IMPACT OF WATER HARDNESS ON BREEDING AND FRY REARING OF Pseudetroplus maculatus (ORANGE CHROMIDE) (BLEEKER, 1862): A POTENTIAL SPECIES FOR SRI LANKA’S ORNAMENTAL FISH INDUSTRY

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.