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Lipid and fatty acid composition of female Pacific bluefin tuna (PBF, Thunnus orientalis) reproductive and somatic tissues in southwestern North Pacific and Sea of Japan spawning grounds are compared. Total lipid (TL) levels are higher in liver than white muscle tissues. An increased gonadosomatic index (GSI) during the early spawning season coincided with decreased TL. Levels of triacylglycerols (TAG) in PBF liver tissues from the Nansei Islands and Sea of Japan, and white muscle in fishes from the Sea of Japan, decreased during the spawning season, while TAG in ovary tissues did not. Concurrent reductions in TL and increases in GSI early in the spawning season suggest TAG depletion was caused by allocation from liver and white muscle tissues to oocytes, that the liver is one of the important lipid-storage organs in PBF, and this species mostly reliant on capital deposits as a mixed capital-income breeder. Differences of docosahexaenoic acid (DHA) levels between spawning grounds were lower in ovary than in muscle and liver tissues. However, eicosapentaenoic (EPA) and arachidonic acid (ARA) levels that influence egg development and embryo and larval growth are significantly higher in PBF tissues from the Sea of Japan than Nansei Islands, which coincided with larval quality. These suggest a maternal effect exists, with egg quality influencing offspring survival, and that the reproductive strategy of PBF varies according to local variation at each spawning ground., Competing Interests: JAPAN NUS Co. Ltd provided support in the form of salary for Yumi Okochi. There are no patents, products in development or marketed products associated with this research to declare. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

The degree of iteroparity in stream-resident forms of masu salmon Oncorhynchus masou was examined using mark-recapture studies in natural streams. In a partially migratory population, at least 10% of resident males survived after maturation and repeatedly matured for up to 5 years. In the landlocked amago salmon subspecies, the post-maturation survival rate was at least 7% and repeat maturation was observed for up to 3 years for both males and females., (© 2018 The Fisheries Society of the British Isles.)

Ontogenetic growth functions provide basic information in biological and ecological studies. Various growth functions classified into the Pütter model have been used historically, regardless of controversies over their appropriateness. Here, we present a novel growth function for fish and aquatic organisms (generalised q-VBGF) by considering an allocation schedule of allometrically produced surplus energy between somatic growth and reproduction. The generalised q-VBGF can track growth trajectories in different life history strategies from determinate to indeterminate growth by adjusting the value of the 'growth indeterminacy exponent' q. The timing of maturation and attainable body size can be adjusted by the 'maturation timing parameter' τ while maintaining a common growth trajectory before maturation. The generalised q-VBGF is a comprehensive growth function in which exponentials in the traditional monomolecular, von Bertalanffy, Gompertz, logistic, and Richards functions are replaced with q-exponentials defined in the non-extensive Tsallis statistics, and it fits to actual data more adequately than these conventional functions. The relationship between the estimated parameter values τ and rq forms a unique hyperbola, which provides a new insight into the continuum of life history strategies of organisms., Competing Interests: The authors have declared that no competing interests exist.

Following general life history theory, immediate reproductive investment (egg mass × fecundity/body mass) in oviparous teleosts is a consequence of both present and past environmental influences. This clarification questions the frequent use of season-independent (general) fecundity formulas in marine fish recruitment studies based on body metrics only. Here we test the underlying assumption of no lag effect on gametogenesis in the planktivorous, determinate-fecundity Atlantic herring ( Clupea harengus ) displaying large plasticity in egg mass and fecundity, examining Norwegian summer-autumn spawning herring (NASH), North Sea autumn-spawning herring (NSAH), and Norwegian spring-spawning herring (NSSH). No prior reproductive information existed for NASH. Compared with the 1960s, recent reproductive investment had dropped markedly, especially for NSAH, likely reflecting long-term changes in zooplankton biography and productivity. As egg mass was characteristically small for autumn spawners, although large for spring spawners (cf. different larval feeding conditions), fecundity was the most dynamic factor within reproductive investment. For the data-rich NSSH, we showed evidence that transient, major declines in zooplankton abundance resulted in low fecundity over several subsequent seasons, even if Fulton's condition factor (K) turned high. Temporal trends in K slope ( K on total length) were, however, informative. These results clarify that fecundity is defined by ( i ) dynamics of primary (standing stock) oocytes and ( ii ) down-regulation of secondary oocytes, both processes intimately linked to environmental conditions but operating at different timescales. Thus, general fecundity formulas typically understate interannual variability in actual fecundity. We therefore argue for the use of segmented fecundity formulas linked to dedicated monitoring programs.

A laboratory experiment was conducted by varying the undersurface area of nesting substratum and the number of females in an experimental tank to elucidate the determinants of the mating pattern in the stream goby, Rhinogobius sp. cross-band type. Males with larger nests tended to attract two or more females to their nest in a tank. Moreover, males spawned simultaneously with multiple females and entire brood cannibalism by males was rarely observed under a female-biased sex ratio. When males spawned with a single female with low fecundity, however, entire brood cannibalism occurred at a high frequency, suggesting that a male guarding a nest with fewer eggs consumes the brood. Therefore, spawning behaviour of females that leads to a large egg mass would decrease the risk of entire brood cannibalism. In this species, simultaneous spawning by multiple females in a nest serves as a female counter-measure against entire brood cannibalism. These results suggest that a conflict of interest between the sexes through brood cannibalism is a major determinant of simultaneous spawning., (© 2016 The Fisheries Society of the British Isles.)

This study examined the spawning season, spawning frequency and batch fecundity of yellow sea bream Dentex hypselosomus in the East China Sea to reassess the previously reported reproductive characteristics of the species. Time-course sampling showed that this species had a diurnal ovarian maturation rhythm. Late tertiary yolk-stage oocytes appeared 2 days before spawning, starting the process of germinal vesicle movement and breakdown. On the day of spawning, ovulation and subsequent spawning occurred in the early morning (0400-0800 hours). Postovulatory follicles disappeared from the ovaries within c. 24 h of ovulation. Seasonal changes in the ovarian conditions indicated that this species spawned more or less throughout the year, with the peak ranging from spring to autumn. The compositions of the developing oocytes and degenerating postovulatory follicles in the ovaries suggested that most females spawned repeatedly over 2 to 3 consecutive days during the peak of the spawning season. Somatic body condition did not have a significant effect on batch fecundity, but there was a significant relationship between batch fecundity and fork length according to spawning status. Females spawning on consecutive days were more fecund than those spawning every other day. The findings show that this species has much greater reproductive potential than previously estimated.

This report deals with an unusual mode of mitochondrial gene introgression between Cobitis hankugensis (C. sinensis) and C. longicorpus which is mediated by a unisexual hybridogenetic system of diploid-triploid C. hankugensis-longicorpus complex. Mitochondrial DNA sequences of 3329-3330bp encompassing from upstream ND6 to 12S rDNA indicated that mitochondrial genomes from the diploid hybrids, triploid hybrids, and their parental species are almost identical. Because triploid hybrids produce haploid ova with C. hankugensis chromosome set, normal diploid C. hankugensis regenerates upon insemination with C. hankugensis sperm. If the hybrid carries C. longicorpus mitochondrial genome, the regenerated C. hankugensis is a nucleo-cytoplasmic hybrid, thus accomplishing the unusual mode of mitochondrial gene introgression.

An unisexual species (either parthenogenetic or gynogenetic form) often coexists sympatrically with a closely related anisogamous sexual species, forming a unisexual complex. This is puzzling because, all else being equal, a sexual population with the two-fold cost of sex (or the cost of producing males) cannot coexist with a unisexual population. This suggests that some ecological processes are at work to make possible the coexistence of the unisexual complex. Field and laboratory studies suggest that parasitism in a gynogenetic complex of the Japanese crucian carp (Carassius auratus) may play an important role in realizing the coexistence by giving frequency-dependent benefit to sexual population. Here, we study the simple dynamics of host-parasite interactions in which non-specific immune reaction of a sexual host is more effective than that of an unisexual host. We simply assume that the infective individuals are sterile. Stable coexistence of a unisexual species with their sexual relative is possible if pathogens are virulent and if the susceptibility of the unisexual form is more than twice as high as that of the sexual form. The coexistence is more difficult, when the fertility of males is relatively low in gynogenetic complexes. This implies that the coexistence of gynogenetic complexes is more difficult than that of parthenogenetic complexes in which parthenogenesis has no constraint on males. We conclude that parasitism is a promising candidate mechanism for the coexistence of unisexual complexes.