Based on this information, what is this catfish's phenotype for the body color trait?

 - a white body
 - a brown body
The Channel catfish's genotype for the body color gene is bb. The Channel catfish's genotype of bb has only b alleles. The b allele is for a white body. So, the Channel catfish's phenotype for the body color trait must be a white body.
To check this answer, consider whether the Channel catfish's alleles are dominant or recessive. The allele for a brown body (B) is dominant over the allele for a white body (b). This means B is a dominant allele, and b is a recessive allele.
The Channel catfish's genotype of bb has only recessive alleles. An organism with only recessive alleles for a gene will have the recessive allele's version of the trait. So, the Channel catfish's phenotype for the body color trait must be a white body.