|Barros, Margarida - VISITING INT. SCIENTIST|
Submitted to: Journal of Applied Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 8, 1999
Publication Date: August 7, 2000
Citation: BARROS, M.M., LIM, C.E., EVANS, J.J., KLESIUS, P.H. EFFECT OF IRON SUPPLEMENTATION TO COTTONSEED MEAL DIETS ON THE GROWTH PERFORMANCE OF CHANNEL CATFISH, ICTALURUS PUNCTATUS. JOURNAL OF APPLIED AQUACULTURE 10(1) 2000 65-86 Interpretive Summary: Currently soybean meal (SBM) comprises up to 50% of the feed for channel catfish. Replacement of SBM with less expensive plant protein would be beneficial in reducing feed cost. Cottonseed meal (CSM) which ranks second in the US in terms of tonnage among the plant proteins produced, is less expensive than soybean meal on a unit protein basis. However, CSM contains gossypol which has been shown to be toxic for fish. Iron from ferrous sulfate has been used to counteract the toxicity of free gossypol in nongastric animals but no work has been done with fish. Thus, this study was conducted to evaluate the effect of iron supplementation to diets containing different levels of CSM on the growth performance and histopathology of juvenile channel catfish. Results of this study show that best performance was obtained in diets in which 50% of SBM replaced by 27.5% CSM and an amino acid, lysine. Total replacement of SBM with 55% CSM and lysine reduced fish performance due probably to toxicity of free gossypol. A dietary free gossypol of 671 mg/kg may be toxic to juvenile catfish when fed to satiation. Iron from ferrous sulfate at a 1:1 weight ratio of iron to free gossypol had no effect in reducing gossypol toxicity. However, addition of (671 mg/kg) to SBM-based diets improve the nutritional value of the diet.
Technical Abstract: Three practical diets containing 0, 27.5 and 55.0% cottonseed meal (CSM) as replacements of 0, 50 and 100% of soybean meal (SBM) on an equal nitrogen basis were each supplemented with 40, 336 and 671 mg iron/kg. Each diet was fed to juvenile channel catfish 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 WG and FI, possibly due to toxic effect of free gossypol. Supplementation of iron from iron at a 1:1 weight ratio of iron to free gossypol had no effect on gossypol toxicity. Histological examinations showed that fish fed CSM containing (27.5% and 55.0%) diets had increased glycogen accumulation in the liver. Fish fed 55.0% CSM and SBM diets had increased liver necrosis, and liver and anterior kidney pigment deposition. 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. 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 55.0% CSM. Survival, and serum and liver iron content were not affected by dietary levels of CSM, iron or their interaction. Fish fed the 55.0% CSM diets had the lowest body fat and highest moisture content. Dietary level of iron, and the interaction between iron and CSM had no effect on whole body composition.