EFFECT OF LOADING DENSITY AND TEMPERATURE ON RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) INOCULATED WITH PISCIRICKETTSIA-SALMONIS

Piscirickettsiosis is the most important disease affecting farmed salm onids in Chile since 1989. It is produced by a rickettsial agent named Piscirickettsia salmonis which has been described in all species of s almonids reared in seawater. The effect of water temperature (degrees C) and fish loading density (k/m(3)) on piscirickettsiosis was evaluat ed. Rainbow trout (Oncorhynchus mykiss) (n=300) were inoculated by int raperitoneal injection with P. salmonis (0.2 ml in 10(5.8) TCID50/ml ( LF-89 strain) and divided into three groups (n=100 each one) according to water temperature (8, 14 and 18 degrees C). Subsequently each grou p was divided in two according to loading densities (5 k/m(3) and 20 k /m(3)); 24% cumulative mortality was obtained in the group with highes t density (20 k/m(3)) and 14 degrees C. This was significantly higher than the other groups (p less than or equal to 0.001). These results s uggest that both, temperature and loading density, and their interacti ons, are significant epidemiological factors for the disease.