Fish diseases are one of the main bottlenecks in aquaculture, especially in intensive fish farming systems, representing severe annual costs to producers. One of the best ways to control this problem is using a preventive approach, with sc heduled samplings to the areas of fish production. This allows an early detection of pathogenic agents, leading to a decrease in disease incidence, applied treatments and fish mortality. The Aquaculture Research Station from the Portuguese Institute for th e Ocean and Atmosphere (EPPO-IPMA) is a government facility with a marine fish hatchery and semi-intensive earthen ponds. This implies different disease approaches in each area in the facility.
The fish disease profile at EPPO-IPMA is different in each area of production. This implies that, even if we use preferentially a preventive approach in disease management, the scheduling and type of sampling will take into account the production area (hatchery: marine fish broodstock and larvae, earthen ponds: juv eniles and adults), water temperature, rearing system, tides and the critical periods of disease that can affect the fish species that are produced. For example, in an earthen pond for fish grow out, the main objective of the sampling is to ass ess the fish ectoparasitological load. Therefore, the periodicity and intensity of sampling is modulated regarding the parasitic load in fishes, that is higher in summer when the temperatures and the probability of ectoparasites occurrence are high due to faster population growth . But at larvae stages, the priority is checking the ultraviolet system for the bacterial presence in the water before egg incubation and larval rearing. In this case, the periodicity of sampling will be determined by the larvae phase (depletion of yolk sac, changes from live to inert food, etc). Regular bacterial surveys are also performed to live feed (rotifers and artemia).
Even with th is preventive approach, disease outbreaks can occur in the EPPO-IPMA facilities. In the presence of a fish disease outbreak, a holistic pathological analysis of a fish sample is performed, that includes ecto and endoparasitological analysis, microbiological analyses of liver, spleen and anterior kidney and histological analysis of the different organs of the fish. This allows the detection of possible pathogenic agents. If the fish disease was caused by pathogenic bacteria, antibiogram tests will be performed, and the bacteria will be identified by traditional biochemical methods or molecular techniques. We can also perform molecular identification of parasites.
These approaches allowed us not only to decrease fish loss caused by diseases, but also improve the knowledge of some diseases and fish welfare at EPPO-IPMA facilities, providing also useful information that could be transferred to the aquaculture industry.
This research was funded by project SAÚDE&AQUA (MAR-02.05.01-FEAMP-0009) and DIVERSIAQUA II (MAR2020-P02M01-0656P). M. Moreira was supported by and FCT grant (SFRH/BD/118601/2016).