All types of leaner cuts of meats will digest first and faster than other meats such as chicken, beef, pork etc.
The fish is much easier for your stomach and body to digest so the fish will be digested faster than chicken would be or other meats.
Fish is also very healthy for you as well and can possibly prevent dementia and improve your brain health.
Another reason that fish digests faster than chicken is fish contains more protein than it does fat and fat digests in the stomach and body slower while the protein digests faster in the stomach than chicken does.
Still chicken and turkey digests much better and faster than other meats and are much healthier than beef and pork.