Physicochemical Characteristics of Tilapia and African Catfish from Lake Victoria and Selected Fish Farms from the Counties of Kirinyaga and Machakos in Kenya

Abstract

Fish is important for food security and optimal nutrition. To boost fish supply and subvert rural poverty and malnutrition, the Kenyan government is promoting fish farming. Previous studies have shown that wild and farmed fish vary in their nutritional composition. This study aimed at determining the difference in heavy metal levels, chemical, physical and sensory properties of wild and farmed fish particularly Nile Tilapia (Oreochromis niloticus) and African Catfish (Claris gariepinus) species. Randomized Block Design was used to sample both wild and farmed fish. Wild fish (sample size 128) were obtained from Kisumu through fish vendors from City market Nairobi, while farmed fish (sample size 288) were obtained from selected fish ponds in Sagana and Kamulu which are located in the counties of Kirinyaga and Machakos respectively. Proximate composition, mineral and heavy metal content of the fish were determined using (AOAC) official methods of analysis. Tissue fatty acid composition was determined by gas chromatography. Farmed fish contained significantly (p<0.05) higher moisture content than wild fish. The protein content of wild and farmed fish ranged from 21.9 – 22.1% and 16.0 – 19.2%, respectively. Fat content in wild fish ranged between 3.0 – 3.8% while farmed fish reported 1.9 – 4.8%. Ash content in wild ranged from 1.8 – 2.1% relative to 1.1 – 1.5% in farmed fish. Wild fish was found to contain significantly higher concentrations (p<0.05) of heavy metals relative to farmed fish. The concentration of minerals in wild fish ranged from 2.8 – 3.0 mg/100g of iron, 5.5 – 5.6 mg/100g zinc, and 39.9 – 43.8 mg/100g calcium compared to lower values of 1.9 – 2.4 mg/100g of iron, 28.2 – 37.0 mg/100g calcium and 4.3 – 5.0 mg/100g zinc in farmed fish. Palmitoleic acid (C16:1) and oleic acid (C18:1) were the predominant monounsaturated fatty acids (MUFA) in both farmed and wild fish with significantly higher values of 4.33– 6.7% and 20.5 – 22.4% for wild fish and 4.53-10.8%, 21.2-28.7% for farmed fish. The principal polyunsaturated fatty acids (PUFA) were linoleic acid (C18:2), linolenic (C18:3) (omega 3), linolenic (C18:3) (omega 6), Eicosapentaenoic acid (EPA) (C20:5) and Docosahexaenoic acid (DHA) (C22:6). The content of EPA and DHA were in the range of 1.5-2.4% and 3.0-3.7% for wild fish relative to 0.6-1.6% and 1.5-2.8% for farmed fish. Wild fish also recorded higher levels of TBARS than farmed fish an indication that fatty acids in farmed fish are more stable after cooking than in wild fish. The wild fish had a firm texture range of 3.85-4.99 N compared to farmed fish with 1.63-3.65 N. In addition, wild fish were more preferred in terms of flavor, colour, texture and taste than farmed fish. In conclusion wild fish were nutritionally superior to farmed fish and this could be attributed to the type of feed they consume. Furthermore, wild fish has higher levels of heavy metals relative to farmed fish.