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Fig. 4. Double immunolabelling of serotonin (5-HT, green) and synaptic vesicles
(SV2, red) along a single gill filament with multiple lamellae in (A) O.
mykiss, (B) C. auratus, (C) H. lacerdae and (D) H.
malabaricus. Scale bars, 100 µm. Colocalization appears yellow.
Arrowheads indicate non-5-HT-IR but SV2-IR cells and arrows indicate
non-SV2-IR but 5-HT-IR cells.