World Aquaculture March 2019

66 MARCH 2019 • WORLD AQUACULTURE • WWW.WA S.ORG Feeding Trial Three 5.25-L white plastic tanks were each filled with 5 L of water and a diffuser connected to a blower (Model ACD-9800 Re- sun air pump) was added. Water was exchanged twice daily at 730 and 1730 h. A total of 645 silver catfish fry were equally allotted to the tanks. The crude protein level of 56 percent was maintained through the 12-wk trial while feed sizes were changed as body weight increased. For the first four weeks, extruded feed of 0.2-0.3 mm particle size was fed at 15 percent body weight, divided into eight feedings daily (0800, 1000, 1200, 1400, 1600, 1800, 2000, 2200 h). For weeks 4-8, the feeding regimen was changed to 0.3-0.5 mm particle size fed at 10 percent body weight, divided into six feedings daily (0800, 1030, 1300, 1330, 1800, 2030 h). For weeks 8-12, extruded feed of 0.5-0.8 mm particle size was fed at 5 percent body weight, divided into three feedings daily (0800, 1300, 1800 h). Fry in a Petri dish containing water (Fig. 6) were batch weighed to the nearest 0.01 g with an electronic balance. The total length of fry was determined with a digital caliper to the nearest mm. Measure- ments were carried out every two weeks for 12 weeks. Feeding rate was readjusted following weight and length measurements. Water quality of the experimental rearing tanks was measured daily. Temperature, pH and dissolved oxygen were measured with Hanna digital meter and probe. Ammonia, nitrite and phosphate concentrations were measured with a test kit (PondCare ® Master Liquid Test Kit). Results and Discussion Catfish fry grew from 20 to 770 mg (9 mg/d) and from 11 to 39 mm in 12 weeks (Fig. 7). Growth was greater than that reported by Pangni et al . (2008) of 2.9-4.3 mg/d in a 28-d rearing period in Côte d’Ivoire. The difference in growth performance may have been as a result of the lower protein level (45 percent) of the feed used by Pangni et al . (2008) compared to that used in the study reported here (56 percent). Their research methods of using daily water exchange and aeration to maintain water quality was similar to the approach used in this study. The mean water quality parameters obtained during the study period are shown in Table 2. Apart from ammonia and phosphate, water quality parameters recorded during the study period were within the appropriate ranges for warmwater fishes (DWAF 1996). According to this report, the target water temperature range for larval development and growth was 27-30 C, and the pH tolerance FIGURE 3. Breeding tank with a PVC shelter for spawning. FIGURE 4. Silver catfish eggs after spawning. FIGURE 5. Fertilized silver catfish eggs were incubated in McDonald hatching jars. FIGURE 6. Silver catfish fry in a Petri dish prior to weighing.