Desempenho da Daphnia magna (Straus, 1820) cultivada em efluente de Tilápia do Nilo cultivada em sistema de bioflocos com diferentes relações C:N

Abstract

In aquaculture, systems with minimum water exchange are an alternative to sustainable farming. Biofloc technology (BFT), which consists of the formation of microbial aggregates through the manipulation of the carbon: nitrogen ratio of the culture medium is an option in reducing the emission of effluents. However, the accumulation of nitrogen and phosphate residues over several crop cycles in this system ends up causing significant impacts with the release of effluent into the environment. Therefore, Daphnia magna, which is a microcrustacean of the cladoceran family that benefits from the organic mater present in the aquatic environment, can be used for the bioremediation of this effluent. The cultivation of this microcrustacean is traditionally carried out in a clear water system with the addition of the microalgae Chlorella vulgaris in its diet. In this way, the present work aims to evaluate the performance of D. magna cultivated in effluent waters of the BFT system in different carbohydrate: nitrogen ratios with the inoculation of C. vulgaris microalgae and fish feed supplementation. The experimentation is done with six treatments in triaplicates based on two factors, being : Ratio C: N (10: 1, 15: 1 e 20: 1) and Feed (with addition of fish feed (R) or without addition of fish feed (SR)). The variables of water quality: temperature (°C), dissolved oxygen (mg.L-1), salinity (gL-1), pH, NO2 (mg.L-1), TAN (mg.L-1), hardness and alkalinity were measured throughout the culture. The specific growth rate (TCE), doubling time (TD), maximum mean density (DMX), yield (R) and day of maximum density (DMD) were verified for the growth variables. To the variables pH, temperature, Salinity, TAN, Nitrite and Hardness there were no significant differences (p> 0.05) throughout the culture. Regarding dissolved oxygen there was a significant difference for the ration factor and for the interaction between the ration and feed factors. There was also a significant difference when the alkalinity was treated for the ration factor, the feed factor and for the interaction between them, with an average of 50.93 and 80.37. The pH, dissolved oxygen and temperature were favorable for the proper development of the cladoceran. Although there were statistical differences only for the ration factor, the DMXs were between 1001 ± 283 and 3433 ± 267 org.L-1. The days of maximum density were 12º, 14º and 18º days. The 10SR treatment provided a higher average maximum density of Daphnia magna on the 14th day of cultivation, besides showing TCE, TD and R values higher than the other treatments. However, all treatments allowed the growth of the cladoceran, proving that the use of the effluent is an alternative to the production of live food.