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The aim of this study was to determine the effects of silver nanoparticles (AgNPs; speciation: NM-300 K) in the lab on the behavior of larvae in European Whitefish (Coregonus lavaretus), a relevant model species for temperate aquatic environments during alternating light and darkness phases. The behavioral parameters measured included activity, turning rate, and distance moved. C. lavaretus were exposed to AgNP at nominal concentrations of 0, 5, 15, 45, 135, or 405 µg/L (n = 33, each) and behavior was recorded using a custom-built tracking system equipped with light sources that reliably simulate light and darkness. The observed behavior was analyzed using generalized linear mixed models, which enabled reliable detection of AgNP-related movement patterns at 10-fold higher sensitivity compared to recently reported standard toxicological studies. Exposure to 45 µg/L AgNPs significantly resulted in hyperactive response patterns for both activity and turning rates after an illumination change from light to darkness suggesting that exposure to this compound triggered escape mechanisms and disorientation-like behaviors in C. lavaretus fish larvae. Even at 5 µg/L AgNPs some behavioral effects were detected, but further tests are required to assess their ecological relevance. Further, the behavior of fish larvae exposed to 135 µg/L AgNPs was comparable to the control for all test parameters, suggesting a triphasic dose response pattern. Data demonstrated the potential of combining generalized linear mixed models with behavioral investigations to detect adverse effects on aquatic species that might be overlooked using standard toxicological tests. [ABSTRACT FROM AUTHOR]

Zebrafish larvae (Danio rerio) are among the most used model species to test biological effects of different substances in biomedical research, neuroscience and ecotoxicology. Most tests are based on changes in swimming activity of zebrafish larvae by using commercially available high-throughput screening systems. These systems record and analyse behaviour patterns using visible (VIS) and near-infrared (NIR) light sources, to simulate day (VIS) and night (NIR) phases, which allow continuous recording of the behaviour using a NIR sensitive camera. So far, however, the sensitivity of zebrafish larvae to NIR has never been tested experimentally, although being a critical piece of information for interpreting their behaviour under experimental conditions. Here, we investigated the swimming activity of 96 hpf (hours post fertilization) and 120 hpf zebrafish larvae under light sources of NIR at 860 nm and at 960 nm wavelength and under VIS light. A thermal source was simultaneously presented opposite to one of the light sources as control. We found that zebrafish larvae of both larval stages showed a clear negative phototactic response towards 860 nm NIR light and to VIS light, but not to 960 nm NIR light. Our results demonstrated that zebrafish larvae are able to perceive NIR at 860 nm, which is almost identical to the most commonly used light source in commercial screening systems (NIR at 850 nm) to create a dark environment. These tests, however, are not performed in the dark from the zebrafish´s point of view. We recommend testing sensitivity of the used test organism before assuming no interaction with the applied light source of commonly used biosensor test systems. Previous studies on biological effects of substances to zebrafish larvae should be interpreted with caution. [ABSTRACT FROM AUTHOR]