The present work evaluated the performance of a consortium designed and formed by five fungal species and four bacterial species isolated from the wastewater of a bovine cattle slaughterhouse to biodegrade organic matter in synthetic slaughterhouse wastewater (SSWW). Individual microorganism’s capability evaluation to remove COD and biodegrade SSWW substrates, together with bacteria-fungus confrontation assays, allowed the formation of nine defined consortia of fungi-bacteria according to a design of two factors with three levels (32). Seven defined consortia exhibited a higher COD removal from SSWW (81.9 to 93.0%) than that achieved by the bacteria or fungi consortia alone (74.7 to 77.6%). Moreover, three defined consortia of fungi-bacteria achieved the highest substrate (protein, carbohydrate, and fat) biodegradation in SSWW. The microbial growth in the defined consortia was characterized by adjustment to the logistic model (0.041 < μ < 0.091 h−1, 0.9006 < R2 < 0.9454), whereas the COD removal efficiency was adjusted to a parabolic statistical model (R2 = 0.6201), which showed that a bacterial inoculum between 7 to 20 times greater than the fungal one can lead to the highest consortium capacity to remove COD. This work provides elements that allow designing and forming defined consortia of fungi-bacteria to treat slaughterhouse wastewater with high organic matter levels.