Comparative analysis of Litopenaeus vannamei shrimp production during one or two intensive cycles in BFT system in nurseries in the extreme south of Brazil
Shrimp cultivation in nurseries in southern Brazil is restricted to the hottest times of the year, generally occurring from November to April. This restricted period for shrimp production in the region highlights the need to adopt a strategy that increases productivity and, consequently, profitability during fattening cycles. Thus, this study aimed to compare the production of Litopenaeus vannamei during two short cycles and one long in BFT system in nurseries in the extreme south of Brazil. The study was carried out in six nurseries with a total area of 600 m3 located at the Marine Aquaculture Station of the Federal University of Rio Grande (EMA / FURG) and consisted of two treatments with three repetitions each: two short cycles (CC) with 75 days each duration,the first being held from November 2011 to February 2012 and the second from February to May 2012; and a long cycle (CL) carried out from November to May 2012, totaling 150 days in duration. In the CC treatment, the shrimp were caught at the end of the first short cycle (CC1), in order to subsequently be restocked in the same experimental units used in CC1 for the second short cycle (CC2). The stocking density in all cycles was 42 shrimp / m2 and the average initial weight was 1.20 g in CC1 and CL and 1.40 g in CC2. Daily, water temperature (TºC), dissolved oxygen (O2D) and pH were monitored twice a day. Salinity, total suspended solids (TSS), sedimentable solids (SS), turbidity, nitrogen compounds, alkalinity,chlorophyll a and microorganisms. Biometrics were also carried out weekly to estimate growth and adjust the amount of feed (38% crude protein, Potimar Active 38, Guabi®, Brazil), which was offered twice a day through trays and bidding. A biometry was performed at the end of all cycles to determine the parameters of zootechnical performance. Based on the results obtained at the end of the experiment, an economic analysis was performed to compare the production cost for shrimp during two short cycles and one long cycle in BFT ponds in southern Brazil. Statistical analysis used in this study was the Kruskal-Wallis non-parametric test for water quality parameters and one-way analysis of variance (ANOVA) for the zootechnical performance of shrimp L. vannamei. In both treatments,there was no significant difference in the parameters of water quality, temperature, O2D, nitrogen compounds, phosphorus, SST and alkalinity. In contrast, pH, SS, turbidity and transparency were significantly higher in the CL treatment than in the CC treatment. Despite these differences, most water quality parameters were within the recommended range for cultivation of L. vannamei in both treatments, with the exception of pH and TºC. Cyanobacteria was the predominant group of microorganisms in both treatments, corresponding to 52% of the microbial community in the CL and 49% in the CC. Final average weight (26.41 ± 0.90 g), weekly growth (1.17 ± 0.04 g / week) and weight gain (1.14 ± 0.64 g) were significantly (p <0.05 ) higher in the CL treatment than in the CC treatment (11.70 ± 1.06 g; 0.98 ± 0.11 g / week; and 0.95 ± 0.64 g, respectively).The apparent feed conversion, in turn, was significantly higher in the treatment in the CL (1.57 ± 0.26) than in the CC (1.20 ± 0.12). Survival (68 ± 10.50% for CL and 80 ± 2.75% for CC), biomass (433 ± 79.92 kg for CL and 474 ± 45.65 kg for CC) and productivity (7200 ± 1598 kg / ha / cycle for CL and 7900 ± 913 kg / ha / cycle for CC) did not differ significantly between treatments. The total cost of production was higher in the CC treatment (R $ 18,246.10) than in the CL (R $ 17,324.40). In addition, through data on weight, production and total shrimp costs, the cost of production per kilo and the recipe, presented a recipe of R $ 13.57 / kg of shrimp in the CL treatment while the CC presented a negative balance of R $ 1.12 / kg of shrimp. In this way,among the production strategies in BFT nurseries for the extreme south of Brazil using the experimental conditions of the present study, it is possible to infer that the choice of the most appropriate strategy is a long cycle. However, it is necessary to take into account not only the data on zootechnical performance and production costs, but also the characteristics of local fisheries. These factors can influence the sale price and, consequently, the return on investment.