Vantablack absorbs up to 99.96% and the species of fish absorbs 99.95%. They must be talking about certain cells or pigments rather than the entire fish since they do not appear ultra-black in the images I see.
Found in the paper:
> We used a back-reflectance probe calibrated to a 2% diffuse reflectance standard to measure the reflectance at perpendicular incidence from the blackest undamaged patches of skin.
Found in the paper:
> We used a back-reflectance probe calibrated to a 2% diffuse reflectance standard to measure the reflectance at perpendicular incidence from the blackest undamaged patches of skin.