EFFECT OF PROTEIN LEVEL AND STOCKING DENSITY ON GROWTH PERFORMANCE, SURVIVAL RATE, FEED UTILIZATION AND BODY COMPOSITION OF NILE TILAPIA FRY (OREOCHROMIS NILOTICUS L.)

Abstract

This study was carried out to evaluate the growth response of Nile tilapia; O. niloticus L. to dietary protein levels at two stocking densities. This study was bifactorial designed (3 protein levels × 2 stocking densities). Fish (1.8-2.5 g/fish) was randomly distributed into the aquaria at a rate of 15 or 30 fish/100 L. The temperature was adjusted at 27±1 o C. Fish of each density were fed either a diet containing 25%, 35% or 45% CP with a feeding rate of 4% of life body weight twice daily for 5 days a week for 70 days. The results showed that final body weight, percent weight gain, and specific growth rate (SGR) were positively affected by protein level and inversely affected by stocking density, but not affected by their interaction. Condition factor was significantly affected only by dietary protein levels (P<0.05), while survival rate was not significantly by protein levels or stocking densities. The maximum growth was obtained with 45% CP at low density (10.1 g/fish) whereas the lowest growth was obtained in 25% CP at high density (6.4 g/fish). On the other hand, the reduced growth at high density could be recovered by increasing the dietary protein level. Feed intake increased significantly with increasing dietary protein level only (P<0.01). Feed conversion ratio (FCR), protein efficiency ratio (PER) and protein productive value (PPV) were significantly affected by protein level and stocking density (P<0.01). The best FCR was obtained with 45% protein diet at low density (1.72) and with 35% under low density (1.81) with insignificant difference (P>0.05). The highest values of PER and PPV were obtained with 25% CP at low (1.913 and 30.54%, respectively) and high density (1.720 and 26.64%, respectively) with significant difference (P<0.01). Moisture was significantly affected by protein level only (P<0.05), while crude protein, total lipids and ash were significantly affected by protein level and stocking density. The highest protein content in fish body was obtained with 45% CP at low and high densities (58.0% and 57.9%, respectively; P>0.05). The highest content of body lipids was observed 265 in fish fed 25% protein diet at low and high densities (32.8 and 31.0%, respectively; P>0.05). Significant difference in carcass ash between low and high density of fish was observed (15.6% and 16.8%, respectively; P<0.05). The lowest carcass ash contents were obtained in fish fed 25% protein diet at low and high density with 13.0% and 13.9%, respectively. The difference in the low carcass ash content, however, was not significant (P>0.05).