Search

Fish kills are widespread visible events perceived by the civil society as a major cause for concern about water quality and ecosystem health. Investigations conducted so far have linked fish kills to multiple factors, but extensive studies examining quantitatively the likelihood of fish kills are missing. In the present study, factors related to fish kills in 67 Mediterranean reservoirs located in the Iberian Peninsula were investigated. Moreover, the variation in the likelihood of fish kills with the foreseen consequences of anthropogenically driven climate change upon temperature and precipitation was assessed. During the 23-year period studied (1995–2017) the number of fish kills per reservoir varied from 0 to 3 and happened mostly in Southern reservoirs and during the warmest months, particularly in June. Twelve explanatory variables showed significant differences between reservoirs with and without fish die-offs. Reservoir depth, surface area oxygen and chlorophyll a concentrations were the variables that, together, best discriminated between reservoirs with and without fish kills, explaining 67.2% of the total variation in the occurrence of fish die-offs. The variables retained in the mortality model explained unique parts of that variation, but a considerable amount of the explained variation was shared by all the variables. The number of fish kill events appears to be rising during the examined period and the projection made indicated an increase in the likelihood of fish kills towards the end of the 21st century, particularly for the RCP8.5 emission scenario, with the prevalence of fish kills reaching 0.865 in Southern reservoirs. In the future, oligotrophication is likely the only strategy to consistently reduce fish kills in Mediterranean reservoirs. Image 1 • Factors related to fish kills in Mediterranean reservoirs were investigated. • Number of fish kills happened mostly in the warmest months. • Four variables best discriminated between reservoirs with and without fish kills. • Number of fish kills increased from 1995 to 2017. • The likelihood of fish kill events is projected to increase in the future. [ABSTRACT FROM AUTHOR]

Summary: The Chinese sturgeon (Acipenser sinensis) is an anadromous fish inhabiting the Yangtze River. Migration of Chinese sturgeon from the estuary to upper Yangtze River was blocked by Gezhou Dam, completed in 1981, and a new, much smaller, spawning ground was established below the dam. However, Three Gorges Dam began operating in 2003, altering hydrological conditions in the new spawning grounds and the impact on Chinese sturgeon reproduction was severe. The annual survey of Chinese sturgeon shows that both spawning scale and breeding population decreased during this period. To illustrate the impact of Three Gorges Dam on the spawning grounds and reproduction of Chinese sturgeon, the habitat suitability of spawning grounds on spawning day was simulated using River2D. Results show that the area of suitable spawning grounds positively correlates with the scale of reproduction and both have decreased sharply since 2003. [ABSTRACT FROM AUTHOR]

Wolf herrings (Chirocentridae; Clupeoidei) are commonly found in local fish markets throughout the Indo‐West Pacific region where they constitute an auxiliary source of food and income for local communities. The validity of the two species of wolf herrings, Chirocentrus dorab Forsskål, 1775 and C. nudus Swainon, 1839, is only supported by slight morphological differences. The identification of either species is challenging, especially for juveniles, and precludes accurate assessments of these natural resources at a species level. As a step towards gaining better knowledge of the genetic structure of these fishes, we examined genetic differentiation between these two species by reconstructing their entire mitogenomic sequences using high‐throughput sequencing technology. We found that the mitogenome of each species shared the same gene content and order that were the same for those found in most other teleost fishes. Despite their high morphological similarity, these two species of Chirocentrus were genetically well differentiated (p‐distance = 16.3% at their cytochrome oxidase I). A mitogenomic time‐calibrated phylogenetic analysis showed that wolf herrings originated about 35 million years ago, and they represent a case of morphological stasis. Furthermore, comparison of published and newly determined mitochondrial COI barcode region sequences from 22 individuals revealed species‐level cryptic genetic diversity within C. dorab. Altogether, these mitochondrial data are effective in discriminating species within this genus and informing population genetic relationships within species of wolf herrings. [ABSTRACT FROM AUTHOR]

Human beings are the dominant top predator in the marine ecosystem. Throughout most of the global ocean this predation is carried out by industrial fishing vessels, that can now be observed in unprecedented detail via satellite monitoring of Automatic Identification System (AIS) messages. The spatial and temporal distribution of this fishing effort emerges from the coupled interaction of ecological and socio-economic drivers and can therefore yield insights on the dynamics of both the ecosystem and fishers. Here we analyze temporal variability of industrial fishing effort from 2015-2017 as recorded by global AIS coverage, and differentiated by fishing gear type. The strongest seasonal signal is a reduction of total deployed effort during the annual fishing moratorium on the numerically-dominant Chinese fleet, which occurs during boreal summer. An additional societally-controlled reduction of effort occurs during boreal winter holidays. After accounting for these societal controls, the total deployed effort is relatively invariant throughout the year for all gear types except squid jiggers and coastal purse seiners. Despite constant deployment levels, strong seasonal variability occurs in the spatial pattern of fishing effort for gears targeting motile pelagic species, including purse seiners, squid jiggers and longliners. Trawlers and fixed gears target bottom-associated coastal prey and show very little overall seasonality, although they exhibit more seasonal variation at locations that are further from port. Our results suggest that societal controls dominate the total deployment of fishing effort, while the behavior of pelagic fish, including seasonal migration and aggregation, is likely the most prominent driver of the spatial seasonal variations in global fishing effort. [ABSTRACT FROM AUTHOR]

Bulk carbon and nitrogen stable isotope (SI) ratios (δ 13C and δ 15N) were analysed to investigate the feeding habits of six taxa of mesopelagic fish larvae inhabiting the Kuroshio waters of the northeastern East China Sea. Large variation in tissue SI during early larval periods suggested maternal effects from parent fishes, and non-selective feeding on a variety of plankton species due to poor swimming ability. The similarity between SI ratios measured in larval tissues and those estimated for eggs of an "income breeder" in the spawning area support an "income breeder" strategy in Diaphus slender type and Vinciguerria nimbaria, while Lipolagus ochotensis seemed to show "capital breeder"-like characteristics. SI ratios of the fish larvae studied became relatively constant at species-specific body dry-weights (0.5–1.0 mg), probably due to the commencement of selective feeding, meaning SI ratios during late larval periods could be used for trophic position analysis. There was great overlap (44.6–76.5%) in trophic niche among the larval fishes within the same taxonomic family of Myctophidae. Even if principal diet components cannot be identified with gut contents analyses, diet information from other fish species occupying a similar isotopic niche can thus improve our understanding of the diets of larval fishes. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity might influence evolutionary processes such as adaptive radiations. Plasticity in parental care might be especially effective in facilitating adaptive radiations if it allows populations to persist in novel environments. Here, we test the hypothesis that behavioral plasticity by parents in response to predation risk facilitated the adaptive radiation of three‐spine sticklebacks. We compared the behavior of fathers across multiple ancestral (marine) and derived (freshwater) stickleback populations that differ in time since establishment. We measured behavioral plasticity in fathers in response to a predator found only in freshwater environments, simulating conditions marine males experience when colonizing freshwater. The antipredator behavior of males from newly established freshwater populations was intermediate between marine populations and well‐established freshwater populations. In contrast to our predictions, on average, there was greater behavioral plasticity in derived freshwater populations than in ancestral marine populations. However, we found greater individual variation in behavioral reaction norms in marine populations compared to well‐established freshwater populations, with newly established freshwater populations intermediate. This suggests that standing variation in behavioral reaction norms within ancestral populations might provide different evolutionary trajectories, and illustrates how plasticity can contribute to adaptive radiations. [ABSTRACT FROM AUTHOR]

Highlights • Zebrafish and other fish models are widely accepted in CNS research and drug screening. • Intraspecies behavioral variation plays a key role in fish drug-evoked responses. • Sex, strain and individual differences contribute markedly to intraspecies variance in fish. • Epigenetics, gut microbiota and gene-environment interactions influence intraspecies variance in fishes. • Here, we outline recent findings and discuss the existing challenges in this field. Abstract Intraspecies variation is common in both clinical and animal research of various brain disorders. Relatively well-studied in mammals, intraspecies variation in aquatic fish models and its role in their behavioral and pharmacological responses remain poorly understood. Like humans and mammals, fishes show high variance of behavioral and drug-evoked responses, modulated both genetically and environmentally. The zebrafish (Danio rerio) has emerged as a particularly useful model organism tool to access neurobehavioral and drug-evoked responses. Here, we discuss recent findings and the role of the intraspecies variance in neurobehavioral, pharmacological and toxicological studies utilizing zebrafish and other fish models. We also critically evaluate common sources of intraspecies variation and outline potential strategies to improve data reproducibility and translatability. [ABSTRACT FROM AUTHOR]

Responses of trophic structure to reservoir regulation are important to manage and conserve the river ecosystem influenced by dams. We used stable isotope-derived community-wide metrics to describe spatiotemporal variation in trophic niches and trophic structures of fish assemblages in a tributary of the Three Gorges Reservoir (TGR) in China where water level regulation is put into operation annually. A longitudinally increasing trophic space was discovered in this tributary especially when the water level was low. Trophic diversity declined and trophic redundancy increased from the non-flood period to flood season at the upper backwater region. However, trophic space was more stable in the estuarine site. The site differences were associated with availability of food resource and pathway of consumers, as specifically, disturbance derived from flow pulse at the end of backwater site altered diet composition of the fish consumers, while immense water body in the lower confluence area limited the flood influences as well as promoted exploitation of diverse available sources. Moreover, the declined water level control facilitated the contraction of the trophic niche size at the tail backwater site because of remarkable riverine morphology alternation leading to decreasing water body whereas the rising water level regulation homogenized trophic structure along the downstream river. Our study revealed that there was different response of fish assemblages along longitudinal fluvial gradient to the water level regulation in the reservoir and targeted management and conservation measures are needed for the different sections of the tributary. [ABSTRACT FROM AUTHOR]

The objective of the present study was to analyze the morphometric variations of the three presumed taxa within the Barbonymus group, namely B. gonionotus, referred to locally as naleh; B. schwanenfeldii, referred to locally as lampam-A; and Barbonymus sp. referred to locally as lampam-B. The naleh samples were collected from Nagan Raya District, while lampam-A and lampam-B were collected from Aceh Tamiang District, Indonesia. Traditional morphometric characters were measured in 150 fish samples (50 individuals of every taxon). The results of univariate (ANOVA) and multivariate (Discriminant function analysis, DFA) analyses showed that lampam-A and lampam-B have overlapping morphological characteristics, whereas naleh were distinctly different. Therefore, it is presumed that lampan A and lampan B are the same species of B. schwanenfeldii. It was concluded that the morphometric data indicated that there are two species of Barbonymus in Aceh waters, i.e., B. schwanenfeldii and B. gonionotus. [ABSTRACT FROM AUTHOR]

The aim of the study was to determine the impact of different feed rations (0.5, 0.8, 1.1% fish biomass) on the rearing parameters of pikeperch, Sander lucioperca (L.), reared in a recirculating aquaculture system. The study comprised two experiments. In the first, the material used had been sorted by a mean body weight of 35.5 g, while in the second the pikeperch were divided into three size classes: smallest individuals (class S) with a mean body weight of 59.5 g, medium-sized individuals (class M) with a mean weight of 69.3 g, and largest individuals (class L) with a mean body weight of 84.8 g. The experiments ran for 42 days. At the conclusion of the experiments, the highest body weight and length, daily growth rate, and specific growth rate were attained by the group of fish fed the ration of 1.1% of the fish biomass in both experiments I and II. The feed conversion ratio was also the lowest in this feed ration group, and it differed significantly statistically among the experimental groups (P < 0.05). The feed ration of 0.5% of the fish biomass was only sufficient to maintain vital functions, but it contributed only slightly to growth. The different feed rations did not have a significant impact on the final value of the body weight coefficient of variation of the pikeperch reared in the two experiments. The results of the experiment also indicated that pikeperch is a species with weak stock hierarchy and domination structure. [ABSTRACT FROM AUTHOR]

The ability of cold-adapted species to persist in the face of climate change will depend on the capacity of individuals for thermal acclimation, adaptation, and the degree of physiological variation that exists among populations. We tested the acclimation capacity of cardiac HSP70 and HSP90 in four populations of lake trout ( Salvelinus namaycush ), a cold-adapted salmonid. We acclimated fish to four temperatures (8 °C, 11 °C, 15 °C, and 19 °C) and measured cardiac HSP70 and HSP90 levels by western blot prior to and following an acute (1 h) heat shock at 23 °C. Basal and induced cardiac HSP70 and HSP90 expression was similar among lake trout populations. Induced cardiac HSP70 was significantly lower in heat-shocked lake trout acclimated to 19 °C compared to all other temperatures. Acclimation temperature had no significant effect on cardiac HSP90 prior to heat shock (control HSP90) and a significant effect on HSP90 in heat-shocked fish, although most significant treatment comparisons were marginal. However, for warm-acclimated fish (15 °C and 19 °C), cardiac HSP90 levels were lower in heat-shocked versus control fish. Together, this suggests that the induction temperature of cardiac HSP synthesis may increase with warm acclimation in lake trout. This plasticity in the cardiac HSR could assist lake trout populations in coping with longer periods of thermal stress as predicted by climate change models. The cardiac HSR supports previous research suggesting lake trout thermal physiology may be conserved across a wide geographic range. [ABSTRACT FROM AUTHOR]

We studied the feeding ecology of an endemic cyprinodontid fish, Aphanius marassantensis (Kızılırmak Toothcarp), with special emphasis on seasonal and ontogenetic diet shift. The dietary composition revealed an omnivorous diet with great seasonal and ontogenetic variation. Cladocera and Calanoid Copepods (Diaptomus sp.) dominated the diet in Spring and Summer, whereas the food items of plant origin e.g. filamentous algae and diatoms were the most important components in Autumn and Winter. An ontogenetic diet shift was also demonstrated. While the feeding of juveniles was based mostly on planktonic organisms, adult individuals preferred larger prey taxa, such as Gammarus sp. and Gastropods. There was no significant sex-related variation in feeding with the exception for the volume of gut content. The investigation on the feeding strategy of A. marassantensis suggested a generalised feeding pattern with some specialised individuals. This generalist feeding habits may account for the well-established population of this species in a big reservoir under coexistence of two non-native fish species, Pseudorasbora parva and Atherina boyeri. [ABSTRACT FROM AUTHOR]

Human-induced thermal variability can disrupt energy balance and performance in ectotherms; however, phenotypic plasticity may play a pivotal protective role. Ectotherm performance can be maintained in thermally heterogeneous habitats by reducing the thermal sensitivity of physiological processes and concomitant performance. We examined the capacity of juvenile green sturgeon ( Acipenser medirostris ) to respond to daily thermal variation. Juveniles (47 days post-hatch) were exposed to either stable (15 ± 0.5 °C) or variable (narrowly variable: 13–17 °C day −1 or widely variable 11–21 °C day −1 ) thermoperiod treatments, with equivalent mean temperatures (15 ± 0.5 °C), for 21 days. Growth (relative growth rate, % body mass gain), upper thermal tolerance (critical thermal maxima, CTMax) and the thermal sensitivity of swimming performance (critical swimming speed, U crit ) were assessed in fish from all treatments. Accelerated growth was observed in fish maintained under widely variable temperatures compared to narrowly variable and stable temperatures. No significant variation in CTMax was observed among thermoperiod treatments, suggesting all treatment groups acclimated to the mean temperature rather than daily maximums. The widely variable treatment induced a plastic response in swimming performance, where U crit was insensitive to temperature and performance was maintained across a widened thermal breadth. Maximum U crit attained was similar among thermoperiod treatments, but performance was maximised at different test temperatures (stable: 4.62 ± 0.44 BL s −1 at 15 °C; narrowly variable: 4.52 ± 0.23 BL s −1 at 21 °C; widely variable: 3.90 ± 0.24 BL s −1 at 11 °C, mean ± s.e.m.). In combination, these findings suggest juvenile A. medirostris are resilient to daily fluctuations in temperature, within the temperature range tested here. [ABSTRACT FROM AUTHOR]

Abstract: Aim: We sought to identify direct and indirect effects of factors contributing to establishment and spread of 272 stream fish species. Location: Two hundred and ninety‐seven watersheds in the eastern United States. Methods: We modelled two variables: (1) whether a species had become established outside its native range (establishment) and (2) the number of watersheds in which species established outside their native range (spread). We estimated these variables by comparing historical distributions to a rich data set of contemporary sampling. We calculated metrics of human use (indexing propagule pressure), and gathered species trait data from an open‐access database. We then used piecewise path analysis to estimate direct and indirect effects of human use, native range size and species traits on the two metrics of species introductions. Results: We identified a hierarchical causal structure in which native range size and fishing pressure were important direct determinants of introductions. Species traits had some direct effects, but played a more indirect role. Native range size was significantly affected by thermal tolerance and diet breadth. Likewise, fishing pressure was significantly affected by life history strategy: larger‐bodied, longer‐living and more fecund species were positively associated with fishing pressure. Main conclusions: Functional traits can confer an advantage to some species during the establishment phase, but human use is important for subsequent dispersal throughout the non‐native range. However, human use is non‐random, and is largely a function of species traits. Considering both direct and indirect effects of traits across stages of the invasion process can help to elucidate the full role of traits in species invasions. [ABSTRACT FROM AUTHOR]

Abstract: Preserving remaining nonhybridized populations Cutthroat Trout Oncorhynchus clarkii is a conservation priority often requiring management action. Although proactive programs for Rainbow Trout O. mykiss and hybrid suppression offer a flexible tool, particularly in large interconnected river basins, this management approach is used less frequently than alternatives such as barriers and piscicides. We describe the results of a targeted Rainbow Trout hybrid suppression program spanning 15 years in the upper Snake River, Wyoming, a core stronghold for Yellowstone Cutthroat Trout O. clarkii bouvieri. Initially, Rainbow Trout hybrids were relatively common in the Gros Ventre River, a major tributary to the Snake River. Between 2002 and 2016, 926 individuals of Rainbow Trout ancestry were removed from the Gros Ventre River. Relative abundance of Rainbow Trout hybrids decreased over this time, while the Yellowstone Cutthroat Trout population increased. Temporal genetic data collected in 2007–2008 and again in 2014 demonstrate that the overall proportion Rainbow Trout admixture and the proportion of hybrids in a sample both significantly decreased in the Gros Ventre River and did not increase elsewhere in the Snake River basin. In conclusion, proactive Rainbow Trout suppression appears to have reduced the threat of Rainbow Trout hybridization in this river basin and helped protect an interconnected metapopulation that has a highly diverse life history and genetic variation important for long‐term persistence. [ABSTRACT FROM AUTHOR]

Individuals vary in their baseline levels of stress hormones (predictive homeostasis) and in their stress responses (reactive homeostasis). Variation in normal reactive scope, both predictive and reactive homeostasis, may be important for understanding how endocrine traits respond to selection. Reactive homeostasis is the increase in glucocorticoid (GCs) hormones above baseline. Individuals at different life history stages, such as gestation in females, may show variation in normal reactive scope. We performed an adrenocorticotropic hormone (ACTH) challenge and measured changes in circulating GCs to estimate the reactive scope of female sailfin mollies ( Poecilia latipinna ) at different gestational states. We measured cortisol, primary GC in teleost fishes, to obtain baseline release rates prior to injection with either ACTH or saline control. Using water-borne hormones, we measured cortisol release rates at four time intervals post-injection. Females were then sacrificed to determine the developmental stage of embryos, if present, and the number of developing embryos or mature ova. We found that ACTH-injected females had significant increases in cortisol releases rates, whereas cortisol release rates of control females did not change during the 4 h post-injection period. We found high repeatability in predictive homeostasis of cortisol and moderate repeatability in reactive homeostasis and a phenotypic correlation between predictive and reactive homeostasis. Gestational state did not affect female predictive or reactive homeostasis. We applied the reactive scope model to P. latipinna and gained a further understanding of how among- and within-individual variation in both predictive and reactive homeostasis are partitioned and how these traits vary under certain life-history conditions. [ABSTRACT FROM AUTHOR]

Chamelea gallina is a valuable commercial species in the Mediterranean Sea. The strong fishing pressure on C. gallina in the northern and central Adriatic Sea has paralleled a clear-cut decrease in clam population density and the occurrence of several irregular mortality events. Despite the commercial interest in this species, nothing is known about its genetic sub-structuring at the geographic and/or temporal scale, nor its levels of genetic variability. Analyzing microsatellite genotypes for samples collected in the Adriatic Sea, we detected large geographic genetic homogeneity with gene flow guided by broad scale circulation in the north-south direction. Our results also indicate weak genetic differentiation among size classes at the local and temporal scale. These small genetic differences might be determined by variability of local circulation and reproductive success, partial overlapping generations and high larval mortality rates as suggested by our estimates of the effective number of breeders. In fact, global effective population size estimates over multiple generations are medium-high, but a low number of breeders are responsible for the small clams size class recruitment. Notwithstanding, it was not possible to detect signatures of bottleneck. Future efforts in fishery management should aim to maintain genetic diversity – essential to the long-term sustainability of the resource – and limit effective population size fluctuations while considering the need to improve water quality to avoid mass mortality events. [ABSTRACT FROM AUTHOR]

Queen conch ( Lobatus gigas ), is an economically and culturally important marine gastropod. The species is subject to extensive exploitation throughout large parts of the Caribbean which has led to a decrease in population densities across much of the species’ distribution range. Hence, there is a need for protective measures to safeguard the reproductive stock. This requires a better estimation of its size at maturity, which is best quantified as the thickness of the lip that the shell develops after reaching its maximum length. The lip thickness at 50% maturity (LT 50 ) was determined using a logistic and an accumulation model, from seven representative location of distribution of this species in the Wider Caribbean Region. LT 50 of both females (7–14 mm) and males (4–11.5 mm) varied between different locations in the Caribbean, although it did not correspond with variation in water temperature. In most cases females had a larger LT 50 than males indicating sexual dimorphism. LT 50 values estimated with the logistic model were smaller (7–14 mm for females, 4–11.5 mm for males) than values estimated with the accumulation model (13–26 mm for females, 16–24 mm for males), showing an overestimation of LT 50 in queen conch in previous studies which used the accumulation model to estimate LT 50 . Locations with a relatively high variation in water temperature had a significantly shorter reproductive season. The implementation of adequate minimum size regulation based on lip thickness (ca. 15 mm) and a Caribbean wide seasonal closure (May–September) using the most recent biological information from this study, taking into consideration the local differences in LT 50 and reproductive season, will assist in developing a long term sustainable queen conch fishery in the Caribbean. [ABSTRACT FROM AUTHOR]

This study presents inter-annual variability of otolith growth from 1993 to 2011 and cohort specific sex ratios from 1976 to 2011 in blue grenadier Macruronus novaezelandiae on the west coast of Tasmania. Length-at-age data highlighted that M. novaezelandiae females grow larger than males with mean length-at-age statistically diverging by three years of age and remaining separated thereafter. Statistical differences in both cumulative, and age specific otolith increment widths-at-age between sexes were detected at earlier ages, but these effects were variable and not consistent with the sexual dimorphism observed for mean length at age. No differences between sexes were evident for the ages 8–14 or 7–11 for cumulative increment widths or age specific otolith increment widths-at-age respectively. Inter-annual variation in mean otolith increment widths for the first five increment zones (juvenile zones) showed a trend of declining increment widths from 2006 to 2010. Inter-annual cohort sex ratio variation across year-of-birth was also significant displaying a similar trend to the first-year otolith increment growth profiles. Regression analysis of birth year sex ratio with mean otolith increment widths indicated a significant negative relationship for first year growth with increasing numbers of male offspring. The inter-annual variation in cohort specific sex ratio suggests that environmental factors may be involved with sex determination. When coupled with climate change these influences could have long term consequences for the fitness of the stock and corresponding flow-on effects into the stock assessment process and future management of the stock. [ABSTRACT FROM AUTHOR]

In management of fisheries, knowledge about the species is crucial due to differences in life history traits. The first step is therefore species identification. For many species this task is straightforward, however for some species e.g. the two species of Atlantic redfish Sebastes mentella and Sebastes norvegicus , it can be difficult for an untrained eye. With the goal to separate the two species, we analysed otolith shape variation of S. mentella and S. norvegicus caught on the continental slope of East Greenland using the R package “Shape R”. Results were evaluated against genetic analysis of the same fish, and compared to results of both a visual identification of the two species and a separation based on a linear discriminant analysis on standardised values of fish length, fish weight and otolith weight. It was concluded that the objective otolith shape analysis using the Shape R package analysis achieve a reasonable classification success, however with a clear bias towards S. mentella . Classification using the otolith weight achieved a slightly higher success than the shape analysis making it a promising method. Furthermore, the method is at the same time both objective, less time consuming than the otolith shape analysis and less expensive than genetic analysis. However, the visual classification method of the whole fish had the highest success rate of the three tested methods, which despite the need for trained technicians makes it the most successful method. [ABSTRACT FROM AUTHOR]

Copyright of Brazilian Journal of Biology is the property of Instituto Internacional de Ecologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: Natural selection is often invoked to explain differences in brain size among vertebrates. However, the particular agents of selection that shape brain size variation remain obscure. Recent studies suggest that predators may select for larger brains because increased cognitive and sensory abilities allow prey to better elude predators. Yet, there is little direct evidence that exposure to predators causes the evolution of larger brains in prey species. We experimentally tested this prediction by exposing families of 1000–2000 F2 hybrid benthic‐limnetic threespine stickleback to predators under naturalistic conditions, along with matched controls. After two generations of selection, we found that fish from the predator addition treatment had significantly smaller brains (specifically smaller telencephalons and optic lobes) than fish from the control treatment. After an additional generation of selection, we reared experimental fish in a common environment and found that this difference in brain size was maintained in the offspring of fish from the predator addition treatment. Our results provide direct experimental evidence that (a) predators can indeed drive the evolution of brain size–‐but not in the fashion commonly expected and (b) that the tools of experimental evolution can be used to the study the evolution of the vertebrate brain. [ABSTRACT FROM AUTHOR]

Panglima Besar Soedirman waters reservoir and the Serayu River in Banjarnegara Regency, Central Java is one of the habitats of hampala fish . Hampala fish is a member of the Cyprinidae family, which has economic value but is fully captured from the wild. The study on the genetic diversity using approaches of isozyme analysis needed to support conservation and domestication of the fish in this area. This study was aimed at the genetic variation of the hampala fish population in PB. Soedirman water reservoir and the Serayu River in Banjarnegara Regency based on esterase (EST), acid phosphatase (ACP), peroxidase (PER), and aspartate aminotransferase (AAT). Visualization of the isozyme was carried out employing horizontal electrophoretic technique with potato starch. From the results of this study it can be concluded that the hampala fish from the reservoir of PB. Soedirman, Serayu River area before reservoir and after reservoir, all of which are in Banjarnegara Regency, can visualized isozymes EST, ACP, and AAT well, except PER isozyme. This finding can be used as based information on population genetics and finally can be used for conservation of this fish. The results of this study are expected to be utilized to evaluate the potential genetic condition of hampala fish, which is the basis for conservation strategy and domestication. [ABSTRACT FROM AUTHOR]

Morphometric characters have traditionally been used to describe the population structure of fishes. Body shape variation, which is often environmentally induced, may provide a good record of short-term population structuring. However, factors unrelated to environmental or genetic influences on body morphology may complicate sampling and the use of morphometric features for stock discrimination. In the present study, we used geometric morphometric variables to compare the European sardine Sardina pilchardus putative stocks of the Aegean and Ionian Seas (eastern Mediterranean). Landmark data of fish collected at seven different sites were subjected to canonical analysis of principal coordinates (CAP). The average body condition of sardines from these sites was strongly and linearly related to corresponding scores along CAP1, the axis exhibiting the highest correlation with the morphometric data cloud. The average scores along CAP2 and CAP3 appeared to be linked to morphological differentiation related to temperature effects and prey availability (mesozooplankton biomass). Despite the primary and confounding effect of body condition, discrimination of different morphotypes corresponding to the Aegean and the Ionian Sea stocks was highly significant with 81% correct reallocations for the respective CAP model. [ABSTRACT FROM AUTHOR]

Species substitution, the use of a low value fish in place of a high value fish, is the biggest problem in international trade and the leading cause of fraud in the fisheries arena sector. Current DNA barcoding systems have partly solved this problem but also failed in many instances to amplify PCR targets from highly processed products because of the degradation of a longer barcode marker (~ 650 bp). In the present study, a novel mini barcode marker (295 bp) was developed to discriminate fish species in raw and processed states forms. The barcode primers were cross-tested against 33 fish species and 15 other animal species and found to be universal for all the tested fish varieties. When 20 commercial fish products of five different categories were screened, all commercial fish sample yielded positive bands for the novel fish barcode. PCR product was sequenced to retrieve the species IDs that reflected 55% (11/20) of Malaysian fish products were mislabeled. [ABSTRACT FROM AUTHOR]

Steindachneridion scriptum is an important species as a resource for fisheries and aquaculture; it is currently threatened and has a reduced occurrence in South America. The damming of rivers, overfishing, and contamination of freshwater environments are the main impacts on the maintenance of this species. We accessed the genetic diversity and structure of S. scriptum using the DNA barcode and control region (D-loop) sequences of 43 individuals from the Upper Uruguay River Basin (UUR) and 10 sequences from the Upper Paraná River Basin (UPR), which were obtained from GenBank. S. scriptum from the UUR and the UPR were assigned in two distinct molecular operational taxonomic units (MOTUs) with higher inter-specific K2P distance than the optimum threshold (OT = 0.0079). The COI Intra-MOTU distances of S. scriptum specimens from the UUR ranged from 0.0000 to 0.0100. The control region indicated a high number of haplotypes and low nucleotide diversity, compatible with a new population in recent expansion process. Genetic structure was observed, with high differentiation between UUR and UPR basins, identified by BAPS, haplotype network, AMOVA (FST = 0.78, p < 0.05) and Mantel test. S. scriptum from the UUR showed a slight differentiation (FST = 0.068, p < 0.05), but not isolation-by-distance. Negative values of Tajima's D and Fu's Fs suggest recent demographic oscillations. The Bayesian skyline plot analysis indicated possible population expansion from beginning 2,500 years ago and a recent reduction in the population size. Low nucleotide diversity, spatial population structure, and the reduction of effective population size should be considered for the planning of strategies aimed at the conservation and rehabilitation of this important fisheries resource. [ABSTRACT FROM AUTHOR]

One of the pathogens causing the highest economic impacts on the Chilean salmon industry is the ectoparasite copepod Caligus rogercresseyi , whose abundance is strongly influenced by environmental variables (e.g. salinity and temperature). Infested fish with sea lice reduces appetite, food-conversion efficiency and increase stress level, which results in decreased growth. The skin wounds, caused by the ectoparasite feeding, leave fish exposed to secondary infections and antiparasitics treatment expenses are high. To evaluate the impact of environmental variables on the early development of C. rogercresseyi , egg strings were obtained from mature females (reared in laboratory conditions) and exposed to different combinations of salinity (14, 20, 26 and 32 PSU) and temperature (6, 9, 12, 15 and 18 °C). The hatching success and time, pelagic life time, survival and size of nauplius I, nauplius II and copepodid were quantified. Our results indicate that salinity and temperature have a significant effect on the hatching success of this parasite. Salinities between 26 and 32 PSU result in a hatching success of 100%, whereas lower salinities (14 PSU) reduce hatching success by 60% (at all experimental temperatures) generating an increase in mortality of these early developmental stages. A temperature reduction from 18 °C to 6 °C in culture conditions significantly extended the incubation time of C. rogercresseyi by 50%. Specifically, temperature had a higher impact on nauplius I and nauplius II larvae, increasing development times to 50 and 100 h respectively, when temperature was decreased to 6 °C. Although combination of salinity and temperature have a significant effect on hatching time and survival in C. rogercresseyi , the combination of these variables had no impact on the size of nauplius I, nauplius II and copepodid stage. Thus, the effects on the survival and pelagic life time of the early stage of C. rogercresseyi , might substantially affect the fitness of the species under fluctuating conditions of salinity and temperature. [ABSTRACT FROM AUTHOR]

Understanding dissolved O 2 flux in marine cages, and how individual fish respond to and experience such variation, is critical to optimizing growth and production performance of farmed salmon. We used a high resolution environmental monitoring system to create a 3-dimensional map of a commercial marine cage with respect to salinity, temperature and dissolved O 2 through time, while also tracking the oxygen experience of 4 individually tagged Atlantic salmon. Despite all of the dissolved O 2 measurements at the reference site being physiologically suitable for maximum growth, 1 in 4 of the recordings collected within the cage were below dissolved O 2 levels known to reduce feed intake and growth. Recorded dissolved O 2 in the cage ranged from 26 to 90% saturation with a high degree of vertical, horizontal and temporal variation. Poorest dissolved O 2 conditions consistently occurred at night in the central and down-current cage positions. Dissolved O 2 levels experienced by individual fish ranged from 30 to 90% saturation, with variation within 5 minute intervals as large as 32 percentage points. These results expand the current body of knowledge on environmental variability in marine cages, and provide valuable insights to aid farm managers in focusing mitigation and monitoring efforts when and where they are most needed. [ABSTRACT FROM AUTHOR]

Abstract: Offspring traits are greatly influenced by maternal effects, and these maternal effects may provide an important pathway through which populations can adapt to changing thermal environments. We investigated the effect of egg size on the among‐ and within‐population variation in early life history traits among introduced Great Lakes Chinook salmon (Oncorhynchus tshawytscha) populations under varying thermal conditions. We reared Chinook salmon from three populations in a common‐garden hatchery study at 6.5, 9.4, and 15.2°C and measured a variety of fitness‐related traits during development. We found that most of the among‐population variation in early life history traits was explained by egg size. However, the contribution of egg size to the among‐population variation decreased with an increase in temperature suggesting that other effects, such as genetic, contribute at high temperature. Within populations, egg size explained much of the dam variance and maternal effect for traits in every temperature, whereas egg size generally had little to no influence on the sire variance and heritability. Overall, our results demonstrate the significant contribution egg size makes to shaping early life history phenotypes among and within populations, and suggest that egg size is an important pathway through which offspring phenotypes can evolve on contemporary timescales. [ABSTRACT FROM AUTHOR]

For many fish species, variation in somatic growth can drive changes in population productivity through the dependence of survival, fecundity, and reproductive schedules on size. Changes in growth arise from many density-dependent and -independent sources. Many assessments of temporal variation in somatic growth rely on methods that lack biological underpinning in the model structure to describe observed relationships between size and environmental conditions. However, biologically-based growth models are needed to examine how density-dependent and −independent factors influence the underlying process of growth (i.e., growth = anabolic factors − catabolic factors). Our objective was to extend biologically-based growth models to estimate temporal variation in somatic growth patterns. A set of hierarchical non-linear mixed effects models based off the von Bertalanffy model and length-weight relationship were developed. We applied the models to a Black Crappie (BC; Pomoxis nigromaculatus ) population to assess the impacts of density, chlorophyll A concentration (Chl-a), water level, and temperature on somatic growth. Growth in length was influenced by temperature, with fastest growth at optimal temperatures and slower growth when temperatures were coldest (48% slower) or hottest (82% slower), and was negatively related to density, with 25% slower growth at high density. Weight of age-0 BC was negatively related to chlorophyll A, individuals were 18% lighter at high Chl-a, and positively to temperature, individuals were 10% lighter when water was cooler. Finally, growth in weight of age-1+ BC was negatively related to all factors, with 5–11% lighter fish at high densities, Chl-a, water levels, and temperatures. The model structure developed in this manuscript has broad applicability to populations that have time series data of size-at-age observations, growth increments, or back-calculated sizes and adequate environmental data. [ABSTRACT FROM AUTHOR]

Catch per unit effort (CPUE) is a widely used index of population abundance for informing stock assessments for the purpose of estimating population status and setting fishing policies. However, for CPUE to be an unbiased index, influences that are not related to population abundance (e.g., spatial variation in effort and temporal changes in gear efficiency) must be accounted for in analyses known as CPUE standardization. In longline fisheries, one important factor that can affect CPUE is the spacing between hooks (‘spacing effect’), which influences effective effort and has largely been ignored in previous analyses. Here, we use the Pacific halibut ( Hippoglossus stenolepis ) long-line fishery as a case study to explore the spacing effect. Both commercial and experimental (fishery-independent) data with hook spacing, and a survey-based CPUE series, are available for this fishery. It thus provides a unique opportunity to explore the effect of hook spacing and its effect on CPUE trends. We quantify this effect using non-parametric and parametric relationships inside a spatially-explicit (geospatial) CPUE standardization model for commercial data, and non-linear mixed-effects model for experimental data. We found a clear non-linear spacing effect (i.e., hooks were less effective the closer they were), but accounting for space had a larger effect on CPUE trends than accounting for hook spacing. For this stock, it is likely the effect of hook spacing on CPUE was minimal due to little variation in average hook spacing over time. Regardless, historical and future trends in hook spacing can have important effects on longline CPUE standardization, highlighting the value of collecting this information. Accounting for hook spacing effects in other fisheries may improve estimates of trends in relative abundance and lead to better management. [ABSTRACT FROM AUTHOR]

Abstract: Recent genetic studies, meta‐analyses, and retrospective analyses have documented reduced productivity of wild salmon and steelhead Oncorhynchus mykiss that interbreed with hatchery‐reared fish, raising concerns about the long‐term viability and recovery of at‐risk stocks. In 2007, the Oregon Department of Fish and Wildlife discontinued a Coho Salmon Oncorhynchus kisutch hatchery program at the Salmon River to support recovery of a wild Coho Salmon population in the Oregon Coast Evolutionarily Significant Unit. This decision constituted a unique management “experiment,” allowing for direct measurement of the wild population's response after the discontinuation of a decades‐old hatchery program. We used a before–after, control–impact design to examine whether selected viability metrics of the naturally produced population in the Salmon River changed after the hatchery program ended. We compared metrics for the 2006–2013 broods, representing periods after the hatchery program ended, to those for the 1995–2005 broods, when the hatchery program was still releasing 200,000 smolts annually. We also examined neighboring populations during similar time periods to account for changes or variation due to other factors. Although hatchery‐origin spawners previously had accounted for most of the adults returning to the Salmon River, the naturally produced population did not collapse, and two viability metrics improved significantly after the Coho Salmon hatchery program ended: (1) adult abundance increased and (2) spawn timing expanded and moved closer to the historical timing. Recruits‐to‐spawner ratios in the Salmon River, although initially low, are now approximately equal to those of neighboring populations. The results indicate that hatchery closure can be an effective strategy to promote wild population recovery. However, considerable variability in population trends and environmental conditions will require continued monitoring to verify the long‐term resilience and viability of the wild population. [ABSTRACT FROM AUTHOR]

Abstract: We evaluated the precision of age estimates obtained from sagittal otoliths, scales, and dorsal fin spines from 341 saugeyes (Walleye Sander vitreus × Sauger S. canadensis) collected from six Kansas reservoirs. Between‐reader agreement was greatest for otoliths, followed by dorsal spines and then scales. Coefficient of variation (CV) values for between‐reader comparisons were 1.3–3.1% for otoliths and 13.8–18.2% for dorsal spines. Between‐reader comparisons for scales were the most variable, with CV estimates between 19.9% and 23.1%. Age estimates from otoliths aligned with age estimates from scales more often than with estimates from dorsal spines, although age estimate comparisons between structures were generally variable. Between‐reader agreement for scales and dorsal spines decreased with increasing estimated age; however, agreement for otoliths generally remained high (i.e., >80%) through age 10. Given greater precision relative to other structures, we recommend the use of sectioned otoliths to estimate ages of saugeyes, especially when sacrificing the fish is not a concern. [ABSTRACT FROM AUTHOR]

The spotted knifejaw ( Oplegnathus punctatus ) is a newly emerging fishery species inhabiting the Pacific Ocean around Hawaii, China, Japan and Korean Peninsula. Little information on the mechanism of gonadal development and gametogenesis in this species could be used for research and breeding work. In this study, RNA-seq technology was applied to generate a deep-coverage sequencing data of spotted knifejaw testis and ovary. A total of 262,392,754 reads (ovary 133,403,270, testis 128,989,484) were generated from the cDNA library. After filtering and assembling, a total of 113,794 unigenes were obtained with the N50 of 1658 bp. Unigenes were annotated with multiple public databases, including non-redundant protein databases (NR) (42,460, 37.31%), Swiss-Prot (33,632, 29.56%), eukaryotic Orthologus Groups (KOG) (26,195, 23.02%), Kyoto Encyclopedia of Genes and Genomes (KEGG) (10,978, 9.65%), and Gene Ontology (GO) (30,514, 26.82%). By comparing ovary and testis, 4496 differentially expressed unigenes (1986 in female, 2510 in male) were identified, in which 469 were specially expressed in females and 859 in males. The expression levels of 12 unigenes were confirmed by qRT-PCR. In addition, 35,054 simple sequence repeats were identified. By GO and KEGG analyses, a set of unigenes related to gonadal development and gametogenesis were filtered. foxl2 was deduced to be a key regulator for gonadal development and gametogenesis in females and dmrt1 in males. bmp15 , nanos3 , sox9 and amh were likely to function in the regulation of gonad physiology and germ line cells maintenance in ovary and testis. Interestingly, p53, apoptosis, Jak-STAT and neuroactive ligand-receptor interaction pathways were found to be pivotal in regulating gonadal development and gametogenesis of spotted knifejaw in various aspects. This study provides a fundamental support for further research in reproduction biology, population genetics and functional genomics in spotted knifejaw. [ABSTRACT FROM AUTHOR]

A thermal tolerance study mimicking different stream environments could improve our ecological understanding of how increasing water temperatures affect stream ectotherms and improve our ability to predict organism responses based on river classification schemes. Our objective was to compare the thermal tolerances of stream fishes of different habitat guilds among 3 exposure periods: critical thermal maximum (CTmax, increase of 2°C/h until loss of equilibrium [LOE] and death [D]), and 2 longer-term treatments (net daily increase of 1°C) that mimicked spring-fed (SF; 4°C daily increase) and non-spring-fed (NSF; 8°C daily increase) conditions. Fishes in the pelagic habitat guild had a 1°C higher average CTmax than benthic fishes. Thermal responses of species depended on exposure period with higher and increased variation in tolerances associated with the SF and NSF exposure periods. Logperch, Orangebelly Darter, Orangethroat Darter, and Southern Redbelly Dace were more sensitive to thermal increases regardless of SF or NSF treatment than were the 3 remaining species (Brook Silverside, Central Stoneroller, and Redspot Chub), which represented average thermal responses among the species tested. The 3 species that had a higher thermal response to CTmax-D (lethal endpoint of death) also were able to increase their tolerances more than other species in both SF and NSF treatments. Our data indicate finer guild designations may be useful for predicting thermal-response patterns. A diel thermal refuge increases the thermal responses of ectotherms to daily maxima, but the patterns across our SF and NSF treatments were similar suggesting minimum refuge temperatures may be more important than maximums. Nonetheless, stream temperature cooling over a 24-h period is important to ectotherm thermal tolerances, a result suggesting that sources of cooler water to streams might benefit from protection. [ABSTRACT FROM AUTHOR]

The shore stranding of mesopelagic fauna is a recurrent phenomenon in the Strait of Messina (Central Mediterranean Sea). The aim of this paper is to test the influence of lunar phases, winds and seasons upon the frequency of occurrence of strandings of mesopelagic fish. Species abundance in relation to these factors was quantified for the first time. Specimens were collected stranded on the shore along the Sicilian coast of the Strait of Messina between 2008 and 2016. Overall 32 species belonging to seven families (Gonostomatidae, Microstomatidae, Myctophidae, Paralepididae, Phosichthyidae, Sternoptychidae, Stomiidae) were found stranded. Myctophidae was the family including the highest number of species (16), whereas Gonostomatidae was the most abundant in terms of total number of individuals (47.2%), mainly thanks to the species Cyclothone braueri. The moon, which influences the strength of currents (highest during full and new moon phases) and irradiance (higher in some lunar phases, such as the full moon), affected the abundance of stranded mesopelagic fish in the study area. The highest number of stranding events was recorded during the new moon: 34.6% of the total relative abundance of stranded mesopelagic fish. Wind blowing from the sea towards the coastline (southeasterly and easterly winds) created the best conditions for strandings. The highest abundance of stranded specimens was recorded during the winter season. [ABSTRACT FROM AUTHOR]

This study aims to analyze the seasonal variations in seston biochemical compounds (biopolymeric organic carbon (C-BPC), i.e. the sum of proteins, carbohydrates and lipids) in order to infer the bioavailable organic fraction controlling food absorption by mussels cultured in a Galician Ria. Different proxies for high-quality food (including C-BPC) vs. energy absorbed by mussels were explored to elucidate the validity of each proxy in an embayment of intensive mussel cultivation. Our results showed a strong correlation between C-BPC and both the organic fraction ( f ) and the carbon equivalent of Chloropyll- a (C-Chl- a ) in the seston. This fact points to variations in C-BPC (predominantly composed of proteins) are strongly linked with the phytoplankton fluctuations, which in turn are modulated by the seasonal upwelling regime. Maximum total energy absorbed by mussels (about 97%) occurred during the spring phytoplankton bloom, when high-quality organic carbon (high C-BPC) dominated the seston. Minimum energy absorbed (56%) occurred during winter, when continental runoff and local resuspension of surface sediments reintroduce into the water column more refractory organic compounds not favourable to the mussel diet. These results allowed us to establish that parameters such as f , C-Chl- a , and C-BPC have close correlations with physiological responses in mussels and could be used as proxies for food quality. Nonetheless, the use of these high-quality food estimations should be considered according to particularities of each ecosystem. [ABSTRACT FROM AUTHOR]

The growth and metabolic profile of the red seaweed Kappaphycus alvarezii were evaluated after in vitro cultivation with effluents from Pacific shrimp Litopenaeus vannamei farming in bioflocs system (BFT) and commercial extract of the brown seaweed Ascophyllum nodosum (AMPEP). Seaweeds were cultivated for 35 days in sterilized seawater enriched with 50% von Stosch solution (VS – v/v), 25% BFT effluent (BFT – v/v), or pulse-fed AMPEP (at 0.1 g L − 1 for 30 min), and combinations of VS and AMPEP (VS + AMPEP) and BFT and AMPEP (BFT + AMPEP). As control, seedlings cultivated in sterilized seawater were used. K. alvarezii from VS and BFT showed significant higher growth rates, i.e., 1.70 ± 0.14% day − 1 and 1.56 ± 0.08% day − 1 , respectively, while control (0.51 ± 0.05% day − 1 ) and AMPEP (0.57% ± 0.07% day − 1 ) showed lower growth rates. However, in all treatments, "ice-ice" disease was observed in some parts of the thalli. Total phenolic content (92.2 ± 22.4 μg g − 1 ) and flavonoids (18.8 ± 0.6 μg g − 1 ) were higher in BFT, and seedlings cultivated in BFT + AMPEP showed higher carotenoid content (239.3 ± 9.3 μg g − 1 ). Higher DPPH radical inhibition was observed in VS (13.4 ± 1.5%) and VS + AMPEP (13.4 ± 0.6%). Results showed that all treatments affected K. alvarezii growth and secondary metabolism, particularly BFT, which could be consider as a good fertilizer of this species improving also the add-value, because of the increase of phenolics, flavonoids and carotenoids. Statement of relevance This work presents the potential use of effluents from shrimp cultivation as fertilizers of the Kappaphycus alvarezii , improving the growth and the bioactive compounds production. [ABSTRACT FROM AUTHOR]

We present a comprehensive analysis of estimation of fisheries Maximum Sustainable Yield (MSY) reference points using an ecosystem model built for Mille Lacs Lake, the second largest lake within Minnesota, USA. Data from single-species modelling output, extensive annual sampling for species abundances, annual catch-survey, stomach-content analysis for predatory-prey interactions, and expert opinions were brought together within the framework of an Ecopath with Ecosim (EwE) ecosystem model. An increase in the lake water temperature was observed in the last few decades; therefore, we also incorporated a temperature forcing function in the EwE model to capture the influences of changing temperature on the species composition and food web. The EwE model was fitted to abundance and catch time-series for the period 1985 to 2006. Using the ecosystem model, we estimated reference points for most of the fished species in the lake at single-species as well as ecosystem levels with and without considering the influence of temperature change; therefore, our analysis investigated the trophic and temperature effects on the reference points. The paper concludes that reference points such as MSY are not stationary, but change when (1) environmental conditions alter species productivity and (2) fishing on predators alters the compensatory response of their prey. Thus, it is necessary for the management to re-estimate or re-evaluate the reference points when changes in environmental conditions and/or major shifts in species abundance or community structure are observed. [ABSTRACT FROM AUTHOR]

Quantitative recruitment of ichthyofauna into a South African temporarily open/closed estuary (TOCE) was investigated during three distinct hydrological phases: closed overwash, open outflow and tidal mouth conditions. Maximum recruitment densities occurred during outflow conditions and declined when the system became tidally inundated. Recruitment densities were lowest during overwash events. Selective diel variation was evident, with higher night-time densities for each phase. This study highlights the importance of seasonal timing and duration of open conditions and overwash events for structuring ichthyofaunal community composition of southern African TOCEs. [ABSTRACT FROM PUBLISHER]

Although stable isotope analysis is a powerful tool for determining animal diets, migration patterns, and the structure of food webs in aquatic systems, the slow response of isotopic ratios in the traditionally used muscle tissue of fishes often hampers this approach. By analyzing tissues with more rapid isotopic change, this technique can be used over a finer time scale than traditional isotopic analyses. We conducted a diet-switch experiment to compare changes in the stable carbon and nitrogen isotope ratio values ( δ C and δ N, respectively) in epidermal mucus, fin and muscle tissues of three species of freshwater cyprinid fishes. The half-life of the isotopic change ranged from 62 to 144 days in mucus, 57 to 202 days in fin, and 196 to 680 days in the muscle tissue. The isotope ratios in mucus changed more rapidly than those in muscle tissues in the three species examined, similarly to the previously studied three species (catfish, steelhead, freshwater goby), whereas fin showed relatively variable trends in isotopic change. Interspecific variation in the trophic discrimination factor (TDF) was particularly large in the δ C values of fin tissue compared with those in the other two tissues. With generally rapid change and relatively invariable TDF, the use of epidermal mucus in isotope analysis instead of the widely used fin and muscle tissues is advantageous for studying short-term changes in food habits of fishes and food web structures. [ABSTRACT FROM AUTHOR]

Billfishes are important fishery resources traded and consumed worldwide. As morphological traits are usually removed during processing, molecular methods are applied to identify billfish products. In this study, the approaches of quantitative real-time PCR were developed to identify the six billfish species (Istiompax indica,Istiophorus platypterus,Kajikia audax,Makaira nigricans,Tetrapturus angustirostrisandXiphias gladius) widely distributed in the north-western Pacific Ocean. The developed singleplex systems showed high fidelities to each of the six species via either examining the ΔCt values or melting curve patterns. For samples containing multiple species, individual species are identifiable by a quantitative real-time PCR assay that includes all the singleplex systems. A multiplex system was also developed to identify unknown samples composed of a single species. The methods developed in this study provide a fast and high-throughput manner to identify the north-western Pacific billfish species when morphological traits are unavailable, such as in processed products. [ABSTRACT FROM AUTHOR]