22 MARCH 2025 • WORLD AQUACULTURE • WWW.WAS.ORG substrate for American ethanol production is corn, and after fermentation, corn stillage can be used to feed terrestrial animals or further processed and included in fish feeds (Anderson and Almeida, 2019). This nutrient-rich biomass can be further refined into novel alternative ingredients, such as high-protein distillers dried grains (HPDDG) or corn fermented protein (CFP). Both ingredients have superior nutritional value to conventional DDGS (25-30% protein, 6-9% lipid, <14% fiber). This is achieved by fractionating a portion of the fiber and oil, which concentrates the residual proteins from the grains and yeast (Distillers Grains Technology Council, DGTC, 2021). HPDDG (36-48% protein; 4-6% lipid; <12% fiber) and mechanically separated CFP (>48% crude protein; 1-5% lipid; <8% fiber) are protein ingredients with comparable, if not superior, nutritional values to cottonseed meal and dehulled soybean meal, respectively, but amino supplementation may be necessary (e.g., lysine and arginine). Recently published studies have investigated the use of CFP and HPDDG in channel catfish feeds (Nazeer et al., 2022; Paladines-Parrales et al., 2025; Yamamoto et al., 2024b), showing promise as alternative protein sources for catfish feed. Their adoption could create a valuable niche market for both industries, depending on availability and pricing. Fishmeal replacement has been investigated for an array of cultured fish species for a long time. As the demand steadily increases for high-quality protein ingredients from other aquaculture industries or other livestock, the price of forage fishmeal is becoming cost-prohibitive to be included in the feed formulation of omnivore fishes, especially for the U.S. catfish industry. And yet, some formulations for fingerling feeds still rely on this top-shelf ingredient. The high nutrient digestibility, balanced amino acid profile, and absence of antinutritional factors set the menhaden fishmeal as a “gold standard” for the aquaculture feed industry. However, alternative ingredients such as poultry by-product meal and other processed animal proteins (PAPs) have managed to fully replace this ingredient without impairing the production performance of other farmed aquatic animals. In general, rendering by-products have high protein content (ranging from 50-80%), good palatability, and no antinutritional factors, but in some cases, some essential amino acids may be deficient (e.g., lysine, methionine, and tryptophan) when compared to menhaden fishmeal. For catfish, conflicting (insects, crustaceans, mollusks, mammals, birds, etc.), but at the same time with an opportunistic feeding behavior, where ~16-33% of aquatic vegetation could be found in their gastrointestinal tract (Schmitt et al., 2017, 2019). Nevertheless, as they grow larger, blue catfish seem to transition from an omnivorous to a piscivorous feeding behavior. Thus, it is fair to wonder if an inherited carnivorous behavior could be passed from the blue parent to its hybrid offspring, potentially leading to a higher energy requirement and promoting these size disparity issues when offered omnivorous feeds. Another impressive and distinct feature of hybrids is their feeding activity in earthen ponds. Whereas channels appear to emerge from the bottom of the pond to consume the floating extruded feed, the hybrids display an aggressive feeding frenzy while swimming in schools near the surface. These behavioral differences likely require additional energy for metabolism, possibly increasing their requirement for calories. In fact, a recent study in a recirculating system observed that hybrids had better swimming performance and a higher metabolic rate when compared with channels and blues (Gerhart et al., 2024). This highlights the necessity to look back and tailor formulations to optimize the growth performance of this hybrid, especially when it accounts for more than half of U.S. catfish production. Alternative Ingredients Solvent-extracted soybean meal (SBM) and cottonseed meal have been the primary protein feedstuffs in catfish (Ictalurus spp.) formulations during the growth-out life stage (Li and Robinson, 2021). Prices of these commodities have been highly volatile in the past five years due to several global events (e.g., the pandemic in 2020, drought in South America, and international conflicts) that have disrupted the supply chain and greatly impacted feed prices. All livestock sectors struggled during this period, and it was no different for the American catfish industry, where feed prices had record highs in 2022. These events drove apprehension in the industry, and investigating affordable alternative ingredients with steady supply became a priority to minimize surges in feed prices. In this context, a domestic solution can be a higher reliance on corn-derived products from the biofuel industry. The United States is the leading global producer of fuel ethanol, with an output of approximately 57 billion liters/year (Renewable Fuel Association, RFA, 2022). The primary FIGURE 3. Dr. Brian Bosworth, a research geneticist at USDA-ARS, holds two hybrid catfish of noticeably different sizes, despite belonging to the same population.
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