EFFECT OF DIFFERENT DENSITIES OF GREY MULLET (MUGILL CEPHALUS) AND NILE TILAPIA (OREOCHROMIS NILOTICUS) ON GROWTH PERFORMANCE, TOTAL YIELD AND ECONOMIC RETURN IN EARTHEN PONDS
Hassan, A. Abdel-Rahman
Department of Fish Production and Aquaculture Systems, Central Laboratory for Aquaculture Research (CLAR), Agricultural Research Center (ARC), Egypt.
Received 3/ 6/ 2013
Accepted 27/ 6/ 2013
Abstract
The experiment was conducted in twelve earthen ponds (each pond is one feddan) in the graduate village in Khashaa area belong to Kafer El-Sheikh Governorate.
The experimental period extended for 150 days. The aim of this experiment was to find out the optimal stocking rate of mullet which was stocked with Nile tilapia, under polyculture system, using two types of feeding; natural food which enhanced by organic fertilization (poultry manure) and supplementary feeds (artificial feed). The initial average weights of tilapia and mullet fingerlings were 20.2 gm and 12.9 gm, respectively. Twelve ponds were stocked with 8400 of Nile tilapia fingerlings for each pond. Then the twelve ponds were assigned into two groups, each group composed of three treatments in two replicates each. The first treatment of each group stocked with the first stocking rate (SR1) of mullet (1260 fish/pond) (15%), the second treatments of each group stocked with the second stocking rate (SR2) of mullet (2520 fish/pond) (30%) and the third treatment of each group stocked with the third stocking rate (SR3) of mullet (4200 fish/pond) (50%). The three treatments of the first group had the first treatment (fertilized with 500 kg poultry manure every week for each pond) and the three treatments of the second group had the second treatment (supplementary feeding). Results obtained from the experiment could be summarized as follows:
Means of body weights of tilapia and mullet, fed the supplementary feed (containing 25% crude protein) were significantly higher than the same specie fed natural food enhanced by poultry manure as organic fertilization. Body weight of tilapia nilotica increased with increasing mullet stocking rate and amount of supplementary feed Increasing mullet stocking rate was followed by decrease in body weight of mullet and this result may be attributed to the competition between tilapia and mullet for the natural food in the pond. The interaction effect of feeding treatment and stocking rate showed that the two factors act dependently on each other and also each of them had its own significant effect. The interaction was more effective with respect to tilapia fish.
Tilapia and mullet fish gained the largest total gained (6092.21kg/fed) (1694.68 kg/fed) when fed supplementary feed compared with (4984.31 kg /fed) (1420.13 kg/fed) gained by the same specie raised in the ponds fertilized with poultry manure. The total yield for tilapia nilotica and at harvesting, after 150 days increased with each increase in stocking rate mullet . This result indicated the rapid growth rate of tilapia which reflect on total fish production. In general the largest fish production (2877.71kg/fed) for tilapia and mullet was recorded from the pond had the supplementary feed and the third stocking rate (SR3), and the lowest fish yield (2036.75kg/fed) obtained from the pond fertilized with poultry manure and had the first stocking rate (SRI).
The economical analysis revealed increases in variable costs as well as higher net returns when the stocking density increased. However, the rate of return to capital percentage had decreased with the increase of the stocking density. The overall analysis suggested that the ponds fed supplementary feed systems are the most profitable system.
Key words: Polyculture, Tilapia, Mullet, Poultry manure, Supplementary feeding, Growth performance, Total yield, Water quality, Plankton, Economic evaluation.