YELLOWTAIL FLOUNDER OFF NEW ENGLAND 



199 



promise in the first data examined. The study of 

 scales and otoliths was then undertaken. Both 

 show regular growth rings, and while the otoliths 

 may be more easily read in the larger fish, we 

 chose the scales. 7 These are readily readable for 

 several growth rings, are much easier to obtain 

 from the fish, and can be handled with much less 

 trouble in the laboratory. The choice of scales 

 also was influenced to some extent by the fish 

 dealers, who were accustomed to boxing and ship- 

 ping fresh fish to the market. Early in the in- 

 vestigation a substantial part of the catch went to 

 the consumer as whole fish, and as it was desirable 

 to have clean, good-looking fish, several dealers 

 refused to permit the mutilation necessary to ob- 

 tain the otoliths. 



It was then necessary to determine which scales 

 were the most satisfactory to use. Careful exami- 

 nation of 13 different areas on the yellowtail re- 

 vealed that the largest 8 symmetrical scales are 

 located near the anterior end of the caudal 

 peduncle on the eyed side. Scales from this area 

 show more distinct growth rings than do those 

 from other areas; consequently, they were used 

 throughout the investigation. The limits of the 

 area are not critical : scales from near the lateral 

 line on the posterior half of the eyed side are simi- 

 lar in size and in clarity of growth rings. 



The scales were taken from the landings in the 

 same manner as the length measurements (p. 186), 

 and usually they were obtained at the same time : 

 25 fish were measured and scales obtained, and an- 

 other 75 fish were measured. The fish were meas- 

 ured to the nearest half centimeter. They were 

 taken only from catches of vessels fishing in a 

 single statistical subarea in order to make certain 

 of their origin. 



After considerable experimentation with various 

 methods of mounting the scales on slides, it was 

 found that they could be handled speedily and 

 entirely satisfactorily by obtaining an impres- 

 sion on small strips of cellulose acetate, using a 

 rollertype press. The strips, 2y 2 inches long by 

 y 2 inch wide by 0.020 inch thick, were warmed 



'Scott (1954) used otoliths In his studies of the yellowtail 

 from Cape Cod and the Nova Scotlan Banks. He found otoliths 

 about as difficult to read as scales from the Cape Cod area but 

 much easier than scales from the Nova Scotlan area. 



8 The size of the scale Is an Important criterion because the 

 first growth ring appears In a tiny area near the center of the 

 scale and is completely missing from smaller scales near the 

 head and along the edges of the fins. 



on a metal box heated by a 60-watt bulb to a tem- 

 perature a little hotter than the hand could 

 stand. Four or five scales were placed on a strip 

 with the rough sides in contact. The scales were 

 selected without aid of a microscope because the 

 regenerated scales are readily distinguished with 

 the naked eye. The only criteria for the selec- 

 tion of scales to be mounted were that they be 

 symmetrical and lack regeneration. Information 

 concerning the date, locality, length, and sex of 

 the fish was transferred to the strip with a spe- 

 cial celluloid ink. 



The growth rings vary in character according to 

 their position on the scale (fig. 15). The first ring, 

 near the center, is rather indistinct at the magnifi- 

 cation generally used when examining scales. It 

 consists of a group of closely spaced circuli and is 

 terminated by the first complete circulus that can 

 be traced around the anterior portion of the scale, 

 followed by the widely spaced circuli. This first 

 growth ring is so narrow that it might have been 

 considered a "natal" ring; that is, one associated 

 with the larval stage, had it not been for our find- 

 ing yellowtail that possessed this recently com- 

 pleted ring in the spring just before the spawning 

 season. 



Each of the succeeding three growth rings con- 

 sist of a zone of widely spaced circuli enclosed by a 

 zone of closely spaced circuli. The outer circuli of 

 the latter are usually incomplete. The outer edge 

 of the growth zone is marked by a prominent, com- 

 plete circulus, which is concentric with the margin. 

 The second growth ring is always very prominent. 

 It consists of a broad zone in which the circuli are 

 widely spaced at first but gradually come closer 

 together at the outer edge of the ring. The third 

 growth ring is usually about one-half the width 

 of the second, and it, too, consists of widely spaced 

 circuli gradually coming closer together. The 

 fourth ring is about one-third to one-half the 

 width of the third, has very few widely spaced 

 circuli, and in some cases the transition from wide 

 spacing to narrow is abrupt. The fifth and suc- 

 ceeding growth rings are usually very narrow and 

 can be most easily identified if one examines the 

 sides of the scale and attempts to trace the rings 

 around to the apex. These include few, if any, 

 widely spaced circuli. The outer part of the ring 

 usually is just an interruption of the closely spaced 

 circuli. 



