EVALUATION OF COASTAL BERMUDA GRASS PROTEIN ISOLATE AS A SUBSTITUTE FOR FISH-MEAL IN PRACTICAL DIETS FOR CHANNEL CATFISH ICTALURUS-PUNCTATUS

In response to concerns over availability and cost of fishmeal for aqu aculture feeds, a study was conducted to evaluate the suitability of a protein isolate from coastal Bermuda grass Cynodon dactylon for chann el catfish Ictalurus punctatus. The coastal Bermuda grass was treated by soaking in liquid anhydrous ammonia under high pressure at 70 C, a process known as Ammonia Fiber Explosion (AFEX), followed by pressure release, extraction and isoelectric precipitation for isolation of the protein. Amino acid analysis of the isolate (32% crude protein) indic ated a generally balanced profile that was first limiting in methionin e. A feeding trial was conducted in which four isonitrogenous and isoc aloric diets containing incremental levels of the extracted, isolated protein were evaluated. The control diet contained 10% menhaden fishme al and experimental diets were formulated so that the isolate replaced 33, 66 and 100% of the fishmeal on an equal-protein basis. Each diet was fed for 9 wk to triplicate groups of channel catfish fingerlings i nitially weighing approximately 14 g/fish. Apparent protein and organi c matter digestibility of the isolate also was determined utilizing ch romic oxide as an inert marker. Results of the feeding trial indicated that substitution of the isolate at all levels did not significantly (P > 0.05) affect weight gain, feed efficiency, protein efficiency rat io or protein retention of channel catfish. Apparent protein and organ ic matter digestibility coefficients of the isolate were 85 and 89%, r espectively. These data indicate that the isolate was readily digested by channel catfish and was able to replace menhaden fishmeal (at 10% of diet) without adversely affecting fish performance. Additional rese arch to evaluate substitution of other ingredients with the protein ap pear warranted. Further research to optimize protein isolation procedu res also is required.