Section 7. In the executive office shall be an office of the secretary, a department of environmental protection, a department of conservation and recreation, a department of agricultural resources, a department of fish and game, a department of public utilities, and a department of energy resources. Each department shall be headed by a commissioner. Each commissioner shall be appointed and may be removed by the secretary, with the approval of the governor. Each commissioner shall be a person of skill and experience in the field of his appointment. The commissioner of each department may adopt reasonable regulations to allow those employees within his department to testify in civil proceedings so as to further the performance of the department’s business. The commissioner of each department shall appoint all necessary employees within his department, except as may be otherwise provided by law. The positions of commissioner shall not be subject to the provisions of chapter thirty-one or section nine A of chapter thirty. Each commissioner shall perform such functions as may be assigned to him by the secretary and shall devote his full time during business hours to the duties of his position. In case of a vacancy or an emergency, the secretary may appoint a person as acting commissioner for a period not exceeding six months, of any of the above departments, provided, the appointee is a person of skill and experience in the field of his appointment. The positions of the commissioners shall be classified in accordance with section forty-five of chapter thirty and the salaries shall be determined in accordance with section forty-six C of said chapter thirty.