5. Effect of water spinach and duckweed on fish growth performance in poly-culture ponds

Authors: San Thy, Khieu Borin, Try Vanvuth, Pheng Buntha and Preston T.R. (2006) .
Cambodia Journal of Agriculture, January-June 2006, Volume 7, Number 1 page 12-16

Summary : The experiment was carried out at the Centre for Livestock and Agriculture Development ‘CelAgrid' from April 21 to August 20, 2004. A total of 12 ponds were excavated with the capacity of 20 m3 each (4 m length x 2.5 m wide and 1 m deep). The ponds were lined with blue plastic to protect from soil erosion and to avoid filtration of water. After paving the blue plastic, water from pond was pumped into all experimental ponds. Lime ( CaO ) at 200 g/m² was applied at 20 days before stocking with fish, in order to kill parasites and pathogenic organisms if existed and also to increase the pH (Photo 1).

Photo 1: Ponds arrangement all in a row by paving with blue plastic

The Completed Randomized Block Design was used with 3 treatments: the effluent as control (E), effluent with the supplement of water spinach (EWS), and the effluent with the supplement of duckweed (EDW) and each treatment replicated 4 times. Each pond was stocked with three fish species at a density of 3 fishes per m². T he species were tilapia ( Oreochromis niloticus ) , common carp and mrigal ( Cirrhinus mrigal ) . The composition was 40 percent of tilapia, 35% of common carp, and 25% for Mrigal which was equal to 12, 10 and 8 heads (30 fish per 10 m2) of tilapia, common carp and Mrigal respectively. Ponds were fertilized with effluent from a plastic biodigester loaded with pig manure with the rate of 120 kg of nitrogen per ha -1 year -1 . Feed supplementation (water spinach and duckweed) was given twice daily at 8:00 am and 4:00 pm. The feed supplementation was estimated at 5% DM basis of the fish body weight. Duckweed and water spinach were cultivated at CelAgrid. The effluent from biodigester was daily sampling and bulked for the weekly analysis of N, OM , Nitrogen, and Ammonia. The quantity of N was calculated before applying into the fish pond. Fish bodyweight and length were measured at 8:00 am in every 20 days before applying the feed or effluent. The oxygen and pH of the water in the fish pond was measured in every 4 days and each measurement was taken twice at 6:00 am and at 4:00 pm using the DO2 meter (Model 9150). The water temperature was measured three times weekly at 6:00 am , at 12:00 am and at 5:00 pm using thermometer placing in each pond for 5 minutes. Water quality was also measured at 12.00 am in every 2 days using Secchi disk.

Abstract: A total of 360 fingerlings were distributed to twelve ponds of 10 m2 each. The composition of fish in a pond was 40%, 35% and 25% of tilapia ( Oreochromis niloticus ) , common carp ( Cyprinus carpio ) and mrigal ( Cirrhinus mrigal ) respectively. Treatments were effluent (E), effluent plus water spinach (EWS) and effluent plus duckweed (EDW). The level of effluent applied was 120 kg N ha-1. The water spinach and duckweed were given daily at 3 to 5% DM of fish bodyweight from fingerling stage to 120 days old respectively. The water quality (pH, water transparency, water temperature and dissolved oxygen) were similar in all treatments. The survival rate was similar for all species (88.3%, 90.6 and 92.4 % of common carp, mrigal and tilapia respectively) however lower survival rate was in ponds fed duckweed. The daily weight gain was significantly difference between species and supplements except the duckweed ponds. The total daily weight gain was 6.17, 15.2 and 21.2 kg ha -1 day -1 (P=0.012, SE±2.74) resulting a total yield of 1,450, 2,470 and 3,120 kg ha -1 per 4 months (P=0.007, SE±276) for E, EWS and EDW respectively. It is concluded that duckweed and water spinach can be used as a supplement to poly-culture fish although fish gained better with the supplement of duckweed