Testing a simple energy-budget model for yolk-feeding stages of cleaner fish

The use of cleaner fish is an environmentally-friendly approach to combat the salmon louse, threatening commercial salmon farming. Dynamic Energy Budget (DEB) modelling helps understand the bioenergetics of early life stages of the cleaner fish, and can thereby aid optimisation of their culturing. Here, we report on our attempts to parametrise DEBkiss models for the yolk-feeding stages of two cleaner fish species, ballan wrasse (Labrus bergylta) and lumpfish (Cyclopterus lumpus). A range of measurements was taken over early development, including biometry (using imaging), weight and composition, as well as measurements of respiration rate. Despite the previous success of applying the DEBkiss model to early life stages of Atlantic cod, the model failed to capture the patterns of yolk depletion for ballan wrasse. The main issues were related to substantial changes in the water content of both yolk and structure over development, and a stop of growth before disappearance of the yolk sac. These issues require further experimental work to address, especially more efficient proxies for the dry mass of yolk and structure, such that these compartments can be efficiently separated. Nevertheless, apart from the pattern of yolk depletion, the model provides a reasonable explanation of all traits simultaneously. This indicates that model modifications may only need to be minor. For lumpfish, the data set was quite limited for testing of the DEBkiss model, due to the opacity of the egg and the fact that there was only one time point with measurements post hatch. Nevertheless, the data are consistent with the model. The modelling results indicate that both cleaner-fish species may have very similar bioenergetic parameters (and quite similar to Atlantic cod as well); the conspicuous difference in early life history may be mainly caused by the larger yolk provisioning in the egg, and late hatching, in lumpfish. The DEBkiss model is a simple and promising tool for bioenergetics of fish early-life stages. However, its application and in-depth testing is currently limited by the difficulties of obtaining detailed measurements on these life stages.publishedVersio

Automated, high-throughput measurement of size and growth curves of small organisms in well plates

Organism size and growth curves are important biological characteristics. Current methods to measure organism size, and in particular growth curves, are often resource intensive because they involve many manual steps. Here we demonstrate a method for automated, high-throughput measurements of size and growth in individual aquatic invertebrates kept in microtiter well-plates. We use a spheroid counter (Cell 3iMager, cc-5000) to automatically measure size of seven different freshwater invertebrate species. Further, we generated calibration curves (linear regressions, all p =0.9 for Ceriodaphnoa dubia, Asellus aquaticus, Daphnia magna, Daphnia pulex; r 2 >=0.8 for Hyalella azteca, Chironomus spec. larvae and Culex spec. larvae) to convert size measured on the spheroid counter to traditional, microscope based, length measurements, which follow the longest orientation of the body. Finally, we demonstrate semi-automated measurement of growth curves of individual daphnids (C. dubia and D. magna) over time and find that the quality of individual growth curves varies, partly due to methodological reasons. Nevertheless, this novel method could be adopted to other species and represents a step change in experimental throughput for measuring organisms’ shape, size and growth curves. It is also a significant qualitative improvement by enabling high-throughput assessment of inter-individual variation of growth

Predicting mixture effects over time with toxicokinetic–toxicodynamic models (GUTS): assumptions, experimental testing, and predictive power

Current methods to assess the impact of chemical mixtures on organisms ignore the temporal dimension. The General Unified Threshold model for Survival (GUTS) provides a framework for deriving toxicokinetic–toxicodynamic (TKTD) models, which account for effects of toxicant exposure on survival in time. Starting from the classic assumptions of independent action and concentration addition, we derive equations for the GUTS reduced (GUTS-RED) model corresponding to these mixture toxicity concepts and go on to demonstrate their application. Using experimental binary mixture studies with Enchytraeus crypticus and previously published data for Daphnia magna and Apis mellifera, we assessed the predictive power of the extended GUTS-RED framework for mixture assessment. The extended models accurately predicted the mixture effect. The GUTS parameters on single exposure data, mixture model calibration, and predictive power analyses on mixture exposure data offer novel diagnostic tools to inform on the chemical mode of action, specifically whether a similar or dissimilar form of damage is caused by mixture components. Finally, observed deviations from model predictions can identify interactions, e.g., synergism or antagonism, between chemicals in the mixture, which are not accounted for by the models. TKTD models, such as GUTS-RED, thus offer a framework to implement new mechanistic knowledge in mixture hazard assessments

Effects of marine mine tailing exposure on the development, growth, and lipid accumulation in Calanus finmarchicus

Marine tailing disposal (MTD) is sometimes practiced as an alternative to traditional mine tailing deposition on land. Environmental challenges connected to MTD include spreading of fine particulate matter in the water column and the potential release of metals and processing chemicals. This study investigated if tailing exposure affects the marine copepod Calanus finmarchicus, and whether effects are related to exposure to mineral particles or the presence of metals and/or processing chemicals in the tailings. We investigated the impacts of three different tailing compositions: calcium carbonate particles with and without processing chemicals and fine-grained tailings from a copper ore. Early life stages of C. finmarchicus were exposed over several developmental stages to low and high suspension concentrations for 15 days, and their development, oxygen consumption and biometry determined. The data was fitted in a dynamic energy budget (DEB) model to determine mechanisms underlying responses and to understand the primary modes of action related to mine tailing exposure. Results show that copepods exposed to tailings generally exhibited slower growth and accumulated less lipids. The presence of metals and processing chemicals did not influence these responses, suggesting that uptake of mineral particles was responsible for the observed effects. This was further supported by the applied DEB model, confirming that ingestion of tailing particles while feeding can result in less energy being available for growth and development.publishedVersio

Linking toxicant physiological mode of action with induced gene expression changes in Caenorhabditis elegans

Background Physiologically based modelling using DEBtox (dynamic energy budget in toxicology) and transcriptional profiling were used in Caenorhabditis elegans to identify how physiological modes of action, as indicated by effects on system level resource allocation were associated with changes in gene expression following exposure to three toxic chemicals: cadmium, fluoranthene (FA) and atrazine (AZ). Results For Cd, the physiological mode of action as indicated by DEBtox model fitting was an effect on energy assimilation from food, suggesting that the transcriptional response to exposure should be dominated by changes in the expression of transcripts associated with energy metabolism and the mitochondria. While evidence for effect on genes associated with energy production were seen, an ontological analysis also indicated an effect of Cd exposure on DNA integrity and transcriptional activity. DEBtox modelling showed an effect of FA on costs for growth and reproduction (i.e. for production of new and differentiated biomass). The microarray analysis supported this effect, showing an effect of FA on protein integrity and turnover that would be expected to have consequences for rates of somatic growth. For AZ, the physiological mode of action predicted by DEBtox was increased cost for maintenance. The transcriptional analysis demonstrated that this increase resulted from effects on DNA integrity as indicated by changes in the expression of genes chromosomal repair. Conclusions Our results have established that outputs from process based models and transcriptomics analyses can help to link mechanisms of action of toxic chemicals with resulting demographic effects. Such complimentary analyses can assist in the categorisation of chemicals for risk assessment purposes

A biology-based approach for quantitative structure-activity relationships (QSARs) in ecotoxicity.

Quantitative structure-activity relationships (QSARs) for ecotoxicity can be used to fill data gaps and limit toxicity testing on animals. QSAR development may additionally reveal mechanistic information based on observed patterns in the data. However, the use of descriptive summary statistics for toxicity, such as the 4-day LC50 for fish, introduces bias and ignores valuable kinetic information in the data. Biology-based methods use all of the toxicity data in time to derive time-independent and unbiased parameter estimates. Such an approach offers whole new opportunities for mechanism-based QSAR development. In this paper, we apply the hazard model from DEBtox to analyse survival data for fathead minnows (Pimephales promelas). Different modes of action resulted in different patterns in the parameter estimates, and therefore, the toxicity data by themselves reveal insight into the actual mechanism of toxic action

Interpreting toxicity data in a DEB framework: A case study for nonylphenol in the marine polychaete Capitella teleta

Dynamic Energy Budget (DEB) theory provides a powerful framework for interpreting toxicity data, but is not broadly applied in ecotoxicology yet. One of the reasons is the fact that estimation of DEB parameters from experimental data is certainly not a trivial affair. Almost every data analysis raises new questions, which require the formulation of specific mechanistic hypotheses. These hypotheses should be translated into model adaptations, which can subsequently be tested on the data set. In this paper, we demonstrate this procedure by analyzing a case study for ecotoxicity within the DEB framework. The case study we selected is a previously published data set for 4-n-nonylphenol in the polychaete worm Capitella teleta (formerly Capitella sp. I). Particular aspects of interest in this study are an apparent slow initial growth, and low-dose stimulation (hormesis) of growth and reproduction. In this publication, we explicitly discuss our deviations from the standard DEB model in terms of the underlying hypotheses, the existence of alternative hypotheses to explain the data, and how limited additional experiments can be designed to decide between alternative explanations. © 2011 Elsevier B.V