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Abstract
The present study was designed to investigate the advantages and disadvantages of using different organic fertilizers on fish safety and yield and also to investigate the production performance of mixed organic and inorganic fertilizers supplemented with artificial fish feed.
The first experiment aimed to find out the total microbial count on fish reared under different nutritional strategies; no input, compost fertilization; chicken litter fertilization; and artificial fish feed. Quantity of fertilizers was adjusted to add 10 kg N/ha/week to different treatments while ponds received artificial fish feed treatment offered 25% protein floating feed to visual satiation. Eight ponds 200 m2 each were stocked with mixed sex Nile tilapia fingerlings (2 fish/m2) and reared for 14 weeks. At harvest total microbial count was significantly higher (P<0.01) in chicken litter treatment and followed in decreasing order by no input, compost and artificial feed (48.25, 33.5, 33.25 and 27.54 x 103, respectively). The result showed significant difference (P<0.05) in DO among treatments as follows 3.14, 2.29, 1.63 and 1.26 mg/l for treatments of compost, no input, artificial fish feed and chicken litter, respectively. Available phosphorus was significantly higher (P<0.001) in compost treated ponds followed by chicken litter, fish feed and control (0.71, 0.29, 0.14 and 0.11 mg/l, respectively). Also nitrate nitrogen was significantly higher (P<0.05) in compost followed by chicken litter, artificial fish feed and no input (0.78, 0.77, 0.49 and 0.18 mg/l, respectively). The other water quality parameters were not significantly different affected by treatments. Nitrogen and phosphorus retained in harvested fish were significantly higher (P<0.05) in feed treatment compared to chicken litter or compost treatments. Significantly (P<0.05) higher N and P waste were generated from fertilized treatments. Fish yield after 14 weeks rearing duration was significantly higher in artificial fish feed and chicken litter treatments (832 and 771 kg/fed) compared to compost and no input treatments (620.5 and 625 kg/fed respectively).
The second experiment was designed to compare the effect of different fertilizers and feeding strategies on fish growth, yield, water quality, nutrient utilization efficiency and the economic performance. The four fertilization treatments were as follows: compost (T 1); cow manure (T 2); compost and urea plus superphosphate (T 3); and cow manure and urea plus superphosphate(T 4). Twelve earthen ponds 1000 m2 each were used in this trial, three replicate per treatment ponds were stocked with mixed sex Nile tilapia (2 fish/m2) as main cultured species and silver carp for maintain water quality. The result of this experiment showed that mixed fertilizers treatments (T 3 and T 4) achieved significantly higher (P<0.05) fish yield than organic fertilizers alone treatments. Total fish yield in decreasing order was as follows T 4, T 3, T 2 and T 1 (1559.3, 1539.3, 1402.7 and 1396 kg/fed/year, respectively). Result of nutrient budget estimation showed that N retained in harvest fish was significantly higher (P<0.001) in mixed fertilizer treatment T 4 (36.7%) and T 3 (36%) compared to T 1 (33.1%) and T 2(32.9%). While phosphorus retained in fish was not significantly different among treatments and the averages were 29.9, 31.2, 28.6 and 34.8% in T 1, T 2, T 3 and T 4 respectively).
Partial economic analysis showed that benefit cost ratio was significantly higher (P<0.01) in T 3 (54%) and T 4 (49 %) compared to T 1 (36.4%) and T 2 (25.8%). The result of this experiment concluded that mixed organic and inorganic fertilizers strategies increased fish yield, and farm revenue. Furthermore mixed fertilizers achieved better utilization of nutrient inputs which could reduce the environmental impact of aquaculture on the surrounding environment.