Growth, feed utilization and body composition of tilapia (Oreochromis sp.) fed with cottonseed meal-based diets in a recirculating system

The suitability of cottonseed meal (CSM) as a major source of plant protein in feeds for tilapia (Oreochromis sp.) was tested by examining growth and feed intake, feed digestibility, liver gossypol concentrations, feed utilization, and body mineral composition. Juvenile tilapia at an initial average size of 11.8 ± 1.6 g were divided into triplicate groups per dietary treatment and offered five different formulated diets. In these feeds fish meal (FM) protein was gradually replaced by protein from CSM (0, 25, 50, 75, and 100%; diets 1, 2, 3, 4 and 5, respectively). The experiments were conducted in a recirculation system at a water temperature of 27 ± 1°C in glass aquaria for 16 weeks. Tilapia growth did not differ significantly (P > 0.05) with up to 50% substitution of FM with CSM. Fish meal replacement above 50% resulted in significant growth decline with time. Fish fed with 100% FM and diets including 50% CSM had significantly better daily weight gain, daily feed intake and feed efficiency ratio than those fed with 100% CSM. Fish fed with 75% CSM and above had lower concentrations of body iron, calcium and phosphorus than controls (100% FM). Concentrations of total gossypol in diets (ranging from 0.11 to 0.44% in diets 2-5) resulted in proportional increase of total gossypol in fish liver (32.3, 72.3, 99.4 and 132.1 μg g^-1 wet weight) in groups fed with diet 2, 3, 4, and 5, respectively. We concluded that CSM can partially replace FM as a main source of protein in feed for tilapia at not more than 50%. The presence of gossypol in CSM was identified as the major limiting factor for acceptance and utilization of CSM-based diets in tilapia farming.