float fishX = 0;
//float fishY = 300;
//float fishXX = 50;
//float fishYY = 25;

void setup ( ) {
  size ( 1020, 600 );
  background ( 75 );
}
void draw ( ) {
  background ( 75 );
  drawFish ( );
//--  fishDoes ( fishX = 0);
  fishDoes ( );
}
void drawFish ( ) {
  noStroke ( );
  fill ( 150, 250, 250 );
  ellipse ( fishX, 300, 50, 25 );
}
//--void fishDoes ( float fishX ) {
void fishDoes ( ) {
//--  if ( fishX == 0 ) {
  fishX = fishX + 10;
//--  }
}

/*the fish center is shifted too far right when
fishDoes ( )
void fishDoes ( )

the fish center is at fishX=0 when
fishDoes ( fishX = 0 )
void fishDoes ( float fishX )

getting the fish to move if fishX = 0 doesn't work either way
removing the 'if' statement and keeping "fishX = fishX + 10;"..
..and reverting back to "fishDoes ( )" and "void fishDoes ( )" works..
..but only in the positive direction without resetting to beginning
need to find a way to make it work with the if statement
another 'if' statement will be used when fishX = width
the fish must move to the width and back*/