EFFECT OF BIOFLOC ON INFECTION OF TILAPIA FINGERLINGS BY PARASITES
Infection of fish by parasites (protozoa and different worms) may be a severe problem for producers. Controlling and confronting infections often involves the use of chemicals, often affecting the pond environment.
We report here on a study comparing triplicated nursery systems: control treatment using high water exchange and relatively clear water and biofloc treatment using minimal water exchange and low protein feed. 51,000 fingerlings, 1 g. each were stocked into 80 m3 concrete ponds.
A rather severe infection with different parasites (The most common Sessilina, Dactylogyrus, Centrcestus, Trichdina) was detected 12 days following stocking in all ponds. All ponds were treated with Formalin and Bromex.
There-after, the degree of infestation by parasites was followed. Randomly selected samples of fingerlings were sent to the governmental veterinary diagnostic laboratory. Prevalence of the different parasites externally or on the gills was evaluated microscopically. The extent of infections was characterized by 6 grades, from clean to extremely heavy infestation. In order to semi-quanitize the results we gave the clean and the extremely low infestation ponds a value of zero while all higher infestation degrees were given values of one. The standardized degree of infestation was defined as the sum of infestation by the individual parasites grade and the sum of external or gills infestations.
The potential effects of biofloc systems was clearly demonstrated (see table below).
More research on the means to use this effect and on the mechanisms involved is needed.