Biofloc technology (BFT) applied to tilapia fingerlings production using different carbon sources: Emphasis on commercial applications
Introduction
Microbial biofloc has been recognized as an important food source for tilapia (Long et al., 2015; López-Elías et al., 2015; Pérez-Fuentes et al., 2016) and shrimp (Ballester et al., 2010; Brito et al., 2016; Moreno-Arias et al., 2018). Biofloc technology, BFT by its acronym in English, was developed to solve the problems of available space due to high land costs, as well as to reduce the water requirements.
Another advantage of biofloc culture systems is the control of toxic nitrogen compounds, mainly due to the action of heterotrophic and nitrifying bacteria that thrive in biofloc. The accumulation of un-ionized ammonia (NH3) from the metabolism of the cultivated organisms, as well as the dissolved oxygen content, are the main factors that define the load capacity in the aquaculture systems (Timmons et al., 2002). In BFT, NH3 conversion has three pathways: a) photo autotrophic assimilation by algae, b) by autotrophic bacteria that convert NH3 to NO2 and NO3, and c) by the action of heterotrophic bacteria that use the potential sources of ammonia (organic matter) and convert them into microbial biomass (Ebeling et al., 2006; Martínez-Córdova et al., 2015).
Biofloc has a high rate of regeneration. In this system while some materials are degraded, others are generated. The approximate residence time of biofloc has been estimated in 8 h (Avnimelech and Kochba, 2009) and the renewal process can be controlled by the addition of organic carbon. The amount of carbon (C:N ratio) and its source can have a significant influence on water quality maintenance, as well as being related to the abundance of heterotrophic bacteria and nutritional quality of the biofloc (Crab et al., 2010; Du et al., 2018). Bacteria and other microorganisms use carbohydrates (sugars, starch and cellulose) as source of energy. These microorganisms produce high quality biomass, which serves as a basis for various food webs. The percentage of carbon assimilated in respect to the metabolized carbon feed, is defined as the microbial conversion efficiency and is in a range of 40–60% (Avnimelech, 1999). Diverse sources of carbon can produce different fish performance, and in addition to their cost, can influence decisively when choosing which source to use in BFT.
The microbial floc is used as a supplementary feed by the cultured organisms (Martínez-Córdova et al., 2015; Pinho et al., 2017), as they are considered sources of fatty acids, essential amino acids, minerals and vitamins as well as immunostimulants (Martínez-Córdova et al., 2017; Moreno-Arias et al., 2018).
Tilapia farming is one of the most important activities to supply fish protein, the Nile tilapia (Oreochromis niloticus) being the second most reared species in the world (FAO, 2016). The availability of good quality fingerlings at competitive prices is very important to maintain the profitability of the farms. The majority of tilapia studies in biofloc have focused on juveniles (Azim and Little, 2008; Ekasari and Maryam, 2012) and adults (Pérez-Fuentes et al., 2016), meanwhile the research dedicated to fingerlings is scarce. The tilapia breeding companies normally operate with high rates of water exchange, to maintain the water quality, as well as to control the presence of pathogens. Additionally, in tilapia fingerlings production, aquafeeds with high protein content are used; its excessive price increases the production cost.
The microbial protein could be a promissory source of food, since tilapia is an omnivorous species. Microalgae and zooplankton are part of its diet in the natural environment during the fingerling stage (El-Sayed, 2006). In this study, we expected to contribute with information that permits to save pelleted feed, maintaining water quality, producing better quality fingerlings and reducing water use. The objective was to determine the effect of the BFT system using different carbon sources on the productive parameters, demand of feed and water in tilapia fingerlings (Oreochromis niloticus) production.
Section snippets
Experimental design
The study was conducted in a commercial laboratory, Centro Acuícola del Estado de Sonora (CAES), which belongs to the Instituto de Acuacultura del Estado de Sonora (IAES). The experiment was carried out in a greenhouse (3 × 2 m2). The design was simple randomized with three treatments and one control (in triplicate). The treatments (carbon sources) were corn flour (CF), wheat flour (WF), unrefined sugar (SU) and a control (C) traditional system of culture without biofloc and water exchange (10%
Water quality
Throughout the study, dissolved oxygen means ranged from 5.91 to 5.94 mg/L, with no significant differences among treatments. The pH was from 7.78 to 8.64 and temperature averages remained similar, with values from 25.91 to 25.93, the ANOVA test showed no significant differences (Table 1).
The total suspended solids increased according to the culture period. In general, the lowest concentration corresponded to the control treatment (49.6 mg/L, end of the trial), and the highest to the wheat
Discussion
Dissolved oxygen is a limiting factor that affects the metabolism of fish, modifies the rate of consumption and influences growth, in this research remained above 5.9 mg/L. The recorded levels were within the optimum range for tilapia culture (El-Sayed, 2006) and are similar to those obtained by Ekasari and Maryam (2012), who worked with red tilapia on BFT systems. The control treatment maintained oxygen concentrations similar to the treatments in biofloc due to the 10%/day of exchange rate. In
Conclusion
The biofloc system presented advantages over the traditional culture with better FCA and EP, it additionally improves the economic indicators. As a consequence of the observed results, the BFT system emerges as an eco-friendly alternative to produce tilapia fingerlings.
Acknowledgements
To the National Council of Science and Technology (CONACYT) project 206155. The first author received a CONACYT scholarship (571768) to obtain the Master degree. The company Centro Acuícola del Estado de Sonora (CAES) contributed with the facilities and experimental organisms.
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