Comparison between greenwater and clearwater hatchery systems during the masculinization process of silver tilapia, Oreochromis noloticus (Perciformes: Cichlidae)

Abstract

Ryan S Mohammed, Indar W Ramnarine

The growth and survivorship of Silver Nile Tilapia (Oreochromis niloticus) was compared between greenwater systems (containing green algae) and clearwater systems (no algae) while feeding the androgen 17 alpha methyl testosterone. Water chemistry was monitored daily. Algal counts and species identification were done to estimate the composition and density of green algae. Fish length, wet mass, mortality and percentage masculinization were calculated. Compared to clearwater, fish raised in greenwater were significantly larger and heavier (F1, 575 = 1028.28: p<0.001 for length and F1, 575 = 566.48 for mass). In addition there was a significantly higher survivorship in the greenwater system (mean of 85.0% survival in greenwater and mean survival of 61.0% in clear water respectfully, χ2 =67.18, p< 0.001). There were also significantly higher levels of nitrite and ammonia in the Clearwater tanks. Green water systems were found to be overall superior for producing masculinized male silver tilapia fingerlings, than clearwater systems although no significant difference was noted in percentage masculinized (98.8% green water, 97.7% clear water).