Dynamics of nitrogen and phosphorus in the superintensive cultivation of shrimp Litopenaeus vannamei and Farfantepenaeus paulensis without water renewal
The present work aimed to follow the dynamics of nitrogen and phosphorus in a super intensive farming system without water renewal (Zero Exchange Aerobic Heterotrophic System - ZEAH) of marine shrimp of two different species: Litopenaeus vannamei and Farfantepenaeus paulensis. For this purpose, an experiment was carried out over 42 days, which consisted of 3 treatments: 1) VT - stored with L. vannamei juveniles with 0.12g of initial weight and density of 300 cam / m2, 2) TP - with juveniles of F. paulensis with 0.13g of initial weight and density of 300 cam / m2 and 3) TC - without shrimp, only with the addition of feed. The treatments had three repetitions composed of tanks of 210 liters of useful volume and 0.33 m2 of bottom area. Physical and chemical variables such as pH, salinity, temperature,dissolved oxygen were monitored daily (morning and afternoon). The nutrients (ammoniacal nitrogen, nitrite, nitrate, particulate nitrogen, total nitrogen, orthophosphate, particulate phosphorus and total phosphorus), suspended particulate matter, chlorophyll-a and microorganisms were monitored every 3 days and at the end of the experiment a balance was carried out mass for nitrogen and phosphorus. The ZEAH system proved to be quite efficient in mobilizing ammonia. The oxidation of ammonia by nitrifying bacteria was the main process of removing this nutrient, with nitrate corresponding to more than 80% of the inorganic nitrogen dissolved in all the studied treatments. Of the total N and P added by the feed, the shrimp absorbed 42% of N and 35% of P in TV and 21.5% of N and 16% of P in TP,these high values indicate that shrimp are able to make better use of nutrients in the ZEAH system, compared to other farming systems. The accumulation of orthophosphate was more intense in PT compared to vannamei. About 35% of the phosphorus added by the feed was measured as orthophosphate in this treatment. The increase in the availability of phosphorus can cause problems for shrimp farming, such as the appearance of harmful cyanobacteria. In this way, some measures of treatment of the culture water for the removal of this nutrient are presented.