The optimal period for changing the feeding regime of mono-sex male Nile tilapia (Oreochromis niloticus)

Abstract

There has been a lack of information reported on the appropriate period required to replace an original feed formula with a new feed for most fish species. In the current study, a feed containing high protein (HP) was replaced in daily increments of 12.5, 20 and 25% with low protein (LP) feed for mono-sex male Nile tilapia (3.68 ± 0.03 g initial weight) over a nine-week experimental period and the results compared with a control treatment continually fed with the HP feed. At the end of the feeding trial, the body weight, length and specific growth rate did not differ for fish fed with the 20 and 25% replacement levels (P > 0.05), while significantly decreased values were observed for the 12.5% replacement group. The feed conversion ratio was superior for fish receiving the 12.5 and 25% replacement levels, while the protein efficiency ratio showed no differences across all the dietary treatments. Changing the feeding regime had no significant effects on the specific activities of protein- and carbohydrate-digesting enzymes, while significantly lower lipase specific activity was observed for the control group fish. The RNA and RNA/protein ratio were highest in the fish receiving the 25% replacement level, followed by the 12.5 and 20% groups, with the control group lowest, while the protein concentration was lower than the control group at all replacement levels. The amounts of flesh proteins did not differ among all the dietary treatments, nor did the carcass moisture, crude protein or ash, while the crude lipid was higher in all the fish receiving the LP feed. The findings from the current study suggest that the optimal level for replacing the original feed formula with a new feed is 25% per day, which should be used as a practical feeding guideline for mono-sex male Nile tilapia.