MAXIMISING THE BENEFITS OF MULTI-ENZYMES FOR AQUATIC DIETS: POTENTIAL ON GROWTH PERFORMANCES IN TILAPIA

Higher inclusion of plant-based protein s  to sustainably replace fishmeal (FM)  in aquatic feeds has necessitated the inclusion  of micro-additives such as exogenous enzymes to improve digestibility and nutrient availability .  Two tria ls were designed to assess the effects of combining phytase , xylanase and protease in low FM diets on growth, digestibility and intestinal integrity of  red tilapia (Oreochromis niloticus x O. mossambicus ). These experiments were supported by  a  life cycle assessment  (LCA) to evaluate the environmental impacts of enzyme- supplemented diets and  commercial feeds used by the industry.

In trial 1 , tilapia were fed  six diets,   0%, 3% and 5% FM diets with and without xylanase (0.385 g/kg) and phytase (0.075 g/kg). The study showed no significant differences between p erformance efficiencies  (feed intake, FCR,  weight gain) of the enzyme- supplemented 3% FM  diet and the 5% FM control (P<0.05) (Table 1). No enzyme-related effects were noticed for protein dig estibility, however, P digestibility improved by 9% , except at the 0% FM level (P<0.05) . Villus integrity worsened with declining FM levels with no observed improvements in fish fed enzyme supplemented diets.  Cost reduction due to lower FCRs as a result of enzyme inclusion were also observed.  Modest  performance improvements suggested that phytase and xylanase had positive synergistic action but further research was required.

In trial 2 , protease was added to the cocktail. Tilapia were fed five diets, a 2% FM negative control (no enzymes) , 2% FM with phytase + xylanase only , 2% FM with phytase + xylanase + 0.2 g/kg protease, 2% FM with phytase + xylanase and 0.4 g/kg protease, and a 10% FM positive control.  Growth performances improved significantly over the negative control (Table 2) .  Fish fed diet supplemented with 0.2  g/kg protease showed the greatest gain  in weight (26%),  feed intake (19%)  and villi lengths while the diet supplemented with 0.4g/kg protease had the best FCR, all categories mentioned were not statistically different from the performances of fish fed the 10% FM control (P<0.05) .  Highest digestibility gain were observed for diets supplemented with phytase and xylanase only.  Ternary combination of xylanase , phytase and protease (0.2 g/kg) demonstrated great potential in limited FM use for tilapia feeds. Future research should target indigestible dietary components  in order to optimise enzyme dosage and maximise their respective benefits for tilapia production.

LCA outputs showed that the low FM enzyme-supplemented diets had lower impact potentials (global warming, eutrophication, acidification and energy use) . LCA components are recommended for  traditional  least cost formulation programmes to demonstrate  a greater level of  environmental stewardship on the part of aquafeed producers and  in turn  improve  the overall sustainability of the aquaculture industry.