Approaches to the effective utilization of Haplochromis spp. from Lake Victoria. I. Chemical composition in relation to utilization

Abstract

There are over 150 species of the cichlid genus Huplochrornis in Lake Victoria constituting a major underexploited food resource. As an aid to the processing of the deepwater stock, chemical composition data were obtained for the whole fish (separated into weight groups) and for the head, viscera, flesh and residual portions separately. Data are reported for lipid content, fatty acid composition, crude protein, true protein, amino acid composition, ash and moisture content. Materials and methods Fish samplesFour batches of Haplochromis were caught by bottom trawling (depth 25-45 m) from the Kitubulu-Nsazi. Uganda, inshore fishing ground of Lake Victoria during May. October and November 1980, and February 1981. The fish were frozen, packed into insulated boxes and flown to the U.K. They were kept in cold store (-25°C) until analysed. Most of the analytical work was carried out on the February batch. Grouping and portioning of HaplochromisThawed fish were weighed (to the nearest 0.1 g) and the total length (including caudal fin) of each fish was measured (to the nearest mm). The fish were sorted into four weight groups: Group I: 5.9 g and less; Group 11: 6.0-8.9 g; Group 111: 9.0-13.9 g; and Group IV: 14 g and above. These four weight groups corresponded approximately to total lengths of: 80 mm and less, 81-89,90-99 and 100 mm and above, respectively.Analyses were carried out either on the whole fish or on samples taken after dividing the fish into head, viscera, flesh (skinless) and residual portions. The head portion was removed by a single cut immediately behind the pelvic and pectoral fins. Any visceral material cut off with the head portion was removed and included with the viscera.Representative samples for each weight group were taken after passing the whole fish (fifty to 500 fish depending on the weight group) or the portions (from fifty to 500 fish) several times through a mincer. Proximate analysisLipid content was determined by a modified Bligh and Dyer technique (Hanson & Olley, 1963). Crude protein content (total NX6.25) was determined by the Kjeldahl technique. Ash content was determined to 500°C. Moisture content was determined by drying samples to constant weight at 105k2"C. Analyses were carried out in triplicate. Fatty acid compositionLipid was extracted by the modified Bligh and Dyer method using chloroform containing 0.01% BHT and the solvent as evaporated using a rotary evaporator and vacuum pump at room temperature. Methylation.One hundred to 150 mg of lipid was saponified by adding 2 ml toluene and 4 ml sodium hydroxide in methanol (1.5 : 228 W/V) in a 50 ml round-bottomed flask and refluxing for 30 min. After cooling, 5 ml boron trifluoridelmethanol(12-14% w/v) was added and the mixture was refluxed for a further 30 min. The methyl esters were extracted 3 times with 35 ml portions of hexane, dried with anhydrous sodium sulphate and concentrated using a rotary evaporator.Gas chromatography. Chromatographic analysis was carried out using a 2 m column packed with 10% SP 2330 on Chromosorb WAW ...