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Please cite this article in press as: Obirikorang, K.A., et al., Effects of dietary inclusions of oilseed meals on physical characteristics and feed intake of diets for the Nile Tilapia, Oreochromis niloticus. Aquac. Rep. (2015), http://dx. a b s t r a c tThe present study investigated the effects of the inclusion of three oilseed by-products (soybean, copra and palm kernel meals) on some physical characteristics of pelletized feeds as well as on voluntary feed intake and faecal matter production by the Nile tilapia, Oreochromis niloticus. The dietary inclusion of soybean meal resulted in a significantly higher feed bulk density relative to the fishmeal control diet. The inclusions of copra and palm kernel meals, however, resulted in lower feed bulk densities. Sinking rates, water stabilities and nutrient retention efficiencies of feed pellets were directly related to feed bulk densities. The soybean meal diet had the fastest sinking velocities, greatest water stability and highest nutrient retention rates. The dietary inclusion of soybean meal, however, significantly impaired feed intake compared to the other three diets. Mean daily feed intakes of the control, palm kernel meal and copra meal diets corresponded to 28.88, 27.01 and 28.31 g during the experimental period and varied significantly from the mean daily intake of the soybean meal diet which corresponded to 20.01 g. Faecal matter production (g dry mass kg −1 ingested feed) was significantly higher in the tilapia groups fed the copra and palm kernel meals. The results obtained from this study show that 30% inclusions of unrefined forms of copra and palm kernel meal in Nile tilapia diets is possible, without adversely affecting feed intake or pellet nutrient losses prior to ingestion.

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The relationship between gonadal development and the concentrations of four heavy metals Mn, Zn, Fe and Hg in the tissues of the clam Galatea paradoxa was evaluated at the Volta estuary, Ghana, over an 18-month period. Metal concentrations in the clam tissues were highly variable over the sampling period and seemed to be influenced by the reproductive cycle of the clam. Mn concentrations varied over a wide range from 49 to 867 μg/g and exhibited a significant positive correlation with gonadal development (p = 0.0146, r(2) = 0.3190). Zn and Fe concentrations ranged from 13 to 59 μg/g and 79 to 484 μg/g, respectively and both revealed negative relationships between gonad development and metal accumulation (Zn (p = 0.0554, r(2) = 0.0554) and Fe (p = 0.1040, r(2) = 0.1567)). Hg concentrations ranged from 0.026 to 0.059 μg/g over the sampling period and exhibited a slight positive relationship between gonadal development and metal accumulation (p = 0.0861, r(2) = 0.1730).

This research was carried out at two locations, Ada and Aveglo at the Volta Estuary

The inability of Ghana's capture-based fisheries to meet national demand has placed aquaculture in an advantageous position to satisfy this supply deficit. The majority of fish farmers in Ghana, however, resort to local feed mixtures, occasionally in combination with commercial aquafeeds, demonstrating that the sector has not yet reached its full potential in terms of production volumes and efficiency. Fish meal is available in limited quantities and is prohibitively expensive in Ghana, making it essential to develop suitable complete and supplementary diets using low-cost and locally available plant by-products for use in fish grow-out facilities, particularly in tilapia production, which accounts for over 80 % of aquaculture production. This review thus identifies local agro-industrial byproducts with potential use in fish feeds based on their nutritional composition, total annual production, competition for and seasonal availability and dynamics of these products as well as prices. The effects of dietary inclusions of these by-products on fish growth and feed utilisation are also reviewed. Based on the published works and other practical information reviewed, these by-products represent huge potentials as alternative aquafeed protein sources because of their abundance, very affordable prices and healthy nutritional profiles for fish growth. Although this review focuses on Ghana, it can also be of direct benefit to fish farmers, feed manufacturers, researchers and the policy-makers in other regions of the world where these crops and their resulting by-products are produced in commercial quantities.