Effect of the chemical and physical-biological parameters of water on the food consumption of juvenile shrimp Litopenaeus vannamei grown in a clear water and biofloc system
Ammonia and nitrite, a case in high concentration in the cultivated water, can affect several performance and physiological parameters of peneid shrimp. Ammonia and nitrite tend to accumulate and reach high levels, in cultivation systems without water renewal; alkalinity, however, tends to decrease in these cultivation systems. In superintensive cultivation systems without water renewal, bioflocules or suspended solids are composed, which tend to accumulate and reach high concentrations. Bioflocs act to maintain the level of nitrogen and represent a source of nutritional supplementation for shrimp. However, the presence of suspended solids, in excessive quantity, in the cultivated water is capable of causing a negative effect, both on the water quality and on the performance of the shrimp.The present study aimed to evaluate the effect of ammonia, nitrite, alkalinity and suspended solids on food consumption and other performance parameters of Litopenaeus vannamei juveniles grown in water containing bioflocs and filtered, chlorinated and dechlorinated water (clear water). For that, for 3 days, prawns of 4.50 ± 0.27 g, 4.98 ± 0.36 g, 4.06 ± 0.34 g and 3.20 ± 0.22 g were kept in 3 L containers (1 animal / container), respectively under Control, 4, 8 and 12 mg / L ammonia concentrations, Control, 6, 20 and 60 mg / L nitrite, Control, 50, 100 and 200 mg / L alkalinity and Água Clara, 325, 750, 1000 and 1500 mg / L of suspended solids, with 5 repetitions each, in bioflocs and clear water. The temperature, dissolved oxygen, salinity, pH, ammonia, nitrite, nitrate,alkalinity and suspended solids were evaluated daily. Food consumption, measured over a period of 1 hour, was checked once a day and weight gain, specific growth rates and feed conversion and survival were evaluated at the end of the experiments. In the studies of ammonia and nitrite, it appears that the food consumption of shrimp is not affected between nitrite levels and in clear water and bioflocate systems (0.10, 0.07, 0.08 and 0.06 g ration / shrimp / hour and 0.10, 0.10, 0.09 and 0.09 g ration / shrimp / hour, respectively); in the lower concentration of ammonia, Controle, it is positively affected in the biofloc system (0.12 g ration / shrimp / hour). The weight gain and the specific growth rate are positively affected at the lowest levels of nitrite, Control and 6 mg / L, in the biofloc system,and in the lowest concentration of ammonia, Controle, also in the biofloc system, where they present the best results. The feed conversion rate is not affected between nitrite levels and in clear water and biofloc systems; however, in the lowest concentration of ammonia, Controle, in the bioflocals system, is positively affected. And survival is negatively affected in the highest concentration of nitrite, 60 mg / L, in the clear water system; however, between ammonia levels and in clear water and biofloc systems, it is not affected. In the study of alkalinity, it is observed that the food consumption of animals is not affected between the levels of alkalinity and in the systems of clear water and bioflocs (0.06, 0.05, 0.06 and 0.07 g ration / shrimp / hour and 0.08, 0.07, 0.07 and 0.09 g ration / shrimp / hour, respectively).Weight gain and the specific growth rate are positively affected in the highest concentrations of alkalinity, Control and 200 mg / L, in the biofloc system, where they demonstrate the best results. And survival, like food consumption, is unaffected between alkalinity levels and in clear water and biofloc systems. And finally, in the study of suspended solids, it appears that the food consumption of the shrimp is negatively affected in the highest concentration, 1500 mg / L of bioflocules (0.01 g ration / shrimp / hour). And weight gain, specific growth rate and survival, are also negatively affected at the highest level, 1500 mg/L of suspended solids, where they present the worst results. Thus, although some performance parameters of the animals were not affected in the studies carried out,the possibility of exposure to inadequate levels of the chemical and physical-biological parameters of the water, for long periods of time, can negatively affect the shrimp. Thus, the importance of maintaining water quality in conditions appropriate to the cultivated species is emphasized, regardless of the cultivation system adopted, so that its best performance can be demonstrated.