Investigation of the nutritional value of sorghum grain for rainbow trout (Oncorhynchus mykiss) and hybrid striped bass (Morone chrysops x M. saxatilis)

Authors: Sealey, Wendy; Rawles, Steven; TRUSHENSKI, JESSE - Riverence Holdings Llc; ZAREI, MOHAMMED - Virginia Polytechnic Institution & State University; URICK, STEVEN - Virginia Polytechnic Institution & State University; MCALHANEY, ETHAN - Virginia Polytechnic Institution & State University; Bianchine, Tyler; GATLIN, DELBERT - Texas A&M University; CRAFTON, BRENT - United Sorghum Checkoff; SCHWARZ, MICHAEL - Virginia Polytechnic Institution & State University

Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Grain sorghum is commonly included in poultry and cattle feeds. However, limited studies have examined the suitability of grain sorghum as an aquafeed ingredient. To address this deficiency, USDA ARS scientists collaborated with colleagues at Virginia Tech University, Texas A&M University, the US Sorghum Board and a private aquaculture producer to examine the suitability of grain sorghum as a dietary energy source in extruded fish feeds. In vivo digestibility trials were conducted in rainbow trout and hybrid striped bass to determine the available nutrient content of three commercially sourced U.S. grain sorghum hybrids. Based on digestibility data, a growth trial was conducted to test the replacement of wheat flour with U.S. grain sorghum in a practical-type diets for rainbow trout and hybrid striped bass at four inclusion levels (0, 5, 10, and 20%). The digestible energy results from this study suggested similar available energy from U.S. grain sorghum and wheat flour for both rainbow trout and hybrid striped bass. Notably, growth results indicated that U.S. grain sorghum can be used in place of wheat flour without substantially altering the production efficiency of hybrid striped bass. However, the reduced growth observed in rainbow trout at 20% inclusion underscores the need for species-specific feed formulations. The successful incorporation of U.S. grain sorghum in aquafeeds could enhance ingredient flexibility, potentially reducing reliance on wheat and mitigating supply chain risks.

Technical Abstract: Aquafeeds with optimum digestible starch levels can provide benefits in aquaculture but only through the continued identification and characterization of the available nutrient content of novel or lesser utilized starch sources for a larger variety of aquatic species. To address this literature gap, in vivo digestibility trials were conducted in rainbow trout and hybrid striped bass to determine the available nutrient content of commercially sourced U.S. grain sorghum hybrids. Based on digestibility data, a regression design was employed to test the replacement of wheat flour with U.S. grain sorghum in a practical-type diets for rainbow trout and hybrid striped bass at four inclusion levels (0, 5, 10, and 20%). All diets were formulated to contain 40% digestible protein and 18% crude lipid, and balanced to available lysine, methionine, threonine and phosphorus to targets of 3.82, 1.30, 2.14 and 0.6, respectively prior to cooking extrusion. For the growth trials, ten rainbow trout (59.1 ± 0.07 g, initial weight) or ten hybrid striped bass (27.1 ± 0.1 g) were randomly stocked into triplicate replicate tanks per diet (300 L or 500 L, respectively) and fed for eight or nine weeks, respectively to assess effects on growth efficiency. No significant negative effects of U.S. grain sorghum inclusion on hybrid striped bass final fish weight, growth rate expressed as a percent increase, feed conversion ratio, feed intake, body condition indices or whole-body proximate composition were observed. The effects of 20% red. grain sorghum inclusion on rainbow trout final fish weight were explained by the linear model Final fish weigh (g)=248-1.0(Sorghum Inclusion Level). The reduced growth observed in rainbow trout at 20% inclusion levels underscores the need for additional research to examine the potential beneficial effects of further sorghum processing and optimize feed extrusion parameters when U.S. grain sorghum is used in place of wheat flour.