The amphibious teleost Giant mudskipper (Periophthalmodon schlosseri, Pallas 1770) inhabit
muddy plains and Asian mangrove forests. It spends more than 90% of its life outside of the
water, using its skin, gills, and buccal-pharyngeal cavity mucosa to breathe in oxygen from the
surrounding air. All vertebrates have been found to have mast cells (MCs), which are part of the
innate immune system. These cells are mostly found in the mucous membranes of the organs that
come in contact with the outside environment. According to their morphology, MCs have distinctive
cytoplasmic granules that are released during the degranulation process. Additionally, these cells
have antimicrobial peptides (AMPs) that fight a variety of infections. Piscidins, hepcidins, defensins,
cathelicidins, and histonic peptides are examples of fish AMPs. Confocal microscopy was used in this
study to assess Piscidin1 expression in Giant Mudskipper branchial MCs. Our results demonstrated
the presence of MCs in the gills is highly positive for Piscidin1. Additionally, colocalized MCs labeled
with TLR2/5-HT and Piscidin1/5-HT supported our data. The expression of Piscidin1 in giant
mudskipper MCs highlights the involvement of this peptide in the orchestration of teleost immunity,
advancing the knowledge of the defense system of this fish.