To show and hide a FloatingActionButton with the default animation, just call the methods show() and hide().  It's good practice to keep a FloatingActionButton in the Activity layout instead of putting it in a Fragment, this allows the default animations to work when showing and hiding.
Here is an example with a ViewPager:
FloatingActionButton for the first and third TabFloatingActionButton on the middle Tabpublic class MainActivity extends AppCompatActivity {
    FloatingActionButton fab;
    ViewPager viewPager;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        fab = (FloatingActionButton) findViewById(R.id.fab);
        viewPager = (ViewPager) findViewById(R.id.viewpager);
        // ...... set up ViewPager ............
        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageSelected(int position) {
                if (position == 0) {
                    fab.setImageResource(android.R.drawable.ic_dialog_email);
                    fab.show();
                } else if (position == 2) {
                    fab.setImageResource(android.R.drawable.ic_dialog_map);
                    fab.show();
                } else {
                    fab.hide();
                }
            }
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {}
            @Override
            public void onPageScrollStateChanged(int state) {}
        });
        // Handle the FloatingActionButton click event:
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int position = viewPager.getCurrentItem();
                if (position == 0) {
                    openSend();
                } else if (position == 2) {
                    openMap();
                }
            }
        });
    }
}
Result:
                