Fig. 10. Control images of seawater-adapted killifish posterior intestine, where the primary antibody (to killifish cystic fibrosis transmembrane conductance regulator, kfCFTR, in this case) was omitted, showing the absence of the secondary antibody goat anti-mouse IgG Oregon Green 488 signal (green fluorescence). Scale bar, 20 µm. (A) Negative control of kfCFTR. Note the sole presence of the Mitotracker Red stain in the enterocytes and its absence from the goblet cells (asterisk). (B) Green channel fluorescence overlaid with bright field has no detectable green signal from the secondary antibody’s fluorescence, indicating a lack of non-specific binding of the second antibody and of ‘bleed-through’ from the red channel.