Fig. 1. Zebrafish free larva at 80 hpf (A) and picture analysis performed. Tail length (A); tail curvature (B1, normal morphology; B2, lordosis—arrow head); pericardial area (C). Scale bar: 0.2 mm.

Fig. 2. Frequency (%) of parameters measured on two populations of developing zebrafish embryos laid by two different genitor groups (Group A, top; Group B, bottom). See text for the measurement procedure. The probability of adequacy between observed values (bars) and theoretical distribution (continuous line: Poisson law; dotted line: Normal law) was estimated with Kolmogorov–Smirnov (KS) and χ² tests. n, number of values; P, probability.

Fig. 3. Normal (A, control) and abnormal development of zebrafish embryos exposed to model toxicants (B, propranolol; C, malathion) for different observation times and different exposure concentrations. C, cyphosis, L, lordosis, POe, pericardial edema, SOe, sac-yolk edema. The dotted line indicates the theoretical straight back axis.

Fig. 4. Major effects of model toxicants on zebrafish embryo development, in relation to exposure concentration. (A) Effect of propranolol on heart rate at 48 hpf (mean±SD). (B) Effect of malathion on frequency of tail deformations (lordosis, cyphosis, and total of impaired embryos). (C) Effect of cadmium on the hatching time (HT₅₀±IC_95%); the symbols are the experimental data (control, white square; Cd treated, black circles) and the dotted line is the logarithmic regression. Same letters indicate no statistically different (ANOVA, Tukey's HSD). The asterisks indicate a significant difference between control (χ²). α0.05.

Overview of the toxic bioassay guidelines based on the early life stage of freshwater fish

The OECD guidelines take into account the OECD members’ related national standards.

Main developmental period of early development of zebrafish and corresponding toxicological endpoints considered

Effects of model toxicants (propranolol, malathion, cadmium) on zebrafish early life stages

The values are the highest tested concentration (μM) without effect on the considered endpoint. —, indicates no-effect at the highest tested concentration (NOEC).

Review of the embryotoxic effects of malathion for fish

T (°C), temperature in Celsius degrees; h/dpf, hours/days postfecundation; EC₅₀, concentration inducing 50% of effect; NOEC, no observable effect concentration; LOEC, lowest observable effect concentration; effect concentration; , increase; , decrease.