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Table 2 Criteria for the grading of embryos into normal, mild and severe phenotypes at 48 hpf

From: Methylxanthines induce structural and functional alterations of the cardiac system in zebrafish embryos

Morphological endpoints Normal Mild Severe
Head Flexed Straight Extended
Tail Properly detached and straight Normal length and curved Short length and curved
Anterior-posterior (AP) axis Normal head and tail position AP axis mildly disrupted AP axis not well formed
Yolk Transparent Bigger than control and/or deformed At least double than size of control with necrosis
Heart beat Regular with synchronous contractions Slow or fast Slow or fast with asynchronous contractions
Pericardial edema Absent Mild Moderate to big
Blood circulation Regular and continuous flow Irregular and/or decreased flow Absent flow
Somites V-shaped C-shaped Straight
Chorda Smooth, straight and well demarcated border Tortuous border with bulging Tortuous and not well demarcated border