A comparison of recirculation aquaculture systems versus biofloc technology culture system for on-growing of fry of Tinca tinca (Cyprinidae) and fry of grey Mugil cephalus (Mugilidae)

Abstract

The on-growing of tench Tinca tinca fry (1.81 ± 0.6 g) and grey mullet Mugil cephalus fry (0.65 ± 0.2 g) was carried out using two different culture systems, recirculation aquaculture system (RAS) and biofloc technology culture system (BFT), to compare their performance and evaluate the technical feasibility of rearing both species using an alternative method. After an on-growing period of 50 days, it was possible to verify that the survival rate, fish size in terms of body weight and length, condition factor (K), specific growth rate, gained biomass and apparent feed conversion rate of M. cephalus fry were significantly higher (P < 0.05) in RAS in comparison to those obtained using BFT. For Tinca tinca, results were similar for all the measured variables except for the condition factor, that was significantly higher in BFT (P < 0.05). Water quality parameters remained within the optimum ranges reported for freshwater fish species using RAS. In BFT, despite the constant addition of glucose, total ammonium concentrations were relatively high (2.89 ± 1.25 mg NH4+/L for tench and 3.74 ± 1.34 mg NH4+/L for mullet) because the small volume of water in tanks (90 L) and the use of inert diets with high protein levels (> 50%). Ammonia could only be stabilized when the feed was replaced with one with a lower protein content (35%). The proximate composition of the bioflocs showed that the composition varied according to the fish species considered: with mullet, the protein (17.34 ± 1.40%) and fat (2.36 ± 0.03%) were present in higher concentration than in tench (8.92 ± 0.38% and 2.18 ± 0.18%, respectively), indicating that regardless of the use of the same BFT procedures, bioflocs developing for both species were different. The microbial diversity in the tank water and the intestinal microbiota of fish were examined by restriction fragment length polymorphism (RFLP) and found to be different depending on the system used for on-growing. Thus, in the RAS system the microbial diversity was somewhat higher than in the BFT. As a conclusion, present results indicated that Tinca tinca seem to be able to adapt to the BFT systems.