Nile tilapia (Oreochromis niloticus) is one of highest produced species in inland aquaculture in South-East Asia with a rapid increase in the last 30 years. One factor causing the production increase is the addition of fish feed. However, feeding enriches the water with nutrients and contaminates surrounding water bodies when discharged without treatment.
Biofloc in water bodies acts as a natural water treatment agent that can decompose organic waste in ponds and transform it into protein biomass. However, commercial feed often produces organic waste with an imbalance C:N ratio to support the growth of microbiota particularly due to the lack of carbon in fish feces. This study aims to investigate the effects of substituting starch-rich ingredients (Control-diet) with non-starch polysaccharides (NSP) rich ingredients (High-NSP-diet) on nitrogen (N), phosphorus (P), and carbon (C) retention use efficiency by fish and biofloc. The NSP ingredients mostly come from palm kernel meal, rice bran, and corn gluten feed. Both diets are equal in protein but the High-NSP-diet contains triple fiber.
There is a trend that the High-NSP-diet results in a lower fish average daily gain compared to the Control-diet (around 11% lower, p-value>0.05). Both treatments result in similar biofloc characteristics (N, P, C concentration). However, nutrients were better used by biofloc under the High-NSP-diet. This was shown by a lower retention efficiency (RE) of N, P, and C in the water of almost 4%, 12%, and 7%, respectively, as compared to the Control-diet (Figure 1). RE of N and C were similar between both diets from week 0 to week 4. Then, from week 4 to week 6, biofloc in the High-NSP-diet shows a statistically higher RE of C and N than the Control-diet (33-43% higher), indicating a richer carbon in the water of the High-NSP-diet pond after four weeks.
Economic calculation shows that the High-NSP-diet can save feed production costs to 3,630 IDR/kg. Therefore, incorporating of High-NSP-diet has the potential to reduce feed costs without sacrificing much on fish production, and to improve nutrient use efficiency.