NATURAL HISTORY OF REDFISH, ETC., OF TEXAS 185 



end of May, 1927, this year class (about 1 year old) reached a modal length of 19 to 

 20 centimeters (7.4 to 7.8 inches). 



Study of the scales of the spotted trout was undertaken in the hope that seasonal- 

 growth checks might be found and from them the annual growth and age of the 

 species determined to a greater degree of accuracy than was possible from inspection 

 of the length frequencies. From annual winter-growth checks (found to have been 

 formed on most of the trout scales examined) it was possible to arrive at a reliable 

 estimate of the age and growth of this species up to the seventh or eighth year of life. 



The age of a fish, in years, according to the scale method of age determination, 

 generally is found by counting the annuli or annual winter bands or checks, which 

 supposedly are produced by a slower rate of growth during the cold months of the 

 year. The length of the fish at the end of each year of life is computed from the 

 series of measurements of a scale from a fish of known length. Given the total 

 length of the scale, the length included in its annulus of year X, and the length of the 

 fish from which the scale is taken, the length attained by the fish at the end of year X 

 is determined by the use of the following [formula,^in which the jthird term is the 

 unknown. 



Length of scale included in annulus of year X 

 Total length of scale 



Length of fish at end of year X 



Length of fish at time of capture 



Repeating the above formula for the annulus of each evident year of life, the 

 length attained by the fish at the end of each successive year is computed. From 

 these lengths the annual increment in growth is obtained by simple subtraction. 



It is not within the scope of the present paper to discuss in detail the various 

 phases of the scale method of age determination. Most workers have found the 

 scale method to be essentially correct, and it is upon this assumption that the writer 

 presents the results obtained from a study of spotted-trout scales. The scales of 

 the gray trout (Cynoscion regalis) provided material for a paper by Taylor (1916), 

 and the reader is referred to Taylor's work for such information as may be of interest 

 pertaining to the more theoretical aspects of scale study applied to the sea trouts 

 (Cynoscion regalis and nebulosus). 



The spotted sea trout is a typical warm-water shore fish, which appears very 

 sensitive to the cold and which customarily departs into deeper and warmer water 

 throughout its range on the coming of winter. Along the Texas coast, even as far 

 south as the Rio Grande, this movement into deeper water is evident in the late fall 

 and winter. A cessation of growth probably accompanies lowering of temperature 

 and is reflected on the scale of the fish by a marked change in pattern and structure. 

 The general character of these annual winter scale-growth checks consists in the 

 formation of incomplete bilateral circuli that tend to become compressed, coalesced, 

 or broken. A certain lack of distinctness is apparent in many of these winter checks 

 (annuli), probably due to the intermittent cold weather that obtains along the Texas 

 coast. 



From approximately 2,000 unselected spotted trout taken with experimental 

 fishing gear (excluding about 1,000 fish under 10 centimeters (3.9 inches) in length. 



