Estimation of Fish Biomass Using Environmental DNA

Environmental DNA (eDNA) from aquatic vertebrates has recently been used to estimate the presence of a species. We hypothesized that fish release DNA into the water at a rate commensurate with their biomass. Thus, the concentration of eDNA of a target species may be used to estimate the species biomass. We developed an eDNA method to estimate the biomass of common carp (Cyprinus carpio L.) using laboratory and field experiments. In the aquarium, the concentration of eDNA changed initially, but reached an equilibrium after 6 days. Temperature had no effect on eDNA concentrations in aquaria. The concentration of eDNA was positively correlated with carp biomass in both aquaria and experimental ponds. We used this method to estimate the biomass and distribution of carp in a natural freshwater lagoon. We demonstrated that the distribution of carp eDNA concentration was explained by water temperature. Our results suggest that biomass data estimated from eDNA concentration reflects the potential distribution of common carp in the natural environment. Measuring eDNA concentration offers a non-invasive, simple, and rapid method for estimating biomass. This method could inform management plans for the conservation of ecosystems

Global patterns of conservation research importance in different countries of the world

Conservation research is essential to help inform the science-based management of environments that support threatened and endangered wildlife; however, research effort is not necessarily uniform across countries globally. Here, we assessed how the research importance of conservation is distributed globally across different countries and what drives this variation. Specifically, we compared the number of conservation/ecological articles versus all scientific articles published for each country in relation to the number of endangered species, the protection status and number of ecosystems, and the economic status of each country (gross domestic product (GDP) per capita). We observed a significant and positive relationship between the proportion of conservation and ecology articles to all scientific articles with respect to the number of endangered species and the proportion of endangered species that are protected in a country, as well as GDP per capita. In conclusion, knowledge about the conservation and economic status of countries should be accounted for when predicting the research importance of conservation and ecology

Trophic Position and Metabolic Rate Predict the Long- Term Decay Process of Radioactive Cesium in Fish: A Meta-Analysis

Understanding the long-term behavior of radionuclides in organisms is important for estimating possible associated risks to human beings and ecosystems. As radioactive cesium ( 137 Cs) can be accumulated in organisms and has a long physical halflife, it is very important to understand its long-term decay in organisms; however, the underlying mechanisms determining the decay process are little known. We performed a meta-analysis to collect published data on the long-term 137 Cs decay process in fish species to estimate biological (metabolic rate) and ecological (trophic position, habitat, and diet type) influences on this process. From the linear mixed models, we found that 1) trophic position could predict the day of maximum 137 Cs activity concentration in fish; and 2) the metabolic rate of the fish species and environmental water temperature could predict ecological half-lives and decay rates for fish species. These findings revealed that ecological and biological traits are important to predict the long-term decay process of 137 Cs activity concentration in fish

Using environmental DNA to estimate the distribution of an invasive fish species in ponds.

Knowledge of the presence of an invasive species is critical to monitoring the sustainability of communities and ecosystems. Environmental DNA (eDNA), DNA fragments that are likely to be bound to organic matters in the water or in shed cells, has been used to monitor the presence of aquatic animals. Using an eDNA-based method, we estimated the presence of the invasive bluegill sunfish, Lepomis macrochirus, in 70 ponds located in seven locales on the Japanese mainland and on surrounding islands. We quantified the concentration of DNA copies in a 1 L water sample using quantitative real-time polymerase chain reaction (qPCR) with a primer/probe set. In addition, we visually observed the bluegill presence in the ponds from the shoreline. We detected bluegill eDNA in all the ponds where bluegills were observed visually and some where bluegills were not observed. Bluegills were also less prevalent on the islands than the mainland, likely owing to limited dispersal and introduction by humans. Our eDNA method simply and rapidly detects the presence of this invasive fish species with less disturbance to the environment during field surveys than traditional methods

An application of PCR-RFLP species identification assay for environmental DNA detection

Recent advancement of environmental DNA (eDNA) methods for surveying species in aquatic ecosystems has been used for various organisms and contributed to monitoring and conservation of species and environments. Amphibians are one of the promising taxa which could be monitored efficiently by applying quantitative PCR (qPCR) or next generation sequencing to eDNA. However, the cost of eDNA detection using these approaches can be quite high and requires instruments that are not usually installed in ecology laboratories. For aiding researchers in starting eDNA studies of amphibians, especially those not specialized in molecular biology, we developed a cost efficient protocol using PCR-RFLP method. We attempted to detect eDNA of three Japanese Rana species (Rana japonica, Rana ornativentris, and Rana tagoi tagoi) in various spatial scales including an area close to the Fukushima nuclear power plant where the environment is recovering after the disaster in 2011. Our PCR-RFLP protocol was successful in detecting Rana species in static water in both laboratory and field; however, it could not detect Rana species in non-static water samples from the field. Even a more sensitive detection method (standard qPCR) was unable to detect frogs in all non-static water samples. We speculate that our new protocol is effective for frogs living in lentic habitats, but not for lotic habitats which may still require the gold standard of field observation for detection approach

Parameter coefficients for log₁₀ half-life of ¹³⁷Cs activity concentration in fish bodies estimated by all stepwised models of GLMM.

<p>The models were selected by a downward stepwise procedure using Akaike Information Criteria (AIC). AIC, AIC differences (Δ<i>i</i>), and Akaike weights (ω<i>i</i>) were shown. Coefficients in bold indicate significant values at the 0.05 level.</p

Illustration of the conceptual decay processes of ¹³⁷Cs activity concentration in fish bodies.

<p>Illustration of the conceptual decay processes of ¹³⁷Cs activity concentration in fish bodies.</p

Presence and non-detection of bluegill sunfish, <i>Lepomis macrochirus</i>, in ponds on the mainland or on surrounding islands based on the detection of environmental DNA (eDNA).

<p>The difference in proportion is significant between the ponds on the mainland and islands (Fisher’s exact test, <i>p</i> = 0.0066).</p

Effects of ecological/biological traits of species on maximum day of ¹³⁷Cs activity concentration in fish.

<p>Effects of a) trophic position of species, b) body mass (g, wet weight) of species, and c) inverse temperature (1/kT) of the environment on log₁₀ maximum day (day) of ¹³⁷Cs activity concentration in fish. Line indicates a significant relationship by the best GLMM, with the coefficient and intercept estimated by GLMM.</p