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Abstract
Three basal diets containing 0, 27.5, and 55% solvent-extracted cottonseed meal (CSM) as replacements of 0, 50, and 100% of solvent-extracted soybean meal (SBM) on an equal nitrogen basis were each supplemented with three levels (40, 336, and 671 mg) of iron (Fe) from ferrous sulfate heptahydrate (3×3 factorial experiment). Each diet was fed to juvenile channel catfish, Ictalurus punctatus in triplicate aquaria twice daily to apparent satiation for 10 weeks. Dietary levels of CSM significantly affected weight gain (WG), feed intake (FI), feed efficiency ratio (FER), protein efficiency ratio (PER), and apparent protein utilization (APU), with diet containing 27.5% CSM provided the best performance. Total replacement of SBM by CSM decreased weight gain and feed consumption, possibly due to toxic effect of free gossypol. Supplementation of dietary iron from iron sulfate heptahydrate at a 1:1 weight ratio of iron to free gossypol had no effect on gossypol toxicity. Histological examinations of fish fed CSM containing (27.5% and 55%) diets had increased glycogen accumulation in liver as compared to that of fish fed the SBM-based diets. Fish fed 55% CSM and 0% SBM-based diets had increased liver necrosis and liver and anterior kidney pigment deposition. These parameters were not evident in fish fed diets containing 27.5% CSM. Dietary levels of iron and interactions between CSM and iron had no effect on the liver, spleen, or anterior head kidney histology. WG, FI, PER, and APU were significantly affected by the interaction between dietary levels of CSM and Fe. For SBM-based diets, these parameters linearly increased with increasing dietary level of iron. This effect was not observed for diets in which 50 and 100% of SBM were replaced by 27.5 and 55% CSM. Survival, and serum and liver iron content were not affected by dietary levels of CSM, iron, or their interaction. The effect of CSM on whole body composition was seen only for fish fed the 55% CSM diets, with fish fed these diets having lowest fat and highest moisture content. Dietary level of iron and the interaction between iron and CSM had no effect on whole body composition.
