Open access publications in the SLU publication database

Abstract

This thesis investigated the effects of dietary protein replacement of fishmeal or soybean meal with spent brewer’s yeast (SBY) in farmed tilapia and giant freshwater prawns. The effect of rearing tilapia and prawn in two different rearing systems, clear water recirculating aquaculture system (CW-RAS) and biofloc recirculating aquaculture system (Bio-RAS), were also investigated.

The fish reared in Bio-RAS displayed higher growth, a higher protein efficiency ratio and a lower feed conversion rate than fish reared in CW-RAS. This difference between systems was not as apparent in the growth and protein efficiency ratio of freshwater prawns.

In freshwater prawns, the survival rate was not affected by aquaculture water system nor by the replacement of fishmeal with SBY. The growth performance of prawns was not significantly different between any dietary treatments in Bio-RAS or CW-RAS. Significant differences were only found between brewer’s yeast replaced fishmeal at 60% in a CW-RAS and at 40% in Bio-RAS.

Tilapia reared in CW-RAS with replacement of fishmeal with SBY showed a significantly (p<0.05) lower weight gain, daily weight and specific growth rate than fish in Bio-RAS when all diet groups per treatment was combined. However, at diet group level this difference was significant only in the 100% replacement group of CW-RAS when compared with the control in Bio-RAS.

The protein requirement experiment showed that 27% and 31% crude protein can be used for tilapia in Bio-RAS and CW-RAS, respectively. The study demonstrated that tilapia reared in the Bio-RAS had a higher capacity to compensate for a reduction in dietary protein levels, as demonstrated by a higher growth rate than in fish reared in CWRAS. The apparent digestibility of crude protein by tilapia was high in diets with high crude protein, but there was no difference between the two rearing systems.

SBY replace up to 100% of soybean meal without a significant reduction in tilapia growth. Tilapia exhibited the best performance when fed a diet where 30% soybean meal was replaced with SBY.

This thesis concludes that SBY represents a sustainable, high-volume protein substitute for fishmeal and soybean meal in tilapia and giant freshwater prawn production and that the protein requirement of tilapia can be reduced if reared in a high-density microbial environment, i.e. a so-called Bio-RAS.