Fig 1.
Scheme of the experimental set-up of the NIR light experiments.
(A) The custom-built computer vision system shows the position of the test vessel in the middle of the set-up, the camera above the test vessel and the position of the light sources. The computer vision system was totally covered so that no light from the surrounding area could enter the system. (B) A detailed view of the set-up: For each experiment, one larva was placed into the test vessel. The IR sensitive camera was set 35 cm above the vessel, and both light sources were 10.5 cm away from the test vessel. A thermal source opposite to the NIR/VIS light served as a control. We switched the position of light and thermal sources after each trial to exclude side biases. The vessel was divided into 2 halves with an imaginary line, one half illuminated by the light source (VIS/NIR), one half radiated by the thermal source (control side) (drawing of zebrafish larva by Kimmel et al. 1996 [12]).
Table 1.
Spectral characteristics of the used light sources (VIS, NIR 860 nm and NIR 960 nm) for phototactic experiment.
Fig 2.
Swimming activity [%] of 96 hpf (blue circles) and 120 hpf (red triangles) zebrafish larvae under different light sources.
The x-axis indicates the three tested light sources and the y-axis shows the swimming activity (%) of the zebrafish larvae. Shown are mean ± standard error. Sample size in each experiment: N = 30. ***P < 0.001. (VIS = visible light (blue-white-light, 440–700 nm, 860 nm = NIR light with peak illumination at 860 nm; 960 nm = NIR light with peak illumination at 960 nm).
Fig 3.
Mean allocation time [s] of both larval stages of zebrafish larvae under different light conditions.
Bars present mean allocation time [s] ± standard error (which sum up to 150 s) of zebrafish larvae (A: 96 hpf, B: 120 hpf) in halves of vessels illuminated with NIR light (white bars) and radiated by the thermal control (dark grey bars) (N96hpf/VIS = 3, N96hpf/860 nm = 20, N96hpf/960 nm = 22, N120hpf /VIS = 20, N120hpf /860 nm = 28, N120hpf /960 nm = 28). The x-axis represents the wavelengths of the three different used light sources (VIS (440–700 nm), 860 nm; 960 nm) and asterisks indicate significant differences compared to thermal control (**P < 0.01, ***P < 0.001, n.s. = not significant).
Fig 4.
Sector diagram of allocation preference for 96 hpf zebrafish.
The blue bars represent the mean allocation time [%] of zebrafish larvae in the test vessel under VIS light (A), NIR light at 860 nm (B) and under NIR light at 960 nm (C). The diagram is divided into 24 sectors, whereby each sector illustrates 15° (Left side: N96hpf/VIS = 2, N96hpf/860 nm = 10, N96hpf/960 nm = 9; Right side: N96hpf/VIS = 1, N96hpf/860 nm = 12, N96hpf/960 nm = 11; except larvae below 20% activity threshold).
Fig 5.
Sector diagram of allocation preference for 120 hpf zebrafish.
The blue bars represent the mean allocation time [%] of zebrafish larvae in the test vessel under VIS light (A), NIR light at 860 nm (B) and under NIR light at 960 nm (C). The diagram is divided into 24 sectors, whereby each sector illustrates 15° (Left side: N120hpf/VIS = 10, N120hpf/860 nm = 15, N120hpf/960 nm = 15; Right side: N120hpf/VIS = 10, N120hpf/860 nm = 13, N120hpf/960 nm = 13; except larvae below 20% activity threshold).
Table 2.
Length of the mean directional vector R. Missing data result from activity level below threshold (for sample size see Figs 4 and 5).
Table 3.
Mean temperature [°C] ± standard deviation of the used light sources (N = 30) and the temperature differences between the thermal source and the light source.