Abstract:
Pseudetroplus maculatus is an euryhaline fish valued as an ornamental fish worldwide, for its bright
coloration, small size and active swimming behaviour. However, its lower survival rate under captive
conditions has limited its use in Sri Lanka’s aquarium trade. This study was conducted to address the
low survival rates by investigating the effect of water hardness on the breeding and fry rearing of P.
maculatus. The brooders were collected from Kala Oya located in Northwestern province of Sri
Lanka. The effects of water hardness on breeding and fry rearing were examined under four different
hardness levels representing various regions: 35.00 ppm (Kandy), 71.20 ppm (Dambulla – Control),
90.00 ppm (Matara) and 178.00 ppm (Jaffna) each tested in triplicates. Male and female fish were
separately acclimated to the experimental water hardness for two weeks. They were fed with a
commercial diet with crude protein (42.0%), fat (10.0%) and minerals twice daily at a rate of 5% of
body weight. Breeding experiments were conducted using twelve glass tanks (32 L capacity), each
with a substrate of small rocks and sand. Individual pairs were introduced into each breeding tank in
the evening, and breeding trials were carried out in two separate phases. Two fry rearing experiments
were performed with and without parental care in different water hardness levels using a stocking
density of 5fry/L (total 35fry/tank). Postlarvae were fed with egg yolk and Artemia while fry were
offered Artemia and micro worms ad libitum. Growth performance and survival rates of the fry were
monitored over a period of six weeks. No significant difference in breeding success (P > 0.05) was
observed across the different water hardness conditions in both breeding trials. Pre- and post spawning behaviours remained consistent under all experimental conditions. Although water hardness
did not influence fertilization rates or egg hatchability, comparatively higher spawning rates were
recorded at 90 ppm and 178 ppm hardness levels. In the first trial, the highest length (11.1 ± 4.45
mm), specific growth rate in length (SGR-L, 2.8%), weight gain (52.7 ± 21.13 mg), and specific
growth rate in weight (SGR-W, 5.6%) were recorded at 178.00 ppm water hardness. In the second
trial, the highest length (11.1 ± 3.96 mm), SGR-L (2.9%), weight gain (55.9 ± 21.53 mg), and SGR-W
(5.7%) were observed at 71.20 ppm water hardness. The highest survival rate of fry was recorded at
90 ppm water hardness, with 178 ppm exhibited the second-highest survival rate. Parental care had a
significant positive impact on fry survival. Additionally, P. maculatus fry exhibited a negative
allometric growth pattern under all water hardness conditions. Water hardness levels of 90.00 ppm
and 178 ppm are recommended to achieve higher breeding success and fry survival rates in P.
maculatus.
