2000 EFFECT OF ORGANIC FERTILIZATION , SUPPLEMENTARY FEEDING AND STOCKING RATE ON GROWTH PERFORMANCE OF NILE TILAPIA AND SILVER

Six ponds (20 ́50 m) were stocked by 1000 of Nile tilapia fingerlings for each pond. The six ponds assigned into two groups, each group composed of three ponds, the first pond stocked with the first stocking rate (SR1) of silver carp (100 fish/pond), the second pond stocked with the second stocking rate (SR2) of silver carp (200 fish/feddan) and the third pond of each group stocked with the third stocking rate (SR3) of silver carp (300 fish/pond). The three ponds of the first group had the first feeding treatment (fertilization with 50 kg poultry litter every week for each pond) and the three ponds of the second group had the second feeding treatment (fish feed containing 30% crude protein). Results obtained can be summarize as follows: Means of body weights of Nile tilapia from the 4 week up to the 14 week of the experiment, fed the supplementary feed (containing 30% crude protein) were significantly higher than the same specie fed natural food enhanced by poultry litter as organic fertilization. Body weights of silver carp showed the opposite results. Body weight of Nile tilapia increased with increasing silver carp stocking rate. Increasing silver carp stocking rate was followed by decrease in body weight of silver carp. Using supplementary feed increased body length and body depth of Nile tilapia more than the other feeding treatment. The opposite trend was obtained with silver carp. Condition factors for Nile tilapia and silver carp were paralleled with previous fish growth results. The effect of stocking rate on condition factor of Nile tilapia and silver carp are different within the whole period of the experiment. The values of SGR of Nile tilapia from the first week up to 14 week of the experiment and within biweekly intervals, show that, using supplementary feed gave higher values than using poultry litter in most intervals. The opposite results was obtained with respect to silver carp. The increasing stocking rate, SGR of Nile tilapia increased, while SGR of silver carp decreased. The best SGR values for tilapia, due to the interaction between feeding treatment and stocking rate, were recorded with fish during the first four weeks as the rates ranged between 3.76-4.57 while in the rest weeks the rates ranged between 0.962.86. The best SGR values for silver carp were recorded with fish during the first eight weeks (0.37-1.83) while in the rest weeks the rates ranged between 0.38-1.13. The total yield for Nile tilapia and silver carp at harvesting, after 14 weeks increased with each increase in stocking rate. In general the largest fish production (270 kg) for tilapia and silver carp was recorded from the pond had the supplementary feed and the third stocking rate (SR3), and the lowest fish yield (180 kg) obtained from the pond fertilized with poultry litter and had the first stocking rate (SR1). EFFECT OF ORGANIC FERTILIZATION 1776 INTRODUCTION Polyculture, between tilapia and other aquatic species, is an established option when natural food from different pond niches are independently exploited by fish, when there is a market for all species in culture and when their combination provides an economic benefit which is high enough to cover extra labour expenses required to grade and sort fish at sampling and harvesting. The aim of this experiment was to find the optimal stocking rate of silver carp can be stocked with Nile tilapia under the polyculture system of aquaculture, using two types of feeding, natural food which enhanced by organic fertilization (poultry litter) and supplementary feeds (artificial feed). MATERIALS AND METHODS The present experiment was conducted during the period between 15 may and 1 September 1995 (14 weeks) in six fresh water earthen ponds each of a total area of 0.25 feddan at the Central Laboratory for Aquaculture Research at Abbassa village, Sharkia Governorate, Egypt. Fish used The fish used in this experiment included Nile tilapia(Oreochromis niloticus) which is an efficient converter of p****hytoplankton but can utilize a wide variety of foods. Ponds were stocked also with silver carp (Hypophthalmichthys molitrix) which feeds primary on phytoplankton. Tilapia fingerlings were obtained from Abbassa hatchery, the average weight of fingerlings was 11.3 gm. Silver carp were obtained from the production ponds in Abbassa farm and where their average body weight of silver carp was 164 gm. Experimental ponds and stocking rate Six experimental earthen ponds (1000 m , 20 ́50 m) and 130 cm depth are supplied with fresh water from Ismaellia canal. The six ponds were stocked by 1000 of Nile tilapia fingerlings for each pond. Then the six ponds assigned into two groups, each group composed of three ponds, the first stocked with the first stocking rate (SR1) of silver carp (100 fish/pond), the second pond stocked with the second stocking rate (SR2) of silver carp (200 fish/pond) and the third pond of each group stocked with the third stocking rate (SR3) of silver carp (300 fish/pond).The three ponds of the first treatment group had the first feeding treatment (fertilization with poultry litter) and the three ponds of the second treatment group received supplementary feed as described in table (1). IBRAHIM, et al. 1777 Table (1): Stocking density of Nile tilapia and silver carp under the two feeding treatments. Treatment Stocking density pond No. stocking density per pond stocking density per feddan Fertilization with SR1 1 1000 tilapia+100 silver carp 4000 tilapia+400 silver carp Poultry litter SR2 2 1000 tilapia+200 silver carp 4000 tilapia+800 silver carp (T1) SR3 3 1000 tilapia+300 silver carp 4000 tilapia+1200 silver carp Supplementary SR1 4 1000 tilapia+100 silver carp 4000 tilapia+400 silver carp Feed (3% of body SR2 5 1000 tilapia+200 silver carp 4000 tilapia+800 silver carp Weight) T2 SR3 6 1000 tilapia+300 silver carp 4000 tilapia+1200 silver carp The three ponds in the first treatment were fertilized with 50 kg poultry litter every week for each pond throughout the experimental period to stimulate the natural foods. The fish in the three ponds of the second treatment were fed fish using feed containing 30% crude protein. Feed was offered six days per week (except Friday) during the experimental period. The feeding rate was 3% of the total fish mass presented in each pond and the feed amount was adjusted biweekly for each pond separately according to the biomass. Chemical analysis of poultry litter and fish feed are presented in table (2). Table (2): Chemical analysis of poultry litter and supplementary feed. No. of Poultry litter Supplementary feed Item Samples Mean±SE Mean±SE Moisture% 5 4.23±0.35 9.46±0.35 Crude protein% 5 10.50±0.26 29.77±0.26 Crude fat% 5 1.01±0.08 2.60±0.08 Crude fibre% 5 30.02±0.98 5.40±0.98 Ash% 5 19.15±0.34 9.10±0.34 Fish samples and measurements Random samples (50 fish from tilapia and 30 fish from silver carp from each pond) were taken biweekly during the experimental period. During this experiment, body measurements (body weight, (in gm) body length and body depth in cm) were recorded 8 times on at biweekly interval throughout the whole experiment period. The first one recorded at the time of pond stocking with fish and the last one at harvesting. EFFECT OF ORGANIC FERTILIZATION 1778 Condition factor was determined by using the following formula: K= [ weight (g) / length (cm)] ́100 specific growth rate was calculated according to Jauncey and Rose (1982). Harvesting At the end of the experiment (1 September, 1995), ponds were gradually drained from the water and fish were harvested by seining and transferred to fiberglass tanks and carried to the processing centre where they washed, and the fish of the two species (tilapia and scarp) were sorted and collectively weighed. Statistical analysis The statistical analysis of data of the experiments was carried out by applying the computer program Harvey (1990) by adopting the following fixed model: Yijk = m + Ti + Sj + (TS)ij + eijk where: Yijk = observation of the ijk-th fish; m = overall mean; Ti = fixed effect of the i-th treatment; Sj = fixed effect of the j-th stocking density within the i-th treatment. TS)ij = interaction between the effect of i-th treatment and j-th stocking density and eijk = a random error. Differences among means were tested for significance according to Duncan’s multiple range test (1955). RESULTS AND DISCUSION