The Law taught fish with scales are clean and without scales unclean. Does this teaching apply to us now or only to Israelites?

The simple answer to your question is Romans 10:4, "For Christ is the end of the law for righteousness to everyone who believes." The purpose of the Law was to show how now imperfect human beings cannot keep a perfect Law, and thus we desperately needed Christ to fulfill it. "Therefore the law was our tutor to bring us to Christ, that we might be justified by faith. But after faith has come, we are no longer under a tutor." Galatians 3:24, 25.  The Israelite who has not accepted Christ by faith, is thus still under the Law, but the Christian is not.