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— 292 — — Experiments on Fish Nursing of Climbing Perch in Concrete Tanks The growth of climbing perch larvae in three treatments (I: 500 larvae/m3, II: 1,000 larvae/m3, III: 1,500 larvae/m3) is presented in table 8 . The results show that the mean final weight reaches the highest value (3.1 g/fish) in treatment II, and the lowest value (2.0 g/fish) in treatment III, with statistically significant differences (p < 0.05) between treatments I, II and III after forty-five days. On the other hand, there were significant differences (p < 0.05) in survival rates of larvae between treatments I, II and III. The highest survival rate (16.5 %) was obtained for treatment I, while the lowest value was 4.9 % observed for treatment III. Generally, low survival rate of the climbing perch fingerlings in both treatments may be due to unsuitable home-made feed and lack of natural food in the early larval stage in nursing systems. Table 8 Mean growth o f climbing perch larvae (1) reared in concrete tanks at different stocking densities (treatment I: 500 1/m', treatment II: 1,000 1/ m \ treatment III: 1,5001/ m3) Treatments Time • At stocking • At 15 days • At 30 days • At 45 days • Survival rate (%) I II III Mean weight (g) Mean weight (g) Mean weight (g) 0.001 0.058 ± 0.042 0.879 ± 0.078 2.237 ± 1.632 ■ 16.54 ± 2.45 ■ 0.001 0.015 ± 0.1 1 6 1.673 ± 0.8 0 0 3.057 ± 1.125 6 14.27 ± 2 .2 4 6 0.001 0.027 ± 0.025 0.972 ± 1.260 2.041 ± 1.923 “ 4.900 ± 3.15 1 (a,b) values in each column sharing same superscript are not significantly different (p > 0.05). — Experiments on Fish Nursing of Climbing Perch in Earthen Ponds The growth rate of larvae in earthen ponds (tab. 9) was a little faster than in concrete tanks using artificial home-made feed and was similar to those using natural food at the same stocking density of 1,000 larvae/m2. The survival rate of climbing perch nursing in earthen ponds fluctuated from 5.9-10.7 %. This low result is due to high predation of fry and fingerlings in earthen ponds. Table 9 Mean weight (g) and length (cm) o f climbing perch rearing in ponds Parameters 3 days* 10 days 17 days 24 days 31 days 38 days 45 days L (mm) W (g ) Mean STD Mean STD 305 0.0002 9.0 0.1 0.0336 0.0067 * At stocking (3 days after hatching). 21 0.5 0.2034 0.0990 29 0.3 0.5905 0.0786 38 0.4 1.2005 0.4171 45 0.5 2.0365 0.8159 50 0.4 3.321 1.166
— 293 — 3.1.4.5. Experiment 3: Mean Growth of Fish in Intensive Pond Culture System — Water Quality Parameters in Intensive Culture Systems Figure 9 shows that DO concentrations in intensive culture systems ranged from 4.5 to 6.25 ppm and 4.25 to 5.25 ppm for treatment I and II respectively, the average content of DO in treatment I (4.83 ±1.13 ppm) was higher (p < 0.05) than in treatment II (4.5 ± 0.53 ppm). However, the acceptable DO for climbing perch was reached ( K ie m 2000). Time (months) * Treatment I —■— Treatment II Fig. 9. — Fluctuation of DO concentrations in intensive culture system. The ammonium concentrations in intensive systems ranged from 0.8 to 1.7 ppm and 0.9 to 2.8 ppm for treatment I and II respectively (fig. 10). The average of ammonium in treatment I (1.53 ± 0.4 ppm) was lower (p < 0.05) than treatment II (0.91 ± 0.71 ppm). However, these values are still acceptable for fish growth. The P-P0 4 3 concentrations in intensive culture system were high (fig. 11). P-PO4 3 ranged from 0.11 to 0.5 ppm in treatment I, and the average of P-PO4 3 in treatment I was 0.13 ± 0.09 ppm. P-PO43 ranged from 0.35 to 1.03 ppm in treatment II and the average of P-P04 3 was 1.03 ± 1.46 ppm. There were significant differences (p < 0.05) between the treatments. According to P h u (2000), suitable P-PO4 3' in pond culture ranged from 0.1 to 0.3. In comparison with our result, the P-P04 3' values were suitable for fish growth in the culture system. The results presented in figure 12 show that COD content in treatment I ranged from 13.57 to 16.93 ppm, the average of COD was 13.6 ± 2.9 ppm. These
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KONINKLIJKE ACADEMIE VOOR OVERZEESE
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ERRATUM Mededelingen der Zittingen
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— 369 — Nominations Par Arrêt
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— 373 — «De evacuatie uit Cong
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