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Certain spawning areas of the critically endangered Lake Saimaa landlocked Atlantic salmon (Salmo salar m. sebago) have been recently restored by excavator- and helicopter-scattered gravel, but the success of applied methodologies has remained open. Here, we monitored the spawning-related movements and redds occurrence of transported semi-wild and hatchery-reared salmon in the restored River Ala-Koitajoki, eastern Finland, using radiotelemetry and snorkeling. Nearly all fish accepted the newly restored spawning habitats in the river that maintains a low flow rate (only 4 [m.sup.3] * [s.sup.-1]). The movements of females released up to 2 weeks before spawning time were restricted mainly to the closest rapids from the release site, and most of the movements were directed downstream. Semi-wild and hatchery background fish exhibited similar mobility, which was more variable among males. A majority of redds were found in restored areas, and both helicopter- and excavator-scattered gravels were accepted as spawning substrates. Our results indicate that natural reproduction of the studied landlocked salmon population can be successfully returned to its original spawning river by restoration of habitats and transfer of spawners. Resume : Certains lieux de frai du saumon atlantique de lac (Salmo salar m. sebago) du lac Saimaa, qui est en voie de disparition, ont ete restaures a l'aide de gravier repandu par excavatrice et par helicoptere, mais le succes des methodes employees n'est pas encore etabli. Nous avons surveille les deplacements associes au frai et la presence de nids de frai de saumons semi-sauvages et eleves en ecloserie transportes dans la riviere Ala-Koitajoki, une riviere restauree de l'est de la Finlande, en utilisant la radiotelemetrie et la plongee avec tuba. Presque tous les poissons ont accepte les habitats de frai nouvellement restaures dans cette riviere qui maintient un faible debit (seulement 4 [m.sup.3] * [s.sup.-1]). Les deplacements des femelles relachees jusqu'a 2 semaines avant le moment du frai se sont principalement limites aux rapides les plus proches du site de lacher, et la plupart des deplacements etaient vers l'aval. Les poissons semi-sauvages et issus d'ecloseries presentaient une mobilite semblable, qui etait plus variable parmi les males. La majorite des nids de frai trouves etaient dans des zones restaurees, et tant les graviers repandus par helicoptere que par excavatrice etaient acceptes comme substrats de frai. Nos resultats indiquent que la restauration d'habitats et le transfert de geniteurs peuvent permettre le retour de la reproduction naturelle dans la riviere de frai d'origine pour la population de saumons de lac etudiee. [Traduit par la Redaction], Introduction Restorations of the spawning and nursery habitats are widely applied to enhance ecological state of regulated and degraded rivers (Pennell et al. 2007; Marttila et al. 2019; Pulg et [...]

Several Finnish populations of salmonids have been maintained exclusively by stocking hatchery-reared fish for several generations, and it is crucial to know whether domestication has affected fitness-related traits and to assess how the developmental environment influences fish phenotypes. Here, we focused on Lake Saimaa landlocked salmon (Salmo salar m. sebago) and studied the role of the early rearing environment in trait formation by comparing juveniles (fingerlings) from three backgrounds: (i) semi-wild (stocked as alevins), (ii) standard hatchery, and (iii) enriched hatchery conditions We compared juvenile morphology, swimming performance, and capability of feeding on natural prey in early winter. We found no differences between standard and enriched hatchery conditions. Semi-wild fish consumed more prey items, but wet mass of stomach contents did not differ among backgrounds. Swimming endurance was comparable among backgrounds. Semi-wild fish had slenderer body shape and longer fins than hatchery-reared fish. The lack of performance differences between hatchery juveniles and their semi-wild conspecifics is possibly due to reduced phenotypic plasticity caused by extremely low levels of genetic diversity in this population. Comme plusieurs populations finlandaises de salmonides ont ete maintenues exclusivement grace a l'ensemencement de poissons eleves en ecloserie pendant plusieurs generations, il importe de savoir si la domestication a eu une incidence sur des caracteres associes a l'aptitude et d'evaluer l'influence du milieu de developpement sur les phenotypes des poissons. Nous nous penchons sur les saumons d'eaux interieures du lac Saimaa (Salmo salar m. sebago) et etudions le role du milieu de l'elevage precoce dans la formation de caracteres en comparant de jeunes saumons (alevins d'un an) de trois origines distinctes, a savoir (i) des individus semi-sauvages (alevins vesicules au moment de l'ensemencement), (ii) eleves en ecloserie dans des conditions normales et (iii) eleves en ecloserie dans des conditions enrichies. Nous comparons la morphologie des jeunes saumons, leur performance de nage et leur capacite a se nourrir de proies naturelles au debut de l'hiver. Nous ne relevons aucune difference entre les individus issus d'ecloseries dans des conditions normales et enrichies. Les poissons semi-sauvages consomment un plus grand nombre de proies, mais la masse humide des contenus stomacaux ne varie pas selon l'origine des poissons. Les poissons semi-sauvages ont des corps plus elances et des nageoires plus longues que les poissons eleves en ecloserie. L'absence de differences sur le plan de la performance entre les jeunes poissons issus d'ecloseries et leurs congeneres semi-sauvages est possiblement due a une plasticite phenotypique reduite causee par des degres extremement faibles de diversite genetique dans cette population. [Traduit par la Redaction], Introduction Many natural salmonid populations are threatened by various human activities, such as overharvesting and construction of hydropower dams. Dams often severely block the movements of migratory fishes and thus [...]

Endangered wild fish populations are commonly supported by hatchery propagation. However, hatchery‐reared fish experience very different selective pressures compared to their wild counterparts, potentially causing genotype‐by‐environment interactions (G × E) in essential fitness traits. We experimentally studied early selection in a critically endangered landlocked Atlantic salmon population, first from fertilization to the swim‐up stage in a common hatchery setting, and thereafter until the age of 5 months in two contrasting rearing environments. Swim‐up progeny were moved either to standard indoor hatchery tanks involving conventional husbandry or to seminatural outdoor channels providing only natural food. After the first summer, sampled survivors were assigned to their families by genotyping. Early survival until the swim‐up stage was mostly determined by maternal effects, but also involved significant variation due to sires and full‐sib families (potential genetic effects). High on‐growing survival in hatchery tanks (88.7%) maintained a more even distribution among families (relative share 1.5%–4.2%) than the seminatural environment (0.0%–5.4%). This heterogeneity was mostly maternal, whereas no independent paternal effect occurred. Heritability estimates were high for body size traits in both environments (0.62–0.69). Genetic correlations between the environments were significantly positive for body size traits (0.67–0.69), and high body condition in hatchery was also genetically linked to rapid growth in the seminatural environment (0.54). Additive and phenotypic growth variation increased in the seminatural environment, but scaling effects probably played a less significant role for G × E, compared to re‐ranking of genotypes. Our results suggest that not only maternal effects, but also genetic effects, direct selection according to the environmental conditions experienced. Consistently high genetic variation in growth implies that, despite its low overall genetic diversity and long history in captive rearing (>50 years), this landlocked Atlantic salmon population still possesses adaptive potential for response to change from hatchery rearing back to more natural conditions. [ABSTRACT FROM AUTHOR]

Size-specific body growth responses to warming are common among animal taxa, but sex-specific responses are poorly known. Here we ask if body growth responses to warming are sex-dependent, and if such sex-specific responses vary with size and age. This was tested with sex-specific data of back-calculated individual growth trajectories, in European perch (Perca fluviatilis) from a long-term whole-ecosystem warming experiment (6.3 °C above the surrounding sea). Warming led to both size- and sex-specific differences in growth responses. Warming had a consistent positive effect on body growth of females, but negative effects on male growth at size > 10 cm and age > 2 years. These sex-specific growth responses translate to an increased degree of female-biased sexual size dimorphism (in length-at-age) with warming. Although the exact temperature-mediated effects underlying differential growth responses could not be resolved, results imply global warming may have highly different effects during ontogeny of male and female perch. Such effects should be considered in climate warming scenarios concerning fish growth, population size-structure, and dynamics of aquatic food webs that include fish exhibiting sexual size dimorphism. [ABSTRACT FROM AUTHOR]

Management of inland recreational fisheries would benefit from stock abundance and size structure data. Feasibly standardised angling methods such as ice fishing could produce representative catch‐per‐unit‐effort (CPUE) information on the abundance of different‐sized fish in small lakes. Here, we first used standard Nordic multimesh gillnets to obtain number‐per‐unit‐effort (NPUE), biomass‐per‐unit‐effort (BPUE) and size structure data on Eurasian perch (Perca fluviatilis) stocks in 11 small boreal lakes in summer. Second, the same lakes were ice‐fished by voluntary anglers using a pre‐defined, loosely standardised protocol to obtain angling‐based NPUE, BPUE, and length frequency distributions. Effects of environmental variables such as water oxygen concentration and light penetration on angling catch rates were controlled statistically. Neither perch Nordic gillnet NPUE nor BPUE corresponded to ice‐fishing CPUEs. However, the length distribution of the catch did not differ between methods. Our results imply that traditional ice fishing applying natural baits is relatively unselective for fish size and could produce valid length‐based indicators for management purposes while angling CPUE was poorly related to Nordic gillnet CPUE. [ABSTRACT FROM AUTHOR]

Visual transect counting of large‐bodied fish using artificial light at night in a shallow littoral zone (<1 m water depth) is introduced as a complementary survey method for fishes such as common bream Abramis brama and northern pike Esox lucius that are under‐represented in standard gillnet surveys. The results suggest that transect counting at night and applying necessary corrections for environmental variables could provide a simple and repeatable method to assess the presence and abundance of large‐bodied fishes in lakes with satisfactory water clarity. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) exposure can impair the traits of aquatic animals associated with reproduction. In natural lakes Cd is typically detected at concentrations below 0.001 mg l−1. The authors investigated the impact of ultra‐acute Cd exposure on sperm motility in European whitefish (Coregonus lavaretus). They activated sperm with water containing various nominal concentrations of Cd and recorded sperm motility parameters. Only the highest Cd concentration (500 mg l−1) was associated with decreased sperm swimming velocity and increases in both the percentage of static cells and curvature of the sperm swimming trajectory. The results indicate that environmentally realistic concentrations of Cd during the sperm motility activation are not critically harmful to male C. lavaretus fertilization potential. [ABSTRACT FROM AUTHOR]

The tendency towards two-year cyclicity is considered typical of many Fennoscandian vendace populations, especially in fluctuation of recruitment, based on time series of individual lakes. We used two robust indicators to identify and quantify two-year cycles in vendace population proxy time series at different life-stages — spawning stock biomass (SB), density of newly hatched larvae (LD) and recruitment (REC) — from 22 Finnish lakes. Then we applied Fisher's meta-analytical test to assess the adequacy of the evidence to support the hypothesis that vendace population dynamics include two-year cyclicity. The results supported this hypothesis for REC but not for SB or LD. Yet, the indicators and test are conservative and time-series of SB and LD are shorter than those for REC. The appearance of cycles in REC is associated with high post-recruitment mortality, consequently practically only one spawning per cohort. Cycles may be typical for the recovery period from low abundance period also. Still, some populations with moderate post-REC mortality and non-cyclic SB abundance exhibited cycles in REC. Such dynamics presuppose the existence of more complex regulation based on the interaction of different life stages. [ABSTRACT FROM AUTHOR]

In a large majority of animal species, the only contribution of males to the next generation has been assumed to be their genes (sperm). However, along with sperm, seminal plasma contains a wide array of extracellular factors that have many important functions in reproduction. Yet, the potential intergenerational effects of these factors are virtually unknown. We investigated these effects in European whitefish (Coregonus lavaretus) by experimentally manipulating the presence and identity of seminal plasma and by fertilizing the eggs of multiple females with the manipulated and unmanipulated semen of several males in a full‐factorial breeding design. The presence of both own seminal plasma and foreign seminal plasma inhibited sperm motility, and the removal of own seminal plasma decreased embryo survival. Embryos hatched significantly earlier after both semen manipulations than in control fertilizations; foreign seminal plasma also increased offspring aerobic swimming performance. Given that our experimental design allowed us to control potentially confounding sperm‐mediated (sire) effects and maternal effects, our results indicate that seminal plasma may have direct intergenerational consequences for offspring phenotype and performance. This novel source of offspring phenotypic variance may provide new insights into the evolution of polyandry and mechanisms that maintain heritable variation in fitness and associated female mating preferences. [ABSTRACT FROM AUTHOR]

Through the recent increases in abundance, pikeperch (Sander lucioperca) has not only become a valuable target for recreational and commercial fishing, but also the most important top predator in many lakes. Generally oligotrophic Lake Höytiäinen (283 km2) sustains one of the most economically valuable pikeperch stocks in Finland, and its annual fisheries yield (up to 5.5 kg/ha) is exceptionally high among Finnish lakes. Here, we followed seasonal movements of fish using conventional tagging, and studied short‐term and long‐term diet of pikeperch by stomach content and stable isotope analyses to examine if the movements were motivated by prey availability. A clear seasonal migration pattern was observed: in summer, 80% of the tag recoveries were obtained from the shallow and mesotrophic northern and western areas, whereas in autumn and winter, the deep and oligotrophic southern area dominated in the recaptures. The diet of pikeperch consisted of the most abundant fish species in the lake, perch (Perca fluviatilis) and roach (Rutilus rutilus), as well as insects. Stable isotope analysis indicated a shift from a dominance of pelagic food sources to littoral food sources during the growing season of pikeperch. Our results suggest that the pikeperch migrations facilitate efficient material transfer from the mesotrophic part while the deeper and oligotrophic part offers a favourable overwintering environment. [ABSTRACT FROM AUTHOR]

Inter‐relations between water quality and piscivore populations have remained poorly studied but their quantification is crucial for the ecosystem‐based management of inland waters. Here, we aimed to estimate the relative strength of bottom‐up and top‐down trophic interactions between water quality and fish community composition using a comparative approach. Our main hypothesis was that lakes with an abundant piscivore (mainly pikeperch, Sander lucioperca, Percidae) stock would have better water quality than similar lakes with a poor piscivore stock.We used structural equation models on biomass catch per unit of effort data from standard gillnet test fishing to examine the effects of predators (pikeperch, pike [Esox lucius, Esocidae] and piscivorous perch [Perca fluviatilis, Percidae]) on cyprinids (Cyprinidae), and the effects of cyprinids, nutrients, and lake depth on water quality measured as chlorophyll‐a concentration and turbidity. We derived the dataset covering a single summer snapshot of 138 Finnish pikeperch lakes from national databases.Nutrients and lake depth index, the main principal component describing positive effects of nutrient concentrations and negative effects of lake depth, had a positive effect on chlorophyll‐a concentration and turbidity. Pikeperch had a detectable negative effect on both planktivorous and benthivorous cyprinids. While pike also had a negative effect on benthivorous cyprinids, both groups of cyprinids had a positive effect on pikeperch and pike. Supporting the strong, fish‐independent bottom‐up regulation, no significant relationships were detected between the cyprinids and water quality.This study suggests that the bottom‐up effects override the top‐down effects, and despite pikeperch is an efficient piscivore, the observed stock levels did not cascade down to improved water quality. Thus, in lake restoration, reductions of nutrient loading appear more efficient than biomanipulation aimed to strengthen the top‐down links. [ABSTRACT FROM AUTHOR]

Historically, Finnish rivers supported vital populations of migratory salmonids. Presently, these species are more or less endangered due to extensive damming and hydropower production. In this article, we study the main legal and scientific drivers for re-evaluating some of the existing hydropower operations in Finland. We argue that there is a need for re-evaluation on the basis of legal obligations stemming largely from EU law and new scientific knowledge. Theoretically, our setting opens up a classical adaptive governance problem in how to address laws and past decisions that are based on outdated assumptions about the functioning of social-ecological systems. [ABSTRACT FROM AUTHOR]

The European whitefish, Coregonus lavaretus (L.), is a highly polymorphic species consisting of several distinct ecotypes or forms. In the Koitajoki watercourse, south-eastern Finland, there exists a pair of indigenous sympatric whitefish ecotypes with distinct gill raker numbers. In the watercourse, supplemental stocking was initiated in the 1960s to compensate recruitment failure of whitefish caused by water level regulation for hydroelectric purposes. We investigated the genetic differentiation and possible hybridization between the two forms using 21 microsatellite loci and by assessing the temporal changes in the distribution of gill raker numbers. The distribution of gill raker number shifted from bimodality to trimodality in less than 15 years during the 1980s and 1990s, implying putative hybridization of these forms. Significant genetic differentiation was found between the two forms (FST = 0.034). In addition, Bayesian inference of population structure as well as a discriminate analysis of principal components (DAPC) identified two genetic clusters largely coincident with these forms. A high degree of genetic admixture was found in phenotypically intermediate individuals, which also differed slightly from the indigenous forms as indicated by the DAPC scatterplot. Taken together, the results suggest that human actions such as stockings and water level regulation are the most likely factors contributing to the reduction of reproductive isolation between the sympatric whitefish forms. [ABSTRACT FROM AUTHOR]

Sexual dimorphism is common across the animal kingdom, but the contribution of environmental factors shaping differences between the sexes remains controversial. In ectotherms, life-history traits are known to correlate with latitude, but sex-specific responses are not well understood. We analyzed life-history trait variation between the sexes of European perch ( Perca fluviatilis L.), a common freshwater fish displaying larger female size, by employing a wide latitudinal gradient. We expected to find sex-dependent latitudinal variation in life-history variables: length at age, length increment, and size at maturity, with females showing consistently higher values than males at all latitudes. We further anticipated that this gender difference would progressively decrease with the increasingly harsh environmental conditions toward higher latitude. We hypothesized that growth and length increment would decrease and size/age at maturity would increase at higher latitudes. Our results confirmed female-biased sexual size dimorphism at all latitudes and the magnitude of sexual dimorphism diminished with increase in latitude. Growth of both sexes decreased with increase in latitude, and the female latitudinal clines were steeper than those of males. Hence, we challenge two predominant ecological rules (Rensch's and Bergmann's rules) that describe common large-scale patterns of body size variation. Our data demonstrate that these two rules are not universally applicable in ectotherms or female-biased species. Our study highlights the importance of sex-specific differences in life-history traits along a latitudinal gradient, with evident implications for a wide range of studies from individual to ecosystems level. [ABSTRACT FROM AUTHOR]

Pikeperch populations typically differ substantially in life-history traits. Here, we evaluated the potential of variable size limits to ensure ecologically and evolutionarily sustainable fishing of six important Finnish inland pikeperch stocks using a carefully parameterized age-, size-, and maturity-structured evolutionary population model. Individual growth rates of the Oulujärvi and Vesijärvi stocks were the fastest and least resource-limited. The Höytiäinen, Vanajavesi and Pääjärvi stocks were strongly regulated by density-dependent food availability. Minimum size limit ensuring the highest yields was clearly higher for the fast-growing stocks than for the strongly food-limited stocks. Implementation of a maximum size limit 200 mm above the minimum size limit (MSL) would allow the stocks to tolerate stronger fishing mortality rate, but the 200 mm slot appeared too wide to significantly prevent evolution towards earlier maturation. To ensure maximal stability of yield and minimal evolutionary effect, fishing mortality rates should be restricted to relatively low values. [ABSTRACT FROM AUTHOR]

Fish are known for their high phenotypic plasticity in life-history traits in relation to environmental variability, and this is particularly pronounced among salmonids in the Northern Hemisphere. Resource limitation leads to trade-offs in phenotypic plasticity between life-history traits related to the reproduction, growth, and survival of individual fish, which have consequences for the age and size distributions of populations, as well as their dynamics and productivity. We studied the effect of plasticity in growth and fecundity of vendace females on their reproductive traits using a series of long-term incubation experiments. The wild parental fish originated from four separate populations with markedly different densities, and hence naturally induced differences in their growth and fecundity. The energy allocation to somatic tissues and eggs prior to spawning served as a proxy for total resource availability to individual females, and its effects on offspring survival and growth were analyzed. Vendace females allocated a rather constant proportion of available energy to eggs (per body mass) despite different growth patterns depending on the total resources in the different lakes; investment into eggs thus dictated the share remaining for growth. The energy allocation to eggs per mass was higher in young than in old spawners and the egg size and the relative fecundity differed between them: Young females produced more and smaller eggs and larvae than old spawners. In contrast to earlier observations of salmonids, a shortage of maternal food resources did not increase offspring size and survival. Vendace females in sparse populations with ample resources and high growth produced larger eggs and larvae. Vendace accommodate strong population fluctuations by their high plasticity in growth and fecundity, which affect their offspring size and consequently their recruitment and productivity, and account for their persistence and resilience in the face of high fishing mortality. [ABSTRACT FROM AUTHOR]

Many ejaculate traits show remarkable variation in relation to male social status. Males in disfavoured (subordinate) mating positions often invest heavily on sperm motility but may have less available resources on traits (e.g., secondary sexual ornaments) that improve the probability of gaining matings. Although higher investments in sperm motility can increase the relative fertilization success of subordinate males, it is unclear whether status-dependent differences in sperm traits could have any consequences for offspring fitness. We tested this possibility in whitefish (Coregonus lavaretus L.) by experimentally fertilizing the eggs of 24 females with the sperm of either highly-ornamented (large breeding tubercles, dominant) or less-ornamented (small tubercles, subordinate) males (split-clutch breeding design). In comparison to highly-ornamented individuals, less-ornamented males had higher sperm motility, which fertilized the eggs more efficiently, but produced embryos with impaired hatching success. Also offspring size and body condition were lower among less-ornamented males. Furthermore, sperm motility was positively associated with the fertilization success and offspring size, but only in highly-ornamented males. Together our results indicate that male investments on highly motile (fertile) sperm is not necessarily advantageous during later offspring ontogeny and that male status-dependent differences in sperm phenotype may have important effects on offspring fitness in different life-history stages. [ABSTRACT FROM AUTHOR]

Although the temporal consistency of resting metabolic rate in individual animals is generally considered to be a universal phenomenon, studies on invertebrates are still scarce. Here, we studied the repeatability of standard metabolic rate in the signal crayfish (Pacifastacus leniusculus). We measured oxygen consumption twice on the same individuals, on average in 97-day intervals. At intermolt stage, the standard metabolic rate was a repeatable trait. However, molting increased significantly the minimum metabolic rate, thus emphasizing the role of animal physiological state in determining the rate of metabolism. [ABSTRACT FROM AUTHOR]

Mutual ornamentation (i.e. the expression of secondary sexual characters) in both sexes is a relatively common but rarely studied phenomenon in the animal kingdom. In the present study, we investigated whether mutual ornamentation is indicative of offspring embryonic survival and predator-avoidance ability in whitefish. We crossed ten randomly selected females and ten randomly selected males in all possible combinations resulting in 100 sib groups, and hypothesized that fitness (measured as offspring survival) of elaborately ornamented parents would be higher in both sexes of whitefish. Parental effects were found in both studied traits: effects of female and female-male interaction were significant for the embryonic mortality, whereas only paternal effect was found for the offspring predator-avoidance ability. As expected, increasing number of the female breeding tubercles was associated with low embryonic mortality, although male ornamentation was not indicative of offspring survival. The present study, together with earlier data, clearly demonstrate that offspring fitness is affected by parental identity, and suggest that mutual ornamentation in this species may indicate the genetic quality of individuals in both sexes. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, , 593-601. [ABSTRACT FROM AUTHOR]

Procedures for the determination of standard metabolic rate (SMR) are variable and subjective in respirometry. We examined the oxygen consumption profile of six fish species (three salmonids and three cyprinids) in respirometry, and analysed the implications for the determination of SMR. In addition, we used data on Arctic charr (Salvelinus alpinus) and bleak (Alburnus alburnus) to define, how the length of a measuring period affects the determination of SMR and to investigate the temporal consistency of SMR. Fish activity in the respirometer differed between the species and there was a family-specific response to change in illumination. In salmonids, switching off the lights resulted in an increased oxygen consumption rate for hours, whereas in cyprinids the response was shorter or totally absent. In Arctic charr and bleak, individual oxygen consumption profiles remained unchanged between the consecutive trials. The results emphasize the importance of taking species-specific responses into account when determining SMR. [ABSTRACT FROM AUTHOR]

Sexual ornamentation often consists of multiple components. Different sexual signals may indicate different aspects of mate quality or reflect quality in different time scales. On the other hand, same signals can have a dual function and are used both in male–male competition and courtship. Many fish species are capable of rapidly altering their colouration (ephemeral colour changes), but this capability is usually ignored in sexual selection studies. Here, we used experimentally manipulated social environments to study the ephemeral colour changes in multicomponent sexual signals of male minnows ( Phoxinus phoxinus) during male–male competition and female choice. We found that the dominant males courted the females more actively and had redder and/or darker skin colouration than the subordinate males. Furthermore, darkness difference between subordinate and dominant males increased in the presence of female, which suggests that the male–male competition may increase the honesty of signalling and thus facilitate female choice. In support of this hypothesis, females had a strong behavioural preference towards the more colourful males, which may indicate female choice. As colourful males often had a higher social status than paler individuals, it is possible that females base their preference on male status, not only the colouration per se. In any case, our results suggest that sexual ornamentation of male minnows may signal status, courting activity and superior quality of the males and that these signals may have a dual function in both male–male competition and female choice. Females preferred different ornamental traits (dark and red colour patterns) relatively equally, indicating that mate choice is based on multiple cues. [ABSTRACT FROM AUTHOR]

In theory, selection for effective camouflage (i.e. dull coloration) in fish should be strongest when the conditions for visual predation are most favourable, such as in structurally simple pelagic habitats. By contrast, in more sheltered (e.g. littoral) habitats, selection may favour effective intra-specific communication (i.e. bright coloration) (at the expense of crypsis). Poor transparency, as in highly humic waters, should constrain colour adaptations. We investigated phenotypic variation in body coloration of Eurasian perch ( Perca fluviatilis L.) in littoral and pelagic habitats of four humic boreal lakes. Perch from the most transparent lake had the lightest and less coloured belly and perch were more colourful in the littoral habitats than in the pelagic areas, with the pattern being clearest in the most transparent lake. In addition, perch in the most transparent lake exhibited sexual dichromatism, with males having a more colourful belly than the females, whereas no indications of sexual dichromatism were found in more humic lakes. Moreover, in the most transparent lake, the condition of fish correlated with bright belly coloration in the littoral, but with dull belly coloration in the pelagic habitat. The results obtained in the present study suggest that selection on perch coloration may differ between lakes as a result of visual properties of the water, and within lakes as a result of divergent selection for camouflage and communication in pelagic and littoral habitats. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 47–59. [ABSTRACT FROM AUTHOR]

The ‘good genes’ hypothesis predicts that males advertise their quality with different sexual ornaments and that females are able to recognize the genetic quality of males by evaluating these characteristics. In the present study, we investigated the parental effects on offspring performance (feeding and swimming ability of newly-hatched larvae) and examined whether male ornamentation indicates offspring success in performance trials of whitefish ( Coregonus lavaretus Linnaeus). Offspring first-feeding success had a strong paternal effect and it was also positively correlated with the size of male breeding tubercles, indicating that breeding ornamentation of males can function as an honest indicator of their genetic quality. In addition, the observed positive correlation between male tubercle size and condition factor suggests that highly ornamented males are efficient foragers and that this trait may have a heritable basis. By contrast to feeding success, only a maternal effect was found in the swimming ability of the larvae. Clear family-specific differences observed in both measures of performance strongly suggest that parental identity may have important effects on larval survival in the wild. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 532–539. [ABSTRACT FROM AUTHOR]

We examined oxygen consumption and growth rates of juveniles i,1 three Finnish Atlantic salmon (Salmo salar) stocks (Neva, Saimaa, Teno) reared at the same fish farm. The meas urements were carried out four times: in winter 2005, early spring 2006, autumn 2006 and late spring 2007 using fish hatched in February 2005, and the size and temperature ranges were wide. The salmon stocks differed in their geographical origin and native habitat presumably selecting for differences in physiological parameters. The southernmost Neva stock had higher values of a relative standard metabolic rate (rSMR) at the yolk-sac stage than the Teno stock, and the northernmost Teno stock had a higher growth rate (SGR) values at the smolt stage than the two other stocks. In addition, the stocks differed in physiological parameters characteristic of smolting: the post-smolts in the northernmost Teno stock had significantly higher rSMR and SGR, and lower condition factor values than the ones in the two other stocks. [ABSTRACT FROM AUTHOR]

Plastic pollution has posed a significant environmental concern being widely spread in terrestrial and aquatic ecosystems. Nanoplastic particles (NPs: <1000 nm) have been drawing attention for their potential toxicological implications on organisms. Aquatic animals are increasingly exposed to NPs but their effects on many aquatic invertebrates remain inadequately known. Here, we assessed the effects of 25 nm polymethylmethacrylate NPs on the swimming behaviour and gut microbiome composition of juveniles of an ecologically important detritivore, the Gammarus pulex (Crustacea: Amphipoda: Gammaridae), during a 10-day exposure period at two different concentrations (2 mg/L and 20 mg/L). Our results indicate that NPs treatments may increase swimming behaviour in G. pulex. Moreover, exposure to low concentration of NPs seems to increase bacterial diversity, while high concentration seems to reduce diversity. Taxonomic analysis revealed Rickettsiella and Aeromonas as dominant genera, exhibiting concentration-dependent responses to NPs. The increased swimming activity observed may indicate potential stimulatory effects of NPs on their locomotor behaviour. Additionally, shifts in microbial diversity may indicate the sensitivity of the gut microbiota to environmental stressors, reflecting also potential ecological implications. Further investigation is needed to elucidate the underlying mechanisms driving the detected responses and to assess the potential ecological consequences of NPs pollution on G. pulex in contaminated environments., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

The sperm pre-fertilization environment has recently been suggested to mediate remarkable transgenerational consequences for offspring phenotype (transgenerational plasticity, TGB), but the adaptive significance of the process has remained unclear. Here, we studied the transgenerational effects of sperm pre-fertilization thermal environment in a cold-adapted salmonid, the European whitefish ( Coregonus lavaretus ). We used a full-factorial breeding design where the eggs of five females were fertilized with the milt of 10 males that had been pre-incubated at two different temperatures (3.5°C and 6.5°C) for 15 h prior to fertilization. Thermal manipulation did not affect sperm motility, cell size, fertilization success or embryo mortality. However, offspring that were fertilized with 6.5°C-exposed milt were smaller and had poorer swimming performance than their full-siblings that had been fertilized with the 3.5°C-exposed milt. Furthermore, the effect of milt treatment on embryo mortality varied among different females (treatment×female interaction) and male-female combinations (treatment×female×male interaction). Together, these results indicate that sperm pre-fertilization thermal environment shapes offspring phenotype and post-hatching performance and modifies both the magnitude of female (dam) effects and the compatibility of the gametes. Generally, our results suggest that short-term changes in sperm thermal conditions may have negative impact for offspring fitness. Thus, sperm thermal environment may have an important role in determining the adaptation potential of organisms to climate change. Detailed mechanism(s) behind our findings require further attention., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2018. Published by The Company of Biologists Ltd.)

Sexual dimorphism is common across the animal kingdom, but the contribution of environmental factors shaping differences between the sexes remains controversial. In ectotherms, life-history traits are known to correlate with latitude, but sex-specific responses are not well understood. We analyzed life-history trait variation between the sexes of European perch ( Perca fluviatilis L.), a common freshwater fish displaying larger female size, by employing a wide latitudinal gradient. We expected to find sex-dependent latitudinal variation in life-history variables: length at age, length increment, and size at maturity, with females showing consistently higher values than males at all latitudes. We further anticipated that this gender difference would progressively decrease with the increasingly harsh environmental conditions toward higher latitude. We hypothesized that growth and length increment would decrease and size/age at maturity would increase at higher latitudes. Our results confirmed female-biased sexual size dimorphism at all latitudes and the magnitude of sexual dimorphism diminished with increase in latitude. Growth of both sexes decreased with increase in latitude, and the female latitudinal clines were steeper than those of males. Hence, we challenge two predominant ecological rules (Rensch's and Bergmann's rules) that describe common large-scale patterns of body size variation. Our data demonstrate that these two rules are not universally applicable in ectotherms or female-biased species. Our study highlights the importance of sex-specific differences in life-history traits along a latitudinal gradient, with evident implications for a wide range of studies from individual to ecosystems level.