INTRODUCTION xxv 



shape, size, and position of the fins are important, and 

 the number of rays especially so. 



Males often have a larger and broader head and 

 larger fins than females, and there may be other 

 sexual differences, especially at the breeding season. 

 Young fish usually differ from the adults in the longer 

 head, larger eye, shorter snout, and smaller mouth, 

 and the shape and relative size of the fins may change 

 considerably during growth. 



