DIGESTIBILITY AND AMMONIA EXCRETION RATES OF LOW-COST NURSERY DIETS FOR NILE TILAPIA Oreochromis niloticus FRY

In Ghana nursery facilities are generally missing from the aquaculture production chain and this compels fish farmers to purchase fish directly from the hatcheries at very small sizes to stock in grow-out ponds which sometimes results in high mortalities. Some farmers have adopted the practice of nursing fish before stocking in grow-out ponds in Ghana but formulated commercial feeds are prohibitively expensive. This research is thus a preliminary study to evaluate the potential for using mixtures of soybean and copra meals as partial replacements of fishmeal in feeds for Nile tilapia (Oreochromis niloticus) fry/fingerlings.

Nutrient digestibility and postprandial ammonia excretion rates were examined. Three iso-nitrogenous (48%), and isolipidic (7%) diets (Diet 1, 2 and 3) were formulated with the oilseed mixtures as partial replacements to fishmeal (Table 1) and with a fishmeal-based commercial diet serving a as control. Diets were randomly assigned to triplicate groups of fish (Initial mean weight 0.89g±0.14 g) for the digestibility trials which spanned a total of nine (9), days. The partial inclusion of oilseed meals did not significantly affect apparent protein and lipid digestibilities although ash and dry matter digestibilities were significantly reduced (p<0.05). The inclusions of the plant proteins caused an increase in ammonia excretion (Fig 1). Overall, the oilseed diets showed some potential although further refinements of ingredient might be required to improve somatic growth, dry matter digestibility and reduce ammonia excretion rates.