Does ingestion of duckweed (Lemna minor) improve the growth and productive performance of juvenile Nile tilapia (Oreochromis niloticus) given formulated feeds in a recirculation system?

The present study evaluated the effect of voluntary ingestion of duckweed (Lemna minor) on the growth and productive performance of Nile tilapia (Oreochromis niloticus) reared in a recirculation system (RAS). The constant availability of fresh lemna was compared with a control treatment without supplementation. In both treatments, the fish were fed a commercial feed for 28 days. The experimental design was completely randomized with two treatments and seven replications. Nile tilapia juveniles (21.95 +/- 0.22 g) were acclimated in 14 tanks (70 l) with a density of 10 fish per tank. All fish were fed daily with an extruded commercial diet (32% CP), three times a day, until apparent satiety. An amount of lemna was manually collected daily, washed, drained, and treated with absorbent paper to remove excess surface water, and then weighed and supplied to the tilapia tanks. Daily consumptions of feed and lemna were quantified. At the beginning of the experiments and after 28 days, all fish were fasted for 24 h, then anesthetized with eugenol (50 mg l(-1)), and weighed individually. Nile tilapia juveniles grown in a RAS can voluntarily ingest up to 0.5% of live weight in fresh lemna with no effects on growth and productive performance. The amount of lemna consumed decreased over time, from 0.5 to 0.2% of body weight. The fish that were exposed to lemna consumed less feed in the first week of the experiment, but this reduction was compensated over time with no impact on the total feed consumption (478.59 +/- 21.74 g).