A comparison
of two types of biological filter for an intensive fish farm
Aquaflow
Technical Leaflet 2003-141
European
Network for the Dissemination of Aquaculture RTD Information
(Q5CA-2000-30105) and previously FAIR-3837, URL: http://www.aquaflow.org/
A series of tests were conducted in order to
determine the most suitable filter media for the biological filters of a
recirculating, intensive aquaculture farm in Portugal. The farm, Viveiro
Vila Nova S.A., grows sea bass (Dicentrarchus
labrax) and gilthead sea bream (Sparus
aurata).
The efficiency of two filter media –
“bio-grog”, a porous ceramic material, and “bio-ring”, plastic rings
– was assessed through an eight month monitoring programme of four
biological filters used in the company’s nursery and hatchery units. The
concentration of nitrogenous compounds (ammonia, nitrites and nitrates) was
determined by means of spectrophotometer analysis. In order to understand
better the results, determination of the level of metabolites throughout the
different growth phases of the gilthead sea bream and sea bass larvae was
made, as well as tests to estimate the amount of metabolites produced by the
live prey supplied to the fish larvae (rotifers
and Artemia).
Although both filter media presented similar
efficiencies throughout most of the monitoring period, the results of the
last two months in the nursery unit showed, with the increase in the
nitrogen compounds, that the “bio-grog” is more efficient in eliminating
these compounds. Data obtained during the growth of the fish larvae clearly
show that feeding the larvae with pellets resulted in increased levels of
ammonia. Tests performed on the live prey revealed that, for rotifers (Brachionus plicatilis) produced the highest levels of metabolites at
the highest density tested (30/40 individuals per ml), while the highest
levels of metabolites of Artemia were
recorded at the intermediate density (3 nauplii/ml).
Based on the general results obtained, the
“bio-grog” seems to be the most suitable filter media although it is
currently more expensive than ‘bio-ring’ (“bio-grog” costs
1,111€/m³+VAT and ‘bio-ring’ costs 290€/m³+VAT).
The “bio-grog” has a specific surface area that is much higher than the
“bio-ring” (1,200,000m²/m³ as compared with just
220m²/m³). In lower nitrogenous compound
concentrations (around 0.15mg/l of ammonia), the two filter materials have
similar efficiencies. However, at higher nitrogen levels (equal or greater
than 0.5mg/l of ammonia) that are very common in the rearing systems,
“bio-grog” is much more efficient, especially at the on growing stage of
the fish, with abundant distribution of pelletised feed and a lower feeding
efficiency.
*This work was done by the graduating student Vânia
Cristina Palma Roberto at the private enterprise.
For more information:
Ana
Pinheiro
Viveiro Vila Nova S.A.
Foros do Galeado
7645-073 Vila Nova de Milfontes
Portugal
Tel.: +283 997048
E-mail: ana.pinheiro@viveirovilanova.com