Abstract
To test the effect of different stocking densities on their growth, survival rate, and number of marketable fish, advanced larvae (0.14±0.035 g) of koi carp, Cyprinus carpio vr. koiwere cultured for 90 days in 150-L concrete tanks at different densities: 0.1 fish/L (D1); 0.2 fish/L (D2); 0.3 fish/L (D3); 0.4 fish/L (D4); and 0.5 fish/L (D5). There were three replicates for each treatment, where the fish were fed daily, slightly in excess of satiation to eliminate the possibility of food supply being a limiting factor to growth. The D4 and D5 treatments recorded significantly higher (P < 0.05) values of ammonium-N, nitrite-N, nitrate-N, phosphate, and specific conductivity, and significantly lower (P < 0.05) values of dissolved oxygen, compared to the other treatments. Weight gain for koi carps stocked at D1 (7.28 g) was significantly higher (P < 0.05) than that of fish in the other treatments. There was a significant difference in survival rates of koi carps among the treatments ranging from 62.43% in D5 to 93.26% in D1. The number of marketable fish above a set size of 4 g was significantly higher (P < 0.05) in D3, compared to other treatments with higher or lower stocking densities. Therefore, a stocking rate of 0.3 fish/L would be suggested as optimal.