TILAPIA (Oreochromis niloticus) PERFORMANCE IN CLEAR-WATER RAS, BIOFLOC, AND HYBRID NURSERY SYSTEMS
Biofloc-based production systems convert waste to microbial biomass, contained largely on small, suspended "biofloc" particles, which can be consumed by tilapia. Fingerling and adult tilapia growth has been shown to increase in biofloc systems when compared to clear-water recirulating aquaculture systems (RAS) due to their consumption of biofloc, however the effects of biofloc on tilapia fry growth are unclear. Both clear-water and biofloc systems have production advantages and disadvantages; hybrid systems combining features of both have recently been proposed in an attempt to optimize animal performance. This study compared the growth rate of tilapia fry in clear-water RAS, biofloc, and hybrid systems.
Twelve 0.19 m3 tanks were stocked with 55 tilapia fry at an average weight of .17g per fish in the KSU Production Technologies Building. Three treatments were created: 1.) clear-water RAS (CW), 2.) Biofloc (BF), and 3.) Hybrid (HY) systems, these were each randomly assigned to four replicate tanks. The CW tanks had a settling chamber, a foam fractionator, and an external biofilter containing plastic biomedia. The BF tanks only had a settling chamber to control solids concentration, and the HY systems used a settling chamber and an external biofilter. All systems were fed the same amount of feed 3 times daily. Ammonia, nitrite, nitrate, turbidity, and TSS/VSS were measured weekly and fish weights were sampled biweekly.
We found no significant difference between tilapia growth in the three systems. Fish in the hybrid treatment had the highest average weight and the highest specific growth rate (SGR). HY tanks had an average weight of 10.5g/fish, CW averaged 10.1g/fish, and BF tanks averaged 10.1g/fish. SGR was 18.2 in the HY systems, 17.3 in the CW systems, and 17.3 in the BF systems. The variability between tanks in both average weights and SGR was significantly higher in the BF systems than clear-water and hybrid systems. Ammonia, nitrate, and TSS/VSS levels were not significantly different between treatments. Nitrite and turbidity levels were significantly higher in the BF systems versus the other system types, although nitrite never exceeeded tilapia tolerance levels. Although some previous research indicates that tilapia fingerlings and adults have higher growth in biofloc, the results of this study indicate that tilapia nursery system design may have little impact on overall growth. System managers may therefore choose the lowest cost system for tilapia nurseries. This would likely be biofloc systems, as they have the least amount of filtration; however, the oxygen consumption and potenital need for greater aeration in biofloc systems should be explored further.