Abstract
This study investigated the content of selected minerals (P, Ca, K, Na, Mg, Fe and I) in local feed ingredients used by tilapia fish farmers in Tanzania. Analyses were performed on 26 local feed ingredients collected at four different geographical locations in Tanzania (Dar es Salaam, Morogoro, Mbeya and Mwanza). The samples were taken randomly from fish farmers, fish feed producers, fingerling producers and animal feed shops or centers near fish farms in each region. The results showed a wide range of mineral concentrations. The highest levels of P was found in fish skeletons (17.8 g kg-1), of Ca in limestone (107.3 g kg-1), of K in gallant soldier (51.0 g kg-1), of Na in marine shrimp (Exhippolysmata oplophoroides) (11.7 g kg-1), of Mg in prawn head waste (4.2 g kg-1), of Fe in azolla (2355 mg kg-1) and of I in full fat soybean (447 mg kg-1). The data on mineral content in feed ingredients can be used as a platform for better-targeted feed formulation for tilapia farming systems. In conclusion, the data suggest that if more than two ingredients are used in the diet, this may be sufficient to meet the mineral requirements of all cultured tilapia species and their hybrids, without inclusion of any mineral premix.
Highlights
In Tanzania, fish farmers raise tilapia (Oreochromis niloticus) in extensive systems and/or semi-intensively through fertilisation of the fish culture system and provision of supplementary feeds (Chenyambuga et al, 2014)
The availability of good-quality fish feed for tilapia fish farmers is a major concern in the development of the aquaculture industry, in Tanzania and across the entire East Africa region
The results from the present study revealed a wide range of mineral concentrations in feed ingredients used by tilapia fish farmers in Tanzania
Summary
In Tanzania, fish farmers raise tilapia (Oreochromis niloticus) in extensive systems and/or semi-intensively through fertilisation of the fish culture system (ponds and tanks) and provision of supplementary feeds (Chenyambuga et al, 2014). The majority of tilapia fish farmers in Tanzania feed their fish with locally available feedstuffs of both plant and animal origin. In order to formulate nutritionally appropriate supplementary feeds for fish, accurate data on the nutrient content of different dietary components are required. There are some limited data available (based on proximate analysis) on the major nutrient composition (i.e. crude protein, crude fat, crude fibre and ash) of commonly used feed ingredients in Tanzania (FAO, 1987). Information on the mineral content of locally available feed ingredients in Tanzania is lacking. Minerals play an important role in the maintenance of normal metabolic and physiological functions in fish and other animals, which include muscle contraction, blood clotting, enzyme activity, transmission of nerve impulses, metabolism and electrolyte balance (Tacon, 1987; Dato-Cajegas and Yakupitiyage, 1996; Assey et al, 2009). Lack of essential minerals in the fish diet may lead to mineral deficiency, resulting in conditions such as anaemia, osteoporosis, stunted growth and genetic disorders (Tacon, 1987; Dato-Cajegas and Yakupitiyage, 1996; Fumio et al, 2012; Bhandari and Banjara, 2015)
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