EFFECTS OF DIFFERENT SALINITIES ON SURVIVAL, OSMOLALITY, AND BLOOD CHARACTERISTIC OF JUVENILE RABBITFISH Siganus guttatus
As a euryhaline species, rabbitfish tolerant to wide of salinity. However, it is important to determine the salinity range where rabbitfish can survive and grow normally. This study aimed to determin the effects of different salinities on growth and stress levels of juvenile rabbitfish S. guttatus.
The treatments were eight different salinities which were 5 ppt (A), 10 ppt (B), 15 ppt (C), 20 ppt (D), 25 ppt (E), 30 ppt (F), 35 ppt (G) and 40 ppt (H). Juvenile of rabbitfish with mean body weight of 18.8
5.5 g were used as tested fish. Each salinity was adjusted either by diluting seawater with freshwater or by evaporating it to obtain high salinity of 35 and 40 ppt. Twenty aquaria with capacity of 20 L were used to accomodate the 8 salinities as the treatments with triplicates. Juvenile of rabbitfish were stocked with density 5 ind./aquarium. The observed variables were body colour changes, plasma osmolality, blood leucocryte and hematocrite, survival, and growth.
After 14 days observation, the results showed that only one fish dead in G groups . Body colour of the fish did not much change from bright white yellowish to dark in C and D groups, compare to other 6 groups. Osmolality plasma increased by increasing the sanility up to 35 ppt and further decreased at the highest salinity of 40 ppt. The lowest osmolality was found in A group which was 357.7 mOsm/kg and the highest was 77.7 mOsm/kg observed in G group. Plasma osmotic rates of fish reared in 5 and 10 ppt was hiperosmotic while fish reared in 15 to 40 ppt was hypoosmotic (Table 1).
Salinity also affected the leukocrite and hematocrite where the lowest percentage of leukocrite was found in H group which was 64.09 ± 5.97% and the highest percentage was at C group (75.62 ± 10.54%) (Fig. 1).
Based on survival rate, juvenile rabbitfish can tolerate salinity of 5 to 40 ppt but the osmolality condition is approaching isotonic in 10-15 salinity.