^ That is correct according the the MFK species profiles.
While I've never kept rays, I did a lot of research here on the subject when I was considering buying a teacup ray. The tank sizes you have could house a young reticulated ray for a long time; however, if you know upgrading is not going to be an option at any point in the future, perhaps it's best to consider alternative bottom-dwellers.
also, while it's not approved on this forum, I've seen people keep retics in 48"x24" aquariums.