Gill slit fistulas are caused by abnormal fusion of the gill grooves, resulting in incomplete closure, and patients are advised to seek prompt medical attention. Gill slit fistula, including the 1st, 2nd, 3rd and 4th gill slit fistula, are caused by the fusion process of the corresponding gill groove is abnormal, resulting in incomplete closure, such as the 1st gill slit fistula is caused by the 1st and 2nd gill arches are not fused properly, the 2nd gill slit fistula is caused by the 2nd gill groove is incomplete closure of gill groove is the ectodermal depression of the gill organ in the embryonic period. The main symptom of gill slit fistula is intermittent or persistent secretion overflow from the external fistula, and some patients may be conscious of bad breath, the disease can be secondary to infection, manifested as purulent secretion overflow from the fistula, redness, swelling and pain around the fistula. Patients with gill slit fistula should seek medical attention in time, follow the doctor’s instructions for appropriate treatment, generally a better prognosis.