Abstract:
Ornamental fish industry in Sri Lanka plays an important role as a national income
generating source. Sailfin Molly is an indigenously bred exotic ornamental fish
species which is produced in Sri Lanka. It is documented that hardness of water
affects the growth rate of Sailfin Molly. Therefore, present study aimed to
determine whether the total harness value of natural waters of Sri Lanka affects the
growth rate of-Sailfin Molly, and to determine the hardness level that shows the
optimum growth rate of the fish. A three series of water samples which contained
different total hardness values were prepared using three different natural water
sources (K = Kanchikulama, G = Galgamuwa, M = Muruthawela). Series of water
samples were made by diluting the natural water source by dechlorinized tap water.
The series of water samples with different total hardness values were G l, G2, G3,
G4, Kl, K2, K3 and Ml (Gl = 368.6 ppm, G2 & K1 = 292 ppm, G3 & K2 = 150
ppm, G4, K3, & Ml - 36 ppm). Four replicates were used for each hardness level.
Five fingerlings were kept in each replicate. Amount of food was adjusted weekly
as 5% of the body weight. Total length, and weight were measured weekly, and
growth rate was calculated. Experimental was divided into two major phases. First
phase was a period of 0 - 21 days which was the fingerling stage. Second phase
was a period of 74 - 130 days which was a more mature stage.
It was observed that the growth rate of fishes in Gl, G2, G3, and G4 water samples
are significantly different in both phases (01 & 02). Also growth rate of fishes in
Kl, K2 and K3 water samples have no any significant difference in both phases (01
& 02). Considering growth rate of fishes m all the water samples which were
prepared from three natural water bodies were not significantly different in phase
01, but has significance in phase 02 for growth rate by weight. It was also found
that there is a significant difference between the growth of fish reared in G3, and
K2 (same harness level) in phase 02 for growth rate by weight. Fishes in Gl
sample has obtained the maximum total length increase, and Ml has obtained the
maximum weight gain during the 18 weeks of study period. This study also shows
the growth rate of fishes are significantly different in phase 02 for the growth rate
by weight, among all the water samples studied. Weight is a better measurement
for calculate the growth rate of Sailfin Molly.
According to the present study, significant difference found in Gl, G2, G3 and G4
sample series indicate that different concentration of an intrinsic factor (probably
bivalent cations) may have affected on growth rate.
