Gavage has been used for many years in mammalian toxicology and experimental animal biology, as a direct oral administration method. It has the advantage of providing an exact dosage per body weight; however, gavage is not considered applicable to small fish like zebrafish (Danio rerio), owing to the difficulty associated with handling. In this study, a new gavage method for zebrafish was developed to minimize stress and damage to their digestive tracts, without the need for anesthesia. This device allows us to hold the zebrafish firmly in a predetermined position without directly touching them. This method involves holding the fish with a novel device and uses a specific syringe for dosing the test substance into the digestive organs. An acute oral toxicity test of potassium dichromate was conducted in adult zebrafish to demonstrate the new gavage method. No mortality was observed in the vehicle (water) control group. Furthermore, the median lethal dose (LD₅₀) values of potassium dichromate in male and female zebrafish were 103 and 195 mg/kg body weight, respectively. These values are directly comparable to the values in rats.