Pd/a Crsp Sixteenth Annual Technical Report

An experiment was conducted to assess the effect of different harvest draining techniques of fish ponds on water quality and fish growth in subsequent culture cycles. Fifteen tilapia ponds of 200 m2 were harvested using five different harvest draining techniques. After harvest, these ponds were stocked with Nile tilapia (Oreochromis niloticus) at 2 fish m-2. Fish with an initial size of 11 to 13 g were cultured for 106 days in a fertilized pond system. Harvest draining techniques as treatments were: (A) Ponds were not drained, and fish were harvested by seining using tea seed cake as an anesthetic toxicant; (B) Ponds filled with canal water were completely drained after liming, and fish were harvested from a harvesting pit; (C) Ponds filled with canal water were completely drained, and fish were harvested from a harvesting pit; (D) Ponds filled with drainage water from harvest of adjacent ponds used in a previous experiment (equivalent to Treatment E of this study) were half-drained and seined twice, then completely drained to collect the remaining fish; and (E) Ponds filled with canal water were half-drained and seined twice, then completely drained to collect the remaining fish. None of the treatment means of water quality parameters (dissolved oxygen, pH, Secchi disk depth, alkalinity, total ammonium nitrogen, nitrite nitrogen, nitrate-nitrite nitrogen, total nitrogen, soluble reactive phosphorus, total phosphorus, chlorophyll a, total suspended solids, and volatile suspended solids) were significantly different (P > 0.05) between treatments. Similarly, fish growth, net fish yield, and survival did not differ (P > 0.05) between treatments. Fish growth and net yield from undrained ponds (Treatment A) were 1.32 ± 0.15 g d-1 and 15.7 ± 4.2 kg ha-1 d-1, respectively. Fish growth and net yield from ponds filled with drainage water of other ponds (Treatment D) were 1.11 ± 0.16 g d-1 and 17.3 ± 3.1 kg ha-1 d-1. The results suggest that environmental impacts of pond draining can be minimized either by harvesting fish without draining or by draining pond water into empty ponds without affecting the water quality for fish growth. SIXTEENTH ANNUAL TECHNICAL REPORT 132 draining and collection of remaining fish from a harvesting pit; and T5) Ponds received the same draining and harvesting technique as in treatment T4, but the pond water was drained into the empty ponds of treatment T4 (not discharged). The experiment incorporated three blocks. The locations of the treatments within blocks were assigned on a random basis, with the exception that ponds in treatments T4 and T5 had to be adjacent to facilitate drainage of water from ponds in treatment T5 to ponds in treatment T4. All the ponds except those in treatments T1 and T4 were refilled with canal water. Ponds in treatment T1 were undrained, whereas ponds in treatment T4 were refilled with drainage water from ponds in treatment E (equivalent to treatment T5) during harvest of the previous experiment (Lin et al., 1998). Pond water depths were maintained at 1.2 ± 0.1 m by weekly topping with canal water. All ponds were fertilized weekly with 1.2 kg urea (28 kg N ha-1) and 0.7 kg triple superphosphate (TSP) (7 kg P ha-1). Sex-reversed male Nile tilapia of 11.5 to 13.2 g size were stocked at 2 fish m-2 on 15 July 1997. Fish were cultured for 106 days and harvested on 29 October 1997. Pond water column samples, taken biweekly at 0900 h, were analyzed for total alkalinity, total ammonium nitrogen, nitrite nitrogen, nitrate-nitrite nitrogen, total nitrogen, soluble reactive phosphorus, total phosphorus, chlorophyll a, total suspended solids, and total volatile solids using standard methods (Raveh and Avnimelech, 1979; APHA, 1980; Egna et al., 1987). Temperature, dissolved oxygen, pH (at 20 cm below the surface), and Secchi disk depth were also measured in situ according to the same schedule. In addition, monthly diel measurements of temperature, dissolved oxygen, pH, alkalinity, and total ammonium nitrogen were conducted at 0600, 0900, 1400, 1600, 1800, and 0600 h in each pond. Data were analyzed statistically by analysis of variance using the Statgraphics 7.0 statistical software package. Mean fish growth (g d-1), net fish yield (kg ha-1 d-1), and survival (%) were calculated for each treatment. Means and ranges of water quality parameters from biweekly measured data were also calculated for each treatment. All means were given with Treatment Pond # Mean Stocking Size (g) Mean Harvest Size (g) Mean Growth (g d-1) Net Fish Yield (kg ha-1 d-1) Survival (%) T1 3 11.5 118.1 1.01 16.3 83 6 12.0 170.3 1.49 22.6 78 11 12.8 167.7 1.45 8.1 33 Mean 12.1 152.0 1.32 15.7 65 ± SE 0.4 17.0 0.15 4.2 16 T2 1 11.5 294.0 2.67 39.2 75 7 12.2 113.3 0.95 15.0 81 12 13.2 110.4 0.93 11.4 67 Mean 12.3 172.6 1.52 21.9 74 ± SE 0.5 60.7 0.58 8.7 4 T3 2 11.8 137.5 1.19 23.0 97 8 12.5 61.1 0.46 4.4 59 15 12.5 116.5 0.98 4.3 30 Mean 12.3 105.0 0.88 10.6 62 ± SE 0.2 22.8 0.22 6.2 19 T4 4 12.2 96.6 0.80 11.0 73 10 12.2 148.1 1.28 20.3 81 13 12.8 145.9 1.26 20.5 83 Mean 12.4 130.2 1.11 17.3 79 ± SE 0.2 16.8 0.16 3.1 3 T5 5 11.8 128.0 1.10 18.9 88 9 12.2 113.1 0.95 16.0 86 14 13.0 110.9 0.92 15.3 85 Mean 12.3 117.3 0.99 16.7 86 ± SE 0.4 5.4 0.06 1.1 1 Table 1. Mean stocking size, harvest size, growth, net fish yield, and survival of Nile tilapia cultured for 106 days in earthen ponds in different treatments: (T1) undrained ponds; (T2) limed, completely drained, and filled with canal water; (T3) completely drained and filled with canal water; (T4) half drained, seined, completely drained, and filled with drainage water of T5; and (T5) half drained, seined, completely drained, and filled with canal water. THAILAND RESEARCH 3 133 ± 1 standard error (SE), and differences were considered significant at an alpha level of 0.05.