Summary Concerns regarding the rapid loss of endemic biodiversity, and introduction and spread of non‐indigenous species, have focused attention on the need and ability to detect species present in communities at low abundance. However, detection of rare species poses immense technical challenges, especially for morphologically cryptic species, microscopic taxa and those beneath the water surface in aquatic ecosystems. Next‐generation sequencing technology provides a robust tool to assess biodiversity, especially for detection of rare species. Here, we assess the sensitivity of 454 pyrosequencing for detection of rare species using known indicator species spiked into existing complex plankton samples. In addition, we develop universal small subunit ribosomal DNA primers for amplification of a wide range of taxa for detailed description of biodiversity in complex communities. A universality test of newly designed primers for the hypervariable V4 region of the nuclear small subunit ribosomal DNA (V4‐nSSU) using a plankton sample collected from Hamilton Harbor showed that 454 pyrosequencing based on this universal primer pair can recover a wide range of taxa, including animals, plants (algae), fungi, blue‐green algae and protists. A sensitivity test showed that 454 pyrosequencing based on newly designed universal V4‐nSSU primers was extremely sensitive for detection of very rare species. Pyrosequencing was able to recover spiked indicator species with biomass percentage as low as approximately 2·3 × 10−5% when 24 artificially assembled samples were tagged and sequenced in one PicoTiter plate (i.e. sequencing depth of an equivalent of 1/24 PicoTiter plate). In addition, spiked rare species were sometimes recovered as singletons (i.e. Operational Taxonomic Units represented by a single sequence), suggesting that at least some singletons are informative for recovering unique lineages in ‘rare biospheres’. The method established here allows biologists to better investigate the composition of aquatic communities, especially for detection of rare taxa. Despite a small‐scale pyrosequencing effort, we demonstrate the extreme sensitivity of pyrosequencing using rare species spiked into plankton samples. We propose that the method is a powerful tool for detection of rare native and/or alien species.

Cryopreservation causes osmotic changes and oxidative damage that have sublethal and lethal effects on spermatozoa. We examined these osmotic and oxidative effects on common carp spermatozoa motility; membrane integrity; levels of thiobarbituric-acid-reactive substance (TBARS) and carbonyl groups (CP); and the activity of superoxide dismutase (SOD), glutathione reductase, and glutathione peroxidase (GPx). Sperm was diluted in dimethyl sulfoxide (DMSO) and ethylene glycol-based extenders, followed by equilibration, freezing, and thawing. Equilibration in DMSO extender resulted in a significant reduction of spermatozoa motility, but motility was induced in those spermatozoa following dilution with saline buffer, which usually inhibits undiluted spermatozoa motility. Spermatozoa velocity and membrane integrity decreased with both extenders following freezing and thawing. No significant difference in levels of TBARS or CP, or in SOD activity, was seen in samples equilibrated with either extender. The freeze/thaw process induced significantly higher levels of TBARS, CP, and GPx activity, but did not affect the level of SOD. Glutathione reductase activity was inhibited in samples exposed to DMSO extender. Ethylene glycol should be considered a preferred cryoprotective agent for common carp spermatozoa to reduce osmotic and oxidative stress during cryopreservation.

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Biological invasions are impacting biota worldwide, and explaining why some taxa tend to become invasive is of major scientific interest. North American crayfish species, particularly of the family Cambaridae, are prominent invaders in freshwaters, defying the “tens rule” which states that only a minority of species introduced to new regions become established, and only a minority of those become invasive and pests. So far, success of cambarid invaders has largely been attributed to rapid maturation, high reproductive output, aggressiveness, and tolerance to pollution. We provide experimental evidence that females of one cambarid species particularly widespread in Europe, the spiny-cheek crayfish Orconectes limosus, are capable of facultative parthenogenesis. Such reproductive mode has never before been recognized in decapods, the most diverse crustacean order. As shown by analysis of seven microsatellite loci, crayfish females kept physically separated from males produced genetically homogeneous offspring identical with maternal individuals; this suggests they reproduced by apomixis, unlike those females which mated with males and had a diverse offspring. Further research is needed to clarify what environmental conditions are necessary for a switch to parthenogenesis in O. limosus, and what role it plays in natural crayfish populations. However, if such reproductive plasticity is present in other cambarid crayfish species, it may contribute to the overwhelming invasive success of this group.

Sperm proteins in the seminal plasma and spermatozoa of teleostean and chondrostean have evolved adaptations due to the changes in the reproductive environment. Analysis of the composition and functions of these proteins provides new insights into sperm motility and fertilising abilities, thereby creating possibilities for improving artificial reproduction and germplasm resource conservation technologies (e.g. cryopreservation). Seminal plasma proteins are involved in the protection of spermatozoa during storage in the reproductive system, whereas all spermatozoa proteins contribute to the swimming and fertilising abilities of sperm. Compared to mammalian species, little data are available on fish sperm proteins and their functions. We review here the current state of the art in this field and focus on relevant subjects that require attention. Future research should concentrate on protein functions and their mode of action in fish species, especially on the role of spermatozoa surface proteins during fertilisation and on a description of sturgeon sperm proteins.

We estimated the heritability of growth-related traits (weight and length at ages one summer, first spring and two summers) in a synthetic mirror carp strain (HSM) in the Czech Republic. The four generation pedigree was obtained from parentage assignment of three factorial mating designs with microsatellite markers, and included 195 fish without phenotypes (48 G0, 147 G1) and 1321 fish with phenotypes (674 G2, 647 G3). Animal model heritability estimates over generations were in the range 0.21-0.33 for length and in the range 0.31-0.44 for weight. The genetic correlation between length and weight was high (0.97). The correlations between growth measurements in the first and in the second summer of age were moderate to low (0.34-0.67). Divergent selection for length at two summers of age was performed on G2 fish, and response to selection was evaluated by comparing the offspring of the selected sires in G3, in a communal test where genetic groups were identified by microsatellite parentage assignment. The response to upwards selection was moderate and indicated a realized heritability value of 0.24 to 0.34. No response to downwards selection was observed. We conclude that although selection for growth seems to be feasible in common carp, it would be a longterm process before results are visible.