A polyculture experiment was carried out on the Tilapia species(Wild Oreochromis niloticus and Oreochromis aureus ),Common carp(Cyprinus carpio Ham.),gray mullet(Mugil cephalus ), Grass carp (Ctenopharyngodon idella) and Silver carp (Hypophthalmichthys molitix) with the objectives to evaluate the effects of fertilizer types and rice bran (12.8% crude protein) as supplementary feed in fertilized ponds on growth performance in terms of average body weight (ABW), specific growth rate(SGR),feed conversation ratio(FCR) and total fish production of these fishes, water quality parameters and economic returns under polyculture in semi-intensive fish culture system supplemented with rice bran.
Seven earthen ponds(each = 4200 m2 surface area) were randomly applied with no replicates. Each pond was stocked with 6000 wild Oreochromis Tilapia species,2000 Common carp,1000 gray mullet ,500 Grass carp and 500 silver carp. Four treated ponds were supplemented with rice bran at the rate of 5% of wet fish body weight daily and for a period of six months(180 days).
In this experiment, all the experimental ponds received the same quantity of N and P but the sources were different as given in Table 2.treated ponds showed a significant increase (P<0.01) in fish production. Results showed that organic + inorganic fertilizers + rice bran as supplementary feed remained the best treatment for maximum net marketable fish production of 2855.2 ±22.92 kg/fed/180 days , while the net marketable fish production under the effect of T1 ,T2 , T3, T4 , T5 and T6 were found to be 2418.2 ±11.89 , 1558.8 ±19.63 ,1617.5 ±17.47, 2159.0 ±12.78, 2330.3 ±15.29and 2657.7 ±10.15 kg/fed/180 days , respectively .Thus for getting optimal fish production the fertilization of pond with supplementary feed is recommended.
Results indicated that most of water quality parameters were influenced by fertilization type while supplementary feed had a little effect. Factor analysis demonstrated that four factors (Phytoplankton decomposition, Photosynthesis, chemical reactions and supplementary feed ) were responsible for more than 77% of the explained variability that affected all water quality variables.. All water quality parameters were in the proper range of the growth of all fish species used in this experiment.
Results of tow-way ANOVA indicated that fertilizer type was effective than supplementary feed on water quality parameters. The (T7) had the highest average of water quality parameters and plankton densities(cells/m3)which led to the higher fish growth that received organic , inorganic and feed may be attributed to the increase in organic matter contents of this pond that may lead to consume natural food and release ammonia in a form of feces much greater than that in the other treatments. On the other hand, both of water temperature and pH were not affected neither by fertilizer type nor by supplementary feed. Both of total orthophosphate(PO4- mg/l) and total alkalinity had significantly higher concentrations when ponds treated with chemical fertilizers than ponds treated with organic fertilizers,
In conclusion, fish culture growth was better, water quality, fish production and consequently economic returns can be optimized with in the treatment with organic and chemical fertilizers plus supplementary feeding than feeding alone or fertilization alone for polyculture in terms of economic efficiency and net revenue. The study suggested that maximizing production efficiency would require the combination of the three nutrient input sources (feed , organic and inorganic fertilizers). The study throw the lights on the importance of the need to increase yields of fish culture to meet the needs of small holder farmers raising fish for household consumption.