Effects of fermentation methods on the nutritive value of water hyacinth for Nile tilapia Oreochromis niloticus (L.) fingerlings

This study was conducted to evaluate the effects of different fermentation methods on the nutritive value of water hyacinth (WH) for Nile tilapia fingerlings. Fresh dry hyacinth (FH), molasse-fermented hyacinth (MF), cow rumen content-fermented hyacinth (RF) and yeast-fermented hyacinth (YF) were incorporated into nine isonitrogenous (35% CP), isocaloric (450 kcal GE/100 g) test diets, as a replacement of dietary wheat bran at 10% and 20% substitution levels. The test diets were fed to triplicate groups of fish fingerlings (1.1 g average body weight) stocked in 20-l fiberglass tanks, in a closed, recirculating indoor system, twice a day, at 5% body weight/day, for 50 days. The control diet (WH-free) produced significantly better weight gain, specific growth rate (percent SGR) and feed utilization efficiency than WH-based diets. Growth rates and feed utilization efficiency of fish fed WH at 10% inclusion level were not significantly affected (P > 0.05) by WH fermentation methods. At 20% inclusion level, fish performance was further reduced (P < 0.05); however, fermented WH produced better performance (P < 0.05) than fresh WH. Molasse-fermented WH was utilized more efficiently than yeast-fermented and cow rumen-fermented WH, respectively. These results indicate that fermentation of WH may only be necessary when incorporated into Nile tilapia diets at greater than or equal to 20% inclusion levels. (C) 2003 Elsevier Science B.V. All rights reserved.