The objective of every fish farmer is to achieve maximum growth under the least food cost commonly referred to as the Feed Conversion Ratio (FCR). Under BFT this objective is no different. In bioenergetics this is referred to as the point where Recovered Energy (RE) is highest (see modified graph after Jobling, 2011 below).

Poor visibility of feeding response under BFT requires a basic understanding of bioenergetics and the energy costs of raising a kilogram of fish (1 kg in wet body weight gain in a cohort or population of fish as MJ DE kg-1) and the use of appropriate feeding rate models.

The key to harvesting the benefits of BFT at Chambo Fisheries lay in the following practices:

1) The formulation and use of C/N ratio feeds – C/N ratio feed passage through the digestive system of tilapias – which then permits the use of bioenergetic feeding rate models;

2) Tuning feeding rates based upon the use of bioenergetic models built into a BFT decision support tool developed to guide feeding practices and assist with auditing achieved performance (feeding rates, feed conversion, Net Energy Retention (NER) and Net Protein Retention (NPR), input-output Nitrogen recovery ratio’s etc);

3) Manipulation of meal intervals and meal sizes at intervals pinned to Gastric Evacuation Rates (GER) > 80% to maximize the digestive capacity of feed presented.

Optimum feeding rates which count in the energy contribution of biofloc grazing by filter feeding tilapias is then discovered iteratively by manipulating the Natural Food Contribution factor (NFCf) added to a modified bioenergetic feeding rate model.

NFCf was found to repeatedly range between 20-25% of the daily Digestible Energy (DE) requirements of 5g to 220g fish under large-scale conditions at Chambo Fisheries when feeding a 20.2% protein feed (approx. C/N ratio of 15.5:1).