World Aquaculture - June 2023

WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2023 29 last ten weeks, morning DO fell to 0.5 mg/L, even with mechanical aeration. In LD ponds, morning DO was above 6 mg/L, slowly decreasing from the second month to levels between 2.5 and 4.5 mg/L. In the third month, morning DO was around 1 mg/L until the end of the trial. In the IPRS, during the time when morning DO was measured, it ranged from 4.1 to 6.5 mg/L. Ammonia and nitrite concentrations were low and within expected ranges and much lower than lethal dose (Evans et al. 2006). The pH varied between 8.3 in the morning and 8.5 in the afternoon. Results In evaluating the production performance of the three tilapia production systems, it is important to emphasize that there are two main market segments for tilapia in Colombia. For the domestic market, usually red tilapia are marketed whole, without viscera, at a market size of around 0.5 kg. For the export market, usually Nile tilapia are harvested at 0.8-1 kg and filleted in processing plants. The other point to emphasize is that the difference between “high” (CONTINUED ON PAGE 30) daily feeding rates were 71 kg/ha in HD ponds, 148 kg/ha in LD ponds and 247 kg/ha in IPRS ponds. Water Quality Temperature and dissolved oxygen concentration (DO) were measured daily in the morning between 0500 and 0700 hr and in the afternoon between 1600 and 1800 hr. Total ammonia-nitrogen (TAN), nitrite-nitrogen and pH were measured weekly at noon. In some cases there was a gap in recordkeeping due to the absence or maintenance of measuring equipment. The average temperature ranged between 25.6 C in the morning and 28.3 C in the afternoon (Table 2). However, there were hot days when the temperature exceeded 30 C and a negative impact was noted on fish health. When temperature increased during the hottest time of the year, tilapia are more susceptible to infection by Streptococcus (Biswas et al. 2018). In HD ponds, morning DO was between 5 and 5.5 mg/L for the first two months (Fig. 3). As tilapia biomass and feeding rate increased, morning DO declined to around 4 mg/L. During the TABLE 3. Summary of the comparison among traditional ponds stocked at high density (HD), low density (LD) and an IPRS. Treatments with the same letter indicate no statistical difference. HD LD IPRS Stocking density (fish/m2) 5.5 3.9 13.7* Final weight (g) 489 1143 589 Harvest yield (kg/ha) 14,657 c 26,576 b 36,971 a Culture period (d) 231 a 237 a 147 b Weight gain (g/d) 2.12 c 4.74 a 3.69 b FCR 1.07 a 1.31 b 1.29 ab Survival (%) 73.5 76.6 61.8 * In IPRS, the stocking density is based on pond volume and is equivalent to 13.7 fish/m2 in a traditional pond. TABLE 1. Characteristics of the selected fish lots. Treatment Pond ID Pond area Fish stocked Stocking density Initial fish (ha) (number) (f ish/m2) weight (g) HD C4 3.12 179,538 5.8 15 L9 1.90 97,127 5.1 7 LD L15 1.83 70,000 3.8 19 L19 2.55 100,980 4.0 21 IPRS L8 1.15 157,246 13.3 49 TABLE 2. Water quality in treatments HD, LD and IPRS in Nile tilapia production. HD LD IPRS AM PM AM PM AM PM T (C) 25.6 28.3 26.3 28.5 28.6 29.9 pH 8.3 8.5 7.4 8.1 7.1 7.4 Ammonia 0.0 0.25 0.0 0.0 0.01 0.01 Nitrite 0.5 0.0 0.0 0.0 0.0 0.0