Abstract
The high cost of fish meal in tilapia diets warrants the potential use of cottonseed meal (CSM) as an alternative source of high quality protein. The effects of varying levels of CSM (0, 25, 50, 75 and 100%) as fish meal protein replacement on growth, blood parameters, spleen characteristics, free and bound gossypol in blood plasma, haemoglobin and haematocrit were determined in tilapia. Gossypol (C 30 H 30 O 8 ) is a polyphenolic substance found in cottonseed that has known toxic effects in fish. Tilapias ( n = 219, average weight = 11.3 ± 3.9 g) were randomly distributed into 15, 32‐L glass aquaria, representing five dietary treatments and three replicates per treatment. Each aquarium containing 13–16 fish was supplied with thermoregulated, recirculating water (27 ± 1 °C) at 1 L min −1 flow rate and photoperiod was constant (12 h L/12 h D). Fish fed 25–50% CSM protein replacement showed similar body weights and total lengths as the controls at the completion of the 16‐week trial. Fish fed 75 and 100% CSM protein replacement showed a significant decline in body weight and total length. Fish fed 25–100% CSM protein replacement had significantly lower haematocrit and haemoglobin (ANOVA/LSD, P P