The following recommendations may be applied to all diseases, their agents, and susceptible species as listed in the Aquatic Manual, and are designed to assist with the development of surveillance methodologies. Where possible, the development of surveillance systems using these recommendations should be based on the relevant information in the individual disease chapters in the Aquatic Manual. These recommendations are also applicable to non-listed diseases that may be of importance to a country or region, such as new or emerging diseases. There is sometimes a perception that surveillance can only be conducted using sophisticated methodologies. However, an effective surveillance system can also be developed by making use of gross observations and already available resources.