Abstract

This experiment was conducted over a culture period of five months (twenty weeks) to assess the effects of using biofloc technology (BFT) on enhancement of white leg shrimp (Litpenaeus vannamei) growth yield performance and survival as well as water quality in super-intensive culture ponds. Six ponds were designed with an area 0.3 ha per pound. Each pond was stocked at a density of 500 shrimp/m2 of Litopenaeus vannamei post larvae with an average initial weight of 0.26 g. Three ponds were used as triplicates for biofloc technology (BFT) treatment and the other three ponds were used as triplicates for water exchange system treatment (control). The results of all physicochemical parameters indicated that the quality of water was an optimal and suitable for L. vannamei culture in both treatment ponds. Biofloc ponds had significantly lower levels of TAN and NO2-N than control ponds. These results showed that there were accepted interactions between TAN and NO2-N in water since ammonia is converted to nitrite by nitrifying bacteria. On the contrary, the levels of NO3-N were higher in biofloc ponds than in control ponds. Although, DO range (5.0 - 6.18 mg L-1) recorded at biofloc ponds were slightly lower than control ponds range, but it's still within the optimal limit for the survival and growth of L. vannamei shrimp. 
Using two-way ANOVA, the main effects of biofloc treatment had shown significant differences on all water quality parameters except on NO3-N and temperature (P > 0.05). The results of two-way ANOVA showed that there was very high significant interaction (P < 0.001) in some growth parameters like WG, DWG, SGR and production of biofloc and control ponds throughout the cultural period (months). Whilst, there were no significant interaction in values of PER, FCR and survival (P > 0.05) between treatments and period of shrimp culture (months). The values of WG, DWG and production were high (3.55±0.13 g, 0.122±0.01 g d-1 and 13.27±1.6 MT pond-1, respectively) in biofloc ponds and low (3.02±0.19 g, 0.104±0.01 g d-1 and 11.89±5.34 MT pond-1 respectively) in control ponds. The results of growth parameters such as WG, DWG, SGR, PER and FCR in waters treated with biofloc were significantly higher than the results in control treatment. These might be due to the synergistic effects of the enhanced water quality, increasing bacterial and zooplankton densities in ponds waters.