Morphometrics, growth and nutritional characterization of selected bivalves' species from Lake Victoria

Abstract

Fish is a major source of animal protein to most people in Uganda. However, production from capture fisheries has declined, mainly due to overfishing. Aquaculture, which is a viable option to meet the fish demand is constrained by the high costs of feeds. This study determined nutritional status of selected bivalve genera of Lake Victoria and assessed their potential for cultivation for use in aquafeeds. Allometric relationships between Shell length (SL) and Flesh mass (using the model, W= aLb), and the proportion of the flesh mass to the total mass of the bivalves were established. Proximate and amino acid profiles were estimated from the molluscs’ flesh. Coelatura sp. bivalves were cultured in bucket unit systems, in sand and mud substrates for 196 days using aquaculture effluent. Proximate composition in the bivalves was analyzed according to AOAC (2000) methods. The bivalve amino acids were analyzed by the Southern Grain African Laboratory (SAGL), Pretoria, South Africa. In the studied bivalves, growth in shell length was faster than corresponding unit increase in soft tissues, with ‘b’ values ranging from 1.918 to 2.582, and the flesh mass contributed about one-third of the total mass of the whole animal. Crude protein (CP), fat, carbohydrates, fiber, and ash ranged between 29.77-51.0%, 1.48-10.64%, 16.7-31.60%, 0.00-0.98% and 13.51-30.51%, respectively. Eighteen amino acids were estimated in four bivalve species. Among them, the Essential Amino Acids (EAA) recorded for the bivalves were 18.02%, 20.97%, 24.96% and 23.79% for Coelatura sp., Chambardia sp., Mutela sp. and Nitia sp., respectively. Concentrations of the Non Essential Amino Acids (NEAA) were 18.02%, 22.89%, 26.01% and 23.79% for Coelatura sp., Chambardia sp., Mutela sp. and Nitia sp., respectively. The highest EAA found in the bivalves was leucine, followed by arginine and lysine, whereas aspartic and glutamic acids were the highest NEAA recorded. Tryptophan, and the sulpur amino acids, methionine and cysteine, in that order were detected in low proportions. The estimated cost of protein per kilogram of BM (3.72 US$/kg) was comparatively lower than that of mukene (4.38 US$/kg) but higher than that of Soya bean meal (0.93 US$/kg). The study demonstrated that the bivalves of Lake Victoria have high nutritional status, with Chambardia sp. and Mutela sp. being the largest bivalves (with the fastest rates of increase in flesh mass per unit increase in shell length) that could be farmed for flesh production for inclusion in fish feeds. Key words: Aquafeed, bivalves, bivalve meal, nutritional composition, shell length-flesh mass relationship