ARI Volume 2 Number 1.pdf - Zoo-unn.org

Influence of dietary protein content on gross protein:energy efficiency of Clarias gariepinus 213diet such as the type of dietary protein and theexperimental condition. This makes it difficult tocompare studies. The need to relate all reportsabout the dietary requirements and the nutritionalresponse studies of fish has been suggested byOgunji and Wirth (2001).Other studies (Jauncey, 1982; Wang etal., 1985; and Ogunji and Wirth, 2000) have alsoidentified the protein requirements of different fishspecies with varied results on the effect of proteinon growth rate, food conversion and bodycomposition. Variability in protein requirementscould possibly be due to the different effects of thefree amino acids supplied by the dietary proteinsand the consequent catabolism of tissue proteins.It has been reported that α-keto acids resultingfrom the catabolism of free amino acids are usedas a source of energy or carbon for fat synthesisor for glycogenesis (Kim et al., 1992). Theworkers also maintained that amino acid oxidationis principally influenced by the level of protein (oramino acid) or other energy sources in the diets.In addition, in the circulatory fluid of animalsincluding fish, most lipids form complexes withprotein (Gotto et al., 1986) in the form oflipoproteins, which are the major carriers of lipidsand other hydrophobic compounds (Ando andMori, 1993). It is therefore possible that a lack ofadequate protein may result in loss of serumlipoprotein thereby affecting the transport andstorage of lipids in C. gariepinus. Therefore, adeficiency of protein may impede physiologicalfunctions and further reiterates the need foroptimal dietary protein for effective fish rearing.This study investigated the influence of dietaryprotein content on gross efficiency of foodconversion and protein utilization of African catfish(C. gariepinus) fry and also studied other growthand nutritional parameters of the species that areaffected by dietary protein intake.MATERIAL AND METHODSExperimental Procedure: Four hundred andeighty (480) advanced fry (mean initial weight,1.60 ± 0.24 g) of C. gariepinus were randomlyallotted to 8 triplicate 25 L plastic baths at 20 fryper bath, replicated three times and allowed toacclimatize for 14 days in the Research Laboratoryof Ebonyi State University, Abakaliki, Nigeria. Thefish were fed for 56 days with eight diets, seven ofwhich were formulated to yield 28, 31, 34, 37, 40,43 and 46% crude protein content while the 8 thdiet comprised a 48.8% crude proteinmicroencapsulated whole egg diet (M). Grosscomponents of diets calculated with Pearson’ssquare method (De Silva and Anderson, 1995) isshown in Table 1. Temperature readings of waterwere taken thrice daily with a maximum andminimum thermometer while the pH was recordedwith a pH meter (model PH J – 201 L). The waterconductivity was measured with a conductivitymeter and dissolved oxygen was measured withHach test kit FF3.The fish were fed at four-hourly intervalstarting from 0800 h, at the rate of 5% (liveweight basis) of their total biomass per day inthree portions. Weekly weighing of the fish wascarried out with the aid of a Mettler balance(model P 1210) and the feed administered wasadjusted in accordance with the body weight offish. Owing to the fouling of water by faeces andother feed debris, the plastic baths were cleanedon weekly (7 days) basis and replenished withclean tap water.Analytical Procedure: The proximate compositionsof both the experimental diets and fish wereanalysed by methods described by Windham(1996). Crude protein was determined by microkjeldahl method, fat by soxhlet extraction method,fibre by the ceramic fibre filter method and ash bycombusting in muffle furnace at 600º C for 2 h.The digestible carbohydrate content was computedby obtaining the difference between the % crudeprotein + % fat + % fibre + % ash contents and100%. The amino acid concentrations of sampleswere determined by acid hydrolysis and highperformance liquid chromatography (HPLC)method as described by Ogungi and Writh (2001).Determination of Growth and NutrientParameters: The mean weight gain (MWG) offish was computed following Ishwata (1969)method. The daily rate of growth (DRG) wascalculated from the relationship between the meanincrease in weight per day and the body weight offish, thus: DRG = (mean increase in weight)/(bodyweight of fish). The daily rate of feeding (DRF)was obtained from the expression: DRF = (meanration per day)/(body weight of fish). While thegross efficiency of food conversion (GEFC) wascalculated from the relationship between the dailyrate of growth (DRG) and daily rate of feeding(DRF): GEF = DRG/DRF.The nitrogen metabolism (Nm) was derived usingthe method of Dabrowski (1977), thus:(0.549)(a + b)hNm = ,2where: a = initial weight of fish, b = final weightof fish, h = experimental duration in days.The net protein utilization (NPU) was estimatedaccording to Miller and Bender (1955) method,thus:b - No + NmNPU =,1b