HOW TO STUDY FISHES 19 



response. The bass sees a glittering minnow and strikes at it. An 

 artificial minnow affects him similarly and he reacts towards it in the 

 same way. One of the most complicated mental phenomena the writer 

 has observed in fishes was illustrated by two Porgies in a tank at the 

 New York Aquarium. One of these had a bullying attitude, the other 

 one a cringing attitude. From time to time the former would dart in the 

 direction of the latter, which would slink away in evident alarm. Though 

 the difference of size between the two was insignificant, clearly the former 

 was ruling the tank, and they both knew it, that is, each one was ad- 

 justed mentally to reply to stimuli in a way appropriate to the role he 

 was playing. A parallel human situation would be associated with 

 definite emotional states of mind, whence we may argue that the fish is 

 capable of such. 



How TO Describe and Identify a Fish 



The first problem which faces the student of fishes is to differentiate 

 between the many species. The sea is large, and thousands of distinct 

 species of fishes find a place in it. Fresh waters, especially those of the 

 cold or temperate north, harbor a comparatively small number. The 

 species vary in every conceivable particular from the minute structure 

 of their bone and the form of the internal organs to the proportions of the 

 body or the number of rays in the fins. A few simple characters and 

 proportions are customarily used in comparative descriptions of fishes, 

 and it is necessary to master these before a specimen can be properly 

 identified, that is, assigned to the name by which it is known in litera- 

 ture. All measurements are taken in a straight line, as with a pair of 

 dividers. A fish's length is by custom the distance from the tip of the 

 snout to the base of its tail fin. Its depth is the greatest vertical distance 

 from the upper to the lower contour of the body, exclusive of fins. The 

 length of the head is measured from the tip of the snout to the most 

 posterior point on the border of the gill-cover exclusive of spines which 

 may project still further backward. The eye measurement is the greatest 

 diameter of same. The maxillary measure is taken from the tip of the 

 snout to the posterior end of the maxillary, or movable bone in the side 

 of the upper jaw. The interorbital is the least distance between the eyes 

 across the top of the head. The snout is measured from its tip to the 

 front of the eye. These absolute measurements are of little value, as a 

 fish's size is not fixed (unlike the size of a bird, for instance, which is 

 constant within a few millimeters for a given species), and a given 

 species of fish may vary considerably in size, even when full-grown. 



