Effect Of Stocking Density In Polyculture System On Growth Performance Of Cultured Fish And Productivity Of Earthen Ponds.
Nabil, F. Abdel- Hakim
Ahmed, M. Zaglul
(Department of Animal Production, Faculty of Agriculture, Al-Azhar University, Cairo, Egypt.)
Mahmud, H. Awad.
(General Authority for Fish Resources Development – Kafr El- Sheikh.)
The presented study was carried out in a private fish farm located in the area of Tolompat 7, Riyad, Kafr El- Sheikh Government, Nile Delta district, North Egypt. The study aimed to evaluate the effect of stocking density of different fish species on growth performance, feed conversion, chemical body composition and economic efficiency. Three stocking densities each on one Feddan area in replicates were performed in the present study. The first stocking density was the traditional stocking density in the study area 16000 fish/Feedan (T1) (12000 Nile Tilapia Oreochromis niloticus + 3000 Tobara Liza ramada + 1000 Bouri Mugel cephalus). The second treatment included the stocking density 19200 fish/Feddan (T2 14400 Ttilapia + 3600 Tobara + 1200 Bouri) and the third (T3) treatment was stocked with 22400fish /feddan (16800 Tilapia + 4200 Tobara + 1400 Bouri). Each treatment was carried out in replicates each of one Feddan (4200m2) area and study lasted 24 weeks after start. The initial weights of the experimental fish were 25g., 10g. and 15g. for Tilapia; Tobara and Bouri, respectively. The experimental fish were fed on a diet containing 25% protein at a rate 3% & the fish biomass daily. The diet was offered in two portions at 10.00am.and 2.00 pm daily fish samples were taken from each pond every 15 days to calculate the feeding rate for the next period water quality parameters were determined every two weeks. Water dissolved oxygen and PH were determined twice weekly. Results obtained are summarized in the followed.
<!--[if !supportLists]-->1- Averages of final weights of Tilapia decreased significantly with each increase in the stocking density the same trend was observed with total weight gain and relative growth.
<!--Final body weight, total weight and gain and relative growth rate of Bouri and Tobara rate significantly with each increase in the stocking density.
<!--[if !supportLists]-->3- Stocking density released significantly differences in dry matter, protein NFE and gross energy contents of tilapia whole bodies. On the other hand stocking density released significantly differences in whole body composition parameters of Bouri and Tobara.
<!--[if !supportLists]-->4- Feed conversion ratio (kg. of feed required for each kg. /gain in weight) increased with each increase in the stocking density.
<!--[if !supportLists]-->5- Water quality parameters including water temperature, dissolved oxygen, PH value, total ammonia, nitrate, nitrite and salinity, were within the permissible levels required for the tested species.
<!--[if !supportLists]-->6- Total fish yield kg. /feddan increased significantly with each increase in the stocking density.
<!--Percentages of net returns over costs for T1, T2 andT3 were 50.59, 44,97, and 12.92%,respectively indicating the most profitable stocking density of tilapia and Bouri and Tobara lay between 16000 and 19200 fish /feddan.
Based on the obtained results a stocking density of 16000 fish /feddan (1200 tilapia + 300 Tobara + 1000 Bouri) is recommended in the study area for higher profit. Increasing thestocking density may require frequent pond water exchange and intensive water aeration and higher feeding rates.
Key words:stocking density; Nile tilapia, Mullet species growth parameters, pond fish yield
The total fish production from all resources in Egypt during (2012) was estimated by 1371975 tons <!--(GAFRD, 2012)<!-- and all aquaculture activities contributed by 1017738 tons during the same year which represented about 74.18% of the total national fish production. During 2012 Egypt imported 335023 tons <!--(GAFRD, 2012)<!-- to increase the fish per capita consumption in the country from 16.48 to 20.55 kg/year. The facts mentioned above reflect the importance of aquaculture activities in securing the fish protein demand for Egyptian people. Because of the limited fresh water resources required to increase the production of fresh water fish species (Tilapia, Mullets and Carp species) it is necessary to develop system to increase the production of fish vertically by performing new methods concerned with fish feeding , fish cultured species and the fish stocking density.
Applying the developed method in aquaculture activities could help the fish farmer to increase his production vertically per unit area.In aquaculture, ‘stocking density’ should denote the concentration at which fish are initially stocked into a system. However, it is generally used to refer to the density of fish at any point of time. It is considered to be one of the important factors that affect fish growth, feed utilization and gross fish yield <!--(Liu and Chang, 1992)<!--. The full utilization of space for maximum fish production through intensive culture can improve the profitability of the fish farm. Fish intensification by increasing stocking density is also found suitable to overcome the problem of land shortage <!--(Khattab et al., 2004; Chakraborty and Banerjee, 2010)<!--. <!--Chang (1988)<!-- reported that fish stocking density is an important factor used aquaculture as it can affect natural food availability, the efficient utilization of food resource and total fish yield in ponds. polyculture of fish is usually used to combine omnivorous tilapia sp.with benthphagic mullet sp. to take advantage of various feeding pond riches <!--(Malecha et al., 1981)<!--. In addition, the polyculture aims to increase productivity by a more efficient utilization of the ecological resources in the aquatic environment <!--(Lutz, 2003)<!--.When the concentration of different species are adequate in the polyculture pond, the growth rate of plankton,macrophytes benthos and nekton (other than the stocked fishes) keep pace with the rate of consumption by the cultured fisher <!--(Bíró, 1995)<!--. The objective of the present study were to evaluate the effects of increasing stocking densities of Tilapia and mullet species reared in polyculture system in earthen ponds on growth performance. Feed utilization plankton abundance gross yield and profitability under the Egyptian conditions.