Muscle excitation and contraction involves the release of Ca2+ ions from the Sarcoplasmic Reticulum. Muscle contraction occurs when Ca2+ ions, which are stored inside the Sarcoplasmic Reticulum (SR), are released by the SR release channels called the Ryanodine Receptors (RyR). There are three main isoforms of Ryanodine Receptors found in various muscle types throughout the body. The RyR1 isoform is expressed predominantly in skeletal muscle and areas of the brain, while the RyR2 and RyR3 are expressed in cardiac tissue and smooth muscle respectively. Fish express two fiber-type specific RyR1 isoforms that are phylogenetically closely related, slow twitch and fast twitch. Fish possess two main types of skeletal muscle, red and white muscle. Red muscle is used in routine sustained activities and has slow twitch RyR. In comparison to red muscle, white muscle mass is usually large for short periods of powerful bursts and utilizes the fast twitch RyR. Previous studies have shown an unusual condition in which the slow twitch specific RyR transcript retains an intron when expressed in fast (white) muscle. In our study we have detected the retained intron in both red (slow) and white muscle. We conducted research on Yellow Fin tuna (Thunnus Albacares) and Albacore tuna (Thunnus Alalunga) to determine weather the intron retention exsist in them as well as the Blue Marlin (Makaira Nigricans) for which the full length sequence was originally characterized.