Utilização de fertilizantes orgânicos para indução de alimento natural no cultivo do camarão nativo Farfantepenaeus subtilis (Pérez-Farfante, 1967)

Abstract

The marine shrimp Farfantepenaeus subtilis has a high potential for the aquaculture. However there are some feeding and nutrition problems in captivity, resulting in low growth and high feed conversion ratio. This work aimed to evaluate the natural food induction in F. subtilis culture, through different fertilization regimes. Were adopted four treatments and three replicates, using three organic fertilizers: wheat bran – FT (28 g.m-²); rice bran – FA (28 g.m-²); molasses – ML (40 mL.m-²); and one control – CT, with inorganic fertilizers (2 mg.L-1 nitrogen and 0.2 mg.L-1 phosphorus). For this, were utilized twelve 500 L fiber glass tanks stocked with 30 shrimps.m-2 (2.57±1.27 g). Artificial commercial feed with 35% of crude protein was offered in feeding trays three times a day (08:00 12:00 and 16:00). Plankton, benthos and water samples were collected fortnightly during the culture. Results showed no significant difference (P≥0.05) in survival among the organic fertilizers treatments, but showed statistical difference (P<0.05) among FT (94.4%) and CT (61.1%). About the natural food organisms, there was no significant difference (P≥0.05) among planktonic groups. In the phytoplanktonic community there was predominance of Cyanophyta (21,340, 25,340, 22,810 and 19,630 cell.L-1, respectively, in FA, FT, ML and CT treatments). In the zooplanktonic community the major representants were rotifers (4,240, 1,820, 3,360 and 3,170 org.L-1,respectively, in FA, FT, ML and CT treatments). Among the benthos, the phytobenthos also was represented by Cyanophyta, but there was statistical difference (P<0.05) only in Euglena group, where FA (7,822 cell.L-1) was different (P<0.05) from FT (256,267 cell.L-1) and CT (239,299 cell.L-1) treatments. In the zoobenthonic community it was registered the predominance of rotifers and nematodes, showing significant difference (P<0.05) in rotifers group in ML (9,200 org.L-1) treatment, when compared with CT (3,778 org.L-1) and FT (2,711 org.L-1) treatments. Nematodes differed (P<0.05) in FA (3,944 org.L-1) when related to FT (12,222 org.L-1) and ML (28,222 org.L-1) treatments, which also predominated in mesobenthonic community (1.7, 6.4, 9.0 and 3.2 ind.m-² in FA, FT, ML and CT, respectively), with no significant difference (P≥0.05) among the treatments. It was concluded that in the experimental conditions adopted both organic and inorganic fertilizers effects were similar related to natural food induction.