawn timing, hindering study of such processes. To this end, we developed two reproductive tags (RTs; internal and external) and evaluated their performance assessing spawn timing of female yellow perch (Perca flavescens). Internal RTs performed well, especially in comparison to external RTs, displaying consistent long-term tag retention and clear tag release synchronized with egg mass release during spawning. These results demonstrate the utility of internal RTs to investigate previously unexplored mechanisms of reproductive timing. [ABSTRACT FROM AUTHOR]

In this study, we analyzed gene expression profiles, plasma steroids concentrations, and gonadal morphology throughout the reproductive cycle of female Cichlasoma dimerus (Heckel, 1840), a monogamous cichlid fish exhibiting social hierarchies. Fish were analyzed at six phases encompassing their annual cycle, namely resting (during the nonreproductive period), prespawning, 30 h post spawning, 4 days post spawning, 10 days post spawning, and subordinate (during the reproductive period). The histological and histomorphometric analysis showed that C. dimerus exhibits asynchronous ovarian development. Similar to resting females, subordinate females showed low gonadosomatic index, reduced expression levels of vitellogenin ( vtgAb), zona pellucida ( zpB), gonadal aromatase ( cyp19a1A), and low concentrations of plasma sex steroids, thus indicating that social intimidation by dominant conspecifics elicited reproductive arrest. In reproductively active females, a direct positive correlation between plasma estradiol, vtgAb expression, percentage of late vitellogenic oocytes, and gonadosomatic index was observed. These parameters were maximal at the prespawning phase, decreased at 30 h post spawning and 4 days post spawning, and then reached a peak at 10 days post spawning. Our results indicate that female C. dimerus become spawning capable after 10 days post spawning, coincidently with the shortest time interval between successive spawns recorded in captivity. [ABSTRACT FROM AUTHOR]

Early life stages of fish spawned on the Norwegian continental shelf have long been suggested to depend on eggs and nauplii from the crustacean zooplankton Calanus finmarchicus for survival. Calanus finmarchicus overwinters in the deep basins of the Norwegian Sea, and gravid females must be advected onto the shelf prior to spawning if eggs and nauplii larvae are to serve as food for fish larvae. In this study, cross-shelf advection of C. finmarchicus is simulated over 52 years (1960-2011) using a numerical ocean model coupled with an individual-based model. The results suggest that cross-shelf transport of C. finmarchicus is surprisingly stable across years and that transport is particularly concentrated immediately upstream of the two major spawning areas for the Northeast Arctic cod (Gadus morhua) and the Norwegian spring-spawning herring (Clupea harengus), namely Lofoten and Møre, respectively. Two large topographical features, the Træna Trough and the Norwegian Trench, appear to be funnelling C. finmarchicus onto the shelf in these two areas. This could suggest that the fish spawning grounds outside Møre and Lofoten are, in part, maintained owing to stable interannual food supply in spring. [ABSTRACT FROM AUTHOR]

We report the incidence of male intersex in adult Pacific lamprey ( Entosphenus tridentatus (Richardson, 1836)) during their pre-spawning migration in fresh water. Although 'hermaphrodites' have been suggested in other adult lampreys, this is the first detailed description and discussion of this phenomenon. A total of 0.5% of our adult Pacific lamprey from Willamette Falls (2 out of 427 adults) were intersex, with oocytes in the testes. This phenomenon was identifiable only by histological examination. The testes of the intersex males were immature, in the beginning stages of meiosis. One intersex male possessed primary growth or perinucleolar stage oocytes loosely interspersed throughout the testes, and the other possessed at least 6 mid-vitellogenic oocytes (0.6 mm, mean long diameter) separate from the testes. Because premetamorphic lamprey can possess both female and male gonial cells, we hypothesize that intersex is a remnant larval trait and that these fish failed to fully develop into males during metamorphosis. [ABSTRACT FROM AUTHOR]

A computational model of oocyte growth dynamics (i.e., oocyte recruitment, growth, and spawning) in a batch-spawning fish, fathead minnow (FHM, Pimephales promelas), has been developed. The model provides a quantitative link between oocyte growth dynamics and biochemical processes in FHMs through the absorption of vitellogenin (a lipoprotein precursor of egg yolk proteins) into oocytes, which contributes significantly to oocyte growth in fish. The model simulates the number and volume of oocytes in different batches within a FHM ovary. Model-predicted clutch sizes and spawning intervals matched the experimental data well for both unexposed FHMs and FHMs exposed to 17β-trenbolone (a relatively stable metabolite of trenbolone acetate, a synthetic androgen used as a growth promoter in livestock). Overall, the model presents a novel approach to simulating oocyte growth dynamics in a batch-spawning fish and meets an urgent need in ecotoxicological studies to link the effects of endocrine disrupting chemicals at a biochemical level to adverse effects upon reproduction. [ABSTRACT FROM AUTHOR]

Population mean egg size of salmonids increases with the mean size of gravels in which a population spawns. A long-standing hypothesis is that large larvae cannot navigate small-gravel interstices, so mothers must decrease per-offspring investment when spawning gravels are small. We manipulated the size of incubation gravels and egg size of Atlantic salmon ( Salmo salar) to test whether size-related entombment of larvae occurs. We find little evidence of size-related entombment, but we find evidence that gravel size does not affect all larval sizes equally. Larger larvae emerge from small gravels before development is complete and with a visible yolk sac, possibly due to oxygen limitation in small gravels. Smaller larvae always complete development in the gravel and emerge without a yolk sac. Although growth and survival may increase with juvenile size following yolk-sac absorption, juveniles with yolk sacs may fare worse when depredation rates are high. The egg size - gravel size correlation may therefore reflect increased postemergence mortality among larger offspring in small-gravel environments. Alternatively, compaction stress in fine gravels coupled with size asymmetries in larval strength may have caused the patterns that we observed, in which case our data may not help explain the egg size - gravel size correlation. [ABSTRACT FROM AUTHOR]

Some female Pacific salmon (Oncorhynchus spp.) arrive at spawning grounds but fail to complete spawning prior to death. One hypothesis regarding egg retention is that some individuals do not have sufficient time on spawning grounds for successful completion of spawning. We investigated this hypothesis by quantifying the relationships among arrival timing, reproductive longevity, and egg retention in female sockeye salmon (Oncorhynchus nerka) from Weaver Creek Spawning Channel (British Columbia, Canada) in 2006. 250 females were tagged over three sampling periods and followed until death. Earlier-arriving females lived longer than later-arriving females (p < 0.001), but patterns of egg retention were not different across sampling dates (p > 0.40). Complete spawners tended to establish a redd sooner after arrival than incomplete spawners (p = 0.001); there was no relationship between spawning completion and reproductive maturity or fork length (p > 0.30). Consistent with the time limitation hypothesis, females retained a lower proportion of eggs with increasing reproductive longevity. Several long-lived females (>7 days) failed to spawn completely before death, indicating that time limitation was not a factor for spawning success in all females. Further research examining the role of individual-specific behavioural physiology on egg retention in sockeye salmon is needed. Certaines femelles de saumons du Pacifique (Oncorhynchus spp.) arrivent aux sites de reproduction, mais ne complètent pas la fraie avant de mourir. Une hypothèse sur la rétention d'œufs veut que certains individus ne passent pas assez de temps sur les sites de reproduction pour compléter la fraie avec succès. Nous avons examiné cette hypothèse en mesurant les relations entre le calendrier de l'arrivée, la longévité reproductive et la rétention des œufs chez des saumons rouges (Oncorhynchus nerka) femelles dans le chenal de fraie de Weaver Creek (Colombie-Britannique, Canada) en 2006. Nous avons marqué 250 femelles lors de trois périodes d'échantillonnage et les avons suivies jusqu'à leur mort. Les femelles qui arrivent tôt vivent plus longtemps que celles qui arrivent tard (p < 0,001), mais les patrons de rétention des œufs ne varient pas d'une date d'échantillonnage à une autre (p > 0,40). Les femelles qui complètent leur reproduction ont tendance à s'établir sur les frayères plus tôt après leur arrivée que celles qui ne la complètent pas (p = 0,001); il n'existe pas de relation entre l'achèvement de la fraie et la maturité sexuelle ou la longueur à la fourche (p > 0,30). En accord avec l'hypothèse de la limitation temporelle, les femelles retiennent une proportion plus faible de leurs œufs à mesure que leur longévité reproductive s'accroît. Certaines femelles à longévité élevée (>7 jours) ne réussissent pas à compléter leur reproduction avant la mort, ce qui indique que la limitation temporelle n'est pas un facteur dans le succès de la fraie chez toutes les femelles. Il existe un besoin de travaux futurs sur le rôle de la physiologie comportementale spécifique aux individus sur la rétention d'œufs chez le saumon rouge. [ABSTRACT FROM AUTHOR]

In April 1995, a spawning aggregation of 'northern' Atlantic cod (Gadus morhua) (10 000 t) appeared in Smith Sound, Newfoundland, growing to 26 000 t by year 2000. The origin of the founder year classes (primarily the 1990 and 1992 year classes) and potential for expansion remains controversial, with genetic isolation used to justify reopenings of coastal fisheries. We investigated the origin using historical, demographic, and genetic data. History provided no evidence of large aggregations before 1995. Demographics in the early 1990s suggested few spawners in Smith Sound, but many in the adjacent Bonavista Corridor. The strong 1990 year class was not evident until 1995 and the strong 1992 year class until 1997 (both age 5 and first maturity). Genetic study of six microsatellite loci from 791 cod from overwintering aggregations in Smith Sound and offshore regions indicated little to no differentiation (FST) among southern groups (Smith Sound, Bonavista Corridor, Halibut Channel). These results provide a perspective that these groups comprise a metapopulation and that the Smith Sound aggregation arose not from self-recruitment but immigration. By 2009, the aggregation had dispersed, with large concurrent increases in the Bonavista Corridor. En avril 1995 est apparu dans le détroit de Smith, Terre-Neuve, un rassemblement reproducteur de morues franches (Gadus morhua) (10 000 t) « du nord » qui a atteint 26 000 t en l'an 2000. L'origine des classes d'âge fondatrices (principalement les classes annuelles de 1990 et 1992) et leur potentiel d'expansion sont toujours des sujets de controverse et leur isolement génétique a servi à justifier la réouverture des pêches côtières. Nous en avons recherché l'origine à l'aide de données historiques, démographiques et génétiques. Historiquement, on ne trouve aucune indication de grands rassemblements avant 1995. Les données démographiques du début des années 1990 indiquent la présence de peu de reproducteurs; mais il y avait de nombreux reproducteurs dans le corridor adjacent de Bonavista. La forte classe annuelle de 1990 n'est pas en évidence avant 1995 et la forte classe annuelle de 1992 pas avant 1997 (toutes les deux d'âge 5 et à leur première maturité). L'étude génétique de six locus microsatellites chez 791 morues provenant des rassemblements d'hiver du détroit de Smith et des régions du large montre peu ou pas de différentiation (FST) entre les groupes du sud (détroit de Smith, corridor de Bonavista, chenal Halibut). Ces résultats semblent démontrer que ces groupes forment une métapopulation et que le rassemblement du détroit de Smith provient non d'un recrutement local mais de l'immigration. En 2009, le rassemblement s'était dispersé et d'importants accroissements simultanés se sont produits dans le corridor de Bonavista. [ABSTRACT FROM AUTHOR]

Migrating anadromous fish may transfer marine-derived nutrients to oligotrophic tidal fresh water. River herrings (genus Alosa Linck, 1790) are the dominant anadromous genus in Virginia, USA. This study investigates whether marine nutrients derived from spawning Alosa spp. were incorporated into benthic invertebrates by using the stable isotopes of carbon and nitrogen. Spawning Alosa spp. had higher δ13C and δ15N values (-18.5‰ and 13.9‰, respectively) than resident freshwater omnivorous fishes (-25.7‰ and 11.8‰, respectively). In a tidal stream supporting abundant spawning Alosa spp., 13C and 15N enrichment was observed in stream amphipods (Gammarus fasciatus Say, 1818) coincident with the spawning migration of Alosa spp. The δ13C value for G. fasciatus increased from -28.5‰ to -26.0‰ from early to late April then fell to -28.1‰ in early June. A similar trend was observed in mayflies (Heptageniidae). Particulate organic matter and sediments from both streams remained depleted in 13C (between -29‰ and -28‰) and 15N (between 0.5‰ and 3.0‰) during the spawning run of Alosa spp. It is estimated that between 5% and 35% of amphipod biomass may be derived from marine carbon brought to tidal fresh water by spawning Alosa spp. Les poissons migrateurs anadromes peuvent transférer des nutriments d’origine marine aux eaux douces de marée oligotrophes. Les aloses (genre Alosa Linck, 1790) sont le genre dominant de poissons anadromes en Virginie, É.-U. Notre étude examine à l’aide des isotopes stables de carbone et d’azote si les nutriments marins dérivés de la fraie des Alosa spp. sont incorporés dans les invertébrés benthiques. Les Alosa spp. en fraie possèdent des δ13C et des δ15N (respectivement -18,5 ‰ et 13,9 ‰) plus élevés que ceux des poissons omnivores résidants des eaux douces (respectivement -25,7 ‰ et 11,8 ‰). Dans un chenal de marée contenant de nombreux Alosa spp. en fraie, nous avons observé un enrichissement en 13C et en 15N dans les amphipodes lotiques (Gammarus fasciatus Say, 1818) qui coïncide avec la saison de fraie des Alosa spp. La valeur de δ13C de G. fasciatus a augmenté de -28,5 ‰ à -26,0 ‰ du début à la fin d’avril, puis est retombé à -28,1 ‰ au début de juin. Une tendance semblable a été observée chez les éphéméroptères (Heptageniidae). La matière organique particulaire et les sédiments des deux chenaux sont restés appauvris en 13C et en 15N (respectivement entre -29 ‰ et -28 ‰) durant la migration de fraie des Alosa spp. (respectivement entre 0,5 ‰ et 3,0 ‰). Nous estimons qu’entre 5 % et 35 % de la biomasse des amphipodes peut provenir du carbone marin apporté dans les eaux douces de marée par les Alosa spp. en fraie. [ABSTRACT FROM AUTHOR]

Discerning population genetic structure is challenging for highly vagile open water animals, as contemporary gene flow may obscure historic phylogeographic patterns. We examined genetic variation among all 10 major river and reef spawning groups of walleye (Sander vitreus vitreus) in Lake Erie for evidence of isolation by distance, segregation by physiographic partitions, and natal site fidelity using 10 nuclear DNA microsatellite loci. Results revealed that although most spawning groups were distinguishable, relationships did not correspond with physiographic basins or distances among localities. Bayesian analyses showed connectivity among some southern shore spawning groups, which included the largest-sized groups. Significant genetic divergence was discerned among walleye spawning in the river systems of eastern Lake Erie, as well as in two sites in western Lake Erie, along with marked isolation from Lake St. Clair. Population structure of Lake Erie walleye thus appears to reflect the interaction of two different intrinsic factors: isolation due to natal site fidelity that maintains patterns of divergence, and connectivity due to individuals that stray from their natal sites to spawn. [ABSTRACT FROM AUTHOR]