FEATURE
this purpose, but keep in mind that its iron content is variable and it may contain only 20 percent iron. In this case, it will take 50 pounds of this compound to deliver 10 pounds per ton of CSM at a 1:1 ratio of iron to gossypol.
Extreme variability in the toxicity of gossypol
Gossypol is the first concern of aquaculture nutritionists when considering cottonseed products as a protein source. Extreme variability in toxicity to gossypol exists among aquaculture species. Toxicity trials with aquatic species utilizing CSM of known gossypol levels or purified gossypol acetic acid (GAA) have been reported. Based on multiple research trials, one concludes that the major farmed-fish species (catfish, tilapia, trout), especially adults, are moderately tolerant to gossypol. Shrimp also are very tolerant due to the absence of iron as an oxygen-carrying molecule in shrimp blood. As mentioned previously, the binding of gossypol with hemoglobin iron is the primary mechanism of gossypol toxicity. As gossypol accumulates in the blood of an animal over time the oxygen carrying capacity of the blood is diminished and fluid accumulates in the thoracic cavity, making it that much more difficult for the animal to thrive. Additional stress and age exacerbate this toxic process. Fowler (1980) found that salmon could tolerate between 22 percent and 34 percent of their diets as CSM without adverse effects (gossypol levels not reported). In trout, particularly juveniles, research by Lee et al. (2001) demonstrated that up to 15 percent CSM could be included in the diet without detrimental effects. CSM is digested relatively well by both fish and crustaceans. However, CSM is reported to be less digestible by several aquatic
species than is soybean meal (SBM) with a few exceptions. Red Drum and Palmetto “Wiper” Hybrid Bass appear to digest CSM better than SBM. Processing conditions at cottonseed oil mills are highly variable, having a direct impact on product quality. If extreme heat is applied in an effort to bind gossypol, protein quality also can be damaged. It is very important to have a gossypol analysis conducted by a competent laboratory before using CSM in an aquaculture feed. Total amino acids apparent availability coefficients typically are lower for CSM than SBM, averaging 74.4 percent versus 82.2 percent for channel catfish (Wilson et al. 1981) and 78.4 percent versus 95.7 percent for Australian Silver Perch (Allan et al. 2000), respectively. Lysine availability is severely deficient in CSM (60.4 percent-84.9 percent) as compared to SBM (85 percent-96.7 percent) based on perch, catfish, rockfish and trout research. Lysine binding to gossypol renders it unavailable to the animal.
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