Modbus serial has 2 flavors - RTU & ASCII. The main body consists of RTU address, Function code, start address, data quantity, data. The pre-emble & post-emble to the main body differs between RTU & Ascii.
Modbus TCP has 2 flavors also. It is obviously on Ethernet. In more popular MBTCP version - The main body is same. The pre-emble & postemble are different. In less popular version the serial message is packed into the TCP packet envelope.