COMBINATION OF PRE-GELATIZED AND ISO-MALTOSE ON THE PELLET CHARACTERISTICS AND SUBSEQUENT EFFECTS ON THE FEEDING EFFICIENCIES AND NUTRITIVE VALUE OF AFRICAN CATFISH, Clarias gariepinus

The two main functions of starch in aquafeeds are to act as a binder as well as an inexpensive energy source to fish.  Both these characteristics can potentially be improved through pre-gelatinization, which usually involves the application of heat and water to degrade the less digestible regions of starch.  While this can improve both the pellet characteristics as well as fish growth, a potential downside can include less intestinal bacteria.  This may be mitigated by the inclusion of a prebiotic, which is an indigestible carbohydrate that can act as a substrate for beneficial bacteria in the intestine.  In this study, we compared different diets that consisted of native tapioca starch (TS), TS with isomaltose (TS+Iso), pre-gelatinized TS (PGTS) and PGTS with isomaltose (PGTS+Iso) on the growth, feeding efficiencies, whole-body proximate composition, and liver glycogen content to African catfish (Clarias gariepinus) after 7 weeks. Pellet characteristics were also measured that included bulk density (BD), pellet durability index, water solubility index (WSI), water absorption index (WAI), and water stability (WS).

All diets were isonitrogenous and isolipidic and in the isomaltose diets, this was added at 0.5%.  Triplicate groups of 15 fish (initial mean weight = 7.51 g) were fed their respective diets to apparent satiation.  

Results showed that the WSI and WAI were significantly higher by in the PG diets than the others, while the pellet durability index was slightly better.  There are no significance differences between treatments in growth of catfish (p > 0.05), but feed intake was significantly less in the PGTS and PGTS+Iso treatments.  Crude protein and lipids were significantly lower and higher in the PGTS treatments, but the crude protein content was significantly improved when Iso was present with PGTS (i.e. the PGTS+Iso diet).

Overall, the PGTS+Iso diet could be recommended since this significantly reduced feed intake, but without compromising growth.  This result, along with better pellet characteristics, could substantially reduce feeding costs during the production of C. gariepinus.