Effect Of Dietary Phosphorus On Protein Intake And Productive Protein Value Of Young Hybrid African Catfish (Pisces: Clariidae)

Abstract

Three hundred and sixty four weeks old advanced fry of the hybrid African catfish (Clarias gariepinus (♀) x H. Heterobranchus bidorsalis (♂)) (mean weight, 1.25 ± 0.02 g) were obtained from the hatchery of the African Regional Aquaculture Centre (ARAC), Port Harcourt, Nigeria and held in 15 aerator-fitted glass tanks (55 x 30 x 30 cm³-1). The diets were compounded isonitrogenous at 38% crude protein (CP) with 4 inclusion levels (0.60, 0.80, 1.00, 1.20%) of phosphorus (P) applied as monocalcium phosphate {Ca₃ (PO₄)₂}. The inclusion levels of the conventional feed ingredients (yellow maize, soyabean meal, blood meal and rice bran) were staggered in accordance with their protein and P contents and in order to achieve the desired dietary P levels. The average weekly feed intake (FFW), protein intake (PI), feed conversion ratio (FCR) and proximate composition of fish and diets were determined. Also, productive protein value (PPV), the ratio of retained body protein-to-protein intake was determined. The average weekly feed intake increased with dietary P increase for 0.60 (1.46 g), 0.80 (1.57 g), 1.20 (1.80 g) and not for 1.00% (1.44 g). This increasing response trend was demonstrated in the FCR and PPV of fish where the 1.00% dietary P had the best fish response and the 1.20% dietary P had the least response. This result also paralleled the least values of protein and fat depositions recorded for 1.20% dietary P level whereas the other dietary P levels and the control were comparatively higher. It was evident that the experimental fish probably demonstrated a consistent response to increasing dietary P level between 0.60 and 0.80% P for FFW, FCR, PPV and PI, and the values obtained were respectively lower than the value for control. There was depression in protein deposition between 0.60% P (19.25%) and 0.80% P of (18.94%) while fish fed the control diet deposited more quantity of protein (19.63%). Conversely, there was an enhanced fat deposition as the dietary P increased from 0.60 to 0.80% while the control diet paralleled that of 0.60% P. However, the mean lipid content of fish decreased with increasing P level. Generally, there was no significant effect (P > 0.05) of increasing the dietary P level on the response of fish to FFW, FCR, PI and PPV.


Key words: Catfish hybrid, dietary phosphorus level, protein intake, productive protein value, protein deposition.


Journal Of Agriculture And Social Research Vol. 5 (1) 2005: 18-24