Apparent nutrient digestibility of seaweeds by rainbow trout (Oncorhynchus mykiss) and Nile tilapia (Oreochromis niloticus)

The apparent digestibility coefficients (ADCs) of four seaweeds, Poiphyra dioica, Ulva spp., Gracilaria vermiculophylla and Sargassum muticum, were evaluated in rainbow trout and Nile tilapia. Porphyra, Ulva and Gracilaria were produced in land-based integrated multi-trophic aquaculture (IMTA). This production method resulted in increased protein content when compared to wild specimens and to the wild-harvested Sargassum. For both, trout and tilapia, the ADC of the experimental diets was generally lower than the reference diet, though in trout, protein digestibility of Gracilaria diet was similar to the reference diet (90%). In terms of the calculated seaweed ADC, the results vary significantly according to the seaweed and fish species. In trout, protein ADC of Gracilaria (88%) was significantly higher than all other seaweed (66-80%). Best lipid ADC was recorded for Gracilaria (97%), although not significantly different from Porphyra (94%). In tilapia, protein ADC was higher for Ulva (63.4%) and Sargassum (65.1%) than for the other seaweed. In lipid ADC, Gracilaria was significantly lower (82%) compared to all other test seaweed (91-95%). Overall trout seems to digest better Gracilaria, whereas tilapia does better with Ulva and Sargassum. The results demonstrate that IMTA-seaweed can be considered good ingredients for fish feed. (C) 2012 Elsevier B.V. All rights reserved.