Rearing European Eel (Anguilla anguilla) Elvers in a Biofloc System

Abstract

European eel (Anguilla anguilla) elvers (initial body weight (BW) = 3 g) were raised in triplicate for 60 days in a biofloc system (BFT) at 21 °C. Data from the current first study evaluating this farming technology indicated that European eel elvers adapted well to BFT systems as data on growth performance (specific growth rate = 1.48% ± 0.13 BW/day and FCR = 1.05 ± 0.09) indicated, with production costs using BFT being lower than conventional RAS units. The most critical issues associated with this aquaculture system were the maintenance of the biofloc in tanks by the regular addition of refined sugar (46% C) to keep a relationship for C:N of 20:1, and the prevention of emergence of opportunistic pathogens like the monogenean Pseudodactylogyrus sp. The overall results of this study in terms of elvers' performance and quality and the composition of the biofloc material and its microbial composition indicated that BFT, which is considered to be one of the most cost-effective, sustainable, and environmentally friendly farming systems due to its zero water exchange and improvement of feed conversion ratio by the dietary contribution of bioflocs, may be satisfactorily used for farming European eels elvers at a density of 2 kg/m³. However, further studies are needed to test this technology with older eel stages.

Keywords: European eel; biofloc; biofloc microbiota; sustainable aquaculture.

Figure 1

General view of the experimental BFT tank showing the muddy colour of water due to the growth of biofloc particles and the strong aeration provided to keep biofloc particles in suspension in the water column (A). View of the Inhoff cones used for regular evaluation of suspended solids in the system (B). Detail of a biofloc particle under the binocular microscope for its measurement (C). Detail of a biofloc particle in which nematodes attached to the organic matter of the biofloc may be seen, and some isolated protozoans may be identified (D).

Figure 2

Dendograms (UPGMA method, GeneTools) from RFLP analysis of microbial samples collected from fish intestine, water, and biofilm samples in BFT and RAS systems. Each restriction enzyme used is shown in the upper left corner of the corresponding dendogram. BA = A. anguilla from biofloc tanks; RA = A. anguilla from RAS; BSA = biofloc sludge from tanks containing A. anguilla; RASW = water sample from RAS tank; BFAW = water sample from biofloc tank containing A. anguilla.