WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2023 31 ranging from 1.07 (HD) to 1.31 (LD). Feed conversion ratios were ranked (best to worst) HD > IPRS = LD. It was unexpected that FCR in HD ponds was the best, as was the similarity in FCR between IPRS and LD ponds, despite the difference in final mean weight and culture period. Differences in survival apparently were not reflected in FCRs. Discussion This study evaluated the production performance of Nile tilapia at different stocking densities and in two culture systems, traditional ponds and IPRS technology. Stocking density is considered a priority factor in aquaculture that affects fish growth (Di Marco et al. 2008). Previous studies in different species have shown that, at a higher culture density, fish exhibit a decrease in growth rate and, in turn, the feed conversion rate is affected (Procarione et al. 1999, Di Marco et al. 2008, Irwin et al. 1999, Kristiansen et al. 2004, Schram et al. 2006, Ntanzi et al. 2014, Gindaba et al. 2017). In addition, survival is reduced at high stocking density (Schram et al. 2006, Majumder et al. (2017). High density exerts many negative impacts, such as competition for food and shelter and a rapid outbreak of disease if it occurs (Mamunur Rahman et al. 2016). Evaluations of different stocking densities in Nile tilapia culture suggest using low densities to obtain greater survival and growth in a short period of time (Moshiur Rahman et al. 2016, Majumder et al. 2017). This study also demonstrates that changing technology from open pond culture to IPRS results in a substantial increase in yield, from 14.7-26.6 t/ha in open ponds to 37.0 t/ha in IPRS. In comparison with other production trials in IPRS, the growth rates obtained on this commercial farm (4.35 g/d) was consistent with the range of growth rates reported from other farms (3.78-5.53 g/d) (Arana et al. 2020a, 2020b). Conclusions • Stocking Nile tilapia at 5.5 fish/m² results in production that is about 12 t/ha less than stocking 3.9 fish/m² and more than 22 t/ha less than with IPRS technology. • Good feed conversion ratio can be obtained in HD and LD ponds and IPRS. • IPRS maintained dissolved oxygen at levels acceptable for the species (>4.0 mg/L), with 0.0 mg/L ammonia and nitrite. • Continuous aeration and the extraction of solid wastes in the IPRS technology increases the allowable feeding rates that maintains acceptable water quality. • Based on the culture performance of tilapia in IPRS, there is a capacity to produce 2.5 harvests per year. Notes Esau Arana, Mildred Avila, Oscar Botero and Jesse Chappell United States Soybean Export Council (USSEC) 16305 Swingley Ridge Road, Suite 200, Chesterfield, MO 63017, USA References Arana, E., V. Fuentes, G. Thiriez, J. Amezquita and J. Chappell. First trial growing vaccinated Nile tilapia in IPRS in Colombia. 2020a. Global Aquaculture Advocate, Vol 227/April 14, 2020. (CONTINUED ON PAGE 32) FIGURE 4. Growth curve of tilapia stocked in ponds at low density (orange circles), high density (blue circles) and in IPRS (green circles).