TOWARD MORE ENVIRONMENTALLY FRIENDLY AQUACULTURE: EFFECT OF DIETARY EXOGENOUS ENZYMES (NATUZYME®) ON NITROGEN AND PHOSPHORUS RETENTION AND EXCRETION IN NILE TILAPIA (Oreochromis niloticus)

Yasser T.A. Moustafa1* and Talaat N.A. Amer2

1Department of Limnology, 2Department of Fish Nutrition, Central Laboratory for Aquaculture Research (CLAR), Agriculture Research Center, Egypt.

*Corresponding author’s e-mail: [email protected]

Abstract

The present study investigated the effect of commercial enzymes mixture, Natuzyme® (NZ) in all-plant based diets on the retention and excretion of both nitrogen (N) and phosphorus (P) in Nile tilapia (Oreochromis niloticus). Five iso-nitrogenous (28 % crude protein) and iso-energetic (425 kcal / 100 g) diets were formulated. Fishmeal-based diet (FM-diet) served as a positive control and four soy bean meal-based diets (SBM-diet) were supplemented with 0, 0.5, 1 and 1.5 g NZ/kg diet, respectively. The diets were offered twice daily to apparent satiation in triplicate fish groups (2.52g/fish) for 12 weeks. The N and P supply were significantly higher (p≤0.05) with FM-diet, while the lowest nutrients supply was recorded with SBM+NZ1 diet. The apparent retention rate % (ARR%) for N and P showed a positive relation with the level of NZ. The highest ARR% for N and P were obtained with SBM+NZ4 diet, while the lowest ARR% values were recorded with SBM+NZ1 diet. The highest fish N content was measured with FM-diet, whereas the highest P content was achieved with SBM+NZ4 diet. The excreted N% and P g/aquarium showed an opposite trend of ARR%. The NZ had a significant reducing effect on the inorganic fraction of both excreted N and P, where it reduced the dissolved in-organic nitrogen (DIN) as a percent of excreted N and orthophosphate  as a percent of excreted P. This study provided fundamental insight to enhance N and P retention efficiency of Nile tilapia and to reduce their excretion through using ‟environmentally-friendly” additive NZ in plant based diets which in turn limit or at least postpone the eutrophication problem.

Keywords: Nile tilapia, O. niloticus; all-plant diets; exogenous enzymes; nitrogen and phosphorus retention and excretion; sustain environment.