A series of feeding trials were conducted in raceway-type aquariums with semi-purified diets for the purpose of biologically evaluating aquatic plants as diet ingredients for channel catfish. A protein concentrate extracted from water hyacinth was compared with casein for protein efficiency ratio (PER) with channel catfish fingerlings. The possibility that growth factors may be contributed by small amounts of dehydrated aquatic plant meal in the diet was tested by adding 5 or 10% water hyacinth meal or alfalfa meal to vitamin-free and vitamin-sufficient purified diets and to commercial-type diet formulations. Weight gains and mortalities were used as criteria for evaluating the experimental diets. The lengths of the feeding trials were 4 to 8 weeks depending upon the responses of the fish to the treatments. The PER (g gain per g protein fed) for the water hyacinth protein, 0.34, was much lower than that for casein, 4.87. Both hyacinth meal and alfalfa meal improved fish growth when added to vitamin-free diets but not when added to vitamin-sufficient diets. Water hyacinth meal provided significantly higher weight gains and lower mortalities than did commercial alfalfa meal when fed in vitamin-free diets. Water hyacinth meal did not improve the growth of fish when the plant meal was fed as 10% of commercial-type diets. The most feasible nutritional contribution of water hyacinth to channel catfish nutrition appears to be the supplementation of growth factors, when fed at low percentages, in vitaminpoor diets.
