The need for precise estimates of chemical components of fish is common among the fields of aquaculture, fish health, and bioenergetics in fisheries management. Proximate composition is a widely used tool for obtaining this level of information but is time consuming and requires homogenization of the entire fish, limiting the ability to obtain additional information from the same individual. Exploratory chemical component analysis of differing body regions of age‐1 (215‐290‐mm) striped bass Morone saxatilis suggests that the abdominal wall (belly flap) is an appropriate surrogate for estimating whole‐body proximate composition. Belly flaps showed strong linear relationships with total lipid composition (R2 = 0.91) and moisture (R2 = 0.82) but were more variable with respect to protein (R2 = 0.22) and ash (R2 = 0.26). Equations derived from these linear relationships allowed for accurate estimation of total‐body energy, water, lipid, dry mass, fat‐free dry mass, and protein (R2 > 0.89). Strong linear relationships were also found for belly flap lipid and moisture and the same components measured in fillets (lipid: R2 = 0.82; moisture: R2 = 0.73). We conclude that sampling an otherwise unused portion of the fish can provide precise chemical compositional information without sacrificing product and can allow for additional information to be obtained from the same organism.