Efficient productivity and lowered nitrogen and phosphorus discharge load from GH-transgenic tilapia (Oreochromis niloticus) under visual satiation feeding

Given the need for culturable species with reduced nutrient discharge loading, in particular those suitable for closed recirculating aquaculture systems (CRASs), we determined the N and P discharge load from the ‘all-fish’ GH-transgenic tilapia (GHTi) of our produced line under satiation feeding with respect to its growth characteristics. In Experiment I, we monitored the growth performance of F3 GHTi of this line compared with age-matched non-transgenic siblings under satiation feeding. F3 GHTi tilapia exhibited a 0.8- to 1.6-fold greater specific growth rate relative to their non-transgenic siblings for the body weight interval examined. For ~ 72 g body weight, the condition factor was found to be significantly higher than in non-transgenic siblings (~ 1.2 times). In Experiment II, we examined the productivity of F4 GHTi compared with that of a common domestic strain of tilapia (CTi) under satiation feeding over a time interval required to reach a similar market size (BW of GHTi: 154.7 ± 14.9 g, CTi: 156.0 ± 17.4 g) from a similar initial size (BW of GHTi: 18.7 ± 3.3 g, CTi: 18.3 ± 3.9 g). The greater efficiency of productivity of GHTi was reflected in the 69 days shorter duration at a 1.4-fold higher specific growth rate and 37.3% higher feed efficiency when fed 38.1% less diet. Moreover, the total nitrogen (N) and phosphorus (P) discharge loads from GHTi were lower, being 50.1 and 61.1% of those of the control fish, respectively. The market size GHTi contained significantly lower levels of all body compositions due to the 8.6–13.1% greater moisture content. Early adult GHTi showed incomplete bone mineralization, and late adult GHTi were observed to have skeletal abnormalities. Body ash, calcium (Ca), and P contents in CTi whole body increased with growth while they decreased in GHTi. Furthermore, the Ca:P ratio in CTi increased from 1.70 to 1.88, while it decreased from 1.66 to 1.57 in GHTi. These data indicate that an optimal diet needs to be developed to meet the altered nutritional requirements of GH-transgenic tilapia.