Growth Performance of GMT and Mixed Sex Nile Tilapia Oreochromis niloticus on Natural and Supplemental Feeds

Attention has been focused on genetically-improved stocks and strains of tilapia. A greenhouse recirculating aquaculture system (RAS) of three 540 L tanks stocked with 100 37.2 g genetically male tilapia (GMT) Nile tilapia, Oreochromis niloticus, and three identical tanks with the same number of 38.1 g mixed sex Nile tilapia, was used to measure response to floating 3.0 mm catfish pellets (32 % protein) fed once per day at four different rates based on body weight day-1 (2-4 % BW day-1). Feed rate and amount were changed every 14 days based on growth measurements. For growth comparisons on natural feeds (primarily phytoplankton), two 10.5 m3 net pens were each stocked in August with 105 7.7 g Nile tilapia m-3 of each group in each of two 1.0 ha blue catfish Ictalurus furcatus fingerling ponds and not fed. Fish were harvested in November. GMT fish outperformed mixed sex fish on both feed sources, and at most feed rates. In RAS trials at 2, 2.5, 3.0 and 4.0 % BW feeding, percentage growth day-1 was 1.95, 2.11, 2.21 and 3.31 for GMT, and 1.60, 2.22, 1.97 and 2.86 for mixed sex; and the associated food conversion ratio (FCR) was 1.54, 1.37, 1.37 and 1.04 and 1.64, 1.35, 1.42 and 1.20, respectively. At harvest in net pens, GMT fish were 25 % larger than mixed sex. Growth was 1.3 and 1.0 g day-1 on natural food sources for GMT and mixed sex, respectively